PERMIS-2007

FOREWORD

SPONSORS

PerMIS 2008 

PERFORMANCE METRICS

FOR 

INTELLIGENTSYSTEMS(PERMIS) WORKSHOP

National Institute of Standards and Technology, Gaithersburg, Maryland USA

August 19 - 21, 2008

Edited by

R. Madhavan

E.R. Messina

NIST Special

Publication 1090
FOREWORD

The 2008 Performance Metrics for Intelligent Systems (PerMIS'08) Workshop will be the eighth in the series 

that started in 2000, targeted at defining measures and methodologies of evaluating performance of intelligent

systems. The workshop has proved to be an excellent forum for discussions and partnerships, dissemination 

of ideas, and future collaborations in an informal setting. Attendees usually include researchers, graduate 

students, practitioners from industry, academia, and government agencies. 

PerMIS’08 aims at identifying and quantifying contributions of functional intelligence towards achieving 

success. Our working definition of functional intelligence is “the ability to act appropriately in an uncertain 

environment, where appropriate action is that which increases the probability of success”, and success is 

“the achievement of behavioral goals” (J. Albus, 1991). In addition to the main theme, as in previous years, 

the workshop will focus on applications of performance measures to practical problems in commercial, 

industrial, homeland security, and military applications. Topic areas include, but are not limited to:

Defining and measuring aspects of a system:

• The level of autonomy

• Human-robot interaction

• Collaboration & coordination

• Taxonomies

• Biologically inspired models

Evaluating components within intelligent system

• Sensing and perception

• Knowledge representation, world models, ontologies

• Planning and control

• Learning and adaption

• Reasoning

Infrastructural support for performance evaluation

• Testbeds and competitions for intercomparisons

• Instrumentation and other measurement tools

• Simulation and modeling support

Technology readiness measures for intelligent systems

Applied performance measures in various domains, e.g.,

• Intelligent transportation systems

• Emergency response robots (search and rescue, bomb disposal)

• Homeland security systems

• De-mining robots

• Defense robotics

• Hazardous environments (e.g., nuclear remediation)

• Industrial and manufacturing systems

• Space/Aerial robotics

• Medical Robotics & assistive devices

PerMIS 2008
PerMIS’08 will feature five plenary addresses and seven special sessions. The plenary speakers are worldclass experts in their own field and we are confident that the attendees will be able to benefit from their 

presentations. This year, there is a special session for every (parallel) general session. Over the course of 

three days, there will be twelve sessions related to performance of intelligent systems covering an array of 

topics from medical systems to manufacturing, mobile robotics to virtual automation, human-system interaction to biologically inspired models, and much more.

Special thanks are due to the Program Committee for publicizing the workshop, the special session organizers for proposing interesting topics and bringing together researchers related to their sessions, and the 

reviewers who provided feedback to the authors, and helped us to assemble an excellent program. We much 

appreciate the authors submitting their papers to this workshop and for sharing their thoughts and experiences related to their research with the workshop attendees. 

PerMIS’08, is sponsored by NIST with technical co-sponsorship of the IEEE Washington Section Robotics 

and Automation Society Chapter and in-cooperation with the Association for Computing Machinery (ACM) 

Special Interest Group on Artificial Intelligence (SIGART). As in previous years, the proceedings of PerMIS will 

be indexed by INSPEC, Compendex, ACM’s Digital Library, and are released as a NIST Special Publication. 

Springer Publishers are back again this year to raffle off some of the books that will be displayed at their 

booth during the course of the workshop. Selected papers from this workshop will be considered for inclusion

in an edited book volume by Springer. We gratefully acknowledge the support of our sponsors.

We sincerely hope that you enjoy the presentations and the social programs!

Raj Madhavan Elena Messina

Program Chair General Chair

SPONSORS

 

 

PerMIS 2008
PROGRAMCOMMITTEE

General Chair:

Elena Messina (Intelligent Systems Division, NIST, USA) 

Program Chair:

Raj Madhavan (Oak Ridge National Laboratory/NIST, USA)

S. Balakirsky (NIST USA)

R. Bostelman (NIST USA)

F. Bonsignorio (Heron Robots Italy)

G. Berg-Cross (EM & I USA)

J. Bornstein (ARL USA)

P. Courtney (PerkinElmer UK)

J. Evans (USA)

D. Gage (XPM Tech. USA)

J. Gunderson (GammaTwo USA)

L. Gunderson (GammaTwo USA)

S. K. Gupta (UMD USA)

A. Jacoff (NIST USA)

S. Julier (Univ. College London UK)

M. Lewis (UPitt USA)

R. Lakaemper (Temple Univ USA)

T. Kalmar-Nagy (Texas A & M USA)

A. del Pobil (Univ. Jaume-I Spain)

S. Ramasamy UALR USA)

L. Reeker (NIST USA)

C. Schlenoff (NIST USA)

M. Shneier (NIST USA)

E. Tunstel (JHU-APL USA)

PerMIS 2008
Table of Contents

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Sponsors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii

Program Committee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

Plenary Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x

Workshop Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii

Author Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi

Technical Sessions

TUE-AM1 Performance Evaluation

Evolution of the SCORE Framework to Enhance Field-Based Performance Evaluations

of Emerging Technologies

[Brian Weiss, Craig Schlenoff] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Reliability Estimation and Confidence Regions from Subsystem and Full System Tests

via Maximum Likelihood

[James Spall] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Fuzzy-Logic-Based Approach for Identifying Objects of Interest in the PRIDE

Framework

[Zeid Kootbally, Craig Schlenoff, Raj Madhavan, Sebti Foufou] . . . . . . . . . . . . . . . . . . 17

Identifying Objects in Range Data Based on Similarity Transformation Invariant Shape

Signatures

[Xiaolan Li, Afzal Godi, Asim Wagan] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Stepfield Pallets: Repeatable Terrain for Evaluating Robot Mobility

[Adam Jacoff, Anthony Downs, Ann Virts, Elena Messina] . . . . . . . . . . . . . . . . . . . . . . 29

Potential Scaling Effects for Asynchronous Video in Multirobot Search

[Prasanna Velagapudi, Paul Scerri, Katia Sycara, Huadong Wang, Michael Lewis]. . . 35

TUE-AM2 Special Session I: Cognitive Systems of EU Cognition Programme

Cognitive Systems of EU Cognition Programme*

[Patrick Courtney]

i
The Rat’s Life Benchmark: Competing Cognitive Robots

[Olivier Michel, Fabien Rohrer] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

The iCub Humanoid Robot: An Open Platform for Research in Embodied Cognition 

[Giorgio Metta, Giulio Sandini, David Vernon, Lorenzo Natale, Francesco Nori] . . . . 50

An Open-Source Simulator for Cognitive Robotics Research: The Prototype of the iCub 

Humanoid Robot Simulator

[Vadim Tikhanoff, Angelo Cangelosi, Paul Fitzpatrick, Giorgio Metta, Lorenzo Natale,

Francesco Nori] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Symbiotic Robot Organisms: REPLICATOR and SYMBRION Projects

[Serge Kernbach, Eugen Meister, Florian Schlachter, Kristof Jebens, Marc Szymanski,

Jens Liedke, Davide Laneri, Lutz Winkler, Thomas Schmickl, Ronald Thenius, Paolo

Corradi, Leonardo Ricotti] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62

Virtual Agent Modeling in the RASCALLI Platform

[Christian Eis, Marcin Skowron, Brigitte Krenn] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

TUE-PM1 Human-System Interaction

Evaluation Criteria for Human-Automation Performance Metrics

[Birsen Donmez, Patricia Pina, Mary Cummings] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77

Assessing Measures of Coordination Demand Based on Interaction Durations

[Michael Lewis, Jijun Wang] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

The Gestural Joystick and the Efficacy of the Path Tortuosity Metric for Human/Robot

Interaction

[Richard Voyles, Jaewook Bae, Roy Godzdanker] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91

Modeling of Thoughtful Behavior with Dynamic Expert System

[Vadim Stefanuk] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

TUE-PM2 Special Session II: Architectures for Unmanned Systems

UAV Architectures*

[George Vachtsevanos]

Architectures for Unmanned Systems*

[James Albus]

Levels-of-Autonomy of the ASTM F41 Unmanned Maritime Vehicles Standard*

[Mark Rothgeb]

ii
Ontological Perspectives for Autonomy Performance

[Hui-Min Huang, Elena Messina, Tsai Hong, Craig Schlenoff] . . . . . . . . . . . . . . . . . . 101

WED-AM1 Metrics & Measures

Robotic Systems Technical and Operational Metrics Correlation

[Jason Schenk, Robert Wade] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .108

Survey of Domain-Specific Performance Measures in Assistive Robotic Technology

[Katherine Tsui, Holly Yanco, David Feil-Seifer, Maja Mataric] . . . . . . . . . . . . . . . . . 116

Refining the Cognitive Decathlon

[Robert Simpson, Charles Twardy] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

Using Metrics to Optimize a High Performance Intelligent Image Processing Code

[Scott Spetka, Susan Emen, George Ramseyer, Richard Linderman] . . . . . . . . . . . . . 132

Measurement Techniques for Multiagent Systems

[Robert Lass, Evan Sultanik, William Regli] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

RoboCupRescue Robot League: 2008 Overview*

[Adam Jacoff, Andreas Birk, Johannes Pellenz, Ehsan Mihankhah, Raymond Sheh,

Satoshi Tadokoro]

WED-AM2 Special Session III: Performance Metrics for Perception in Intelligent

Manufacturing

Performance of Super-Resolution Enhancement for Flash LADAR Data

[Shuowen Hu, Susan Young, Tsai Hong] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

Performance Evaluation of Laser Trackers

[Bala Muralikrishnan, Daniel Sawyer, Christopher Blackburn, Steven Phillips, Bruce

Borchardt, Tyler Estler] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

Preliminary Analysis of Conveyor Dynamic Motion for Automation Applications

[Jane Shi] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

3D Part Identification Based on Local Shape Descriptors

[Xiaolan Li, Afzal Godil, Asim Wagan] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

Calibration of a System of a Gray-Value Camera and an MDSI Range camera

[Tobias Hanning, Aless Lasaruk] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

Dynamic 6DOF Metrology for Evaluating a Visual Servoing System

[Tommy Chang, Tsai Hong, Mike Shneier, German Holguin, Johnny Park,

Roger Eastman]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173

iii
WED-PM1 Autonomous Systems

Integrating Reification and Ontologies for Mobile Autonomous Robots

[James Gunderson, Louise Gunderson] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .181

Quantification of Line Tracking Solutions for Automotive Applications

[Jane Shi, Rick Rourke, Dave Groll, Peter Tavora] . . . . . . . . . . . . . . . . . . . . . . . . . . . .189

Mobile Robotic Surveying Performance for Planetary Surface Site Characterization 

[Edward Tunstel] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200

Evaluating Situation Awareness of Autonomous Systems

[Jan Gehrke] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206

WED-PM2 Special Session IV: Results from a Virtual Manufacturing

Automation Competition

NIST/IEEE Virtual Manufacturing and Automation Competition: From Earliest

Beginnings to Future Directions

[Stephen Balakirsky, Raj Madhavan, Chris Scrapper] . . . . . . . . . . . . . . . . . . . . . . . . . .214

Analysis of a Novel Docking Technique for Autonomous Robots

[George Henson, Michael Maynard, Xinlian Liu, George Dimitoglou] . . . . . . . . . . . . 220

Partitioning Algorithm for Path Determination of Automated Robotic Part Delivery

System in Manufacturing Environments

[Payam Matin, Ali Eydgahi, Ranjith Chowdary] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .224

Algorithms and Performance Analysis for Path Navigation of Ackerman-Steered 

Autonomous Robots

[George Henson, Michael Maynard, George Dimitoglou, Xinlian Liu] . . . . . . . . . . . .230

THU-AM1 Model-based Performance Assessment

Wireless Communications in Tunnels for Urban Search and Rescue Robots

[Kate Remley, George Hough, Galen Koepke, Dennis Camell, Robert Johnk, Chriss

Grosvenor] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236

A Performance Assessment of Calibrated Camera Networks for Construction Site

Monitoring

[Itai Katz, Nicholas Scott, Kam Saidi] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

A Queuing-Theoretic Framework for Modeling and Analysis of Mobility in WSNs

[Harsh Bhatia, Rathinasamy Lenin, Aarti Munjal, Srini Ramaswamy,

Sanjay Srivastava] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248

iv
Towards Information Networks to Support Composable Manufacturing

[Mahesh Mani, Albert Jones, Junho Shin, Ram Sriram] . . . . . . . . . . . . . . . . . . . . . . . . 254

3D Reconstruction of Rough Terrain for USARSim using a Height-map Method

[Gael Roberts, Stephen Balakirsky, Sebti Foufou] . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

THU-AM2 Special Session V: Quantitative Assessment of Robot-generated Maps

Characterizing Robot-Generated Maps: The Importance of Representations and 

Objective Metrics*

[Chris Scrapper, Raj Madhavan, Stephen Balakirsky]

Using Virtual Scans to Improve Alignment Performance in Robot Mapping

[Rolf Lakeamper, Nagesh Adluru] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265

The Role of Bayesian Bounds in Comparing SLAM Algorithms Performance

[Andrea Censi] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271

Map Quality Assessment

[Asim Wagan, Afzal Godil, Xiaolan Li] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278

Discussion: Roadmap for Map Evaluation Frameworks

THU-PM1 Special Session VI: Biologically Inspired Models of Intelligent Systems

Introduction to Biological Inspiration for Intelligent Systems

[Gary Berg-Cross] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283

Overview of Biologically Inspired Cognitive Architectures (BICA)*

[Alexei Samsonovich]

Recent modeling and Rapid Prototyping Experience Aimed at Building Architectures of

Cognitive Agents*

[Giorgio Ascoli]

Applying Developmental-Inspired Principles to the Field of Developmental Robotics

[Gary Berg-Cross] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288

Discussion of Biologically Inspired Models

[Panel]

THU-PM2 Special Session VII: Medical Robotics

Overcoming Barriers to Wider Adoption of Mobile Telerobotic Surgery: Engineering,

Clinical and Business Challenges

[Gerald Moses, Charles Doarn, Blake Hannaford, Jacob Rosen] . . . . . . . . . . . . . . . . 293

v
Calibration of a Computer Assisted Orthopaedic Hip Surgery Phantom

[Daniel Sawyer, Nick Dagalakis, Craig Shakarji, Yong Kim] . . . . . . . . . . . . . . . . . . . 297

HLPR Chair – A Novel Patient Transfer Device

[Roger Bostelman, James Albus, Joshua Johnson] . . . . . . . . . . . . . . . . . . . . . . . . . . . 302

Robotic Navigation in Crowded Environments: Key Challenges for Autonomous

Navigation Systems

[James Ballantyne, Salman Valibeik, Ara Darzi, Guang-Zhong Yang] . . . . . . . . . . . .306

Note: * Presentation Only

vi
FOREWORD

The 2008 Performance Metrics for Intelligent Systems (PerMIS'08) Workshop is the eighth in the series that 

started in 2000, targeted at defining measures and methodologies of evaluating performance of intelligent 

systems. The workshop has proved to be an excellent forum for discussions and partnerships, dissemination 

of ideas, and future collaborations in an informal setting. Attendees usually include researchers, graduate 

students, practitioners from industry, academia, and government agencies. 

PerMIS’08 aims at identifying and quantifying contributions of functional intelligence towards achieving 

success. Our working definition of functional intelligence is “the ability to act appropriately in an uncertain 

environment, where appropriate action is that which increases the probability of success”, and success is 

“the achievement of behavioral goals” (J. Albus, 1991). In addition to the main theme, as in previous years, 

the workshop focuses on applications of performance measures to practical problems in commercial, 

industrial, homeland security, and military applications. Topic areas include, but are not limited to:

Defining and measuring aspects of a system:

• The level of autonomy

• Human-robot interaction

• Collaboration & coordination

• Taxonomies

• Biologically inspired models

Evaluating components within intelligent system

• Sensing and perception

• Knowledge representation, world models, ontologies

• Planning and control

• Learning and adaption

• Reasoning

Infrastructural support for performance evaluation

• Testbeds and competitions for intercomparisons

• Instrumentation and other measurement tools

• Simulation and modeling support

Technology readiness measures for intelligent systems

Applied performance measures in various domains, e.g.,

• Intelligent transportation systems

• Emergency response robots (search and rescue, bomb disposal)

• Homeland security systems

• De-mining robots

• Defense robotics

• Hazardous environments (e.g., nuclear remediation)

• Industrial and manufacturing systems

• Space/Aerial robotics

• Medical Robotics & assistive devices

PerMIS 2008 vii
PerMIS’08 features five plenary addresses and seven special sessions. The plenary speakers are world-class 

experts in their own field and we are confident that the attendees will be able to benefit from their 

presentations. This year, there is a special session for every (parallel) general session. Over the course of 

three days, there will be twelve sessions related to performance of intelligent systems covering an array of 

topics from medical systems to manufacturing, mobile robotics to virtual automation, human-system interaction to biologically inspired models, and much more.

Special thanks are due to the Program Committee for publicizing the workshop, the special session organizers for proposing interesting topics and bringing together researchers related to their sessions, and the 

reviewers who provided feedback to the authors, and helped us to assemble an excellent program. We much 

appreciate the authors submitting their papers to this workshop and for sharing their thoughts and experiences related to their research with the workshop attendees. 

PerMIS’08, is sponsored by NIST with technical co-sponsorship of the IEEE Washington Section Robotics 

and Automation Society Chapter and in-cooperation with the Association for Computing Machinery (ACM) 

Special Interest Group on Artificial Intelligence (SIGART). As in previous years, the proceedings of PerMIS will 

be indexed by INSPEC, Compendex, ACM’s Digital Library, and are released as a NIST Special Publication. 

Springer Publishers was back again this year to raffle off some of the books that were displayed at their booth

during the course of the workshop. Selected papers from this workshop are being included in an edited book 

volume by Springer. We gratefully acknowledge the support of our sponsors.

We sincerely hope that you enjoy the presentations and the social programs!

Raj Madhavan Elena Messina

Program Chair General Chair

SPONSORS

 

 

PerMIS 2008 viii
PROGRAMCOMMITTEE

General Chair:

Elena Messina (Intelligent Systems Division, NIST, USA) 

Program Chair:

Raj Madhavan (Oak Ridge National Laboratory/NIST, USA)

S. Balakirsky (NIST USA)

R. Bostelman (NIST USA)

F. Bonsignorio (Heron Robots Italy)

G. Berg-Cross (EM & I USA)

J. Bornstein (ARL USA)

P. Courtney (PerkinElmer UK)

J. Evans (USA)

D. Gage (XPM Tech. USA)

J. Gunderson (GammaTwo USA)

L. Gunderson (GammaTwo USA)

S. K. Gupta (UMD USA)

A. Jacoff (NIST USA)

S. Julier (Univ. College London UK)

M. Lewis (UPitt USA)

R. Lakaemper (Temple Univ USA)

T. Kalmar-Nagy (Texas A & M USA)

A. del Pobil (Univ. Jaume-I Spain)

S. Ramasamy UALR USA)

L. Reeker (NIST USA)

C. Schlenoff (NIST USA)

M. Shneier (NIST USA)

E. Tunstel (JHU-APL USA)

PerMIS 2008 ix
ABSTRACT

We hypothesize that adding computational cognitive reasoning components to intelligent systems will result

in three benefits:

Most if not all intelligent systems 

must interact with humans, who are 

the ultimate users of these systems. 

Giving the system cognitive models 

can enhance the human-system interface by allowing more common 

ground in the form of cognitively 

plausible representations and qualitative reasoning. By using cognitive 

models, reasoning mechanisms and 

representations, we believe that we 

can yield a more effective and efficient interface that accommodates 

the user.

Since the resulting system in interacting with the human, giving it behaviors that are more natural to the human can also result in more natural 

interactions between the human and 

the intelligent system. For example, 

mobile robots that must work collaboratively with humans can actually result in less effective interactions if its behaviors are alien or non-intuitive to the human. By 

incorporating cognitive models, we can develop systems whose 

behavior is more expected and natural.

One key interest is in measuring the performance of intelligent 

systems. We propose that an intelligent system that is cognitively

enhanced can be more directly compared to human level performance. Further, if cognitive models of human performance 

have been developed in creating the intelligent system, we can 

directly compare the intelligent systems behavior and performance in the task to the human subject behavior and performance.

In this talk, I will present several instantiations of developing 

cognitively enhanced intelligent systems.

BIOGRAPHY 

Alan C. Schultz is the Director of the Navy Center for Applied 

Research in Artificial Intelligence at the Naval Research Laboratory in Washington, DC. His research is in the areas of humanrobot interaction, cognitive robotics, evolutionary robotics, learning in robotic systems, and adaptive systems. He is the recipient 

of an Alan Berman Research Publication Award, and has published over 90 articles on HRI, machine learning and robotics. 

Alan is currently the co-chair of the AAAI Symposia Series, and 

chaired the 1999 and 2000 AAAI Mobil Robot Competition and 

Exhibitions. 

PLENARY SPEAKER

Mr. Alan Schultz

Navy Center for 

Applied 

Research in 

Artificial 

Intelligence 

(NCARAI), USA

Cognitively 

Enhanced 

Intelligent 

Systems

Tues. 8:30 am

ABSTRACT 

Haptics is the science and technology of experiencing and creating 

touch sensations. This talk will examine the role of haptics in three types 

of medical systems: surgical robotics, 

surgical simulators, and rehabilitation 

robotics. Robot-assisted surgery can 

improve the outcomes of medical 

procedures by enhancing accuracy 

and minimally invasive access, 

thereby reducing patient trauma and 

recovery time. However, the current 

lack of force and tactile information is 

hypothesized to compromise system 

performance. With approaches ranging from psychophysical studies to 

control systems engineering, we are 

designing teleoperated robots capable of providing haptic feedback in 

challenging surgical environments. 

Haptic information is also needed for 

accurate surgical simulation. Surgical 

simulators present a safe and potentially effective method for surgical 

training, and can also be used in 

robot-assisted surgery for pre- and 

intra-operative planning. I will describe experiments to determine 

the mechanics of interaction between surgical instruments and 

tissues, as well as techniques for accurate patient-specific modeling. Finally, rehabilitation through robotically enabled orthotics 

and prosthetics inherently requires understanding and appropriate generation of haptic interactions. Our recent work in this area 

includes motor control augmentation with an exoskeleton robot, 

and studies of the role of haptic proprioception in prosthetic limb 

use.

BIOGRAPHY

Allison M. Okamura received the BS degree from the University 

of California at Berkeley in 1994, and the MS and PhD degrees 

from Stanford University in 1996 and 2000, respectively, all in 

mechanical engineering. She is currently an associate professor 

of mechanical engineering and the Decker Faculty Scholar at 

Johns Hopkins University. She is associate director of the 

Laboratory for Computational Sensing and Robotics and a thrust 

leader of the NSF Engineering Research Center for ComputerIntegrated Surgical Systems and Technology. Her awards include 

the 2005 IEEE Robotics Automation Society Early Academic 

Career Award, the 2004 US NSF CAREER Award, the 2004 JHU 

George E. Owen Teaching Award, and the 2003 JHU Diversity 

Recognition Award. Her research interests are haptics, 

teleoperation, medical robotics, virtual environments and 

simulators, prosthetics, rehabilitation engineering, and 

engineering education.

PLENARY SPEAKER

Prof. Allison 

Okamura

The Johns 

Hopkins 

University, USA

Haptics in 

Medical 

Robotics: 

Surgery, 

Simulation, 

and 

Rehabilitation

Tues. 2:00 pm

PerMIS 2008 x
ABSTRACT

In industrial robotics, system 

integration is a rather common 

business. Robot manufacturers 

typically team up with a number 

of so-called system integrators, 

which design robot cells, 

assembly lines and entire 

manufacturing plants out of 

“standardized” components, 

such as manipulators, sensors, 

tools, and conveyor systems.

In service robotics the situation is 

in no way comparable. Service 

robots are typically considered as 

mass products, which are 

designed like dish washers or 

play stations. System integration 

is simply part of the regular 

product design.

It would be rather irrelevant to 

discuss this issue any further, if 

the design of a service robot for 

some specific application was a 

task like the design of a dish washer. As a matter of fact, the two 

tasks have not much if anything at all in common.

The design of a service robot is more the result of the ingenuity 

of an engineer rather of established procedures or 

methodologies or even technologies. Typically every new service 

robot is design from scratch. Not too seldom, the service task 

itself and the operational constraints are not too well understood, 

neither is the business model under which the automation of a 

service could become an economic success. A plenitude of 

components such as sensors, actuators, operating systems, 

algorithms are available but no common recipe for integrating 

and compiling them into a competitive product.

Service robotics today is in a situation very much comparable to 

the situation of the car industry in 1885, when Carl Benz built the 

first car. The industry is virtually not existing. Potential players 

and investors are skeptical because not only a realistic market 

but also a realistic technology assessment gives them a rather 

fuzzy picture.

This situation has motivated the German Ministry for Education 

and Research to invest into a so-called technology platform for 

service robotics. Other funding agencies such as the European 

Commission are implementing similar initiatives.

In my presentation I will talk about the German Service Robotics 

Initiative, which as a major activity pushes the development of 

such a technology platform. The platform is considered as a 

vehicle for understanding and managing the requirements for 

system integration in service robotics. I will talk about a first 

approach of this Initiative to incrementally integrate, evaluate and 

harmonize available off the shelf components and their interfaces 

to simplify and accelerate the development of new service 

robots. I will also talk about the lessons learned in this Initiative 

and how they are currently being picked up in other initiatives to 

promote the development of harmonized and/or standardized 

building blocks for service robots.

BIOGRAPHY

Erwin Prassler received a master's degree in Computer Science 

from the Technical University of Munich in 1985 and a Ph.D. in 

Computer Science from the University of Ulm in March 1996. For 

his doctoral dissertation he received the AKI dissertation award 

in September 1997. Between 1986 and 1989, Dr. Prassler held 

positions as a member of the scientific staff at the Technical 

University of Munich and as a guest researcher in the Computer 

Science Department at the University of Toronto. In fall 1989, he 

joined the Research Institute for Applied Knowledge Processing 

(FAW) in Ulm, where he headed a research group working in the 

field of mobile robots and service robotics between 1994 and 

2003. In 1999, Dr. Prassler entered a joint affiliation with 

Gesellschaft fur Produktionssysteme (GPS) in Stuttgart, where 

directed the department for Project Management and Technology 

Transfer. In this function, Dr. Prassler coordinated the MORPHA 

project (Interaction and Communication between Humans and 

Intelligent Robot Assistents, www.morpha.de) one of six national 

research projects in the field of Human Machine Interaction 

funded by the German Ministry for Education and Research. In 

March 2004, Dr. Prassler was appointed as an Associate 

Professor at the Bonn-Aachen International Center for 

Information Technology. Together with Prof. Rolf Dieter Schraft, 

director of Fraunhofer IPA in Stuttgart, he is currently coordinating the German Service Robotice Initiatve DESIRE 

(www.service-robotik-initiative.de), a joint national research 

project involving 7 academic and 6 industrial partners.

PerMIS 2008

PLENARY SPEAKER

Prof. Erwin Prassler

Applied Science 

Institute, Germany

Incremental 

Integration, 

Evaluation, and

Harmonization 

of Components

of a Reference 

Platform for 

Service 

Robotics

Wed. 8:30 am 

xi
ABSTRACT

A mature systems engineering 

discipline is exemplified by aerospace 

engineering where purpose-built 

vehicles are designed while regularly 

consulting system level performance 

models to help guide the design 

optimization process. Robotics has 

not yet identified such rich and 

universal performance models but 

useful performance models do arise 

naturally in the performance of the 

work. This talk will discuss a large 

number of field robotic systems in an 

attempt to identify some system level 

constraints, tradeoffs and metrics 

which seem to be valuable in 

formulating the quest for an optimal 

system. Examples include the hard 

constraints of safe real-time 

replanning, the optimal update rate of 

a visual servo, the related tradeoff 

between systematic and random 

error accumulation in mapping, and 

the relative completeness of planning 

search spaces and its affect on winning robot races.

BIOGRAPHY

Dr. Alonzo Kelly is an associate professor at the Robotics Institute of Carnegie Mellon University. He has also worked as a 

member of the technical staff at MD Robotics, Canada and at 

NASA's Jet Propulsion Laboratory. His research typically concerns wheeled mobile robots operating in both structured and 

unstructured environments. His work spans many sub-specialties 

of mobile robots including control, position estimation, mapping, 

motion planning, simulation, and human interfaces. It also spans 

many application areas including outdoor unmanned ground vehicles, agricultural and mining vehicles, planetary rovers, and

indoor automated guided vehicles.

ABSTRACT

Robotics is emerging as a promising

tool for training of human functional 

movement. The current research in 

this area is focused primarily on 

upper extremity movements. This 

talk describes novel designs of three

lower extremity exoskeletons, intended for gait assistance and training of motor-impaired patients. The 

design of each of these exoskeletons is novel and different. Force 

and position sensors on the exoskeleton provide feedback to the 

user during training. The exoskeletons have undergone tests on 

healthy and chronic stroke survivors

to assess their potential for treadmill

training. These results will be presented. GBO is a Gravity Balancing 

un-motorized Orthosis which can 

alter the gravity acting at the hip and

knee joints during swing. ALEX is an

Actively driven Leg Exoskeleton 

which can modulate the foot trajectory 

using motors at the joints. SUE is a bilateral Swing-assist Unmotorized Exoskeleton to propel the leg during gait. This research

was supported by NIH through a BRP program.

BIOGRAPHY

Prof. Agrawal received a Ph.D. degree in Mechanical Engineering 

from Stanford University in 1990. He is currently the Director of 

Mechanical Systems Laboratory. He has published close to 200 

journal and conference papers and 2 books in the areas of 

controlled mechanical systems, dynamic optimization, and 

robotics. Dr. Agrawal is a Fellow of the ASME and his other 

honors include a Presidential Faculty Fellowship from the White 

House in 1994, a Bessel Prize from Germany in 2003, and a 

Humboldt US Senior Scientist Award in 2007. He has served on 

editorial boards of numerous journals published by ASME and 

IEEE. 

PerMIS 2008

PLENARY SPEAKER

Prof. Sunil Kumar 

Agrawal 

University of 

Delaware, USA

Robotic 

Exoskeletons

for Gait 

Assistance 

and Training 

of the Motor 

Impaired

Thurs. 8:30 am

PLENARY SPEAKER

Prof. Alonzo Kelly 

Carnegie Mellon

University, USA

Various 

Tradeoffs and

Metrics of 

Performance 

for Field 

Robots

Wed. 2:00 pm

xii
PerMIS 2008 

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08:15 Welcome & Overview

08:30 Plenary Presentation:

Alan Schultz 

Cognitively Enhanced Intelligent Systems

09:30 Coffee Break

10:00 TUE-AM1 Performance Evaluation

Chairs: James Spall & Craig Schlenoff

• Evolution of the SCORE Framework to Enhance Field-Based 

Performance Evaluations of Emerging Technologies

[Brian Weiss, Craig Schlenoff]

• Reliability Estimation and Confidence Regions from Subsystem and Full 

System Tests via Maximum Likelihood [James Spall]

• Fuzzy-Logic-Based Approach for Identifying Objects of Interest in the 

PRIDE Framework

[Zeid Kootbally, Craig Schlenoff, Raj Madhavan, Sebti Foufou]

• Identifying Objects in Range Data Based on Similarity Transformation 

Invariant Shape Signatures

[Xiaolan Li, Afzal Godil, Asim Wagan]

• Stepfield Pallets: Repeatable Terrain for Evaluating Robot Mobility

[Adam Jacoff, Anthony Downs, Ann Virts, Elena Messina]

• Potential Scaling Effects for Asynchronous Video in Multirobot Search 

[Prasanna Velagapudi, Paul Scerri, Katia Sycara, Huadong Wang, 

Michael Lewis]

12:30 Lunch

14:00 Plenary Presentation:

Allison Okamura

Haptics in Medical Robotics: Surgery, Simulation, 

and Rehabilitation

15:00 Coffee Break

15:30 TUE-PM1 Human-System Interaction

Chairs: Michael Lewis & Birsen Donmez

• Evaluation Criteria for Human-Automation Performance Metrics

[Birsen Donmez, Patricia Pina, Mary Cummings]

• Assessing Measures of Coordination Demand Based on Interaction 

Durations [Michael Lewis, Jijun Wang]

• The Gestural Joystick and the Efficacy of the Path Tortuosity Metric for 

Human/Robot Interaction

[Richard Voyles, Jaewook Bae, Roy Godzdanker]

• Modeling of Thoughtful Behavior with Dynamic Expert System 

[Vadim Stefanuk]

19:00 Reception

PROGRAM PERMIS

xiii
PerMIS 2008 

August

08:15 Welcome & Overview

08:30 Plenary Presentation: 

Alan Schultz 

Cognitively Enhanced Intelligent Systems

09:30 Coffee Break

10:00 TUE-AM2 Special Session I: Cognitive Systems of EU Cognition Programme

Organizer: Patrick Courtney

• Cognitive Systems of EU Cognition Programme* [Patrick Courtney]

• The Rat’s Life Benchmark: Competing Cognitive Robots

[Olivier Michel, Fabien Rohrer]

• The iCub Humanoid Robot: An Open Platform for Research in Embodied

Cognition [Giorgio Metta, Giulio Sandini, David Vernon, Lorenzo Natale, 

Francesco Nori]

• An Open-Source Simulator for Cognitive Robotics Research: The 

Prototype of the iCub Humanoid Robot Simulator 

[Vadim Tikhanoff, Angelo Cangelosi, Paul Fitzpatrick, Giorgio Metta, 

Lorenzo Natale, Francesco Nori]

• Symbiotic Robot Organisms: REPLICATOR and SYMBRION Projects 

[Serge Kernbach, Eugen Meister, Florian Schlachter, Kristof Jebens, 

Marc Szymanski, Jens Liedke, Davide Laneri, Lutz Winkler, Thomas 

Schmickl, Ronald Thenius, Paolo Corradi, Leonardo Ricotti]

• Virtual Agent Modeling in the RASCALLI Platform

[Christian Eis, Marcin Skowron, Brigitte Krenn]

12:30 Lunch

14:00 Plenary Presentation:

Allison Okamura

Haptics in Medical Robotics: Surgery, Simulation, 

and Rehabilitation

15:00 Coffee Break

15:30 TUE-PM2 Special Session II: Architectures for Unmanned Systems

Organizers: Roger Bostelman & James Albus 

• UAV Architectures*

[George Vachtsevanos]

• Architectures for Unmanned Systems*

[James Albus]

• Levels-of-Autonomy of the ASTM F41 Unmanned Maritime Vehicles 

Standard*

[Mark Rothgeb]

• Ontological Perspectives for Autonomy Performance

[Hui-Min Huang, Elena Messina, Tsai Hong, Craig Schlenoff]

19:00 Reception

PROGRAM PERMIS

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*Presentation Only

xiv
PerMIS 2008 

W

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08:15 Overview

08:30 Plenary Presentation:

Erwin Prassler

Incremental Integration, Evaluation, and Harmonization of 

Components of a Reference Platform for Service Robotics

09:30 Coffee Break

10:00 WED-AM1 Metrics & Measures

Chairs: Scott Spetka & Robert Wade

• Robotic Systems Technical and Operational Metrics Correlation 

[Jason Schenk, Robert Wade] 

• Survey of Domain-Specific Performance Measures in Assistive Robotic 

Technology [Katherine Tsui, Holly Yanco, David Feil-Seifer, Maja Mataric]

• Refining the Cognitive Decathlon [Robert Simpson, Charles Twardy]

• Using Metrics to Optimize a High Performance Intelligent Image 

Processing Code [Scott Spetka, Susan Emeny, George Ramseyer, 

Richard Linderman]

• Measurement Techniques for Multiagent Systems

[Robert Lass, Evan Sultanik, William Regli]

• RoboCupRescue Robot League: 2008 Overview*

[Adam Jacoff, Andreas Birk, Johannes Pellenz, Ehsan Mihankhah, 

Raymond Sheh, Satoshi Tadokoro]

12:30 Lunch

14:00 Plenary Presentation:

Alonzo Kelly

Various Tradeoffs and Metrics of Performance for

Field Robots

15:00 Coffee Break

15:30 WED-PM1 Autonomous Systems

Chairs: James Gunderson & Edward Tunstel

• Integrating Reification and Ontologies for Mobile Autonomous 

Robots [James Gunderson, Louise Gunderson] 

• Quantification of Line Tracking Solutions for Automotive 

Applications [Jane Shi, Rick Rourke, Dave Groll, Peter Tavora]

• Mobile Robotic Surveying Performance for Planetary Surface Site 

Characterization [Edward Tunstel]

• Evaluating Situation Awareness of Autonomous Systems 

[Jan Gehrke]

18:30 Banquet

PROGRAM PERMIS

*Presentation Only

xv
PerMIS 2008 

August

08:15 Overview

08:30 Plenary Presentation:

Erwin Prassler

Incremental Integration, Evaluation, and Harmonization of 

Components of a Reference Platform for Service Robotics

09:30 Coffee Break

10:00 WED-AM2 Special Session III: Performance Metrics for Perception in 

Intelligent Manufacturing

Organizers: Tsai Hong & Roger Eastman

• Performance of Super-Resolution Enhancement for Flash LADAR Data 

[Shuowen Hu, Susan Young, Tsai Hong ]

• Performance Evaluation of Laser Trackers [Bala Muralikrishnan, Daniel Sawyer, 

Christopher Blackburn, Steven Phillips, Bruce Borchardt, Tyler Estler]

• Preliminary Analysis of Conveyor Dynamic Motion for Automation Applications 

[Jane Shi]

• 3D Part Identification Based on Local Shape Descriptors 

[Xiaolan Li, Afzal Godil, Asim Wagan]

• Calibration of a System of a Gray-Value Camera and an MDSI Range camera

[Tobias Hanning, Aless Lasaruk]

• Dynamic 6DOF Metrology for Evaluating a Visual Servoing System 

[Tommy Chang, Tsai Hong, Mike Shneier, German Holguin, Johnny Park, 

Roger Eastman]

12:30 Lunch

14:00 Plenary Presentation:

Alonzo Kelly

Various Tradeoffs and Metrics of Performance for 

Field Robots

15:00 Coffee Break

15:30 WED-PM2 Special Session IV: Results from a Virtual Manufacturing 

Automation Competition

Organizers: Stephen Balakirsky, Raj Madhavan & Chris Scrapper

• NIST/IEEE Virtual Manufacturing and Automation Competition: 

From Earliest Beginnings to Future Directions

[Stephen Balakirsky, Raj Madhavan, Chris Scrapper]

• Analysis of a Novel Docking Technique for Autonomous Robots

[George Henson, Michael Maynard, Xinlian Liu, George Dimitoglou]

• Partitioning Algorithm for Path Determination of Automated Robotic Part Delivery 

System in Manufacturing Environments [Payam Matin, Ali Eydgahi, Ranjith Chowdary]

• Algorithms and Performance Analysis for Path Navigation of Ackerman-Steered 

Autonomous Robots [George Henson, Michael Maynard, George Dimitoglou, Xinlian Liu]

18:30 Banquet

PROGRAM PERMIS

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PerMIS 2008 

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08:15 Overview

08:30 Plenary Presentation:

Sunil Kumar Agrawal

Robotic Exoskeletons for Gait Assistance and Training of 

the Motor Impaired

09:30 Coffee Break

10:00 THU-AM1 Model-based Performance Assessment

Chairs: Kate Remley & Kam Saidi

• Wireless Communications in Tunnels for Urban Search and Rescue 

Robots [Kate Remley, George Hough, Galen Koepke, Dennis Camell, 

Robert Johnk, Chriss Grosvenor]

• A Performance Assessment of Calibrated Camera Networks for 

Construction Site Monitoring [Itai Katz, Nicholas Scott, Kam Saidi]

• A Queuing-Theoretic Framework for Modeling and Analysis of Mobility 

in WSNs [Harsh Bhatia, Rathinasamy Lenin, Aarti Munjal, 

Srini Ramaswamy, Sanjay Srivastava]

• Towards Information Networks to Support Composable Manufacturing 

[Mahesh Mani, Albert Jones, Junho Shin, Ram Sriram]

• 3D Reconstruction of Rough Terrain for USARSim using a Height-map 

Method [Gael Roberts, Stephen Balakirsky, Sebti Foufou]

12:30 Lunch

14:00 THU-PM1 Special Session VI: Biologically Inspired Models of 

Intelligent Systems 

Organizer: Gary Berg-Cross

• Introduction to Biological Inspiration for Intelligent Systems

[Gary Berg-Cross]

• Overview of Biologically Inspired Cognitive Architectures (BICA)*

[Alexei Samsonovich]

• Recent modeling and Rapid Prototyping Experience Aimed at 

Building Architectures of Cognitive Agents*

[Giorgio Ascoli]

• Applying Developmental-Inspired Principles to the Field of 

Developmental Robotics

[Gary Berg-Cross] 

• Discussion of Biologically Inspired Models [Panel]

16:00 Coffee Break

16:30 Adjourn

PROGRAM PERMIS

*Presentation Only

xvii
PerMIS 2008 

August

08:15 Overview

08:30 Plenary Presentation:

Sunil Kumar Agrawal

Robotic Exoskeletons for Gait Assistance and Training of 

the Motor Impaired

09:30 Coffee Break

10:00 THU-AM2 Special Session V: Quantitative Assessment of Robotgenerated Maps

Organizers: Chris Scrapper, Raj Madhavan & Stephen Balakirsky 

• Characterizing Robot-Generated Maps: The Importance of 

Representations and Objective Metrics*

[Chris Scrapper, Raj Madhavan, Stephen Balakirsky]

• Using Virtual Scans to Improve Alignment Performance in Robot 

Mapping [Rolf Lakeamper, Nagesh Adluru]

• The Role of Bayesian Bounds in Comparing SLAM Algorithms 

Performance [Andrea Censi]

• Map Quality Assessment [Asim Wagan, Afzal Godil, Xiaolan Li]

• Discussion: Roadmap for Map Evaluation Frameworks

12:30 Lunch

14:00 THU-PM2 Special Session VII: Medical Robotics

Organizer: Ram Sriram

• Overcoming Barriers to Wider Adoption of Mobile Telerobotic 

Surgery: Engineering, Clinical and Business Challenges

[Gerald Moses, Charles Doarn, Blake Hannaford, Jacob Rosen]

• Calibration of a Computer Assisted Orthopaedic Hip Surgery 

Phantom

[Daniel Sawyer, Nick Dagalakis, Craig Shakarji, Yong Kim]

• HLPR Chair – A Novel Patient Transfer Device

[Roger Bostelman, James Albus, Joshua Johnson]

• Robotic Navigation in Crowded Environments: Key Challenges for 

Autonomous Navigation Systems [James Ballantyne, Salman 

Valibeik, Ara Darzi, Guang-Zhong Yang]

16:00 Coffee Break

16:30 Adjourn

PROGRAM PERMIS

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xviii
AUTHOR INDEX

Albus, J. ..................THU-PM2

Adluru, N. ................THU-AM2

Ascoli, G. ................THU-PM1

Bae, J. .....................TUE-PM1

Balakirsky, S. ..........WED-PM2

.................................THU-AM1

.................................THU-AM2

Ballantyne, J. ..........THU-PM2

Berg-Cross, G. ........THU-PM1

.................................THU-PM1

Bhatia, H. ................THU-AM1

Birk, A. ...................WED-AM1

Blackburn, C. .........WED-AM2

Borchardt, B. ..........WED-AM2

Bostelman, R. .........THU-PM2

Camell, D. ...............THU-AM1

Cangelosi, A. ...........TUE-AM2

Censi, A. .................THU-AM2

Chang, T. ................WED-AM2

Chowdary, R. .........WED-PM2

Corradi, P. ................TUE-AM2

Courtney, P. .............TUE-AM2

Cummings, M. .........TUE-PM1

Dagalakis, N. ...........THU-PM2

Darzi, A. ..................THU-PM2

Dimitoglou, G. ........WED-PM2

................................WED-PM2

Doarn, C. ................THU-PM2

Donmez. B. .............TUE-PM1

Downs, A. ................TUE-AM1

Eastman, R. ............WED-AM2

Eis, C. ......................TUE-AM2

Emeny, S. ...............WED-AM1

Estler, T. ..................WED-AM2

Eydgahi, A. .............WED-PM2

Feil-Seifer, D. ..........WED-AM1

Fitzpatrick, P. ...........TUE-AM2

Foufou, S. ................TUE-AM1

.................................THU-AM1

Gehrke, J. ...............WED-PM1

Godil, A. ..................TUE-AM1

................................WED-AM2

.................................THU-AM2

Godzdanker, R. .......TUE-PM1

Groll, D. ..................WED-PM1

Grosvenor, C. ..........THU-AM1

Gunderson, J. ........WED-PM1

Gunderson, L. ........WED-PM1

Hannaford, B. ..........THU-PM2

Hanning, T. .............WED-AM2

Henson, G. .............WED-PM2

................................WED-PM2

Holguin, G. .............WED-AM2

Hong, T. ...................TUE-PM2

................................WED-AM2

................................WED-AM2

Hough, G. ...............THU-AM1

Hu, S. .....................WED-AM2

Huang, H-M. ............TUE-PM2

Jacoff, A. .................TUE-AM1

................................WED-AM1

Jebens, K. ...............TUE-AM2

Johnk, R. .................THU-AM1

Johnson, J. .............THU-PM2

Jones, A. .................THU-AM1

Katz, I. .....................THU-AM1

Kernbach, S. ...........TUE-AM2

Kim, Y. .....................THU-PM2

Koepke, G. ..............THU-AM1

Kootbally, Z. ............TUE-AM1

Krenn, B. .................TUE-AM2

Lakeamper, R. .........THU-AM2

Laneri, D. .................TUE-AM2

Lasaruk, A. .............WED-AM2

Lass, R. ..................WED-AM1

Lenin, R. ..................THU-AM1

Lewis, M. .................TUE-AM1

.................................TUE-PM1

Li, X. ........................TUE-AM1

................................WED-AM2

.................................THU-AM2

Liu, X. .....................WED-PM2

................................WED-PM2

Liedke, J. .................TUE-AM2

Linderman, R. .........WED-AM1

Madhavan, R. ..........TUE-AM1

................................WED-PM2

.................................THU-AM2

Mani, M. ..................THU-AM1

Mataric, M. .............WED-AM1

Matin, P. .................WED-PM2

Maynard, M. ...........WED-PM2

................................WED-PM2

Meister, E. ...............TUE-AM2

Messina, M. .............TUE-AM1

.................................TUE-PM2

Metta, G. .................TUE-AM2

.................................TUE-AM2

Michel, O. ................TUE-AM2

Mihankhah, E. ........WED-AM1

Moses, G. ...............THU-PM2

Munjal, A. ................THU-AM1

Muralikrishnan, B. ..WED-AM2

Natale, L. .................TUE-AM2

.................................TUE-AM2

Nori, F. .....................TUE-AM2

.................................TUE-AM2

Park, J. ...................WED-AM2

Pellenz, J. ..............WED-AM1

Phillips, S. ..............WED-AM2

Pina, P. ....................TUE-PM1

Ramaswamy, S. ......THU-AM1

Ramseyer, G. ..........WED-AM1

Regli, W. .................WED-AM1

Remley, K. ...............THU-AM1

Ricotti, L. .................TUE-AM2

Roberts, G. .............THU-AM1

Rohrer, F. .................TUE-AM2

Rosen, J. .................THU-PM2

Rothgeb, M. ............TUE-PM2

Rourke, R. ..............WED-PM1

Saidi, K. ..................THU-AM1

Samsonovich, A. .....THU-PM1

Sandini, G. ...............TUE-AM2

Sawyer, D. ..............WED-AM2

.................................THU-PM2

Scerri, P. ..................TUE-AM1

Schenk, J. ..............WED-AM1

Schlachter, F. ...........TUE-AM2

Schlenoff, C. ............TUE-AM1

.................................TUE-AM1

.................................TUE-PM2

Schmickl, T. .............TUE-AM2

Scott, N. ..................THU-AM1

Scrapper, C. ...........WED-PM2

.................................THU-AM2

Shakarji, C. .............THU-PM2

Sheh, R. .................WED-AM1

Shi, J. .....................WED-AM2

................................WED-PM1

Shin, J. ....................THU-AM1

PerMIS 2008 xix
Shneier, M. .............WED-AM2

Simpson, R. ...........WED-AM1

Skowron, M. ............TUE-AM2

Spall, J. ...................TUE-AM1

Spetka, S. ..............WED-AM1

Sriram, R. ................THU-AM1

Srivastava, S. ..........THU-AM1

Stefanuk, V. .............TUE-PM1

Sultanik, E. .............WED-AM1

Sycara, K. ................TUE-AM1

Szymanski, M. .........TUE-AM2

Tadokoro, S. ..........WED-AM1

Tavora, P. ................WED-PM1

Thenius, R. ..............TUE-AM2

Tikhanoff, V. .............TUE-AM2

Tsui, K. ...................WED-AM1

Tunstel, E. ..............WED-PM1

Twardy, C. ..............WED-AM1

Vachtsevanos, G. ....TUE-PM2

Valibeik, S. ..............THU-PM2

Velagapudi, P. ..........TUE-AM1

Vernon, D. ...............TUE-AM2

Virts, A. ....................TUE-AM1

Voyles, R. ................TUE-PM1

Wade, R. ................WED-AM1

Wagan, A. ................TUE-AM1

................................WED-AM2

.................................THU-AM2

Wang, H. .................TUE-AM1

Wang, J. ..................TUE-PM1

Weiss. B. .................TUE-AM1

Winkler, L. ................TUE-AM2

Yanco, H. ................WED-AM1

Yang, G-Z. ...............THU-PM2

Young, S. ................WED-AM2

PerMIS 2008 xx
ACKNOWLEDGMENTS

These people provided essential support to make this event happen. Their 

ideas and efforts are very much appreciated.

Website and Proceedings

Debbie Russell

Local Arrangements

Jeanenne Salvermoser

Conference and Registration

Mary Lou Norris

Kathy Kilmer

Angela Ellis

Teresa Vicente

PerMIS 2008 

Intelligent Systems Division 

Manufacturing Engineering Laboratory 

National Institute of Standards and Technology

100 Bureau Drive, MS-8230

Gaithersburg, MD 20899 

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attendees!

xxi
Evolution of the SCORE Framework to Enhance FieldBased Performance Evaluations of Emerging 

Technologies

Brian A. Weiss and Craig Schlenoff 

National Institute of Standards and Technology 

100 Bureau Drive, MS 8230 

Gaithersburg, Maryland 20899 USA 

+1.301.975.4373, +1.301.975.3456 

brian.weiss@nist.gov, craig.schlenoff@nist.gov

ABSTRACT

NIST has developed the System, Component, and OperationallyRelevant Evaluations (SCORE) framework as a formal guide for 

designing evaluations of emerging technologies. SCORE captures 

both technical performance and end-user utility assessments of 

systems and their components within controlled and realistic 

environments. Its purpose is to present an extensive (but not 

necessarily exhaustive) picture of how a system would behave in a 

realistic operating environment. The framework has been applied 

to numerous evaluation efforts over the past three years producing 

valuable quantitative and qualitative metrics. This paper will 

present the building blocks of the SCORE methodology including 

the system goals and design criteria that drive the evaluation 

design process. An evolution of the SCORE framework in 

capturing utility assessments at the capability level of a system 

will also be presented. Examples will be shown of SCORE’s 

successful application to the evaluation of the soldier-worn sensor 

systems and two-way, free-form spoken language translation 

technologies. 

Categories and Subject Descriptors

C.4 [Performance of Systems]: measurement techniques, 

modeling techniques, performance attributes. 

General Terms

Measurement, Documentation, Performance, Experimentation, 

Verification. 

Keywords

SCORE, DARPA, ASSIST, TRANSTAC, performance 

evaluation, elemental tests, vignette tests, task tests, speech 

translation, soldier-worn sensor. 

1. INTRODUCTION

As intelligent systems emerge and take shape, it is important to 

understand their capabilities and limitations. Evaluations are a 

means to assess both quantitative technical performance and 

qualitative end-user utility. System, Component and Operationally 

Relevant Evaluations (SCORE) is a unified set of criteria and 

software tools for defining a performance evaluation approach for 

intelligent systems. It provides a comprehensive evaluation 

blueprint that assesses the technical performance of a system and 

its components through isolating and changing variables as well 

as capturing end-user utility of the system in realistic use-case 

environments. SCORE is unique in that: 

x It is applicable to a wide range of technologies, from 

manufacturing to defense systems 

x Elements of SCORE can be decoupled and customized 

based upon evaluation goals 

x It has the ability to evaluate a technology at various stages 

of development, from conceptual to full maturation 

x It combines the results of targeted evaluations to produce an 

extensive picture of a systems’ capabilities and utility 

Section 2 introduces the SCORE framework and its initial 

evaluation design structure. Section 3 presents SCORE’s first 

applications in evaluating technologies developed under the 

Defense Advanced Research Projects Agency’s (DARPA) 

Advanced Soldier Sensor Information System and Technology 

(ASSIST), Phase I and II program along with DARPA’s Spoken 

Language Communication and Translation System for Tactical 

Use (TRANSTAC) Phase II program. Section 4 discusses the 

evolution of the framework necessitated by the advancing goals of 

the ASSIST and TRANSTAC programs. Section 5 describes some 

future efforts (outside of the above military-based programs) that 

are expected to use the SCORE framework. Section 6 concludes 

the paper. 

2. BACKGROUND

2.1 SCORE Development 

Intelligent systems tend to be complex and non-deterministic, 

involving numerous components that are jointly working together 

to accomplish an overall goal. Existing approaches to measuring 

such systems often focus on evaluating the system as a whole or 

individually evaluating some of the components under very 

controlled, but limited, conditions. These approaches do not 

comprehensively and quantitatively assess the impact of variables 

such as environmental variables (e.g, weather) and system 

variables (e.g., processing power, memory size) on the system’s 

overall performance. The SCORE framework, with its 

comprehensive evaluation criteria and software tools, is developed 

to enhance the ability to quantitatively and qualitatively evaluate 

intelligent systems at the component level -- and the system level 

-- in both controlled and operationally-relevant environments. 

SCORE leverages the multi-level Steves/Scholtz evaluation 

framework that defines metrics and measures in the context of 

This paper is authored by employees of the United States 

Government and is in the public domain. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA. 

ACM ISBN 978-1-60558-293-1/08/08. 

1
system goals and evaluation objectives, and combines these 

assessments for an overall evaluation of a system [1]. SCORE 

takes the framework a step further by identifying specific system 

goals and areas of interest. It is built around the premise that, in 

order to get a comprehensive picture of how a system performs in 

its actual use-case environment, technical performance should be 

evaluated at the component and system levels [2]. Additionally, 

system level utility assessments should be performed to gain an 

understanding of the value the system provides to the end-users. 

SCORE defines three evaluation goal types: 

x Component Level Testing – Technical Performance – This 

evaluation type involves decomposing a system into 

components to isolate those subsystems that are critical to 

system operation. Ideally, all of the components together, 

should include all facets of the system and yield a complete 

evaluation. 

x System Level Testing – Technical Performance – This 

evaluation type is intended to assess the system as a whole, 

but in an ideal environment where test variables can be 

isolated and controlled. The benefit is that tests can be 

performed using a combination of test variables and 

parameters, where relationships can be determined between 

system behavior and these variables and parameters based 

upon the technical performance analysis. 

x System Level Testing – Utility Assessments – This 

evaluation class assesses a system’s utility, where utility is 

defined as the value the application provides to the end-user. 

In addition, usability is assessed which includes 

effectiveness, learnability, flexibility, and user attitude 

towards the system. The advantage of this evaluation mode 

is that system’s utility and value can still be addressed even 

when the system design and user-interface are not yet 

finalized (i.e. the working version in place is not perfected). 

For each of these three goal types, the following evaluation 

elements are pertinent: 

x Identification of the system or component to be assessed 

x Definition of the goal/objective(s)/metrics/ measures 

o Goal – For a particular assessment, the goal is 

influenced by whether the intent of the evaluation is to 

inform or validate the system design. The state of 

system maturity also weighs heavily on the goal 

specification 

o Objectives – Evaluation objectives are used to separate 

evaluation concerns. These evaluation concerns also 

include identifying how different variables impact 

system performance and determining which should be 

fixed and which should be modified during testing. 

o Metrics/measures – Depending upon the type of 

evaluation, either technical performance metrics or 

utility metrics would be employed. 

x Specification of the testing environment(s) – Selecting a 

testing environment is influenced by a range of aspects 

including system maturity, intended use-case environments, 

physical issues, site suitability, etc. 

x Identification of participants – The system users, whether 

they are the technology developers and/or end-users needs 

to be determined. Actors that will be indirectly interacting 

with the system through role-playing within the 

environment also need to be identified. 

x Specification of participant training – Technology users 

must be properly instructed (and have time to practice) on 

how to appropriately interact/engage the systems. Likewise, 

the environmental actors require guidance as to how they 

should perform throughout the test(s). 

x Specification of data collection methods – As measures and 

metrics are specified, data capture methods must be 

formulated.

x Specification of the use-case scenarios – The evaluation 

architect must devise the use scenario(s) under which the 

system (or component) will be tested. 

Considering each of these evaluation elements, SCORE takes a 

tiered approach to measuring the performance of intelligent 

systems. At the lowest level, SCORE uses component level tests 

to isolate specific components and then systematically modifies 

variables that could affect the performance of that component to 

determine those variables’ impact. Typically, this is performed for 

each relevant component within the system. At the next level, the 

overall system is tested in a highly structured environment to 

understand the performance of individual variables on the system. 

Lastly, the technology is immersed in a richer scenario that 

evokes typical situations and surroundings in which the end-user 

is asked to perform an overall mission or procedure in a highlyrelevant environment which stresses the overall system’s 

capabilities. Formal surveys and semi-structured interviews are 

used to assess the usefulness of the technology to the end-user. 

3. INITIAL APPLICATIONS 

SCORE was initially applied to intelligent systems developed 

under the DARPA ASSIST and TRANSTAC programs. The 

SCORE-based evaluations also provided the researchers and endusers with the information needed to determine if and when the 

technology will be ready for actual use. The SCORE framework 

identified various key components of the system and evaluated 

them both independently and as a whole, thus helping to 

determine the impact of the individual components on the 

performance of the overall system. This detailed analysis allowed 

the evaluation team, and the sponsor, to more accurately target the 

aspects of the systems that were shown to provide the greatest 

benefit to the overall advancement of the technology. Prior to 

adopting SCORE, DARPA did not have this level of necessary 

detail about system and component performance. 

3.1 ASSIST – Phase I and II 

The DARPA ASSIST program is an advanced technology 

research and development program whose objective is to exploit 

soldier-worn sensors to augment a Soldier’s mission recall and 

reporting capability to enhance situational knowledge within 

Military Operations in Urban Terrain (MOUT) environments [3]. 

This program is split into two tasks with the NIST Independent 

Evaluation Team (IET) focused on evaluating task 2 technology. 

This task stresses passive collection and automated activity/object 

recognition capabilities in the form of algorithms, software, and 

tools that will undergo system integration in future efforts. 

The process of applying the SCORE framework to the ASSIST 

evaluations begins with identifying the specific technologies. The 

technologies were developed by three different research teams. It 

should be noted that there is no single, fully-integrated ASSIST 

system, so each team focused their attention on some unique 

and/or overlapping technologies. The Phase I and Phase II 

capabilities are broken out as follows: 

2
x Image/Video Data Analysis Capabilities 

o Object Detection/ Image Classification (Phase I) 

o Arabic Text Translation (Phase I) 

o Face Recognition and Matching (Phase II) 

x Audio Data Analysis Capabilities 

o Sound Recognition/Speech Recognition (Phase I) 

o Shot Localization/Weapon Classification (Phase I) 

x Soldier Activity Data Analysis Capabilities 

o Soldier State Identification/Localization (Phase I and II) 

Further explanation of these technologies can be found in [3] and 

[4]. The next crucial step is to determine the evaluation goals/ 

objectives and metrics/measures. As outlined by DARPA, at a 

high level, they are: 

1. The accuracy of object/event/activity identification and 

labeling.

2. The system’s ability to improve its classification 

performance through learning. 

3. The utility of the system in enhancing operational 

effectiveness. 

Guided by the SCORE framework, component and system level 

technical performance tests are developed to handle metrics 1 and 

2, while system level utility assessments are designed to address 

the third metric. The quantitative performance tests are 

accomplished through elemental tests, while the qualitative tests 

are done through vignette tests. 

3.1.1 Elemental Tests 

This test type was used to measure technical performance at both 

the component and system levels [4]. Specifically, this test type 

afforded the designer the ability to place tight controls on the 

testing environment including modifying specific test variables in 

order to measure their impact on a technology’s performance. The 

elemental tests that were developed across the ASSIST Phase I 

and II evaluations include: 

x Arabic text translation – This test was designed to evaluate 

the Arabic text translation ability at both the component and 

system levels. Component level elemental tests include 

specific measurements of the technology’s ability to 1) 

Identify Arabic text in an image, 2) Extract Arabic text from 

an image, and 3) Translate Arabic text to English text. The 

system level elemental test measured the technology’s startto-finish ability from capturing an image of Arabic text and 

to successfully translating the text into English.

x Face recognition and matching – Likewise, this elemental 

test evaluated the face recognition technology at the 

component and system levels. The component level test 

occurred in the form of an offline evaluation where test 

images of faces were directly fed into a computer running 

the matching algorithm and compared against a preloaded 

watchlist of images. Accuracy measures were calculated 

based upon the system’s output as compared to the ground 

truth. The system level test evaluated the full 

hardware/software technology package in a controlled 

environment by measuring the time and accuracy for the 

system to capture a person’s image and match them against 

a watchlist.

x Object detection/image classification – This elemental test 

evaluated these technologies at the system level. The test 

began with end-users capturing feature/object-laden images 

of the environment with the evaluation team analyzing their 

output of the number of objects detected/images classified. 

x Shot localization/weapon classification - A system level 

elemental test was designed to evaluate the accuracy of this 

technology’s ability to detect gunshots, calculate a shot’s 

trajectory, localize a shot’s origin, identify the caliber of 

bullet fired and classify the weapon that fired the shot (see 

Figure 1 for an example output). 

x Soldier state/localization – A system level elemental test 

was created to assess the ASSIST system’s ability to 

characterize a Soldier’s actions within indoor and outdoor 

environments.

x Sound/speech recognition – A system level elemental test 

was devised to evaluate the technology’s ability to detect 

specific sounds within the environment. 

Figure 1: Shot localization/weapon classification output 

Once the technologies and their respective elemental tests were 

ascertained, the next step was to define the specific metrics and 

measures. This step also included identifying the influential 

variables that impact performance, specifically highlighting which 

variables should be fixed along with those that should be altered 

during the test(s). More information on this step with respect to 

the ASSIST evaluations can be found in [2] [4]. 

It was now time to identify a suitable testing environment for each 

of these elemental tests. It was determined that the system-level 

elemental tests would be conducted at a MOUT site at the 

Aberdeen Proving Grounds in Maryland. The only exception to 

this was the shot localization/weapon classification test. Since live 

gunfire was necessary to accurately assess this technology and 

safety restrictions were in place at the MOUT site, this technology 

was evaluated at a live fire range adjacent to the MOUT site. 

Locating a test environment for the component level elemental 

tests was less taxing since these could be run practically anywhere 

since they were run on common personal computers (PCs). 

Choosing participants was the next step, specifically those that 

will use the technology (whether it be the members of the enduser population or the technology developers) and those that will 

indirectly interact with the systems (including those playing roles 

within the environments). Per DARPA’s instructions, Phase I 

evaluations had the technology developers use/wear their ASSIST 

systems and shadow the movements of partner Soldiers. This 

restriction was reduced as both researchers and end-users 

(Soldiers) used/wore the systems throughout the Phase II 

evaluations. 

Training of these personnel played a critical role in the 

evaluations. For Phase I that called for the developers to use their 

own systems, the training consisted of familiarizing these 

3
personnel with the scope of the elemental tests, not the technology 

(since they were the ones that created the systems). However, 

when the Soldiers stepped in to use the technology during later 

evaluations, they had to be trained not only on the scope of the 

elemental tests, but also on how to use the technology. Likewise, 

the actors in the environment (e.g. the people whose faces were 

captured to support the face recognition technology, the shooters 

who fired the weapons to test the shot localization/weapon 

classification technology, etc.) all had to be trained on their roles. 

Additionally, it was necessary to determine how data was to be 

collected from the ASSIST technologies (and the environment, 

where necessary). Successfully undertaking this task required that 

the technology outputs are known (which, according to the 

SCORE framework, are highlighted as the technologies for 

evaluation are identified) along with realizing what critical data 

could be captured from the environment. Data collection can be as 

simple as measuring the amount of time it takes for the face 

recognition/matching algorithm to return a match. It can also 

require more complex actions such as an IET member noting 

specific actions of the system-wearer into a voice-recorder and 

then comparing those actions with corresponding times (from 

their audible notes) to that of a technology system-output log file. 

For each of the described elemental tests, data collection methods 

were determined based upon the available output data and the 

metrics necessary for each evaluation. 

Going hand-in-hand with determining the data collection 

methodology and the required personnel were the scenarios in 

which the components/systems were tested. These use-case 

scenarios were developed based upon the expected concept(s) of 

operation (CONOPS) while keeping in mind the technology’s 

current state of maturity. Specifically, CONOPS is a “formal 

document that employs users' terminology and a specific, 

prescribed format to describe the rationale, uses, operating 

concept, capabilities and benefits of a system” [5]. The challenge 

in this step is that CONOPS do not often exist for emerging 

technologies. To surmount this obstacle, the IET developed usecase scenarios with end-user and technology developer input. 

These test scenarios are presented in great detail in [2] [4]. 

Going through these SCORE-prescribed steps in order to assess 

technical performance at the component and system levels 

produced comprehensive evaluations for the above mentioned 

ASSIST technologies. SCORE was also applied to develop 

system level utility assessments in the form of vignette tests. 

3.1.2 Vignette Tests 

This test type was used to perform System Level Testing – Utility 

Assessment of the ASSIST technologies [6]. In this case, utility is 

defined as the value that a technology or piece of equipment 

provides to an end-user. Utility assessments were uniquely 

designed given the technology’s state of maturity. Typically, a 

system’s utility can still be evaluated prior to its full development 

where the intent of the assessment is to inform on the system 

design. Assessments done at the end of a technology’s 

development cycle are intended to validate the value of the 

system. The former evaluation type is known as formative while 

the latter is defined as summative. 

Since the ASSIST technologies were young in development, these 

formative vignette tests took the form of several operationallyrelevant, mini-mission scenarios where end-users employed the 

technology in use-case situations to accomplish their mission 

objectives. Informing the developers about the capabilities of the 

ASSIST technology became the goal in the design and execution 

of the SCORE-driven utility evaluations. It should be noted that 

all of the ASSIST Phase I and II technologies were evaluated 

under vignette tests with the exception of the shot 

localization/weapon classification due to safety considerations. 

Measures were identified in the form of end-user surveys and 

semi-structured interviews. The end-users (Soldiers in the case of 

the ASSIST evaluations) were presented with a suite of survey 

questions that they answered with respect to their recent 

experiences with the technology. Furthermore, the Soldiers were 

interviewed (without the technology developers being present) to 

gain further insight into what features/capabilities they liked, what 

they didn’t like, and what improvements should be made. The 

responses were rolled up into technology utility assessments. 

The Aberdeen MOUT site presented a small-scale, middleEastern-like village where Soldiers frequently train. This test 

environment provided over a dozen single-story and two-story 

buildings that challenged the ASSIST technology-laden end-users. 

The participants selected to use the technology and to interact 

with the end-users in the environment were chosen in an identical 

manner to that of the individuals selected for the elemental tests. 

Phase I started with the researchers wearing their own 

technologies and shadowing the Soldiers during the elemental and 

vignette tests while Phase II put the technology directly on the 

Soldiers. In both phases, extras/environmental actors were 

employed to bring about more realism in the vignette test 

environment. Training for these participants is similar for what 

was done in support of the elemental tests. When the Soldiers 

were wearing the technology, they were provided specific training 

by the research teams so they would be competent in the systems’ 

basic operations. 

Some of the data collection methods are already presented in the 

form of survey instruments and semi-structured interviews. 

Additionally, several evaluation team members were strategically 

placed within the environment to observe the Soldiers, the 

researchers (when they wearing the technology during Phase I), 

and the extras acting within the environment. 

In parallel, the specific vignette mission scenarios were created. 

After considering the various SCORE-prescribed factors and 

interviewing subject matter experts, the following missionscenarios were used throughout the various evaluations in Phase I 

and II included: 

x Presence patrol with deliberate search 

x Presence patrol leading to a cordon and search 

x Presence patrol and improvised explosive device site 

reconnaissance

x Assessment of local village with respect to an upcoming 

election 

x Presence patrol leading to checkpoint operations 

Prior to the execution of each mission, the Soldiers were briefed 

on their specific objectives and told to react accordingly to the 

environment based upon their tactical training. The Soldiers were 

also reminded of the available ASSIST technologies at their 

disposal and instructed to use them as they see fit to accomplish 

their mission objectives. 

Using the SCORE framework, elemental and vignette tests were 

designed and executed to provide the program sponsor with the 

4
requested data in addition to informing the researchers on the state 

of their technologies. The next subsection will show how SCORE 

has been applied to evaluate another technology. 

3.2 TRANSTAC – Phase II 

TRANSTAC is another DARPA advanced technology and 

research program whose goal is to demonstrate capabilities to 

rapidly develop and field free-form, two-way speech-to-speech 

translation systems enabling English and foreign language 

speakers to communicate with one another in real-world tactical 

situations where an interpreter is unavailable [7]. Several 

prototype systems have been developed under this program for 

numerous military applications including force protection and 

medical screening. The technology has been demonstrated on 

PDA (personal digital assistant) and laptop platforms. DARPA 

asked NIST to assess these systems starting in Phase II of this 

program (another team evaluated these systems during Phase I). 

Five different research teams presented systems for evaluations 

during this phase. 

The NIST IET applied the SCORE framework to this program 

because this approach would scale well as the systems continued 

to mature and DARPA wanted both technical performance and 

utility assessments of the technology. Specifically, the following 

test types were conducted during the Phase II evaluations: 

1. System usability testing – providing overall scores to the 

capabilities of the whole system. 

2. Software component testing – evaluating components of a 

system to see how well they perform in isolation. 

The IET implemented a two-part test methodology to produce 

these metrics. Metric 1 was evaluated through the use of 

structured scenarios within live evaluations, while metric 2 was 

evaluated through the use of pre-recorded utterances within 

offline evaluations. 

3.2.1 Offline Evaluations 

The offline evaluations, which represent the Component Level 

Testing – Technical Performance aspect of the TRANSTAC 

evaluation, were designed to test the TRANSTAC systems with 

exactly the same set of data so comparison among the systems 

would truly be “apples-to-apples.” Identical speech utterances, 

both English and foreign language, were fed into each developer’s 

system. These utterances were collected from audio recordings 

from data gathering events. First, an audio file was fed into each 

system to test the systems’ speech-to-text (S to T) capabilities. 

Then a text format to test their systems’ text-to-text (T to T) 

capabilities was fed into each technology. Since the system 

outputs include translated text and speech, metrics were extracted 

through comparison of the system outputs to ground truth. A 

range of metrics including low-level concept transfer and 

automated metrics were extracted from the offline outputs [8]. 

Since this evaluation focused on inputting utterances into each 

development teams’ system, choosing the appropriate test site was 

trivial. For simplicity, the offline evaluation was conducted at the 

same site as the live evaluations since there were tighter venue 

constraints for these tests. Additionally, participant selection and 

training is very straight forward. An offline evaluation specialist 

worked with a member of each research team to ensure that each 

system accepted the offline utterances without incident. 

The use-case scenarios under which the utterances (both audible 

and text speech) were generated stemmed from the supporting 

data collections (and their respective scenarios) that took place 

months in advance of the evaluation. This scenario development 

process began with the IET meeting with the technology’s 

potential end-users, both English-speaking military personnel and 

foreign language experts, to determine the representative usecases in which this type of technology would be most beneficial. 

Once those situations were established, the IET developed 

scenarios that were used in the data collections. The data 

collections brought together English and foreign language 

speakers to talk/role-play through the data collection scenarios 

that produced 10 to 20 minute data collection dialogues. Each of 

the audio dialogues were transcribed and translated. A majority of 

the data was provided to the developers to train their systems 

while the remainder was held out by the IET to create the 

evaluation scenarios. Utterances from the evaluation set were 

selected to be used in the offline evaluation. 

3.2.2 Live Evaluations 

The live evaluations were performed in two different venues, the 

lab and the field (both containing facets of System Level Testing – 

Technical Performance and System Level Testing – Utility 

Assessment) and were conducted with structured scenarios. This 

scenario type provided a set of questions to the English speaker 

that they needed to find answers, while the foreign language 

speaker was given the answers to those questions in paragraph 

format. A dialogue occurred between the two speakers and the 

number of questions that the English speaker was able to get 

answered were noted. In addition, surveys were provided to the 

English and foreign language speakers to gauge their perception 

of the TRANSTAC systems. 

Lab evaluations were designed to test the TRANSTAC systems in 

an idealistic environment, with no background noise and the 

participants being stationary. The TRANSTAC systems were 

placed on a table as opposed to being worn by the speakers. This 

idealistic environment gave the IET and the developers an idea of 

the best that the systems can do at this stage in their development. 

The purpose of the field evaluations was to test the TRANSTAC 

systems in a more realistic environment. This included wellcontrolled background noise, the English-speakers carrying the 

TRANSTAC systems, and both the English and foreign language 

speakers being mobile during the evaluation. 

Twenty structured scenarios (ten in the lab and ten in the field) 

were designed to foster the evaluation dialogues. These scenarios 

were derived from the same held back scenarios that the offline 

scenarios originate. 

The system users for these evaluations were chosen to be potential 

TRANSTAC system end-users including both English-speaking 

military personnel and representative foreign language speakers. 

Training and preparation of these individuals was critical. These 

individuals had to be both trained on the proper usage of the 

TRANSTAC systems, but also had to be educated on the 

procedures and flow of the structured scenarios. This training was 

done sequentially to enable the IET the ability to isolate and 

address any areas of concern. 

Selecting a site for these evaluations required the consideration of 

numerous factors including a location that could support the 

offline, lab, and field evaluations, a spot that could accommodate 

50+ personnel, a site that was available for six consecutive days, 

etc. Ultimately, the NIST campus was selected after extensive 

exploration.

5
3.3 Initial Findings using SCORE 

The ASSIST Phase I and II and TRANSTAC Phase II evaluations 

were successful events that provided DARPA with the necessary 

and detailed results desired by the programs. SCORE is viewed as 

a contributor to this success due to the extensive nature in which it 

laid out these evaluations. Following its prescribed steps and 

addressing each evaluation component ensured that 

comprehensive and relevant evaluations were generated. The 

following section will show how SCORE has evolved to produce 

innovative evaluations as the ASSIST and TRANSTAC programs 

further advance. 

4. EVOLUTION of the FRAMEWORK 

Both the ASSIST and TRANSTAC programs have since moved 

into Phase III. To date, two ASSIST Phase III evaluations have 

been performed while a single TRANSTAC Phase III evaluation 

has already occurred with each program having one more Phase 

III evaluation to go. Since these programmatic goals have changed 

from the previous phases, the SCORE framework has evolved to 

produce the desired metrics. One major innovation is the addition 

of a fourth evaluation goal type, described below: 

x Capability Level Testing – Utility Assessments – This 

evaluation group is proposed to assess the utility of an 

individual capability (where the complete system is made up 

of multiple capabilities), where utility is defined as the value 

the application provides to the system end-user (just as it is 

System Level Testing – Utility Assessments). The benefit of 

this evaluation type is that specific capability utility and 

usability to the end-user can still be addressed even when 

the system and user-interface are still under development. 

This goal type can be inserted into the tiered approach either after 

the Component Level Testing – Technical Performance or the 

System Level Testing – Technical Performance goal types. 

Each of the evaluation elements described in section 2.1 are 

applied to this new goal type. This new SCORE addition will be 

presented within the following discussion of the ASSIST Phase III 

evaluation design whereas further applications of SCORE will be 

discussed in TRANSTAC Phase III evaluation plan. 

4.1 ASSIST – Phase III 

As the ASSIST program moved into Phase III, the program 

evaluation focus was altered to place more emphasis on end-user 

utility assessments as opposed to technical performance. With the 

technologies further along in their development cycles (as 

compared to their status in earlier phases), it was becoming more 

important to gain insight into the end-users’ value of specific 

capabilities. In addition to emphasizing utility assessments, the 

program is now more focused on real-time capabilities as opposed 

to those that support after-mission reporting. Three separate 

research teams produced Phase III evaluation technologies that 

included the following capabilities: 

x Face recognition/matching 

o Face image collection using commercial off-the-shelf 

(COTS) hardware 

o Face image matching displayed on COTS wearable 

interface 

x Real-time information collection and sharing

o Automatic capture of image, audio, and GPS data 

o End-user viewing own-captured data on wearable, 

COTS visual display (see Figure 2) 

o Transmit/receive image and GPS data to/from other 

ASSIST units 

x After-mission reporting 

o Retrieving mission data at specific times and locations 

o Locating field-marked significant actions 

o Observing soldier state analytics 

Figure 2: Soldier using real-time data collection ASSIST system 

To satisfy the program goals, only technical performance 

evaluations were designed for the face recognition/matching 

technology at both the component and system levels. This took 

the form of elemental tests, similar to those outlined in section 

3.1.1. Additionally, system level utility assessments were 

collected for the real-time information sharing and after-mission 

reporting technologies through additional vignettes (comparable 

to those presented in section 3.1.2.). 

However, the need to gather further utility assessments, especially 

of the face recognition/matching technology which was not 

evaluated in the vignette tests during this phase, spawned the 

SCORE evaluation goal type of Capability Level Testing – Utility 

Assessment. This inspired the development of task tests whose 

intent was to assess end-user utility of specific capabilities within 

the various ASSIST technologies. 

After determining the objective of the task evaluations, the IET 

continued down the path of identifying the remainder of the 

SCORE evaluation elements by identifying the necessary 

measures and metrics. The measures extracted from this test 

include IET observer notes (made while following the end-users 

with the technology during the tasks) along with surveys 

presented to the end-users at the conclusion of each task (similar 

to those given at the end of the vignette tests). The data collection 

methods used to gather the observer notes include the use of handheld PDA note-taking devices while the surveys were 

administered via PC. The survey results and observer notes were 

combined to produce the necessary metrics (similar to what was 

done to produce the metrics from the vignette tests). 

These task tests, in addition to the elemental and vignette tests, 

took place at the same Aberdeen MOUT site that supported the 

Phase I and II evaluations. Multiple participants were required for 

the task tests. Soldiers, the ultimate end-users, were selected to 

use/wear the systems throughout the task tests. For the task tests 

(like the other test types), training was a critical component. 

Specific time was set up for the research teams to brief the 

Soldiers on their technology along with allowing them an 

opportunity to have hands-on practice with the various systems. 

Additionally, training time was also allocated for the Soldiers to 

become competent with the specific task tests (both, the test 

objectives and flow). Prior to the Soldiers running these tasks, 

6
they were briefed on the specific task objectives (both with 

respect to using the technology and the tactical goals). Following 

the briefing, the end-users and the IET practiced each of the task 

runs (without the technology) to ensure everyone was competent 

with the tests when it became time to run them with the 

technology. 

The task test scenarios were created in parallel to addressing the 

numerous steps presented above. Tasks were developed to 

specifically address all of the Phase III technology capabilities 

including the following: 

x Street observation and interaction – This task was developed 

to specifically test real-time image sharing across multiple 

ASSIST systems. 

x Presence Patrol – This task was designed to evaluate 

personnel tracking, GPS positioning and map annotation 

capabilities.

x Insurgent Surveillance – This test was created to assess the 

capability of image and map transfer between the laptopbased systems and ground-based wearable ASSIST 

technologies. 

x Insurgent Surveillance and Ambush – This task was created 

to test the ASSIST technology’s ability to calculate soldier 

state analytics.

x Base/entry checkpoint – This task was developed to test the 

face recognition/matching system’s ability to capture 

images in the field and present matches in real-time on the 

system-wearer’s personnel interface. 

These tasks were designed to be between 10 to 15 minutes in 

length where each was run twice. The runs were also set up to 

have three end-users use the relevant ASSIST technology with an 

emphasis on the specified capabilities. Two Soldiers used the 

portable, wearable technology while the other user interacted with 

the laptop-based system. 

Addressing each one of the SCORE framework elements with 

respect to the task tests enhanced the effectiveness of this series of 

evaluations at the most recent ASSIST events. Comprehensive 

utility assessments were collected from the task tests which 

enabled the IET to produce an extensive picture of the current 

state of the ASSIST technologies when combined with the 

elemental and vignette test data. 

This additional Capability Level Testing – Utility Assessment is an 

advancement in the SCORE framework. Additional improvements 

will be shown in the following section discussing the latest phase 

of the DARPA TRANSTAC program. 

4.2 TRANSTAC – Phase III 

Phase III of the DARPA TRANSTAC program continues to 

present the same overall evaluation objectives as presented in 

Phase II. Additionally, this phase brought about additional 

technical performance and utility assessments of several specific 

TRANSTAC technologies including a ruggedized, portable 

hardware platform (known as the Lynx system) and the systems’ 

ability to handle the translation of names, streets, and places 

(simply stated as “names” throughout the rest of this paper) from 

a specific foreign language to English. 

Keeping these goals in mind, offline and live formats (lab venue, 

only) were conducted similar to those run in Phase II to 

accomplish the primary evaluation goals. The SCORE framework 

played a critical role in defining the testing scopes for evaluating 

the Lynx system and the systems’ capability to address names. 

The Lynx evaluation was designed under the System Level Testing 

– Technical Performance and System Level Testing – Utility 

Assessment evaluation goal types. The design of this evaluation 

closely mirrored that of the live lab evaluations. Recall that the 

main TRANSTAC systems were evaluated with both speakers 

sitting at a table interacting with the laptop-based system which 

was placed on the table (as opposed to being worn). To that end, 

the Lynx systems were evaluated in a similar manner where they 

were placed on a table where the English speaker sat on one side 

of the table and the foreign language speaker on the opposite. The 

Lynx test tasked the speakers with transferring as many concepts 

as possible within a ten minute timeframe while adhering to the 

structured scenario format. For the sake of comparison, the same 

structured scenarios that were used in the main evaluation were 

selected for the Lynx evaluation. As in the main test, the 

evaluation team was able to extract technical performance metrics 

through the number of concepts transfer. Additionally, the endusers were administered specific surveys to assess their utility of 

the Lynx technology. 

Because the Lynx platform was different from that of the laptopbased systems, additional training was provided to the end-users 

before this evaluation. This was particularly important so that the 

end-users did not confuse this system’s operation with that of the 

technology they had used earlier (the main laptop system 

evaluations were conducted immediately prior to the Lynx system 

testing). 

The names capability was evaluated under the Component Level 

Testing – Technical Performance and Capability Level Testing – 

Utility Assessment evaluation goal types. This test was conducted 

in both the live lab and offline settings and used the main 

evaluation laptop-based platforms. The only other similarity to the 

main live lab evaluations include the fact that the speakers were 

sitting across from one another at a table and did not have to wear 

the system. 

Since the goal of this evaluation was to isolate the systems’ ability 

to translate names, the SCORE elements directed the IET to 

design unique scenarios to support both the offline and live lab 

venues. This specialized scenario design stemmed back to the data 

collection scenarios. Three unique, names-laden scenarios were 

created as scripted dialogues and recorded by unique speakerpairs. These dialogues were crafted such that there was at least 

one name in each foreign language utterance where it was noted 

whether this name appeared in the names lexicon (a list of names 

that the research teams have access) or if it did not along with 

whether each name was unique (the name can only mean a name) 

or whether it was a “double” (the name can also mean an object, 

etc). This recorded data was used to create the offline names 

evaluation set where all of the recordings were kept by the IET 

(no names data was released to the developers since the intent was 

to prevent the out of lexicon names from being known by the 

researchers ahead of time). The scenarios used in the live names 

evaluations were identical to those scripted ones used in the 

names data collections. 

The offline names evaluation ran similarly to that of the main 

offline evaluation. Specific utterances are selected and fed directly 

into the TRANSTAC systems. However, the measures and 

metrics from this test focused on how the systems specifically 

handled the translations of the names. 

7
The live names evaluation ran in a different manner than that of 

the live main (lab) evaluation. The speakers were provided with 

the scripted names scenarios (as opposed to the standard 

structured scenarios) and instructed to read them verbatim. The 

English speaker began each utterance by stating the number of the 

utterance they were about to read (which alerts the foreign 

language speaker to the current utterance) and then spoke the 

utterance. Since the focus of this evaluation was on the translation 

of names from the foreign language into English, the English 

speaker did not speak into the TRANSTAC system. After hearing 

the English utterance, the foreign language speaker responded 

with their scripted utterance which they spoke into the 

TRANSTAC system. If the English speaker was able to 

understand the name that was communicated, they noted that and 

moved on to the next utterance. If the English speaker was unable 

to ascertain a name from the TRANSTAC output, then they were 

able to rephrase their utterance in any manner they saw fit. 

Likewise, the foreign language speaker, upon hearing the English 

speaker rephrase their utterance, rephrased theirs accordingly to 

convey the desired name. The output of this evaluation produced 

both technical performance and utility assessment data. This took 

the form of measuring the number of names successfully 

transferred and collecting survey responses from the end-users 

regarding their specific names interactions. 

The SCORE framework was successfully employed to address 

additional evaluation goals including the Lynx system and names 

translation capabilities. Likewise, the framework further evolved 

to address progressing needs in the ASSIST program. 

5. FUTURE EFFORTS 

SCORE is still being used to design the remaining ASSIST and 

TRANSTAC Phase III evaluations which will both take place 

before the end of the calendar year. If these programs continue, it 

is envisioned that SCORE will be used to design their successive 

evaluations. 

The SCORE framework is applicable to domains beyond 

emerging military technologies and those solely dealing with 

intelligent systems. Personnel at NIST are applying the SCORE 

framework to the virtual manufacturing automation competition 

(VMAC) and the virtual RoboRescue competition (within the 

domain of urban search and rescue). Their intent is to develop 

elemental tests and vignette scenarios to test complex system 

capabilities and their component functions. Likewise, personnel in 

NIST’s construction metrology group have expressed interest in 

the SCORE framework with respect to designing evaluations 

within the automated construction domain. 

It is envisioned that SCORE will be applied to a broad range of 

technologies, both to design evaluations of emerging components 

and systems along with enhancing evaluation procedures of preexisting technologies. This framework is highly adaptable and 

capable of meeting most any evaluation requirement. 

6. CONCLUSION 

SCORE has proven to be an invaluable evaluation design tool of 

the NIST IET and was the backbone of eight (five for ASSIST 

and three for TRANSTAC) evaluations. Further, it is expected to 

play a critical role in the remaining Phase III ASSIST and 

TRANSTAC evaluations. The NIST IET will continue to apply 

the SCORE framework in future evaluations (including those 

outside of the military community) and will support other 

members in the technology evaluation community who wish to 

leverage it. 

7. DISCLAIMER 

Certain commercial products and software are identified in this 

paper in order to explain our research. Such identification does 

not imply recommendation or endorsement by NIST, nor does it 

imply that the products and software identified are necessarily the 

best available for the purpose. 

8. ACKNOWLEDGMENTS 

The authors would like to acknowledge the DARPA ASSIST/ 

TRANSTAC program manager, Dr. Mari Maeda, and the 

members of the NIST IET for their continued support. 

9. REFERENCES 

[1] Steves, M. and Scholtz, J. 2005. A Framework for Evaluating 

Collaborative Systems in the Real World. In Proceedings of 

the 48th Hawaii International Conference of System Sciences

(HICSS-38), Hawaii. 

[2] Schlenoff, C., Steves, M., Weiss, B.A., Shneier, M., and 

Virts, A. 2006. Applying SCORE to Field-based 

Performance Evaluations of Soldier Worn Sensor 

Technologies. Journal of Field Robotics, Volume 24, (8-9), 

pp. 671-698. 

[3] Schlenoff, C., Weiss, B.A., Steves, M., Virts, A., Shneier, M. 

and Linegang, M. 2006. Overview of the First Advanced 

Technology Evaluations for ASSIST, In Proceedings of the 

2006 Performance Metrics for Intelligent Systems (PerMIS) 

Conference, Gaithersburg, Maryland. 

[4] Weiss, B.A., Schlenoff, C., Shneier, M., and Virts, A. 2006. 

ASSIST: Technology Evaluations and Performance Metrics 

for Soldier-Worn Sensor Systems. In Proceedings of the 

2006 Performance Metrics for Intelligent Systems (PerMIS) 

Conference, Gaithersburg, Maryland. 

[5] CONOPS, http://en.wiktionary.org/wiki/CONOPS,

(Definition retrieved on 07/10/08) 

[6] Steves, M. P. 2006. Utility Assessments for ASSIST 

Systems. In Proceedings of the 2006 Performance Metrics 

for Intelligent Systems (PerMIS) Conference, Gaithersburg, 

Maryland. 

[7] Weiss, B.A., Schlenoff, C., Sanders, G., Steves, M., 

Condon, S., Phillips, J., and Parvaz, D. 2008. Performance 

Evaluation of Speech Translation Systems, In Proceedings of 

the 6th edition of the Language Resources and Evaluation 

Conference. Marrakech, Morocco. 

[8] Sanders, G., Bronsart, S., Condon, S., and C. Schlenoff. 

2008. Odds of successful transfer of low-level concepts: A 

key metric for bidirectional speech-to-speech machine 

translation in DARPA’s TRANSTAC program. In 

Proceedings of LREC 2008.

8
Reliability Estimation and Confidence Regions from

Subsystem and Full System Tests

via Maximum Likelihood 

James C. Spall

The Johns Hopkins University 

Applied Physics Laboratory 

11100 Johns Hopkins Road 

Laurel, Maryland 20723-6099 U.S.A. 

james.spall@jhuapl.edu

ABSTRACT

This paper develops a rigorous and practical method for 

estimating the reliability—with confidence regions—of a 

complex system based on a combination of full system and 

subsystem (and/or component or other) tests. It is assumed that 

the system is composed of multiple processes (e.g., the 

subsystems and/or components within subsystems), where the 

subsystems may be arranged in series, parallel (i.e., redundant), 

combination series/parallel, or other mode. Maximum likelihood 

estimation (MLE) is used to estimate the overall system reliability 

based on this fusion of multiple sources of information. 

Interestingly, for a given number of subsystems and/or 

components, the performance metric (likelihood function) does 

not change with the system configuration; rather, only the 

optimization constraints change, leading to an appropriate MLE. 

The MLE approach is well suited to providing asymptotic or 

finite-sample confidence bounds through the use of Fisher 

information or Monte Carlo sampling (bootstrap). The paper 

establishes formal conditions for the convergence of the MLE to 

the true system reliability. 

Categories and Subject Descriptors

G.3 Probability and statistics 

I.3 Simulation and modeling 

J.2 Physical sciences and engineering 

General Terms

Algorithms, design, experimentation, measurement, performance, 

reliability, theory. 

Keywords

Reliability, parameter estimation, optimization, bootstrap, 

maximum likelihood, likelihood performance metric, Fisher 

information matrix, data fusion.

1. INTRODUCTION 

This paper considers the problem of estimating the 

reliability for a complex system based on a combination of 

information from tests on the subsystems, components, or other 

aspects of the system, and, if available, tests on the full system. A 

key motivation for this setting comes from the fact that it is often 

difficult or infeasible to directly evaluate the reliability of 

complex systems through a large number of full system tests 

alone. Such a difficulty may arise, for example, when the full 

system is very costly (or dangerous) to operate and/or when each 

full system test requires the destruction of the system itself. 

Nevertheless, it is also often the case that there are at least a few 

tests of the full system available; it is obviously desirable to 

include such information in the overall reliability assessment. 

Such full systems tests are often critical to help guard against 

possible mismodeling of the relationship between the subsystems 

and full system in calculating overall reliability. This paper 

develops a method based on principles of maximum likelihood for 

estimating the overall system reliability from a combination of 

full system and subsystem or other tests.1

Certainly, other approaches exist for estimating system 

reliability when the subsystems are independent (see, e.g., Hwang 

et al., 1981; Tang et al., 1997; and Ramírez-Márquez and Jiang, 

2006). However, these approaches do not allow for easy inclusion 

of limited full system tests (when available), and do not 

generalize to include systems where the subsystems may be 

statistically dependent. (Note that the inequality-based reliability 

method of Hill and Spall, 2007, does allow for such dependence 

in producing a bound to the full system reliability, but this method 

requires certain pairwise subsystem tests that may not be feasible 

in practice.) 

A key part of the approach here is the calculation of 

uncertainty (confidence) bounds on the estimates. We discuss the 

Fisher information matrix as a basis for asymptotic bounds and 

also discuss a bootstrap-based method for computing confidence 

regions when the asymptotic bounds are inappropriate. This 

Permission to make digital or hard copies of all or part of this work for 

personal or classroom use is granted without fee provided that copies are 

not made or distributed for profit or commercial advantage and that 

copies bear this notice and the full citation on the first page. To copy 

otherwise, or republish, to post on servers or to redistribute to lists, 

requires prior specific permission and/or a fee. 

 

1

To avoid the cumbersome need to repeatedly refer to tests on subsystems, 

components, and other aspects of the system as the key source of 

information other than full system tests, we will usually only refer to 

subsystem tests; “subsystem tests” in this context should be considered a 

proxy for all possible test information short of full system tests. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA. 

Copyright 2008 ACM 978-1-60558-293-1...$5.00. 

9
bootstrap approach deals with the inadequacies of traditional 

methods based on the asymptotic normality of the MLE. 

Several other approaches have been proposed to deal 

with the inadequacy of asymptotic normality in the context of 

using subsystem tests to estimate full system reliability. For 

example, Myhre and Saunders (1968) use the asymptotic chisquared distribution of the log-likelihood ratio to deal with the 

problem of having confidence intervals outside the unit interval 

[0, 1]. Easterling (1972) treats the system reliability (derived from 

subsystem estimates) as an estimate from data having a binomial 

distribution and then uses standard results on the exact 

distribution of the binomial estimate to get the confidence 

interval; this yields an exact solution in the special case where the 

system is composed of one subsystem (i.e., system = subsystem), 

and an intuitively appealing approximation when there are two or 

more subsystems. Coit (1997) considers the case where there are a 

“large” number of subsystems in either a series or parallel 

configuration; in the series configuration, the logarithm of the 

system reliability is approximately normally distributed by central 

limit theorem effects. Hence, a log-normal distribution is assumed 

for the system reliability, providing the basis for the confidence 

interval. Ramírez-Márquez and Jiang (2006) focus on methods for 

estimating the variance of the reliability estimates, and then use 

these variance estimates together with normal or binomial 

approximations to the distribution of the estimates to form 

confidence intervals. There are also a large number of Bayesian 

methods for forming estimates and uncertainty bounds (e.g., Tang 

et al., 1997); we do not consider these here due to the difficulties 

in specifying reliable prior distributions. 

Section 2 of this paper gives the general MLE 

formulation, showing that one likelihood function (the objective 

function for optimization) applies across all problem settings, 

with only the constraints changing to accommodate the different 

settings. Section 3 considers the case of systems with subsystems 

that are statistically dependent while the system is operating. 

Section 4 establishes that the MLE for the full system reliability is 

stochastically (almost surely) convergent to the true system 

reliability as the amount of test data gets large. Section 5 

discusses the Fisher information matrix and gives explicit forms 

in the special cases of fully series and fully parallel systems. This 

matrix is critical in determining whether there is sufficient 

information to estimate the reliability (the identifiability) and in 

forming asymptotic confidence regions for the MLE. Section 6 

describes a bootstrap-based method for constructing confidence 

intervals that is useful when the asymptotic bounds do not apply. 

Section 7 is a numerical study and Section 8 offers some 

concluding remarks. 

2. THE LIKELIHOOD FUNCTION AND 

MLE FORMULATION 

2.1 General Formulation 

Consider a system composed of p processes, typically 

subsystems and/or components of subsystems. The subsystems 

may be arranged in series, parallel (i.e., redundant), combination 

series/parallel, or other form (e.g., standby systems), subject to 

being able to write down a probabilistic characterization of the 

system that leads to a likelihood function (Leemis, 1995, Chap. 2, 

includes a thorough discussion of the many types of systems 

frequently encountered in practice). While we assume that the test

data for estimating the reliability are statistically independent, we 

do not, in general, require that the processes be statistically 

independent when operating as part of the full system. (In 

principle, it is also possible to formulate a likelihood function 

based on test data that are statistically dependent. That is, the 

testing outcome for process j may be statistically dependent on 

the outcome for process i, for some i z j. We do not pursue that 

extension here.) In the discussion below, the term “operationally 

[in]dependent” is used to refer to the case where the processes are 

statistically independent or dependent (as relevant) when 

operating as part of the full system. 

The general MLE formulation involves a parameter 

vector T, representing the parameters to be estimated, together 

with an associated log-likelihood criterion L(T). Let U and Uj

represent the reliabilities (success probabilities) for the full 

system and for process j, respectively, j = 1, 2, ..., p. The vector T

= [U1, U2,..., Up]

T

; U is not included in T because it will be 

uniquely determined (or bounded) from the Uj and possibly other 

information via relevant constraints. Note that when U is uniquely 

determined by a function of T, then the estimate Uˆ , as determined 

from applying this function to the MLE of T (say ˆ

T ), is the MLE 

of U. This invariance of MLE applies even though the mapping 

from T to U is not generally one-to-one and may not be continuous 

(see, e.g., Zehna, 1966). 

Ultimately, we are interested in an estimate (with 

confidence bounds) for U (derived from the MLE for T). The 

specific definition of T will depend on the details of the system. 

Interestingly, for a given definition of T, the definition of L(T) 

will not depend on how the subsystems are arranged in the full 

system (i.e., L(T) is the same regardless of whether, say, the 

subsystems are in series or parallel). However, the MLE will

change as a function of the system arrangement. This is a 

consequence of the constraints in the optimization problem that is 

solved to produce the MLE, as illustrated below. 

It is generally assumed, at a minimum, that 

success/failure data are available on the p processes within the 

full system. As mentioned above, it is also generally assumed that 

success/failure data are available directly on the full system. In 

cases involving dependent subsystems, it may be desirable that 

the information from the p processes include some data other than 

direct subsystem success/failure data in order to obtain the 

information needed for characterizing the nature of the 

dependence (we say “desirable” because it may be possible to 

estimate bounds to the system reliability in the absence of such 

information). For example, in the dependent-subsystem case 

discussed in Section 3, obtaining data on one critical component 

appearing within multiple subsystems allows for an MLE of U; the 

absence of such data allows the analyst to estimate a lower bound 

to U. 

We now present the general MLE optimization 

problem. Let 4 represent the feasible region for the elements of T. 

To ensure that relevant logarithms are defined and that the 

appropriate derivatives exist, it is assumed, at a minimum, that the 

feasible region 4 includes the restriction that 0 < Uj < 1 for all j

(other restrictions may be included as appropriate). The general 

MLE formulation is: 

10
ˆ arg max ( )

subject to ( , ) 0,

4

f U t

T

T T

T

L

 (2.1) 

where f() is some function reflecting the constraints associated 

with the operation of the full system. In some common cases (e.g.,

fully series and fully parallel cases, with the processes 

corresponding to the subsystems as in Subsection 2.2), the 

inequality in the constraint can be replaced with an equality. 

Let X represent the number of successes in n

independent, identically distributed (i.i.d.) experiments with the 

full system and Xj represent the number of successes in nj i.i.d. 

experiments with process j, j = 1, 2, ..., p. Note that in the 

discussion below there is no notational distinction between a 

random variable (vector) and its realization, with the expectation 

that the distinction should be clear from the context. Let Y

represent the full set of data {X, X1, X2,..., Xp}. From the 

assumption of independence of all test data, the probability mass 

function, say p(Y | T, U), is: 

1 1 1

( )

1 ( ) ( )

1 1

1

system

 processes

( | , ) (1 )

(1 ) (1 ) ,



 

§ ·

U U U  ̈  ̧ © 1

§ · § ·

u U U U U  ̈  ̧  ̈  ̧  ̈  ̧ © 1 © 1

p p

X nX

X n X p X nX

p p

p

p

n p X

n n

X X

	


	


Y T

" p

 (2.2) 

leading to the log-likelihood function L(T) { log p(Y | T, U): 

1

( ) log log(1 )

log log constant,

( )

( ) (1 )

 

 U  U

 U   U  a o ¦¬ 1⁄4

p

j jjj j

j

X nX

X nX

L T

 (2.3) 

where the constant is not dependent on T. Note that the generic 

forms for the above likelihood and log-likelihood apply regardless 

of the specific layout of the subsystems (series, parallel, 

combination series/parallel, or operationally dependent). 

However, the relationship between U and the Uj differs according 

to the layout of the processes. In finding the MLE of T, say ˆ

T , 

this relationship manifests itself as constraints in an optimization 

problem. 

Typically, the MLE is determined via finding a root of 

the score equation w w L( ) T T = 0 (or a normalized form of this 

equation in the asymptotic sample size case), where the score 

vector is 

1

2

a o w wU

« » w w wU « w «

« » « » w wU ¬ 1⁄4 p

T #

L

L L

L

»

» . (2.4) 

The elements of the score vector depend on the constraints. A 

common special case is where the constraints lead to a unique 

differentiable function h () that relates T to U: U = h(T). In that 

case, (2.3) leads to the following form of the score vector in (2.4): 

11 1

1 1 1

1

1

a o

« » 

« » U U ww w « » 

w Uw Uw « »

« »

« »  U U ¬ 1⁄4



    

 p p p

p p

XnX

Xh n Xh

XnX

#

T T T

L . (2.5) 

We will see several illustrations of the form in (2.5) in the 

examples and theoretical results below. 

2.2 Fully Series and Fully Parallel Cases 

To illustrate the general formulation of Subsection 2.1, 

we consider here the two most common “extreme” cases of fully 

series systems and fully parallel systems with the p processes 

corresponding to p operationally independent subsystems. The 

results below can extend readily to common cases of mixed 

(operationally independent) series/parallel systems (see, e.g., 

Leemis, 1995, Sect. 2.1, for a description of such general 

systems). The results here illustrate the setting mentioned in the 

context of (2.5) above, where there exists a differentiable function 

U = h(T). 

From (2.1), the MLE in the series-subsystem case is 

found according to 

ˆ arg max ( )

T4

T L T

1

subject to

 

U U 

p

j

j

, 

while the MLE in the parallel-subsystem case is found according 

to 

ˆ arg max ( )

T4

T L T

1

subject to 1 (1 )

 

U U  

p

j

j

. 

 

In the above series and parallel cases cases, it is straightforward to 

determine the score vector using (2.5). 

Making the substitution U = 1  U p

j j in eqn. (2.5), the

j = 1, 2, ..., p elements of the score vector in (2.4) (or (2.5)) for the 

series case are: 

(1 ) 1

( ) ( )

( )

   U   wU U  U U  U

w j j j

j j jj

L X X n n X X

. (2.6) 

Likewise, making the substitution 1  U = ) 1(1   U p

j j in eqn. 

(2.5) (i.e., U = h(T) = 1  1

(1   U p )j j ), the elements of the 

score vector in (2.4) (or (2.5)) for the parallel case are: 

1

1

(1 )

( ) ( )

 

z

 

  U  wU U U  U

w 

p j j

i

jj j i

i j

X j L X nn X X

. (2.7) 

Except for the degenerate settings of X = n in the series case and 

X = 0 in the parallel case, the solution to w w L( ) T T = 0 must 

generally be found by numerical search methods. (The two 

degenerate cases yield Uˆ j = ( )(   ) j j nX nn and Uˆ j = 

11
X j ( )  j n n , respectively, both of which are the natural—

intuitively obvious—solutions.) 

3. DEPENDENT SUBSYSTEMS 

There are obviously innumerable ways in which 

subsystems can interact while operating as part of a full system. 

The reliability analysis for each such system must be handled 

separately based on the information available. While the 

reliability analysis with operationally dependent subsystems is 

usually more difficult than with operationally independent 

subsystems, the MLE may still be available if the problem can be 

cast in the form of (2.1) with an appropriate constraint. For 

example, in systems that may be represented as a series of m d p

(generally dependent) subsystems, the following expression 

relates the full system reliability to conditional subsystem 

reliabilities: 

 

 

12 1 3 1 2

1

1

1| 1 1 1 1

1 1,

( ) { }{

{ } 

 

U U 

 



m

m j j

PS S PS S S

"PS S 

}

 (3.1) 

where Sj = 0 or 1 is the indicator of whether subsystem j is, 

respectively, a failure or success and U1 = P(S1 = 1). Hence, the 

analyst may have the information needed to implement (2.1) with 

an equality constraint that uniquely defines U if data and/or prior 

information are available to characterize the conditional 

probabilities on the right-hand side of (3.1). 

We illustrate here an application of (3.1) in the 

relatively common setting where dependence gets introduced 

through shared components. That is, it is assumed that two or 

more subsystems share at least one piece of hardware or software 

while the system is operating (e.g., a battery may provide power 

to more than one subsystem). Note that this setting differs from 

that in Jin and Coit (2001), which assumes that multiple 

subsystems share the same type of component, but not the same 

specific component. 

Let us consider the example of m = p  1 t 2 subsystems 

illustrated in Figure 3.1, with C1, C2, ...., Cp representing p

independent components within the subsystems, but with 

component Cp appearing in all subsystems. With the possible 

exception of tests on this shared component (see the discussion on 

constraints below), it is assumed that testing can only be done at 

the subsystem level (i.e., it is not feasible to test each component 

separately). 

Figure 3.1. Series system with dependent subsystems. 

Dependence follows from shared component Cp in all p1

subsystems. 

It is necessary to formulate the constraint f() t 0 in 

(2.1) in order to produce the MLE for the setting of Figure 3.1 

(recall that the test data are assumed to satisfy the standard 

independence assumptions associated with the likelihood function 

in (2.2) as appears in the top line of (2.1)). We now show two 

methods by which the constraint can be implemented, with the 

two methods depending on the level of information available. 

Analogous to the indicator variable Sj = 0 or 1 in (3.1), let Cj = 0 

or 1 indicate the failure or success of component j (so the notation

Cj represents both a label for the jth component and the associated 

indicator variable). Let Uj = P(Sj = 1), j = 1, 2, ..., p  1, and Up = 

P(Cp = 1). 

To derive the constraints via the two methods, we see 

from (3.1) that 

1

2 3 1

1 1

1

1 ,

 

 

U U U

U U U

UU U U 

p p

p j

pp p p j

" (3.2) 

where we have used the independence of the components. Note 

also that (3.2) is analogous (at the component level) to the 

standard series subsystem formulation. That is, U = 

1 ( 1  ) p

j j P C , but that this component-series equality is not 

directly usable in (2.1) due to the above-mentioned restriction that 

it is not feasible to test each component separately. The form in 

(3.2), however, is implementable subject to obtaining information 

about the reliability for the shared component Cp. 

The preferred method for estimation is based on 

separate testing of the common component. Here T = [U1, U2,...,

Up]

T

, as usual, implying that the estimation involves the p 

 

1 

subsystems and the shared component. Then, from (3.2), the 

formulation in (2.1) applies directly with constraint f(T, U) { U 

 1

1 1U U p p p j   j = 0 and associated log-likelihood (2.3) and score 

vector (2.5) (with U = h(T) = 1 1

 1 U U p p p j



 U p

j

 The second method by which the constraint can be 

formulated applies when it is not possible to isolate the shared 

component for separate testing. Here, one simply sets Up = 1 in 

(3.2), yielding a lower bound to U. That is, (2.1) involves the 

maximization of L(T) subject to U t 1

). 

1

j j (i.e., f(T, U) { U 

 1

1

p U j j t 0), where the definition of T is modified to remove Up

(so T is now a vector of dimension p  1). Note that this method is 

most appropriate when the reliability of Cp is high, especially if p

is large (so that the inequality is at least moderately tight). 

 

4. THEORETICAL PROPERTIES 

 This section summarizes the convergence properties 

associated with the MLE formulation above. Note that standard 

i.i.d. MLE theory (e.g., Serfling, 1980, Sect. 4.2) does not apply 

because of the different success/failure probabilities associated 

with the different subsystems. Nevertheless, the structure 

associated with (2.1) and (2.3) allows us to show that the MLE for 

U will converge to the true full system reliability under reasonable 

conditions. 

 First, however, we present a result giving conditions 

under which there is a unique function h(T) relating T to U. 

Lemma 1. Suppose that the constraint in problem statement (2.1) 

can be represented as an equality f(T, U) = 0 with f being a 

continuously differentiable function in both T  4 and 0 < U < 1. 

For a fixed Tc  4, suppose w U wU f (,) Tc z 0 almost surely (a.s.) 

at U such that f ( ) Tc,U = 0. Then there exists an open 

neighborhood of Tc and a unique continuously differentiable 

function h such that for all T in this neighborhood, U = h(T) and 

Subsystem 1 

C1 System 

out

Subsystem p1

Cp Cp Cp1

put

12
1 () (,) (,)  w w Uw U §   ̈ w w wU © 1

h T f f T T

T T

·

 ̧ (4.1) 

Proof. From the fact that the constraint in (2.1) can be represented 

as an equality f(T, U) = 0 and the fact that w Uw f (,) Tc U z 0 for a 

given Tc, the implicit function theorem (e.g., Apostol, 1974, Sect. 

13.4) ensures that there exists an open neighborhood of Tc and 

one, and only one, continuously differentiable function h such 

that for all T in this neighborhood, U = h(T). Further, w w h T is as 

shown in (4.1) in this neighborhood (e.g., Trench and Kolman, 

1972, p. 483). Q.E.D. 

 We now present the following strong (a.s.) convergence 

result for the MLE of U. Let be the true value of the full 

system reliability and = 1 2 be the corresponding 

true value of T. Further, let AN = 


 U 
 T [ ,,, 

 
 UU U T ! p ]

1 2 diag var var var a ( ), ( ), , ( ) w wU w wU w wU ¬ LL L ! p o

1⁄4 be a diagonal 

matrix used to normalize for the variability of the elements in 

w wT L , where N = {n, n1, n2, ..., np} is the collective sample 

size. Proposition 1 below establishes conditions for Uˆ = 
 U + 

o(1) being a root of the normalized score equation, 1 w w NA L T = 

0, where o(1) is a term going to zero as N gets large in the sense 

described below. As usual when working with score vectors, 

however, the Proposition does not guarantee that this solution is 

unique and/or a global maximum of L(T). 

Proposition 1. For constants 0 < C  C+ < 1, suppose the 

feasible region 4 is such that 4 = {T: C  Uj  C+ for all j} and 

that C  U  C+

. Further, suppose that the constraint in problem 

statement (2.1) can be represented as an equality f(T, U) = 0 with f 

being a continuously differentiable function in both T  4 and C

 U  C+. For some strictly positive constants C and Cc and all T

 4 and C  U  C+, suppose C < w U wU f (,) T  Cc and C 

w U wU (,) j f T  Cc for all j. Then, for the problem described in 

(2.1) and (2.3), = + Uˆ o(1) is an a.s. solution to 
 U 1 AN w w L T = 

0 as n + n1 o f, n + n2 o f, ..., n + np o f, where, for each j, 

one of the following three possibilities holds: (i) j n n = o(1), (ii) 

j n n = o(1), or (iii) j n n = O(1) and j n n = O(1). 

Comment. The multiple limits n + n1 o f, n + n2 o f, ..., n + np

o f are true if and only if one of the following three (mutually 

exclusive) possibilities occur: (a) n o f and nj < f for all j, (b) n

< f and nj o f for all j, or (c) n o f and nj o f for at least one 

j. The proof considers these three cases in turn subject to the 

additional constraints (i)  (iii) in the Proposition statement. 

Proof. Note that the conditions of the Proposition are stronger 

than those of Lemma 1. Hence, there exists a differentiable 

function h such that for all T in an open neighborhood of ˆ

T , U = 

h(T) with derivative given by (4.1). Thus, the score vector is given 

by (2.5). 

As stated in the comment following the Proposition 

statement, there are three cases to consider: (a), (b), and (c). In 

case (a) (n o f and nj < f for all j), it is apparent from (4.1), 

(2.5), and the fact that the definition of 4 implies that the terms 

inside the square brackets on the right-hand side of (2.5) are 

bounded (independent of n) and that var(w wU ) L j grows at rate 

proportional to n for any fixed T and U. Hence, in solving for the 

MLE of U = h(T), we know that 

1 1 lim lim (1) a.s.

of of 1

w ww § ·

   ̈  ̧ w Uw Uw © 1

    0 n n

Xh n Xh O n n T T TL

(i.e., 1 lim  of w w n N A L T = 0 a.s. according to (2.3) and the 

assumptions in the Proposition statement), leading to the MLE, 

1 ˆ 
 § · U  oU  ̈  ̧ © 1X O n n a.s., (4.2) 

where we have used the fact that w w h( ) T U j  C(Cc)

1

 > 0, as 

follows by (4.1) and the assumptions w U wU f (,) T  Cc and 

w U wU (,) j f T  C.

The second case (b) (n < f and nj o f for all j) follows 

a pattern analogous to the above. Namely, for the jth component, 

var( ) w wU L j grows at rate proportional to nj for any fixed T and

U, and, therefore, the MLE of each Uj can be found as the solution 

to 

1 1 lim lim (1)

of of 1

w § ·

   ̈  ̧ wU U U © 1

 

 0

j j

jj j

n n jj j j j

XnX

O n n

L , 

where the O(1) term follows from C  U  C+ and the fact that 

w wU ( ) h T j  C1Cc < f. This yields 

1 ˆ 
 § ·

U  oU  ̈  ̧

U © 1

j

j j

j j

X

O n a.s. (4.3) 

From Lemma 1 and the fact that = 0, there exists an 

open neighborhood of 

( , 
 
 f T U ) 
 T and a unique continuously 

differentiable function h such that for all T in this neighborhood, U

= h(T) and 
 U = ( )
 h T . Hence, because (4.3) holds for all j, we 

know that for all nj sufficiently large, can be made sufficiently 

close to 

ˆ

T 
 T to guarantee that lies in this open neighborhood 

a.s., implying, by the continuity of h(T) at , 

ˆ

T 
 T Uˆ = ˆ h( ) T o 
 U

a.s. when n < f and nj o f for all j. 

 Finally, for the third case (c) (n o f and nj o f for at 

least one j), consider a j with nj o f (the case (a) results above 

apply for those j with nj < f). From (2.5), it is known that 

var( ) w wU L j grows at rate proportional to n + nj. Hence, the 

normalized gradient (score vector) with respect to Uj is as follows: 

1 1

1

1 . 1

w w § ·  ̈  ̧ w

 wU  U wU U wU © 1

§ ·

   ̈  ̧

U U © 1

  





j jj j

j jj jj

jj j

n Xn h Xn h

nn nn

n Xn Xn

n n

L

j (4.4) 

When j n n = o(1) (see the assumption in the Proposition 

statement), the first () term on the right-hand side of (4.4) 

dominates as n o f and nj o f. Because w w h( ) T U j  C(Cc)

1

> 0 (see below (4.2)) and because X n o a.s. as n o f, we 

know that 


 U 1 a o  w wU ¬ 1⁄4j j n n L o 0 a.s. as n + nj o f if Uˆ o 
 U . 

13
When j n n = o(1), the second () term in (4.4) dominates as n o

f and nj o f because w w h( ) T U j  C1Cc < f. By the fact that 

X j j n o 
 U j a.s. as nj o f, it is known that 1 a o  w wU ¬ 1⁄4j j n n L

o 0 a.s. as n + nj o f if Uˆ j o 
 U j a.s. If this j n n = o(1) 

setting applies for all j, then, as below (4.3), we know that Uˆ = 

o because h(T) is continuous at and ˆ h( ) T 
 U 
 T 
 U = ( )
 h T ; 

if j n n z o(1) for at least one j, then the case (a) analysis for 

(4.2) shows that o a.s. directly when n o f and nj < f or 

the analysis to follow (

Uˆ 
 U

j n n and j n n are O(1)) applies. That is, 

when n and nj grow proportionally in the sense that both of j n n

and j n n are O(1), then both () terms in the right-hand side of 

(4.4) are significant as n o f and nj o f. From the above 

arguments, therefore, we know that 1 a o  w wU ¬ 1⁄4j j n n L o 0 a.s. 

as n + nj o f if o a.s., as desired. Because the 

case (a) analysis applies to those j such that n o f and nj < f, we 

know that o a.s. as n o f and nj o f for at least one j. 

[U U ˆ ˆ,j ] [ , ] 
 
 U Uj

Uˆ 
 U

The above establishes that = + o(1) is an a.s. 

solution to 

Uˆ 
 U

1 w w AN L T = 0, completing the proof of convergence 

for the three cases associated with n + nj o f for all j. Q.E.D.

5. THE FISHER INFORMATION MATRIX 

 The Fisher information matrix is helpful in at least two 

respects in the reliability estimation problem: (i) It can be used to 

determine when the estimation problem in Section 2 is well posed 

(i.e., when T is identifiable) through an evaluation of the 

conditions ensuring that the FIM is positive definite (e.g., 

Goodwin and Payne, 1977, pp. 104 and 139) and (ii) the inverse 

(average) information matrix is the covariance matrix appearing 

in the asymptotic distribution of the appropriately normalized 

MLE. Hence, when combined with the asymptotic normal 

distribution, the information matrix may be used in constructing 

confidence regions for the MLE when the sample size is 

sufficiently large. More generally, the information matrix 

provides a summary of the amount of information in the data 

relative to T (e.g., Spall, 2003, Sect. 13.3). We restrict our 

attention below to the fully series and fully parallel subsystems 

cases (Subsection 2.2), but the analysis can be modified in a 

straightforward manner for certain other cases, including hybrid 

series-parallel subsystems cases. 

The p u p Fisher information matrix F(T) for a twicedifferentiable log-likelihood function is given by 

2

( ) § · ww w § · T    ̈  ̧  ̈ © 1 wT wT w w © 1 T E E

T T

LL L F =  ̧ T , (5.1) 

where 2 w ww T L T T appearing after the last equality above 

corresponds to the Hessian matrix of the log-likelihood function. 

Let us first compute F(T) for the series case using the 

Hessian-based form appearing after the second equality in (5.1). 

Because 4 = {0 < Uj < 1 for all j}, it is known that the Hessian 

matrix is continuous and, consequently, symmetric. From (2.6), 

the elements of the negative Hessian for the series case of interest 

are: 

2

2 22 2 2

2

when , (1 ) 1

when .

(1 )

( ) ( )

( )

( )

­    U °  

° U U U U  ® wU wU °  U z ° U U U  ̄

w

j jj

j jj

j k

j k

XX n X n X j k

n X j k

L

Then, the corresponding elements of the information matrix F(T) 

= a o ( ) T ¬ 1⁄4 Fjk are: 

2

2 2 when , (1 ) 1

( )

when .

(1 )

( )

­ U U U °  

° U U U  U T ®

° U z ° U U U  ̄

jj j

j j j

jk

j k

nn n n j k

F n j k

 (5.2) 

Likewise, the Hessian can be used to compute F(T) in 

the parallel subsystem case. From (2.7), the elements of the 

negative Hessian in the parallel case are: 

2

2 2 22 2

2

2

(1 ) when , 1 1

(1 )( ) when , 1 1

( )

() ()

( )( )

­    U °  

U U U U °  ® wU wU ° U U  U z ° U U U  ̄



w

jjj

jj j

j k

j k

X nn X X X j k

X X j k

L

leading to the following elements of the information matrix: 

2

(1 ) (1 ) when , 1

( ) (1 )( ) when .

1 1

( )

( )( )

­ U  U U

°  

°U U U T ®

° U U U z ° U U U  ̄

j jj

j j

jk

j k

nn n j k

F n n j k

 (5.3) 

 One can use the expression above to determine if the 

information matrix is positive definite, thereby characterizing the 

identifiability of T. It is clear that both n and the nj can contribute 

to the positive definiteness of F(T). For example, if the nj

dominate n, then increasing all nj at the same rate (in the sense 

that j k n n = O(1) and k j n n = O(1) for all j, k) is sufficient to 

achieve the positive definiteness for sufficiently large sample 

sizes. It is also possible to have n o f subject to the nj growing 

sufficiently rapidly as well. In a practical application, one will 

have to assume values for T prior to carrying out the estimation in 

order to evaluate F(T); these values may be chosen conservatively 

or as “typical” values in determining identifiability. 

The other main interest for application of the 

information matrix is determining approximate confidence 

regions. However, one of the complications in using the standard 

asymptotic normality results is that there are multiple samples 

sizes, n, n1,..., np. Fortunately, the form for F(T) provides 

clarification with respect to this mix of sample sizes. Recall that 

the standard generic form for the asymptotic distribution of MLEs 

is, 

dist 1 sample size MLE true value , ( ) ()   o N 0 F (5.4) 

where dist o denotes convergence in distribution and F is the 

limit of the mean information matrix (i.e., the limit of the 

information matrix averaged over the sample size) (e.g., Hoadley, 

14
1971; Rao, 1973, pp. 415417). In well-posed problems, F is a 

finite-magnitude positive definite matrix. Hence, to within slower 

growth terms, the magnitude of the unaveraged Fisher 

information matrix (à la F(T) above) must grow linearly with the 

increase in the relevant sample size. In the context of the form for 

F(T) above, it is clear that both n and the nj can contribute to the 

growth in magnitude for F(T) (for the “proper” asymptotic 

normality for ). For example, as above, if the nj dominate n, 

then increasing all nj at the same rate (in the sense that 

ˆ

T

j k n n = 

O(1) and k j n n = O(1) for all j, k) is sufficient to achieve the 

necessary growth in the magnitude of F(T). It is also possible to 

have n o f subject to the nj growing sufficiently rapidly as well. 

6. BOOTSTRAP CONFIDENCE 

INTERVALS

 It is well known that the traditional asymptotic 

normality-based methods are often inadequate in constructing 

confidence intervals for reliability estimates. Two factors 

contribute to this inadequacy: (i) sample sizes that are too small to 

justify the asymptotic normality and (ii) confidence intervals from 

the asymptotic normality that fall outside of the interval [0, 1] as a 

consequence of the need to approximate the true asymmetric 

distribution with the symmetric normal distribution (this is 

exacerbated by the fact that practical reliability estimates are 

often very near unity). We now present a bootstrap-based method 

for constructing confidence intervals for the full system reliability 

estimate under the assumption that is uniquely determined 

from . Lemma 1 presented sufficient conditions for such a 

function via the implicit function theorem. 

Uˆ Uˆ

ˆ

T

Bootstrap methods are well-known Monte Carlo 

procedures for creating important statistical quantities of interest 

when analytical methods are infeasible (e.g., Efron and 

Tibshirani, 1986; Ljung, 1999, pp. 304 and 334; and Aronsson et 

al., 2006). The steps below describe a “parametric bootstrap” 

approach to constructing confidence intervals for (parametric 

bootstrap methods sample from a specified distribution based on 

using the estimated parameter values; a standard bootstrap method 

would sample from the raw data). 

Uˆ

Step 0: Treat the MLE , and associated , as the true value of 

T and U.

ˆ

T Uˆ

Step 1: Generate (by Monte Carlo) a set of bootstrap data of the 

same collective sample size N = {n, n1, n2, ..., np} as the real 

data Y using the assumed probability mass function in (2.2) and 

the value of T and U from Step 0. 

Step 2: Calculate the MLE of T, say boot ˆ

T , from the bootstrap 

data Y in Step 1, and then calculate the corresponding full system 

reliability MLE, boot Uˆ . 

Step 3: Repeat Steps 1 and 2 a large number of times (perhaps 

1000) and rank order the resulting boot Uˆ values; one- or two-sided 

confidence intervals are available by determining the appropriate 

quantiles from the ranked sample of boot Uˆ values. 

7. EXAMPLE: DEPENDENT SUBSYSTEMS 

To illustrate the generality of the approach above, let us 

consider an example from Jin and Coit (2001), where the 

subsystems are arranged in series, but where they have shared 

components. The shared components introduce dependencies 

between the subsystems when the full system is operating. The 

system of interest is illustrated in Figure 3.1 above. This study is 

not included here due to space limitations; results are available 

from the author upon request. 

8. CONCLUDING REMARKS 

We have described above an MLE-based approach for 

estimating the reliability of a complex system by combining data 

from full system reliability tests and subsystem (or other) tests. 

The method applies in general systems, where the subsystems 

may be arranged in series, parallel (i.e., redundant), combination 

series/parallel, or other mode. 

This MLE approach provides a means of estimating the 

reliability of systems with relatively few (or even no) full system 

tests while maintaining stated requirements for statistical 

confidence in the full system estimates through the knowledge 

obtained via subsystem tests. By appropriately formulating 

constraints in an optimization problem, the approach 

accommodates general relationships between the subsystems and 

full system, including statistical dependencies among subsystems 

operating within the full system. Interestingly, the MLE objective 

function (i.e., the likelihood or log-likelihood function) has the 

same general form across all settings; only the constraints in the 

optimization problem change. 

We also provided conditions under which the MLE will 

be almost surely (a.s.) convergent to the true system reliability. 

The method includes asymptotic (Fisher information-based) and 

finite-sample (bootstrap) methods for characterizing the 

uncertainty via confidence regions. 

 

9. ACKNOWLEDGEMENTS 

This work was supported by the JHU/APL IRAD 

Program. The author thanks Dr. Coire Maranzano for helpful 

discussions and for verifying some of the calculations. 

10. REFERENCES 

[1] Apostol, T. M. (1974), Mathematical Analysis (2nd ed.), 

Addison-Wesley, Reading, MA. 

[2] Aronsson, M., Arvastson, L. Holst, J., Lindoff, B., and 

Svensson, A. (2006), “Bootstrap Control,” IEEE 

Transactions on Automatic Control, vol. 51(1), pp. 2837. 

[3] Coit, D. W. (1997), “System-Reliability ConfidenceIntervals for Complex-Systems with Estimated Component 

Reliability,” IEEE Transactions on Reliability, vol. 46(4), 

pp. 487493. 

[4] Easterling, R. G. (1972), “Approximate Confidence Limits 

for System Reliability,” Journal of the American Statistical 

Association, vol. 67, pp. 220222. 

[5] Efron, B. and Tibshirani, R. (1986), “Bootstrap Methods for 

Standard Errors, Confidence Intervals, and Other Measures 

of Statistical Accuracy” (with discussion), Statistical

Science, vol. 1, pp. 5477. 

[6] Goodwin, G. C. and Payne, R. L. (1977), Dynamic System 

Identification: Experiment Design and Data Analysis, 

Academic Press, New York. 

15
[7] Hill, S. D. and Spall, J. C. (2007), “Variance of Upper 

Bounds in Inequality-Based Reliability,” Proceedings of the 

American Control Conference, 1113 July 2007, New York, 

NY, pp. 23202321 (paper ThA07.1). 

[8] Hoadley, B. (1971), “Asymptotic Properties of Maximum 

Likelihood Estimates for the Independent Not Identically 

Distributed Case,” Annals of Mathematical Statistics, vol. 

42, pp. 19771991. 

[9] Hwang, C. L., Tillman, F. A., and Lee, M. H. (1981), 

“System-Reliability Evaluation Techniques for 

Complex/Large Systems—A Review,” IEEE Transactions 

on Reliability, vol. R-30, pp. 416423. 

[10] Jin, T. and Coit, D. (2001), “Variance of System-Reliability 

Estimates with Arbitrarily Repeated Components,” IEEE

Transactions on Reliability, vol. 50(4), pp. 409413. 

[11] Leemis, L. M. (1995), Reliability: Probabilistic Models and 

Statistical Methods, Prentice-Hall, Englewood Cliffs, NJ. 

[12] Ljung, L. (1999), System Identification—Theory for the User 

(2nd ed.), Prentice-Hall PTR, Upper Saddle River, NJ. 

[13] Myhre, J. M. and Saunders, S. C. (1968), “On Confidence 

Limits for the Reliability of Systems,” Annals of 

Mathematical Statistics, vol. 39(5), pp. 14631472. 

[14] Ramírez-Márquez, J. E. and Jiang, W. (2006), “On Improved 

Confidence Bounds for System Reliability,” IEEE

Transactions on Reliability, vol 55(1), pp. 2636. 

[15] Rao, C. R. (1973), Linear Statistical Inference and Its 

Applications (2nd ed.), Wiley, New York. 

[16] Serfling, R. J. (1980), Approximation Theorems of 

Mathematical Statistics, Wiley, New York. 

[17] Spall, J. C. (2003), Introduction to Stochastic Search and 

Optimization: Estimation, Simulation, and Control, Wiley, 

Hoboken, NJ. 

[18] Tang, J., Tang, K., and Moskowitz, H. (1997), “Exact 

Bayesian Estimation of System Reliability from Component 

Test Data,” Naval Research Logistics, vol. 44(1), pp. 

127146. 

[19] Trench, W. F. and Kolman, B. (1972), Multivariable

Calculus with Linear Algebra and Series, Academic, New 

York. 

[20] Zehna, P. W. (1966), “Invariance of Maximum Likelihood 

Estimators,” Annals of Mathematical Statistics, vol. 37, p. 

744. 

16
Fuzzy-Logic-Based Approach for Identifying Objects of

Interest in the PRIDE Framework

Zeid Kootbally, Craig Schlenoff and Raj Madhavan∗

National Institute of Standards and Technology

100 Bureau Drive

Gaithersburg, MD, USA

{zeid.kootbally, craig.schlenoff}@nist.gov, raj.madhavan@ieee.org

Sebti Foufou

University of Burgundy

Laboratoire LE2i, UMR CNRS 5158

Dijon, France

sebti.foufou@u-bourgogne.fr

ABSTRACT

On-road autonomous vehicle navigation requires real-time

motion planning in the presence of static and moving objects. Based on sensed data of the environment and the

current traffic situation, an autonomous vehicle has to plan

a path by predicting the future location of objects of interest. In this context, an object of interest is a moving

or stationary object in the environment that has a reasonable probability of intersecting the path of the autonomous

vehicle within a predetermined time frame. This paper investigates the identification of objects of interest within the

PRIDE (PRediction In Dynamic Environments) framework.

PRIDE is a multi-resolutional, hierarchical framework that

predicts the future location of moving objects for the purposes of path planning and collision avoidance for an autonomous vehicle. Identifying objects of interest is an aspect

of situation awareness and is performed in PRIDE using a

dangerous zone, i.e., a fuzzy-logic-based approach representing a hazardous space area around an autonomous vehicle.

Once objects of interest are identified, the risk of collision

between the autonomous vehicle and each object of interest is then evaluated. To illustrate the performance of a

dangerous zone within PRIDE, preliminary results are presented using a traffic scenario with the high-fidelity physicsbased framework for the Unified System for Automation and

Robot Simulation (USARSim).

Keywords

4D/RCS, autonomous vehicle, dangerous zone, fuzzy logic,

∗R & D Staff Member, Computational Sciences and Engineering Division, Oak Ridge National Laboratory, Oak

Ridge, TN 37831, USA.

(c) 2008 Association for Computing Machinery. ACM acknowledges that

this contribution was authored or co-authored by a contractor or affiliate

of the U.S. Government. As such, the Government retains a nonexclusive,

royalty-free right to publish or reproduce this article, or to allow others to

do so, for Government purposes only.

PerMIS’08, August 19-21, 2008, Gaithersburg, MD, USA.

ACM ISBN 978-1-60558-293-1/08/08.

fuzzy space, long-term prediction, moving object prediction,

object of interest, PRIDE, situation awareness

1. INTRODUCTION

Road traffic driving for autonomous vehicles (AVs) is continuing to gain traction both with researchers and practitioners. Funding for research in AVs has continued to grow

over the past few years, and recent high profile funding opportunities have started to push theoretical research efforts

into worldwide development of the most advanced projects.

A leading example of the state of the art in autonomous

driving is the Defense Advanced Research Projects Agency’s

(DARPA) series of grand challenges. In 2007, DARPA presented the Urban Challenge [1] (Victorville, CA, USA), a

research and development program on AVs with the goal

of developing technology that will keep warfighters off the

battlefield and out of harm’s way. This event required each

participating team to build an AV capable of executing simulated military supply missions while merging into moving

traffic, navigating traffic circles, etc.

As demonstrated by the DARPA challenges, one of the

main goal of AVs is to reduce the number of casualties in

traffic accidents. The National Highway Traffic Safety Administration (NHTSA) [12] reported 42 642 killed people

and 2 575 000 injured in motor vehicle crashes for the year

2006. It was also reported that one cause (after speeding)

of these accidents is misjudgment due to carelessness. To

reduce fatalities, many efforts have led to the enhancements

of road designs, imposition of laws and regulations, and improvement of situation awareness (SAw) of the drivers.

Consequently, much effort has been directed towards trying to understand the “human factors” component in vehicle

accidents. As pointed out by Sukthankar [20], a primary

challenge to create an AV that can competently drive in

traffic is the task of tactical reasoning, i.e., the AV should

be able to decide which actions to perform in a particular

driving situation, in real-time, given incomplete information

about the rapidly changing traffic configuration. Humans

are able to understand highly dynamic and complex environments via their cognitive capabilities. One component

of these cognitive capabilities is SAw, namely, the human’s

ability to perceive the environment, comprehend the situa17
tion, project that comprehension into the near future, and

determine the best action to execute [5, 6]. Researchers’

hypothesis is that an AV with human-like SAw capabilities

should improve the mission success of future AV systems [2].

Research has shown that poor SAw is an important cause of

driving accidents [22], hence, an AV should have good capability of early recognition of obstacles and danger prediction.

Adopting the idea that SAw is a key component in driving

safety, the AV community has given considerable amount of

attention on this topic.

The research interest of this paper bears upon a level of

SAw of how other vehicles in the environment are expected

to behave considering their situation. When humans drive,

they need to understand how each object in the environment

moves according to the situation they find themselves in. To

address this need, PRIDE (PRediction in Dynamic Environments), a multi-resolution hierarchical framework has been

developed. This framework provides an AV planning system

with information that it needs to perform path planning in

the presence of moving objects [16]. PRIDE supports the

prediction of the future location of moving objects at various

levels of resolution, thus providing prediction information at

the frequency and level of abstraction necessary for planners

at different levels within the hierarchy.

This paper presents a fuzzy-logic-based methodology to

identify objects of interest within a dangerous zone for an

AV. A dangerous zone is defined as a space with a potential

of hazard. Once objects of interest have been identified, the

risk of collision is then evaluated for an AV with each object

of interest inside the dangerous zone. A simulated scenario

using the Unified System for Automation and Robot Simulation (USARSim) [4] shows preliminary results and demonstrates the performance of a dangerous zone within PRIDE

for identifying objects of interest.

The remainder of this paper is organized as follows: section 2 gives an overview of the PRIDE framework. Section 3 describes SAw within PRIDE and goes into detail

about objects of interest. Section 4 describes the concept

of dangerous zone used to identify objects of interests in

the environment. Section 5 discusses the performance of a

dangerous zone and section 6 concludes this paper.

2. THE PRIDE FRAMEWORK

PRIDE is a multi-resolutional hierarchical framework that

provides an AV planning system with information required

to perform path planning in the presence of moving objects.

This framework supports the prediction of the future location of moving objects at various levels of resolution. PRIDE

is based on the 4D/RCS architecture [8], which provides a

reference model for unmanned vehicles on how their software

components should be identified and organized.

The PRIDE framework provides moving object predictions to planners running at any level of the 4D/RCS hierarchy at an appropriate scale and resolution. The underlying concept of PRIDE lies in the incorporation of multiple

prediction algorithms into a single, unifying framework.

At the higher levels of the framework, the prediction of

moving objects needs to occur at a much lower frequency

and a greater level of inaccuracy is tolerable. At these levels, moving objects are identified as far as the sensors can

detect and a long-term (LT) prediction algorithm predicts

where those objects will be at various time steps into the

future. Higher-level reasoning processes need a global representation of the environment to compute the future location of an AV. PRIDE uses the road network database [14]

(RND) to access different information about the road networks, including individual lanes, lane markings, intersections, legal intersection traversability, etc. The lower levels

of the framework use estimation theoretic short-term (ST)

predictions based on an extended Kalman filter (EKF) to

predict the future location of moving objects with an associated confidence measure. Complete details on the LT

and ST prediction algorithms can be found in previous efforts [11, 16].

PRIDE currently integrates the Mobility Open Architecture Simulation and Tools (MOAST) framework along with

USARSim [17]. This integration provides predictions incorporating the physics, kinematics and dynamics of AVs involved in traffic scenarios. MOAST is a framework that provides a baseline infrastructure for the development, testing,

and analysis of autonomous systems1. MOAST implements

a hierarchical control technique which decomposes the control problem into a hierarchy of controllers with each echelon

(or level) of control adding additional capabilities to the system. USARSim is a high-fidelity physics-based simulation

system that provides the embodiment and environment for

the development and testing of autonomous systems. USARSim utilizes high-quality 3D rendering facilities to create a realistic simulation environment that provides the embodiment of a robotic system. The system architecture on

the integration of PRIDE with the MOAST and USARSim

frameworks is described in previous work [11].

PRIDE also handles drivers’ aggressivity. In this context,

the aggressivity represents the style and driving preferences

of a driver. For example, one would likely assume that a

conservative driver will remain in his lane whenever possible and will keep a gap between his vehicle and the leading vehicle. Conversely, an aggressive driver would have a

higher probability of changing lanes and would be more apt

to tailgate the leading vehicle. One may also find that the

aggressivity of the driver may change over time, e.g., the

driver can be very aggressive when trying to get to a certain lane, but become more passive when he gets there. The

PRIDE framework addresses all the driver types and situations mentioned above. Experiments and corresponding

results performed on aggressivity can be found in previous

work [15].

3. SITUATION AWARENESS

To make assumptions of the future positions of moving

objects, PRIDE has access to a level of SAw of how other

vehicles in the environment are expected to behave considering the road traffic situation. An AV should be able to plan

a path while avoiding any collision with obstacles or other

moving objects on the road. The AV also requires knowledge

of the environment and knowledge on the status of other objects in the environment to be able to drive tactically. The

modeling of other vehicles is the most important aspect of

tactical driving [20]. It is straightforward to model speed

and relative positions, however, it is a challenging task to

model the future behavior of the drivers.

SAw was first discussed in connection with pilot perfor1Autonomous systems in this context refer to embodied intelligent systems that can operate fairly independently from

human supervision.

18
mance in air-to-air combat and was seen as the critical difference between fighter aces and ordinary pilots [7, 10]. Since

its original conception, numerous definitions of SAw have

been proposed. The work presented in this paper uses the

formal definition from Endsley [6] where SAw is described as

[An expert’s] perception of the elements in the environment

within a volume of time and space, the comprehension of

their meaning and the projection of their status in the near

future.

3.1 Situation Awareness Model

The model of SAw within the PRIDE framework is being

developed based on a three-level model provided by Endsley

[6], as sketched in Figure 1.

Figure 1: Endsley’s model of situation awareness

(from [19]).

• Perception: this level of awareness is achieved if AVs

are able to perceive different elements (e.g., vehicles,

roads) in the environment as well as their characteristics (e.g., size, color, location).

• Comprehension: not only the AVs must perceive relevant information in the environment, they also must

combine the perceived data to interpret the situation

correctly.

• Projection: at this level, the AVs have the ability to

anticipate the actions of other vehicles and predict the

future states of the environment.

The perception level for an AV in PRIDE is addressed

through the MOAST/USARSim framework [17] and the RND

[14]. MOAST queries USARSim to retrieve the characteristics of the AVs, such as the speed, the cartesian coordinates, the orientation, and the speed rotation of the wheels.

PRIDE then compares the collected information to the RND

to determine the position of the AV in the environment. The

query returns the type of the road where the AV is positioned, the ID of the lane, the speed limit, and the traffic

flow on the lane.

At the comprehension level, PRIDE combines the elements from the perception level to present a situation for

the AV. For example, a vehicle with high speed (as compared to the speed limit of the road) and high acceleration

could be considered as aggressive for example. Likewise, a

vehicle driving at high speed toward the same uncontrolled

intersection as the AV has a higher probability of collision

than if its speed was lower. Hereby, PRIDE has the ability to

understand the situation by gathering different information

from different sources.

At the projection level, the LT prediction algorithm computes the future position of each AV by first computing all

realistic action sequences. Then, based on a final cost for

performing each action sequence, the LT algorithm chooses

the action with the lowest cost, i.e., the one with the highest

probability (see [16] for more details). The selected action

sequence is based on the actions of other moving objects

and on the situation of the AV itself. The output of the LT

prediction algorithm is a collision-free path for the AV.

3.2 Object of Interest

The goal of PRIDE is to emulate human drivers’ behaviors for AVs. As such, to achieve autonomous driving with

human-like SAw capabilities in the presence of moving objects, the AVs have first to identify objects of interest in the

environment. This section establishes the idea of identification of objects of interest, which is part of the state of the

environment step, as depicted in Figure 1.

At its current state, PRIDE first takes into account all

moving objects in the environment and then tests if any future collision is likely possible. It is obvious here that there

is a need for identifying only specific objects (moving or

static) and then evaluating the danger caused by each object. In real world, a driver pays attention to only a few

objects around him, and obviously not to all of them. Since

time constraints prevent processing all of this information

at every time instant, the driver must intelligently select the

information most critical to the immediate task. Focusing

on some moving vehicles or static obstacles first reduces the

computation time for collision, especially for a large number

of vehicles and obstacles in the environment. Furthermore,

identifying these specific objects constitutes a step further

towards the simulation of a typical driving behavior. The

AV should first focus on objects of interest in the environment that most constrain its available actions [13]. For example, when approaching an intersection with a STOP sign,

the AV can safely ignore the trajectories of the vehicles beyond the intersection, since the STOP sign forces the AV to

come to a halt. The AV should also make strong assumptions about objects in the environment. While observing an

oncoming vehicle, the AV could note its position and velocity, then “forget” about the oncoming vehicle for some

time interval, knowing that the vehicle would not be able

to close the distance in that time. The AV focuses on particular objects at particular time in particular situations.

These objects are termed “objects of interest” and can be

defined as a moving or stationary object in the environment

that has a reasonable probability of intersecting the path of

the autonomous vehicle within a predetermined time frame.

The identification of objects of interest is performed with

the methodology presented in the next section.

4. METHODOLOGY TO IDENTIFY OBJECTS

OF INTEREST

The methodology for the identification of objects of interest consists of two steps:

1. Building a dangerous zone around an AV to identify

objects of interest.

19
2. Evaluating the risk of collision of the AV (called driving risk level) with any object of interest.

4.1 Dangerous Zone

Moving vehicles are subject to physical hazards coming

from any direction, e.g., lateral impacts from the non-respect

of rights-of-way at intersections or from a non-detected vehicle in the blind spot, and rear-end crashes usually due

to inattention, following too closely, or both. Some of these

accidents occur when the driver fails to maintain a safe headway from the leading car because of a perceptual inadequacy

in estimating headways [21].

To effectively model the importance of an object on the

road, PRIDE relates to the concept of dangerous zone (DZ)

[18] to identify objects of interest in the space area around

the AV. A DZ is defined as a space with a potential of hazard.

Within the DZ, objects of interest have a different degree

of risk according to different criteria such as the distance

between an object of interest and an AV.

In conventional methods, the classical definition of “membership” puts an object either inside our outside a zone. The

approach proposed in this paper tries to evaluate the degree

of severity of an object within the DZ by classifying this

object based on several criteria. One criterion would be for

example, the closeness of an object of interest to the AV,

which could be interpreted as close, very close, far, very far.

As such, the effort of this paper describes a DZ by applying multi-dimension fuzzy sets to model gradual changes in

collision severity. The concept of fuzzy space (FS) is used

to present the spatial consideration fuzzy sets in two dimensions.

4.1.1 Fuzzy Space

The concept of FS is based on fuzzy logic and fuzzy sets.

Fuzzy logic is a superset of conventional (Boolean) logic that

has been extended to handle the concept of partial truth.

In 1965, Zadeh introduced fuzzy sets as an extension of the

classical notion of a set to represent uncertain and imprecise knowledge [23]. Fuzzy sets and fuzzy logic are used to

heuristically quantify the meaning of linguistic variables, linguistic terms, and linguistic rules that are specified by the

expert.

Fuzzy logic uses graded statements rather than ones that

are strictly true or false. Fuzzy logic attempts to incorporate the “rule of thumb”2 approach generally used by human

beings for decision making. Thus, fuzzy logic provides an

approximate but effective way of describing the behavior of

systems that are not easy to describe precisely.

Definitions.

To define a FS, the universe of discourse is in the form

of R2. The work proposed in this paper considers the longitudinal distance x and the lateral distance y as linguistic

variables from the relative coordinates of the AV. A typical

linguistic variable is expressed as:

Linguistic Variable(term 1, term 2,. . . , term n)

where n is the number of terms in the linguistic variable.

To define a FS, let X ⊂ R, and x, y ∈ X. Ax and Ay are

the fuzzy sets for the degree of risk as defined below:

2A method of procedure based on experience and common

sense.

Ax = (x, μAx )|x ∈ X, X → [0, 1]

Ay = (y, μAy )|y ∈ X, X → [0, 1]

Figure 2 depicts a trapezoidal membership function for

the longitudinal direction as defined by Equation 1.

μAx (x) = max(min( x − a

b − a

, 1,

d − x

d − c

), 0) (1)

Figure 2: Longitudinal dangerous zone.

The parameters a and d correspond to the “feet” of the

function μAx (x). The parameter d represents the safe distance headway of the AV. This headway is typically defined

in terms of time rather than distance, and a commonly recommended minimum safe headway is 2 s. That way, if a

lead driver initiates a braking action, the following driver

has 2 s to initiate a braking response to the slowing down

of the vehicle ahead. Using several parameters (e.g., current

velocity of an AV, aggressivity, and weather), PRIDE converts the safe time headway into the corresponding distance

headway.

Being able to modify the headway is an interesting point

for the LT prediction algorithm. The LT algorithm computes the future location of moving objects at n seconds

in the future [16]. So far, the time of prediction was established before running the simulation and could not be

changed thereafter. With the ability to change the headway regarding the situation of the AV and the environment,

the time of prediction is also modified in real-time. This

subjects is further discussed in the rest of this paper.

The parameters b and c represent the range of the membership function for which the degree of risk is the highest,

i.e., where the x values are closest to the AV. It is reasonable

to use the length of the AV (information from USARSim)

to define b and c.

For an object far from the AV, the risk of collision is low.

Conversely, for an object closer to the AV, the risk of collision increases to its maximum. The function increases faster

in the rear of the AV, thus describing a greater danger for a

vehicle too close to the leading AV.

Figure 3 shows the bell shape membership function for

the lateral distance as defined by Equation 2.

μAy (y) = 1

1 + | x−c

a |

2b (2)

The parameter b is linked to the width of the lane and is

defined using the RND. The risk of collision grows for any

20
Figure 3: Lateral dangerous zone.

point approaching the AV on its sides. The parameter c locates the center of the curve (0 in this case). The value of

a determines the membership values of the extreme points

(0,1) of the universe when the crisp value, c, coincides with

the center of the universe (0 in this case). The membership function μAy (y) shows an increasing risk of danger for

any object coming closer to the sides of the AV. Similar to

the definition of the longitudinal distance, the membership

function for the lateral distance has the ability to include

the dimension of the AV. In this case, the width of the lane

is taken into account, and thus the width of the AV within

the lane.

Construction of the Fuzzy Space.

Different methods exist for the construction of FSs to describe DZs, such as the minimum intersection, the multiplication intersection, the rotational extension, and the cylindrical extension (see [9] for an exhaustive list).

In this paper, the construction of the FS Axy is performed with the multiplication intersection method. The algebra multiplication μAx (x) μAy (y) is preferred to the fuzzy

logic multiplication min(μAx (x), μAy (y)). As pointed out by

Shahrokhi and Bernard [18], the minimum intersection fuzzy

space is not sufficient to demonstrate all DZs. Furthermore,

the algebra multiplication is more efficient for risk detection.

The multiplication intersection fuzzy space Axy for the longitudinal and lateral distances is defined by Equation 3 and

is depicted in Figure 4.

Axy = μAx μAy (3)

It is important to understand that the fuzzy sets defined

previously are not a standard for all road structures. The

fuzzy sets are tuned according to the type of the road. The

membership functions defined by Equations 1 and 2 are appropriate for a straight road. For a AV approaching an intersection for example, the fuzzy space can be spread over a

larger area and can be represented by a semi-spherical shape

incorporating some parts of the intersection.

4.2 Fuzzy Expert System

As discussed previously, the membership functions depend

on different parameters, e.g., the aggressivity of the driver

to compute the safe distance headway d in Equation 1 (Figure 2). The designer has to intelligently choose relevant

parameters so that the FS could adapt to different situa-

−2 0 2 4 6 8 10 −4

−2

0

2

4

0

0.5

1

Y [m]

X [m]

Fuzzy Space for an autonomous vehicle

Degree of risk

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Figure 4: Fuzzy space Axy.

tions. A fuzzy expert system is used with these parameters

to compute the appropriate FS.

Fuzzy expert systems are rule based controllers where the

inference mechanism is grounded on fuzzy logic. The general

architecture of a fuzzy expert system is depicted in Figure 5.

Figure 5: Architecture of a fuzzy expert system.

• The fuzzification module takes real input values (crisp

values) and maps them to the terms by assigning a

degree of membership. For continuous variable, the

degree of membership is expressed by a membership

function. There is a degree of membership for each

linguistic term that applies to the linguistic input variable.

• The rule base holds the knowledge in the form of a

set of rules, of how best to control the system. In

general, fuzzy controllers are based on control rules

of the type “IF condition” THEN “control” where

condition and control are always fuzzy propositions

(formula of fuzzy logic) of the type “x is A”, where

x is a linguistic variable and A is a linguistic term.

21
condition tells when the rules should be applied and

control describes the action to apply.

• The inference mechanism is the kernel of the fuzzy

controller. The inference mechanism evaluates which

control rules are relevant at the current time and then

decides the fuzzy commands to apply to the process.

• The defuzzification module is needed to translate the

fuzzy output of a fuzzy controller to a numerical representation. Intuitively, defuzzification can be done

using an averaging technique. The work described in

this paper uses the center of gravity method [9], which

is the same method employed to calculate the center

of gravity of a mass.

4.2.1 Linguistic Variables

In this paper, PRIDE uses the aggressivity, the speed, the

weather, and the acceleration as input linguistic variables

and the safe distance headway as the output. The linguistic

variables and the linguistic terms are presented in Table 1.

Variables

Input Output

Speed Aggressivity Weather Acceleration Headway

Terms

Zero Passive Rainy Zero Very Low

Small Normal Snowy Small Low

Medium Aggressive Stormy Medium Medium

Big Sunny Big Big

Very Big

Table 1: Linguistic variables used by the fuzzy expert system.

Once the linguistic variables are established, a set of rules

for the inference mechanism has to be defined. Example of

rules are shown below:

1. IF“Speed is Small”AND“Aggressivity is Normal”

AND“Weather is Sunny”AND“Acceleration is Zero”

THEN “Headway is Low”.

2. IF “Speed is Medium” AND “Aggressivity is Normal” AND “Weather is Snowy” AND “Acceleration

is Small” THEN “Headway is Medium”.

4.3 Evaluation of Driving Risk Level

Any object of interest is likely to lead to a potential collision. To evaluate the driving risk level (DRL) of the AV,

the distribution of the objects of interest within the DZ is

taken into account. Each object of interest is represented

by its position Oxi,yi in the environment. The DRL for each

object of interest Oxi,yi is computed by maximizing the FS

Axiyi as shown by Equation 4 [3].

DRL = max(Axiyi ) (4)

Since the time of prediction coincides with the headway,

the LT cost-based approach computes the cost for an AV to

perform an action sequence. When an object of interest is

identified in the DZ, the LT algorithm computes the cost of

collision of the AV with the object of interest. At this point,

this cost is modified by the value of the DRL computed using

Equation 4.

5. PRELIMINARY RESULTS AND DISCUSSION

This section describes a traffic scenario and demonstrates

the performance of the DZ for an AV. In the following scenario, the dimension of the AV is Length× Width=3.686

m×1.799 m (from USARSim). According to the RND, the

width of the lane is 3.75 m. Finally, the weather is set to

“snowy”.

The chosen scenario is a lane-change maneuver over an

obstacle. The AV and the static obstacle are in lane L1 as

shown in Figure 6.

Figure 6: Vehicle avoiding a static obstacle.

Figure 7 shows the current positions of the AV and the

static obstacle. The negative values for the Y coordinates

are due to the coordinates of this particular road network in

USARSim.

During its trajectory, the AV starts to switch to the left

lane L2 at X=103.6 m and Y=-220 m. At this time, the

distance between the AV and the static obstacle is approximately 5.5 m. The average speed of the AV on this track

was 4 m/s. Since the weather is snowy for this scenario,

the headway is greater (about 6.6 m) than it would be for a

sunny weather.

40 60 80 100 120 140 160 180 −221.5

−221

−220.5

−220

−219.5

−219

−218.5

X [m]

Y [m]

Current Positions

Obstacle

Vehicle

X: 109.1

Y:−220.1 X: 103.6

Y: −220

Figure 7: Current positions of the autonomous vehicle and the static obstacle.

Figure 8 depicts the variation of the DRL computed using

Equation 4 with the static obstacle as object of interest. The

negative values refer to the distance while the AV drives

toward the obstacle (before reaching the obstacle), and the

positive values indicate the distance when the AV drives

away from the obstacle.

It can be seen that the DRL is null while the AV is far

away from the obstacle, before and after passing the obstacle. During this time period, no object of interest is detected

22
−60 −40 −20 0 20 40 60 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Risk of collision and distance

Distance [m]

Driving Risk Level (DRL)

Distance: 6.586 m Distance: 6.27 m

Distance: 3.536 m Distance: 3.32 m

Figure 8: Driving risk level compared to the distance from the obstacle.

by the AV. However, at a distance of 6.586 m from the obstacle, the DRL starts to increase when the object of interest

is identified within the DZ of the AV. The closer the AV is

to the obstacle, the faster the DRL increases, meaning the

higher is the risk of collision. The AV starts to gradually

move to L2 as soon as the value of the DRL is high enough

for a possible danger of collision. The DRL starts to increase

at a distance of 6.5 m from the obstacle, however, the AV

starts to switch to L2 only at a distance of 5.5 m from the

obstacle, i.e., when the DRL is in [0.6 - 0.7] (Figure 8). The

DRL value within this range modifies the cost associated

to the straight path of the AV and thus the LT algorithm

chooses a less expensive action, i.e., swerving to L2 in that

case.

The DRL reaches its highest level (0.9982) for the AV

being at around 3.5 m from the obstacle. While the AV is

moving to L2, the value of the DRL decreases and reaches

0 at 6.27 m away from the obstacle. At this point, since

no object of interest is identified within the DZ, the LT

algorithm modifies the cost associated to the AV driving in

lane L2. A penalty is given to the AV for not being in the

right-most lane, hence the lane switching to L1 at X=120 m

and Y=-218.7 m as depicted in Figure 7.

6. CONCLUSION

The work presented in this paper enhances situation awareness within the PRIDE framework by identifying objects of

interest in the environment. Autonomous driving requires

human-like situation awareness capabilities. Consequently,

autonomous vehicles (AVs) must consider objects of interest

in the environment in order to plan a collision-free trajectory. Identifying objects of interest can be assimilated to a

driver who only focuses on some objects that most constrain

his available actions.

The identification of objects of interest is performed by

a dangerous zones (DZs). In this context, a DZ is a fuzzy

space which represents a hazard area for an AV. The DZ is

built by first assembling relevant parameters, which are then

processed through a fuzzy expert system to adapt the fuzzy

space to different situations. Any object that falls inside

the DZ is identified as object of interest. Once the objects

of interest are identified, the risk of collision of the AV is

evaluated.

The fuzzy space has the advantages in considering the

dimension of the AVs, thus improving collision avoidance.

Another advantage is the modifications of the time of prediction for the LT prediction algorithm in real-time. This

second point is useful to emulate driving tasks taking into

account the current forecast and the variation of the aggressivity for example. Lastly, by first identifying objects

of interest, and only then evaluating the danger pertinent

to these objects, the time of computation of the LT algorithm is theoretically reduced, as compared with the former

version of the LT algorithm.

The concept of DZ has demonstrated reasonable results

with a new way to identify any danger in the environment.

However, the preliminary results were obtained for a single

AV on a simple straight road with a static obstacle. Identifying objects of interest in more complex traffic situations is a

challenge and should be developed in the near future. Since

the concept of DZ was first introduced in industrial systems,

PRIDE already has the capacity of considering DZs before

moving towards simulation in industrial facilities.

7. REFERENCES

[1] DARPA Urban Challenge 2007.

http://www.darpa.mil/GRANDCHALLENGE/, 2007.

[2] J. A. Adams. Unmanned Vehicle Situation Awareness:

A Path Forward. In Proceedings of the 2007 Human

Systems Integration Symposium, 19–21 March 2007.

[3] H. Cai and Y. Lin. A Preliminary Study on a Fuzzy

Driving Risk Model. In Proceedings of the IEEE

International Conference on Systems, Man and

Cybernetics, volume 2, pages 1785–1790, 10–12

October 2005.

[4] S. Carpin, M. Lewis, J. Wang, S. Balakirsky, and

C. Scrapper. USARSim: a Robot Simulator for

Research and Education. In Proceedings of the 2007

IEEE International Conference on Robotics and

Automation (ICRA), pages 1400–1405, 10–14 April

2007.

[5] M. R. Endsley. Design and Evaluation for Situation

Awareness Enhancement. In Proceedings of the Human

Factors Society 32 nd Annual Meeting, volume 1,

pages 97–101, 1988.

[6] M. R. Endsley. Toward a Theory of Situation

Awareness in Dynamic Systems. Human Factors: The

Journal of the Human Factors and Ergonomics

Society, 37(1):32–64, March 1995.

[7] K. Harwood, B. Barnett, and C. Wickens. Situational

Awareness: A Conceptual and Methodological

Framework. In F.E. McIntire, editor, Proceedings of

the 11 th Biennial Psychology in the Department of

Defense Symposium, pages 23–27, 1988.

[8] J. Albus et al. 4D/RCS Version 2.0: A Reference

Model Architecture for Unmanned Vehicle Systems.

Technical Report NISTIR 6910, National Institute of

Standards and Technology, 2002.

[9] R. Jager. Fuzzy Logic in Control. PhD thesis,

Technische Universiteit Delft, The Netherlands, June

1995.

[10] S. Kass, D. Hershler, and M. Companion. Are They

Shooting at Me: An Approach to Training Situational

Awareness. In Proceedings of Human Factors Society

23
34 th Annual Meeting, pages 1352–1356, 1990.

[11] Z. Kootbally, C. Schlenoff, and R. Madhavan. A Brief

History of PRIDE. In Proceedings of the Performance

Metrics for Intelligent Systems (PerMIS) Workshop,

NIST SP 1073, pages 40–47, August 2007.

[12] NHTSA. Traffic Safety Facts 2006: A Compilation of

Motor Vehicle Crash Data from the Fatality Analysis

Reporting System and the General Estimates System.

Technical Report DOT HS 810 818, U.S. Department

of Transportation, National Center for Statistics and

Analysis, U.S. Department of Transportation,

Washington, DC 20590, September 2007.

[13] D. A. Reece. Selective Perception for Robot Driving.

PhD thesis, Carnegie Mellon University, May 1992.

[14] C. Schlenoff, S. Balakirsky, A. Barbera, C. Scrapper,

and J. Ajot. The NIST Road Network Database:

Version 1.0. Technical Report NISTIR 7136, National

Institute of Standards and Technology, July 2004.

[15] C. Schlenoff, Z. Kootbally, and R. Madhavan. Driver

Aggressivity Analysis within the Prediction In

Dynamic Environments (PRIDE) Framework. In

Proceedings of the 2007 SPIE Defense and Security

Symposium, volume 6561, page 65611O, May 2007.

[16] C. Schlenoff, R. Madhavan, and Z. Kootbally. PRIDE:

A Hierarchical, Integrated Prediction Framework for

Autonomous On-Road Driving. In Proceedings of the

2006 International Conference on Robotic Applications

(ICRA), pages 2348–2353, 15–19 May 2006.

[17] C. Scrapper, S. Balakirsky, and E. Messina. MOAST

and USARSim: A Combined Framework for the

Development and Testing of Autonomous Systems. In

Proceedings of the 2006 SPIE Defense and Security

Symposium, volume 6230, 17–21 April 2006.

[18] M. Shahrokhi and A. Bernard. A Fuzzy Approach for

Definition of Dangerous Zone in Industrial Systems. In

Proceedings of the IEEE International Conference on

Systems, Man and Cybernetics, volume 7, pages

6318–6324, 10–13 October 2004.

[19] P. R. Smart, A. Bahrami, D. Braines,

D. McRae-Spencer, J. Yuan, and N. R. Shadbolt.

Semantic Technologies and Enhanced Situation

Awareness. In 1st Annual Conference of the

International Technology Alliance (ACITA), 25–27

September 2007.

[20] R. Sukthankar. Situation Awareness for Tactical

Driving. PhD thesis, Robotics Institute, Carnegie

Mellon University, January 1997.

[21] M. Taieb and D. Shinar. Minimum and Comfortable

Driving Headways: Reality versus Perception. Human

Factors, 43:159–172, 2001.

[22] J. R. Treat, N. S. Tumbas, S. T. McDonald,

D. Shinar, R. D. Hume, R. E. Mayer, R. L. Stanisfer,

and N. J. Castellan. Tri-Level Study of the Causes of

Traffic Accidents. Technical report, National Highway

Traffic Safety Administration, 1979.

[23] L. A. Zadeh. Fuzzy sets. Information and Control,

8:338–353, 1965.

24
Identifying Objects in Range Data Based on Similarity 

Transformation Invariant Shape Signatures 

Xiaolan Li1,2 Afzal Godil1 Asim Wagan1

1

 National Institute of Standard and Technology, Gaithersburg, MD 20899, U.S.A. 2

 Zhejiang Gongshang University, Hangzhou, Zhejiang 310018, China

Contact: lixlan@nist.gov 

ABSTRACT

Identification and recognition of three dimensional (3D) objects 

in range data is a challenging problem. We propose a novel 

method to fulfill the task through two steps: 1) construct the 

feature signatures for the objects in the scene and the models in 

a 3D database; 2) based on the feature signature, find out the 

most similar model which decides the class of the corresponding 

object in the scene. We also evaluate the accuracy, robustness of 

the recognition method with several configurations. Our 

experimental results validate the effectiveness of our method. 

Categories and Subject Descriptors

I.2.10 [Vision and Scene Understanding]: Shape, 

Representations, data structures, and transforms.

General Terms

Algorithms, Performance, Reliability. 

Keywords

Object recognition, accuracy evaluation.

1. INTRODUCTION 

With the development of sensor technology, laser scanners 

along with digital color cameras, sonar sensors and other sensors 

share the role of being “perception organs” of a robot. The 

action of the robot is highly dependent on the information 

obtained from the data collected by the “perception organs”. 

Here is a search and rescue example. When there is a gas leak in 

a dark factory, the robot enters as a rescuer. However, color 

cameras cannot capture images because of the darkness. Laser 

scanning becomes the preferred method for the acquisition of 

the information. Having obtained the range data, the robot first 

differentiates people from other objects, and then, carries on 

different strategies according to the recognition results: helping 

the people, and avoiding other objects. 

Besides the advantage in applications, such as robot 

localization and strategy choice, object recognition in a cluttered 

scene is an interesting and challenging problem in its own right. 

The problem is defined as follows: given a 3D point cloud 

produced by a laser scanner observing a 3D scene, the goal is to 

identify objects in the scene by comparing them to a set of 

candidate objects. This is closely related to 3D shape retrieval. 

The main difference between 3D shape retrieval and the 

recognition problem here is that, for range data, only part of the 

object is captured by the scanner because of the limitation of the 

view angle and the occlusion. The situation of occlusion is 

complicated. For simplicity, we only focus on the case that the 

occlusion does not destroy the silhouette of the objects. As a 

result, a complete outline is preserved, which is used as a source 

to construct the shape representation of the object in the scene. 

For the range data, we start by segmenting it into several 

regions. Then each region’s data is projected into a plane 

perpendicular to the view direction of the scanner to get a 

silhouette. As for the candidate objects in a 3D shape repository, 

their silhouettes are captured from several views. Then Fourier 

Mellin Transform is performed on those images to extract 

similarity transform invariant 2D features. After that, a 

comparison is done between regional range data and the models 

in the database to get the most similar one. The regional range 

data is labeled after the chosen model. 

The rest of this paper is organized as follows. Section 2 

describes some of the related work to our proposed approach for 

identifying 3D objects in range data. The procedures of feature 

extraction and similarity comparison are described in Section 3. 

In Section 4, we provide the recognition results for simulated 

range data and evaluate the accuracy and robustness of the 

approach. Section 5 provides some conclusions.

2. RELATED WORKS 

There exists extensive literature addressing 3D object 

recognition [Bustos05]. For simple scenes, it is straightforward 

to use several basic geometries to represent them, such as 

generalized cylinders [Binford71], superquadrics [Solina90], 

geons [Wu94], and so on. Unfortunately, this kind of 

representation is too abstract to describe complicated real 3D 

objects. Other sophisticated methods have been put forth, 

including visual similarity-based [Chen03] [Vranic03], 

geometric similarity-based [Osada02] [Papadakis07], topologic 

similarity-based [Biasotti04], and local region similarity-based 

[Frome04]. Our approach is closely related to the visual 

similarity-based methods. In this section, we give a brief 

description about this kind of approach. 

(c) 2008 Association for Computing Machinery. ACM acknowledges 

that this contribution was authored or co-authored by a contractor or 

affiliate of the U.S. Government. As such, the Government retains a 

nonexclusive, royalty-free right to publish or reproduce this article, or to 

allow others to do so, for Government purposes only. 

PerMIS’08, August 19-21, 2008, Gaithersburg, MD, USA 

ACM ISBN 978-1-60558-293-1/08/08.

Orthogonal projected silhouette image is the most popular 

when researchers are thinking about using the collection of 2D 

images to represent the 3D shape [Chen03] [Vranic03]. Chen et 

al. [Chen03] first captured 100 silhouettes with 10 different 

configurations of cameras mounted on 10 dodecahedrons. Then 

35 Zernike moments coefficients and 10 Fourier coefficients 

calculated from one image are concatenated as one descriptor. 

After that, the similarities between objects are measured using a 

25
particular metric. Vranic [Vranic03] only use 6 silhouettes, 

which is comparably less than that in [Chen03], because of the 

pre-alignment procedure (PCA). Actually, the recognition power 

of visual similarity-based methods is strongly dependent on the 

2D shape descriptors and the view direction used to capture the 

image. 

 (a) A scene. (b) The corresponding range data. (c) segmented scene. 

Figure 1. The scene. 

Several approaches exist to describe the shape of an image, 

including geometric moments, complex moments, Legendre 

moments, Zernike moments, Fourier descriptors, etc. [Liao96]. 

Fourier and Zernike, which are a contour shape descriptor and a 

region shape descriptor respectively, are superior to the others 

according to the research of Zhang et al [Zhang02]. 

Nevertheless, they do not completely satisfy the invariance 

requirement with respect to similarity transformations (i.e. 

rotation, translation and scale). Under the Fourier-Mellin 

transform framework, which is widely used in image 

reconstruction and image retrieval, complete invariant 

descriptors can be derived [Yu07]. 

In this paper, we investigate a new method for 3D object 

recognition based on orthogonally projected silhouettes under 

the Fourier-Mellin transform framework.

3. IDENTIFICATION PROCEDURE

The whole identification procedure is divided into 2 main parts: 

constructing the 3D descriptors, and computing the similarity 

between the range data and the candidate objects in the database. 

However, a scene usually includes several objects. In order to 

figure out what each object is, we should segment the range 

data. 

Actually, for the range data captured from a certain view 

direction, it can be regarded as an image whose resolution is 

equal to the scanner’s resolution and whose pixel values record 

the depth from the surface of the objects to the scanner. Thus 

thousands of image segmentation methods can be used 

[Sezgin04]. A threshold approach is applied here to segment the 

range data. Figure 1(a) shows a scene, while figure 1(b) is the 

corresponding range data, and figure 1(c) displays the 

segmented result in which different color refers different object. 

3.1. 3D descriptor construction 

For each object in the scene, after the segmentation phrase, a 

silhouette is obtained. Three steps of Fourier-Mellin transform 

are performed on the silhouette to extract a similarity invariant 

feature vector, which is shown in figure 2. 

1) A 2D FFT 

3 3 f

f

f

f

 eyxfvuF dxdy uxj vy)(2 ),(),( S

is applied to the silhouettes. 

Figure 2. The procedure of FMT. 

2) A log polar transform is performed on the images 

composed of the magnitudes of the Fourier coefficients. In this 

step, the resolution of the image can be changed, which defines 

the size of the final descriptor. The resolution is denoted as 

M*M. 

3) Another 2D FFT is carried out on the log polar images to 

obtain the Fourier Mellin coefficients. 

Because of the symmetry property of FFT, we choose the 

magnitudes of the Fourier Mellin coefficients located in the first 

quadrant as the descriptor, that is 

FV= ( c1,c2,...,cK ) (1) 

where K=M*M/4. 

To decrease the size of the feature vector, there is another 

solution to construct it. The coefficients in the first quadrant are 

summed up along x and y directions. Therefore, the form of 

feature vector keeps the same form as in equation (1), in which 

K=M*2. 

Figure 3. The demonstration for capturing 

several silhouettes from defined positions on 

the surface of bounding sphere.

26
For the candidate models, the construction of descriptor is 

similar to that of the objects in the scene. Nevertheless, more 

than one such descriptor is needed to give a complete 

description for the model. Several cameras are placed on the 

surface of a sphere to fulfill this goal, whose center is the center 

of the model and whose radius equals to the model’s max radius 

(shown in figure 3). The positions are defined by the longitude 

and latitude: 

 T M ji T i S 0,20),,( M j dd S , (2) 

where i,j=1,2,...,N. As a result, the descriptor for one candidate 

model is denoted as an array: 

FA=

»

»

»

»

»

1⁄4

o

«

«

«

«

«

¬

a

NN

K

NNNN

K

K

ff f

ff f

ff f

* *

2

*

1

2 2

2

2

1

1 1

2

1

1









 (3) 

3.2. Similarity computation 

To compare descriptor FV eq. (1) with descriptor FA eq. (3), L1 

distance measurement is used. The similarity is evaluated based 

on it: 

min ( ) 1 1 ¦  

K

i

i

j

i j l sim cf , (4) 

where j=1,2,...,N. The smaller the value is for equation (4), the 

more similar the object is to the candidate model.

4. RESULTS AND EVALUATION

The recognition power of the method is tested on a set of 

reference 3D shapes made up of 15 models taken from the PSB 

3D model library [Shilane04]. Figure 4 shows all of them. The 

point clouds used in our experiments were generated using a 

simulation program with resolution 256 by 256, which is 

regarded as query data. It is composed of one car (m1518), one 

person (m168) and one two-story house (m443) from the 

reference 3D model sets, which are all scaled to the normal size 

as in the real world in order to be reasonable. 

The recognition results are shown in figure 5 with N=10, 

M=64. The X axis represents all the reference models in the data 

set, while the Y axis indicates the distance between the query 

object and the models. 

How the noise level affects the recognition results is 

discussed here. Take one object –house – in the query scene as 

an example, we add Gaussian noise to it and get the result with 

different noise levels. The recognition curves for different noise 

level are shown in figure 5. From the plot, we know that the 

noise will change the distance value a little bit, but the 

appearance of the curve keeps similar to the original one (the 

dark blue curve), which shows the robustness of our method. 

 m168 m145 m224 m1518 m1519 m1522 m1337 m1388 

 m437 m443 m453 m82 m103 m1051 m1055 

In the reference data set, m168, m145, m224 belong to class “human”; m1518, m1519, m1522 belong to class “sedan”; m437, 

m443, m453 belong to class “two story house”; the others belong to different classes. 

Figure 4. The reference data set. 

Since the range data can be extracted from different directions, 

the robustness of the algorithm related to the extracting 

directions should be evaluated. The 3D range scanner is placed 

on the surface of the bounding sphere of the scene. And the 

positions are defined by the longitude and latitude (eq. 2) with 

N=15, which means the amount of the range data from different 

directions is 225. The configuration guaranteed the differences 

between the shooting direction of the camera and the scanning 

direction of the range scanner. Taking the model of a person 

(m168) as an example, figure 6 shows the effect of the scanning 

directions, in which the x axis shows the name of the model and 

the y axis shows how many times the object is recognized as the 

model. It shows the accuracy is 87%. 

 (a) Recognition result for “human”. 

(b) Recognition result for “Car”. 

27
We would like to thank the SIMA program and the IDUS 

program for supporting this work.

(c) Recognition result for “House”. 

(d) Recognition result with different noise level for “House”.

Figure 5. The recognition results (a)(b)(c) for all the 

objects in the scene. The X axis records the shapes 

from the reference set. (d) represents the 

recognition results for “House” with different noise 

level. 

Figure 6. The effect of the shooting directions. 

REFERENCES

[Biasotti04] S. Biasotti. Reeb graph representation of surfaces 

with boundary. Proc. of the Shape Modeling International 2004 

(SMI’04), 2004. 

[Binford71] T.O. Binford. Visual perception by computer. IEEE 

Conf. on Systems and Control, Miami, FL, 1971. 

[Bustos05] B. Bustos, D. A. Keim, D. Saupe, T. Schreck, D. V. 

Vranic. Feature-based similarity search in 3D object databases. 

ACM Computing Surveys (CSUR), 37(4):345-387, 2005. 

[Chen03] D.Y. Chen, M. Ouhyoung, X.P. Tian, Y.T. Shen. On 

visual similarity based 3D model retrieval. Computer Graphics 

Forum (Eurographics ‘03), 03: 223-232, 2003. 

[Frome04] A. Frome, D. Huber, R. Kolluri, T. Bulow, J. Malik. 

Recognizing objects in range data using regional point 

descriptors. Proc. of European Conference on Computer Vision 

(ECCV), Prague, Czech Republic, 2004. 

[Liao96] S. X. Liao, M. Pawlak. On image analysis by moments. 

IEEE Trans. Pattern Analysis and Machine Intelligent, 

18(1996): 254-266, 1996. 

[Osada02] R. Osada, T. Funkhouser, B. Chazelle, D. Dobkin. 

Shape distributions. ACM Transaction on Graphics, 21(4):807-

832, 2002. 

[Papadakis07] P. Papadakis, I. Pratikakis, S. Perantonis, T. 

Theoharis. Efficient 3D shape matching and retrieval using a 

concrete radicalized spherical projection representation. Pattern 

Recognition, 40(2007):2437-2452, 2007. 

[Sezgin04] M. Sezgin, B. Sankur. Survey over image 

thresholding techniques and quantitative performance 

evaluation. Journal of Electronic Imaging, 13(1), 146-165, Jan. 

2004. 

[Shilane04] P. Shilane, P. Min, M.Kazhdan, T. Funkhouser. The 

Princeton shape benchmark. Proc. of the Shape Modeling 

International 2004 (SMI'04), 04(00): 167-178, 2004. 

[Solina90] F. Solina, R. Bajcsy. Recovery of parametric models 

from range images: the case for superquadrics with global 

deformations. IEEE Trans. On Pattern Analysis and Machine 

Intelligence (PAMI), Feb. 1990. 

[Vranic03] D.V. Vranic. 3D model retrieval. Ph. D. Dissertation, 

2003. 

[Wu94] K. Wu, M. Levine, Recovering parametric geons from 

multiview range data. CVPR, June, 1994. 

[Yu07] H. Yu, M. Bennamoun. Complete invariants for robust 

face recognition. Pattern Recognition, 40(2007):1579-1591, 

2007. 

[Zhang02] D. S. Zhang, G. Lu. An integrated approach to shape 

based image retrieval. Proc. of 5th Asian Conf. on Computer 

Vision (ACCV), 02: 652-657, January 2002. 

5. CONCLUSION

In this paper, we presented a novel procedure for 3D object 

recognition using the Fourier-Mellin transform. Although FMT 

is widely used in 2D image retrieval and reconstruction, it has 

not been used in 3D shape recognition. We have applied it to 3D 

shape recognition, and the experimental results show its 

effectiveness. Furthermore, how the noise level and the scanning 

direction affect the recognition result is investigated. 

Nevertheless, to guarantee the recognition accuracy, the 

completeness of the silhouette should be kept, which is rare in a 

cluttered and clustered scene. In future work, more stable local 

feature signatures will be introduced to alleviate the effect of 

cluttering and clustering. 

ACKNOWLEDGEMENT

28
Stepfield Pallets: Repeatable Terrain for 

Evaluating Robot Mobility

A. Jacoff, A. Downs, A. Virts, E. Messina 

Intelligent Systems Division, National Institute of Standards and Technology (NIST) 

Gaithersburg, MD 20899-8230, USA 

Email: {adam.jacoff, anthony.downs, ann.virts, elena.messina}@nist.gov 

ABSTRACT

Stepfield pallets are a fabricated and repeatable terrain for 

evaluating robot mobility. They were developed to provide 

emergency responders and robot developers a common 

mobility challenge that could be easily replicated to capture 

statistically significant robot performance data. Stepfield 

pallets have provided robot mobility challenges for the 

international RoboCupRescue Robot League competitions 

since 2005 and have proliferated widely for qualification and 

practice. They are currently being proposed as a standard test 

apparatus to evaluate robot mobility. This paper describes the 

origin and design of stepfield pallets, and discusses their use 

in several proposed standard test methods for response robots. 

Keywords

Stepfield, step field, robot mobility, robot test method, broken 

terrain, rough terrain, artificial rubble, urban search and 

rescue, RoboCupRescue. 

1. INTRODUCTION 

The National Institute of Standards and Technology (NIST) is 

developing standard test methods for emergency response 

robots as part of an ongoing effort sponsored by the 

Department of Homeland Security and the National Institute 

of Justice. A series of workshops with subject matter experts 

from urban search and rescue (US&R) task forces and other 

emergency response organizations defined thirteen robot 

categories and over a hundred specific robot performance 

requirements [1, 2]. Many of these requirements address robot 

mobility in complex terrains, which necessitated repeatable 

test methods to capture statistically significant robot 

performance data. Our approach toward developing mobility 

test methods has relied upon well-defined apparatuses to 

differentiate robot capabilities, and typically use the time to 

negotiate a specified obstacle or path, or the total distance 

traversed, to measure performance. These mobility tests are 

lways conducted with a remote operator station, out of sight 

and sound of the robot but within communications range, to 

emphasize the overall system performance. 

Stepfield pallets were developed to represent complex terrain 

or rubble that is describable, reproducible, and repeatable for 

robot testing. Each pallet consists of a grid of square wood 

posts cut to assorted cubic unit lengths (a unit is the actual 

post width when using metric dimensional lumber) and 

assembled into either symmetric or random topographies 

tending toward flat, perpendicular hill, or diagonal hill 

patterns. Multiple stepfield pallets have been assembled into 

configurations such as the stepfield “dash,” a sequential series 

of five specific pallets in a straight line that has proliferated 

widely for qualification in the international RoboCupRescue 

Robot League competitions [3]. A stepfield “figure-8” has 

also been fabricated using thirteen stepfield pallets and 

surrounding walls to provide a well-defined continuous path 

with turns for robot endurance tests. Dozens of stepfield 

pallets have been configured into a “field” apparatus that 

allows unconstrained negotiation of stepfield terrain features. 

Robot developers and purchasers can replicate these common 

configurations to compare robot performance, improve 

designs, and support operator training. 

2. BIOLOGICALLY INSPIRED TESTS 

The concept of using stepfield pallets to evaluate robot 

mobility in rough terrain derived from researchers 

investigating biologically inspired mechanisms and control 

systems. Researchers at the PolyPEDAL Laboratory at the 

University of California at Berkeley who evaluated 

cockroaches as effective legged mobility systems noted that 

they appeared to negotiate relatively rough terrain for their 

size with almost no loss in speed when compared to 

negotiation of flat surfaces [4]. They constructed terrain 

approximating a fractal surface consisting of 1 cm (0.4 in) 

posts of random height with a variance of 0.5 cm (0.2 in), the 

height of the insect’s center of mass. Extremes of height and 

depth of the terrain surface reached three times the height of 

the insect’s center of mass (see Figure 1A). Researchers in the 

Biomimetics Robotics Laboratory at Stanford University built 

a 16 cm (6 in) hexapod robot that emulated the movement of 

cockroaches. They used strips of wood equal to the robot’s 

“hip” height as obstacles along the robot’s path (see Figure 

1B) [5]. 

a

This paper is authored by employees of the United States Government 

and is in the public domain. 

P

A

erMIS'08, August 19-21, 2008, Gaithersburg, MD, USA 

CM ISBN 978-1-60558-293-1/08/08.

29
  

QuickTimeTM and a

 decompressor

are needed to see this picture

 

QuickTimeTM and a

 decompressor

are needed to see this picture.

Figure 1: A) A cockroach running over a fabricated fractal surface 

at the University of California – Berkeley. (Photo courtesy of Full 

et al.) B) A 16 cm (≈ 6 in) long hexapedal robot named Sprawlita 

modeled after cockroach mobility being tested on hip-height 

obstacles at Stanford University. (Photo courtesy of Clark et al.) C 

& D) A 53 cm (≈ 21 in) long hexapedal robot named RHex, with 

17.5 cm (≈ 7 in) legs, being tested on a scaled up experimental 

“broken terrain” made of wood posts at the University of Michigan 

and McGill University. (Photos courtesy of Saranli et al.)

Researchers at the University of Michigan and McGill 

University scaled up these experimental terrains using an array 

of wood posts cut to various lengths to test their RHex 

hexapedal robot, which itself was inspired from the research 

noted above [6]. They performed extensive mobility 

experiments in this “broken terrain” and others in an effort to 

quantify their robot’s mobility. Their experimental terrain 

used clusters of four posts of similar heights ranging from 10 

cm (≈ 4 in) to 30 cm (≈ 12 in) with random height variations 

up to approximately 20 cm (8 in). 

Stepfield pallets essentially combine the ideas noted above to 

form uneven terrains with elevated ridges as obstacles rising 

to heights roughly relative to the robot dimensions. Several 

inexpensive materials were considered before choosing the 

same simple wood posts used by Saranli et al. to form the 

square flat surfaces. Wood posts provide ruggedness and 

reasonable cost, thought they limit the scale of the discretized 

surfaces to typically available post sizes. However, they are 

easily fabricated and inexpensive enough to allow researchers 

and emergency responders to assemble many stepfield pallets 

into large test apparatuses for practice, evaluation, and 

training. 

Three different scales of pallets provide proportional testing 

for a variety of robot sizes (see Figure 2). Given that 

emergency response robots can be wheeled, tracked, or 

legged, stepfield pallet sizes and the associated ridge heights 

are more generally correlated to overall robot dimensions 

rather than to “hip” height, axle height, or other single 

dimension. To be appropriately proportional to the stepfield 

terrain, a given robot’s footprint should be no larger than 1/4 

to 1/3 the area of a single stepfield pallet. 

Figure 2: Three different scales of random stepfields for testing 

different size robots. In each scale, similar pallet topographies are 

shown using flat, perpendicular hill, and diagonal hill pallets. The 

hill pallets have posts that randomly tend toward the elevated ridges 

(shown in red) while following a few rules for continuity. 

3. STEPFIELD PALLET FABRICATION 

Stepfield pallets are fabricated with a 10x10 grid of square 

wood posts standing on end to form the terrain with a 

containment perimeter on all sides made of similar wood post 

material. The pallet base is made from oriented strand board 

(OSB) plywood with a thickness of at least 16 mm (≈ 0.675 

in) to support the weight of the stepfield when lifted. The 

containment perimeter is fastened to the plywood base using 

screws, but the interior grid of cut posts are free to jostle 

against one another and can be removed and reconfigured as 

necessary. Blocks can be fastened underneath the plywood 

base to allow forklift access for easier reconfiguration of test 

apparatuses made from many stepfield pallets. 

The interior posts that form the terrain for each stepfield pallet 

are cut into four different cubic unit lengths based on defined 

step heights for each scale of stepfield. Each successive scale 

increases the step size by a factor of two in length, width, and 

height. The three different scales of stepfield pallets are 

described below. Note that each pallet’s containment 

perimeter adds two unit lengths in each direction to the overall 

assembly: 

• Small size stepfield pallets have overall dimensions of 60 

cm (≈ 24 in) on a side and are made of a 10x10 grid of 5 

cm (≈ 2 in) cubic steps plus a containment perimeter. 

Each step is made of a single square wood post cut into 

unit lengths of 5 cm (≈ 2 in), 10 cm (≈ 4 in), 15 cm (≈ 6 

in), and 20 cm (≈ 8 in) according to the layouts in Figure 

3. 

 

30
 

Figure 3: Images and sample designs of random stepfield pallets showing cubic unit post heights. Post heights specified as 0 units are filled 

with 5 cm (~2 in) posts to maintain grid spacing. (Left-Right) A) Flat square stepfield pallet. B) Flat cross stepfield pallet. 

C) Perpendicular hill stepfield. D) Diagonal hill stepfield pallet. 

• Medium size stepfield pallets have overall dimensions 

of 120 cm (≈ 48 in) on a side and are made of a 10x10 

grid of 10 cm (≈ 4 in) cubic steps. Each step is made of 

a single square wood post cut into unit lengths of 10 cm 

(≈ 4 in), 20 cm (≈ 8 in), 30 cm (≈ 12 in), and 40 cm (≈

16 in) according to the layouts in Figure 3. 

• Large size stepfields have overall dimensions of 240 

cm (≈ 96 in) on a side and are made of four individual 

120 cm (≈ 48 in) pallets with a terrain pattern that spans 

all four pallets. The terrain is made of a 10x10 grid of 

20 cm (≈ 8 in) cubic steps. Each step is made with a 

cluster of four 10 cm (≈ 4 in) posts cut into unit lengths 

of 20 cm (≈ 8 in), 40 cm (≈ 16 in), 60 cm (≈ 24 in), and 

80 cm (≈ 32 in) according to the layouts in Figure 3. 

These dimensions work well with metric wood found in 

Europe, Asia, and elsewhere. But typical wood posts sizes 

in the United States are actually ≈ 4 cm (1.5 in) and ≈ 9 cm 

(3.5 in) square. This reduces the overall dimensions of the 

stepfield terrains though the ridge elevations can still be cut 

to the metric dimensions. Non-metric stepfield pallets are 

ood for practice, but the standard apparatus will likely be 

he metric version. 

g

t

3.1 Random Pallet Designs 

To make random stepfield pallets easy to proliferate, only 

four different general topographies have been generated: flat 

square, flat cross, perpendicular hill, and diagonal hill (see 

Figure 3). Within a given stepfield pallet, the individual post 

heights are randomly generated using a few rules applied 

and are shown graphically in the cubic unit lengths 

mentioned previously. The following rules are used to 

maintain some continuity in slopes tending toward the 

elevated ridges: 

1. There cannot be a step height difference of more than 

2 cubic units between any two adjacent steps. 

2. For the two generally flat pallet configurations, there 

are 4 locations that are 3 cubic units tall. These are 

the tallest steps on the pallet. The rest of the steps are 

generated randomly while following rule 1. 

3. For the perpendicular hill configurations, the ridge is 

made of 4 cubic unit step heights and extends across 

the entire pallet. Two rows on either side of the ridge 

can range between 2 to 3 cubic units. The remaining 

rows range between 0 to 2 while following rule 1. 

4. For the diagonal hill configurations, the ridge is made 

of 4 cubic unit step heights and extends across the 

entire pallet. Three diagonal rows on either side of the 

ridge can range between 2 to 3 cubic units. The 

remaining rows range between 0 to 2 while following 

rule 1. 

3.2 Half-Cubic Stepfield Pallets 

All of the stepfield pallets discussed so far have been fullcubic stepfields. These are often called red stepfields due to 

31
their placement in the RoboCupRescue competition’s red 

arena for advanced mobility. Half-cubic stepfields have also 

been fabricated which conform to the same general overall 

dimensions but have half step heights. 

Figure 4: An arrangement of half-cubic (orange) stepfield 

pallets.

These so-called orange stepfields provide for complexity in 

robot orientation without challenging mobility for properly 

scaled robots. They are used to make robotic tasks such as 

mapping, directed perception, and mobile manipulation 

more challenging than on simple flat flooring. 

4. ROBOT TEST METHODS 

A suite of mobility and other test methods for emergency 

response robots are emerging through the ASTM 

International standards committee on Homeland Security 

Applications; Operational Equipment; Robots (E54.08.01) 

[7]. Stepfields play a prominent role in several of the test 

methods both to provide challenging and repeatable terrain 

to evaluate robot mobility and to provide complex flooring 

for robotic tasks other than mobility. These test methods are 

always conducted with a remote operator station, out of 

sight and sound of the robot but within communications 

range, to emphasize the overall system performance. 

Several of the test methods that use stepfield pallets are 

discussed below. 

4.1 Stepfield Dash 

The Stepfield Dash is a sequential series of five specific 

pallet types in a straight line: flat square, perpendicular hill, 

flat cross, diagonal hill, flat square (see Figure 5). It has 

proliferated widely for qualification in the international 

RoboCupRescue Robot League competitions, which 

requires new teams to show a video of the robot traversing 

this test method along with submission of a team description 

paper. 

The Stepfield Dash was first introduced into the competition 

arenas at the 2005 German Open. Robots initially had 

difficulty traversing them but the researchers recognized the 

challenge. Later that year, at the 2005 RoboCupRescue 

Championship in Osaka, Japan, several Stepfield Dashes 

were sequenced together to additionally require turning on 

pallets. Only a few robots could finish the course. The robot 

with the fastest time won the best-in-class mobility award. 

Since then, stepfield pallets have been one of the main 

mobility challenges in the competition. 

A   B

Figure 5: A, B) The Stepfield Dash is used for robot qualification 

for the RoboCupRescue Robot League competitions. C) The 2005 

Championship arenas in Osaka, Japan.

4.2 Endurance 

The Endurance test method was designed to measure the 

performance of robots traversing various terrain types 

within a constrained figure-8 course [8]. The advanced 

mobility configuration includes a sequential series of 

stepfield pallets bounded by walls to provide a continuous 

path with turns (see Figure 6). Robots are timed for average 

lap speeds and the total numbers of pallets traversed during 

a single battery cycle. 

32
  

Figure 6: A) The Endurance test method has one lobe of the 

figure-8 with perpendicular hill pallets separated by generally 

flat pallets. B) The other lobe has diagonal hill pallets separated 

by generally flat pallets. The center path of the figure-8 uses flat 

pallets (not shown).

4.3 Confined Space 

The Confined Space test method is essentially a covered 

Stepfield Dash (see Figure 7). The tops of the confined 

spaces are made of inverted stepfield pallets with slight 

modifications; only the tallest step height posts are used to 

minimize weight. They are screwed into the OSB plywood 

base to hold them in place. The minimum gap between the 

upper and lower stepfield posts can be adjusted in 10 cm (≈

4 in) increments. Robots are timed to completely traverse 

the test and the minimum vertical gap is recorded. 

 

Figure 7: The Confined Space test method uses random stepfield 

pallets as stalagmites and stalactites. 

4.4 Manipulator Test Methods 

Half-cubic (orange) stepfield pallets are used as one of three 

flooring options in the Manipulator Dexerity test methods 

(see Figure 8). 

Figure 8: The Manipulator Dexterity: Perception test method is 

shown with half-cubic stepfield terrain for added complexity.

The other two flooring options are flat flooring, typically 

used to capture baseline performance data, and 15 degree 

pitch/roll ramps to tilt the robot while interacting with the 

environment. The half-cubic stepfields provide complexity 

in robot orientation without aggressively challenging 

mobility. 

5. SYMMETRIC STEPFIELDS 

All proposed test methods go through a rigorous process to 

become a standard. One major hurdle is capturing the 

necessary repeatability data for the test method itself. This 

requires testing several representative robots for 10 trials 

each. If the performance range of the proposed test method, 

or repeatability, produces the same result for a given robot 

the test method can be considered valid, though it may 

require a more granular scale. In the case of the random 

stepfield pallets, the opposite is true. For example, robot 

performance across multiple stepfield pallets in the 

Endurance figure-8 with random stepfields can vary widely 

for each lap. Randomly placed posts on any given stepfield 

pallet can cause problems for a particular robot’s mobility, 

or for the remote operator’s obstacle avoidance capability, 

even if it can traverse all the other stepfield pallets with 

relative ease. 

A standard test method must also reproduce the same 

measurable robot performance at different test facilities, 

which is called reproducibility. A given robot must perform 

similarly on a particular test method at Facility A, 

demonstrated by a statistically significant data collection, as 

it does on the same test method fabricated and tested at 

Facility B. Although the random stepfield pallets can be 

replicated with enough precision, particular variants of 

individual random stepfield pallets have proven inconsistent 

for some robots. This may ultimately make the 

standardization of random versions of stepfield pallets 

difficult to achieve. Nonetheless, they can still provide a 

good evaluation and training tool for robots prior to 

deployment. 

Symmetric stepfield pallets provide similar mobility 

obstacles for robots of an appropriate size, but they present 

the same challenges no matter which direction the robot 

approaches (see Figure 9). When assembled into a larger 

test method apparatus, a robot that can traverse a diagonal 

hill, for example, should always be able to traverse any 

other diagonal hill pallet, even if it approaches from the 

opposite direction. Symmetric stepfield pallets were 

included as mobility obstacles in the 2008 RoboCupRescue 

Robot League Championship held in Suzhou, China [9]. 

Over 100 competition missions were conducted, though 

they do not count toward results regarding test method 

repeatability since RoboCupRescue teams have other goals 

and distractions. It appears anecdotally that the symmetric 

stepfields produce more repeatable robot performance than 

random stepfield pallets. More testing is required and the 

designs may evolve, but symmetric stepfields may provide 

the right balance of rigorous mobility challenges in a 

repeatable test method apparatus.

33
 

Figure 9: Symmetric stepfield pallets fabricated in Suzhou, China.

 (Left-Right) A) Flat cross pallet. B) Flat square pallet. C) Diagonal hill pallet. D) New center peak pallet. 

6. CONCLUSIONS 8. REFERENCES 

Stepfield pallets, in both their full-cubic and half-cubic 

variants, have become a central part of several proposed 

NIST/ASTM test methods for response robots. They have also 

proliferated around the world as mobility challenges for 

international competitions. While they provide repeatable 

terrain to challenge and evaluate robot mobility and a remote 

operator’s situational awareness, they have proven to be 

difficult to standardize as a mobility test method. Random 

stepfields can continue to play a key role in helping robots 

move from the laboratory toward practice deployments and 

even to support operator training. But as a standard test 

method apparatus, a more repeatable version of the stepfields 

is necessary. More experimentation is required, but initial tests 

using symmetric stepfield pallets suggest that repeatability in 

robot performance and reproducibility of the test apparatus 

can be achieved. 

[1] Messina, E., "Performance Standards for Urban Search and 

Rescue Robots," ASTM International Standardization News, August 

2006.

[2] Statement of Requirements for Urban Search and Rescue Robot 

Performance Standards, May 2005. 

http://www.isd.mel.nist.gov/US&R_Robot_Standards/Requirements

%20Report%20(prelim).pdf As accessed August 2008. 

[3] RoboCupRescue Robot League competitions. 

http://www.isd.mel.nist.gov/projects/USAR/competitions.htm        As accessed August 2008. 

[4] Full, R. J., Autumn, K., Chung, J. I., Ahn, A., “Rapid negotiation 

of rough terrain by the deathhead cockroach,” American Zoologist, 

38:81A, 1998. 

[5] Clark, J., Cham, J., Bailey, S., Froehlich, E., Nahata, P., Full, R., 

Cutkosky, M., “Biomimetic Design and Fabrication of a Hexapedal 

Running Robot,” Proceedings of the IEEE 2001 International 

Conference on Robotics and Automation, May 2001. 

7. ACKNOWLEDGMENTS 

The authors would like to thank all the emergency responders 

involved in the NIST/DHS Response Robot Evaluation 

Exercises and other supporting events. Their initial set of 

robot requirements provided tangible goals to work toward 

and their ongoing feedback on test method designs has been 

much appreciated. Similarly, thanks to all the robot developers 

who have provided robot practice and training opportunities 

within prototype test methods and ongoing collaborations 

toward developing meaningful and challenging test methods 

for the community. And finally, we would like to thank the 

participants of the RoboCupRescue Robot League 

competitions for their enthusiastic robot testing, proliferation 

of apparatuses, and constructive ideas for new test methods. 

[6] U. Saranli, M. Buehler, and D. E. Koditschek, "RHex: A Simple 

and Highly Mobile Hexapod Robot," Int. J. Robotics Research, 

20(7):616-631, July 2001. 

[7] ASTM International Standards Committee on Homeland Security 

Applications; Operational Equipment; Robots (E54.08.01). 

http://www.astm.org/COMMIT/SUBCOMMIT/E5408.htm 

As accessed August 2008. 

[8] Response Robots Pocket Guide: Test Methods and Robots, 25 

July 2008. 

http://www.isd.mel.nist.gov/US&R_Robot_Stndards/montgomery_co

unty/pocketguide.htm As accessed August 2008. 

[9] RoboCup World Championship, Suzhou, China, 14-20 July 2008. 

http://www.robocup-cn.org./en/index.php As accessed August 2008. 

34
Potential Scaling Effects for Asynchronous Video in 

Multirobot Search 

Prasanna Velagapudi 

Paul Scerri, Katia Sycara 

Robotics Institute 

Carnegie Mellon University 

Pittsburgh, PA 15213 

001-412-268-8825 

pkv@cs.cmu.edu 

Huadong Wang, Michael Lewis 

School of Information Sciences 

University of Pittsburgh 

Pittsburgh, PA 15260 

001-412-624-9426 

ml@sis.pitt.edu 

ABSTRACT

Camera guided teleoperation has long been the preferred mode for 

controlling remote robots with other modes such as asynchronous 

control only used when unavoidable. Because controlling multiple 

robots places additional demands on the operator we hypothesized 

that removing the forced pace for reviewing camera video might 

reduce workload and improve performance. In an initial 

experiment we evaluated the usefulness of asynchronous 

operation for a four robot search task. Participants operated four 

robot teams performing a simulated urban search and rescue 

(USAR) task using conventional streaming video plus a map 

interface or an experimental interface without streaming video but 

with the ability to store panoramic images on the map to be 

viewed at leisure. Search performance was somewhat better using 

the conventional interface; however, ancillary measures suggest 

that the asynchronous interface succeeded in reducing temporal 

demands for switching between robots. Because the advantages 

hypothesized for the asynchronous interface are due to reduction 

in time stress and workload, the four robot condition may have 

simply been too easy to observe this advantage. This view is at 

least partially supported by the reduced switching found in the 

panoramic condition. We have recently collected data for the 

streaming video condition for 4, 8, and 12 robots. In this data we 

found a marked deterioration in performance for the 12 robot 

condition, suggesting that at this level of difficulty asynchronous 

video might have an advantage. In this paper we present data for 

the four robot case comparison and discuss the implications of the 

recent data from larger teams. 

Categories and Subject Descriptors

I.2.9 [Artificial Intelligence]: Robotics—operator interfaces

General Terms

Human Factors, Measurement, Experimentation 

Keywords

Human-robot interaction, metrics, evaluation, multi-robot system 

1. INTRODUCTION 

Practical applications of robotics can be classified by two distinct 

modes of operation. Terrestrial robotics in tasks such as 

surveillance, bomb disposal, or pipe inspection has used 

synchronous realtime control relying on intensive operator 

interaction usually through some form of teleoperation. 

Interplanetary and other long distance robotics subject to lags and 

intermittency in communications have used asynchronous control 

relying on labor intensive planning of waypoints and activities 

that are subsequently executed by the robot. In both cases 

planning and decision making are performed primarily by humans 

with robots exercising reactive control through obstacle avoidance 

and safeguards. The near universal choice of synchronous control 

for situations with reliable, low latency communication suggests a 

commonly held belief that experientially direct control is more 

efficient and less error prone. When this implicit position is 

rarely discussed it is usually justified in terms of “naturalness” or 

“presence” afforded by control relying on teleoperation. Fong 

and Thorpe [10] observe that direct control while watching a 

video feed from vehicle mounted cameras remains the most 

common form of interaction. The ability to leverage experience 

with controls for traditionally piloted vehicles appears to heavily 

influence the appeal for this interaction style. 

Control based on platform mounted cameras, however, is no 

panacea. Wickins & Hollands [31] identify 5 viewpoints used in 

control, three of them, immersed, tethered, and “plan view” can 

be associated with the moving platform while 3rd person 

(tethered) and plan views require fixed cameras. In the immersed 

or egocentric view (A) the operator views the scene from a 

camera mounted on the platform. The field of view provided by 

the video feed is often much narrower than human vision, leading 

to the experience of viewing the world through a soda straw from 

a foot or so above the ground. This perceptual impairment leaves 

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35
the operator prone to numerous, well-known operational errors, 

including disorientation, degradation of situation awareness, 

failure to recognize hazards, and simply overlooking relevant 

information [8, 15]. A sloped surface, for example, gives the 

illusion of being flat when viewed from a camera mounted on a 

platform traversing that surface [11]. For fixed cameras the 

operator’s ability to survey a scene is limited by the mobility of 

the robot and his ability to retain viewed regions of the scene in 

memory as the robot is maneuvered to obtain views of adjacent 

regions. A pan-tilt-zoom (ptz) camera resolves some of these 

problems but introduces new ones involving discrepancies 

between the robots heading and the camera view that frequently 

lead to operational mishaps [6]. A tethered “camera” (B,C) 

provides an oblique view of the scene showing both the platform 

and its 3D environment. A 3rd person fixed view (C) is akin to an 

operator’s view controlling slot cars and has been shown effective 

in avoiding roll-overs and other teleoperation accidents [4] but 

can’t be used anywhere an operator’s view might be obstructed 

such as within buildings or in rugged terrain. The tethered view 

(B) in which a camera “follows” an avatar (think Mario 

Brothers©) is widely favored in virtual environments [16,26] for 

its ability to show the object being controlled in relation to its 

environment by showing both the platform and an approximation 

of the scene that might be viewed from a camera mounted on it. 

This can be simulated for robotic platforms by mounting a camera 

on a flexible pole giving the operator a partial view of his 

platform in the environment [32]. Because of restriction in field 

of view and the necessity of pointing the camera downward, 

however, this strategy is of little use for surveying a scene 

although it can provide a view of the robot’s periphery and nearby 

obstacles that could not be seen otherwise. The exocentric views 

show a 2 dimensional version of the scene such as might be 

provided by an overhead camera and cannot be obtained from an 

onboard camera. This type of “overhead” view can, however, be 

approximated by a map. For robots equipped with laser range 

finders, generating a map and localizing the robot on that map 

provides a method for approximating an exocentric view of the 

platform. If this view rotates with the robot (heading up) it is a 

type D plan view. If it remains fixed (North up) it is of type E. 

An early comparison at Sandia Laboratory between viewpoints 

for robot control [15] investigating accidents focused on the most 

common of these: (A) egocentric from onboard camera and (C) 

3rd person. The finding was that all accidents involving rollover 

occurred under egocentric control while 3rd person control led to 

bumping and other events resulting from obstructed or distanced 

views. In current experimental work in remotely controlled 

robots for urban search and rescue (USAR) robots are typically 

equipped with both a ptz video camera for viewing the 

environment and a laser range finder for building a map and 

localizing the robot on that map. The video feed and map are 

usually presented in separate windows on the user interface and 

intended to be used in conjunction. While Casper and Murphy [5] 

reporting on experiences in searching for victims at the World 

Trade Center observed that it was very difficult for an operator to 

handle both navigation and exploration of the environment from 

video information alone, Yanco et al. [32] found that first 

responders using a robot to find victims in a mock environment 

made little use of the generated map. One possible explanation is 

that video is simply more attention grabbing than other 

presentations leading operators to control primarily from the 

camera while ignoring other information available on their 

interface. A number of recent studies conducted by Goodrich, 

Neilsen, and colleagues [2,6,19,23,32] have attempted to remedy 

this through an ecological interface that fuses information by 

embedding the video display within the map. The resulting 

interface takes the 2D map and extrudes the identified surfaces to 

derive a 3D version resembling a world filled with cubicles. The 

robot is located on this map with the video window placed in 

front of it at the location being viewed. This strategy uses the 

egocentric camera view and the overhead view from the map to 

create a synthetic tethered view of the sort found most effective in 

virtual environments and games [16,26]. The anticipated 

advantages, however, have been difficult to demonstrate with 

ecological and conventional interfaces trading advantages across 

measures. Of particular interest have been comparisons between 

control based exclusively on maps or videos. In complex 

environments with little opportunity for preview maps were 

superior in assisting operators to escape from a maze [19] 

When considering such potential advantages and disadvantages of 

viewpoints it is important to realize that there are two, not one, 

important subtasks that are likely to engage operators [26]. The 

escape task and the accidents reviewed at Sandia involved 

Navigation, the act of explicitly moving the robot to different 

locations in the environment. In many applications search, the 

process of acquiring a specific viewpoint—or set of viewpoints—

containing a particular object may be of greater concern. While 

both navigation and search require the robot to move, an 

important distinction is the focus of the movement. Navigation 

occurs with respect to the environment at large, while search 

references a specific object or point within that environment. 

Switching between these two subtasks may play a major role in 

undermining situation awareness in teleoperated environments. 

For example, since search activities move the robot with respect 

to an object, viewers may lose track of their global position within 

the environment. Additional maneuvering may be necessary to 

reorient the operator before navigation can be effectively 

resumed. Because search relies on moving a viewpoint through 

the environment to find and better view target objects, it is an 

inherently egocentric task. This is not necessarily the case for 

navigation which does not need to identify objects but only to 

avoid them. 

Search, particularly multi-robot search, presents the additional 

problem of assuring that areas the robot has traversed have been 

thoroughly searched for targets. This requirement directly 

conflicts with the navigation task which requires the camera to be 

pointed in the direction of travel in order to detect and avoid 

objects and steer toward its goal. When the operator attempts to 

compromise by choosing a path to traverse and then panning the 

camera to search as the robot moves he runs both the risk of 

hitting objects while he is looking away and missing targets as he 

attends to navigation. For multirobot control these difficulties are 

accentuated by the need to switch attention among robots 

multiplying the likelihood that a view containing a target will be 

missed. In earlier studies [29,30] we have demonstrated that 

success in search is directly related to the frequency with which 

the operator shifts attention between robots over a variety of 

conditions. An additional issue is the operator’s confidence that 

an area has been effectively searched. In our natural environment 

we move and glance about to construct a representation of our 

environment that is informed by planning and proprioception that 

36
knit together the sequence of views. In controlling a robot we are 

deprived of these natural bridging cues and have difficulty 

recognizing as we pan and tilt whether we are resampling old 

views or missing new ones. The extent of this effect was 

demonstrated by Pausch [21] who found that participants 

searching for an object in a virtual room using a headmounted 

display were twice as fast as when they used a simulated handheld 

camera. Since even the handheld camera provides many 

ecological cues we should expect viewing from a moving 

platform through a ptz camera to be substantially worse. 

1.1 Asynchronous Imagery 

To combat these problems of attentive sampling among cameras, 

incomplete coverage of searched areas, and difficulties in 

associating camera views with map locations we are investigating 

the potential of asynchronous control techniques previously used 

out of necessity in NASA applications as a solution to multi-robot 

search problems. Due to limited bandwidth and communication 

lags in interplanetary robotics camera views are closely planned 

and executed. Rather than transmitting live video and moving the 

camera about the scene, photographs are taken from a single spot 

with plans to capture as much of the surrounding scene as 

possible. These photographs taken with either an omnidirectional 

overhead camera (camera faces upward to a convex mirror 

reflecting 360ƕ) and dewarped [20,21] or stitched together from 

multiple pictures from a ptz camera [22] provide a panorama 

guaranteeing complete coverage of the scene from a particular 

point. If these points are well chosen, a collection of panoramas 

can cover an area to be searched with greater certainty than 

imagery captured with a ptz camera during navigation. For the 

operator searching within a saved panorama the experience is 

similar to controlling a ptz camera in the actual scene, a property 

that has been used to improve teleoperation in a low bandwidth 

high latency application [23]. 

1.2 Controlling Multiple Robots 

Because some functions of a MrS such as identifying victims 

among rubble depend on human input, evaluating the operator’s 

span of control as the number of controlled entities scale is critical 

for designing feasible human-automation control systems. 

Controlling multiple robots substantially increases the complexity 

of the operator’s task because attention must constantly be shifted 

among robots in order to maintain situation awareness (SA) and 

exert control. In the simplest case an operator controls multiple 

independent robots interacting with each as needed. A search task 

in which each robot searches its own region would be of this 

category although minimal coordination might be required to 

avoid overlaps and prevent gaps in coverage. Control 

performance at such tasks can be characterized by the average 

demand of each robot on human attention [4]. Under these 

conditions increasing robot autonomy should allow robots to be 

neglected for longer periods of time making it possible for a 

single operator to control more robots. 

 Established methods of estimating MrS control difficulty, the 

neglect tolerance model, NT, [4] and the Fan-out measure [5] are 

predicated on the independence of robots and tasks. In the NT 

model the period following the end of human intervention but 

preceding a decline in performance below a threshold is 

considered time during which the operator is free to perform other 

tasks. If the operator services other robots over this period the 

measure provides an estimate of the number of robots that might 

be controlled. Fan-out refers to maximum number of robots that 

can advantageously controlled under particular conditions. Fanout can be determined empirically as in [5] by adding robots and 

measuring performance until a plateau without further 

improvement is reached or indirectly by predicting the maximum 

number of robots using parameters from the NT model [4]. 

Multi-robot control appears to impact the human operator’s 

workload in three distinct ways: (1) building and maintaining 

awareness, (2) making decisions, and (3) controlling the system. 

Increasing the autonomy level in robotic system, whether 

providing decision support or individual robot autonomy, allows 

us to shift the decision-making and robot control workload from 

the human to the robotic system. On the other hand, increased 

robot autonomy may cause an increase in perception and 

decision-making workloads. Thus, there is a trade-off between the 

autonomy level of the robotic system and the level of human 

intervention. 

Current estimates of human span of control limitations are severe. 

Miller [17], for example, showed that under expected target 

densities, a controller who is required to authorize weapon release 

for a target identified by a UCAV, could control no more than 13 

UAVs even in the absence of other tasks. A similar breakpoint of 

12 was found by [7] for retargeting Tomahawk missiles. Smaller 

numbers (3-9) [6] have typically been found for ground robots 

depending upon task and level of automation. By most estimates, 

however, a team of four robots should be well within an 

operator’s span of control. Two experiments are reported in this 

paper. The first experiment compares a user interface supplying 

streaming video with one in which operators must rely on static 

panoramas for performing a USAR task with a four robot team. 

The second experiment investigates performance at the same task 

for the streaming video interface as the number of robots is 

increased from 4 to 8 to 12 to identify the operators’ limits of 

control. 

2. METHOD 

2.1 USARSim and MrCS 

The reported experiments were performed using the USARSim 

robotic simulation with simulated UGVs performing Urban 

Search and Rescue (USAR) tasks. USARSim is a high-fidelity 

simulation of urban search and rescue (USAR) robots and 

environments we developed as a research tool for the study of 

HRI and multi-robot coordination. USARSim supports HRI in 

ways lower fidelity simulations cannot by accurately rendering 

user interface elements (particularly camera video), accurately 

representing robot automation and behavior, and accurately 

representing the remote environment that links the operator’s 

awareness with the robot’s behaviors. USARSim can be 

downloaded from www.sourceforge.net/projects/usarsim and 

serves as the basis for the Virtual Robots Competition of the 

RoboCup Rescue League. The current version of USARSim 

includes detailed replicas of NIST USAR Arenas, as well as 

large-scale indoor and outdoor hypothetical disaster scenarios, 

and a large outdoor area along the Chesapeake Bay. USARSim 

complements these maps with high fidelity models of commercial 

(pioneer P2-DX, P2-AT, iRobot’s ATRV Jr., Foster-Miller’s 

Talon, and Telerob’s Telemax) and experimental (PER from 

CMU, Zerg from University of Freiburg, Kurt 3D from University 

37
of Osnabruk) robots, including a snake (Soyu from Tohoku 

University), air (Air-robot helicopter) and a large Ackermansteered UGV (Hummer) and sensor models for many common 

robotic sensing packages. USARSim uses Epic Games’ 

UnrealEngine2 [14] to provide a high fidelity simulator at low 

cost. Validation studies showing agreement for a variety of 

feature extraction techniques between USARSim images and 

camera video are reported in Carpin et al. [3]. Other sensors 

including sonar and audio are also accurately modeled. 

Validation data showing close agreement in detection of walls and 

associated Hough transforms for a simulated Hokuyo laser range 

finder are described in [13]. The current UnrealEngine2 integrates 

MathEngine’s Karma physics engine [14] to support high fidelity 

rigid body simulation. Validation studies showing close 

agreement in behavior between USARSim models and real robots 

being modeled are reported in [13,22,27,33]. 

MrCS (Multi-robot Control System), a multirobot 

communications and control infrastructure with accompanying 

user interface developed for experiments in multirobot control and 

RoboCup competition [1] was used. MrCS provides facilities for 

starting and controlling robots in the simulation, displaying 

camera and laser output, and supporting inter-robot 

communication through Machinetta a distributed mutiagent 

system. Figure 1 shows the elements of the MrCS involved in 

this experiment. In the standard MrCS the operator selects the 

robot to be controlled from the colored thumbnails at the top of 

the screen that show a slowly updating view from the robot’s 

camera. Streaming video from the in focus robot which the 

operator now controls is displayed on the Image Viewer. To view 

more of the scene the operator uses pan/tilt sliders (not shown) to 

control the camera. Robots are tasked by assigning waypoints on 

a heading-up map on the Mission Panel (not shown) or through a 

Figure 1. MrCS components for Streaming Video Mode 

teleoperation widget (not shown). The current locations and paths 

of the robots are shown on the Map Data Viewer. 

2.1.1 Panorama Mode 

Our USAR application which requires finding victims and 

locating them on a map needs to use both map and camera views 

[32]. In Panorama mode the operator directs navigation from the 

map being generated with panoramas being taken at the last 

Figure 2. MrCS components for Asynchronous Panorama 

Mode 

waypoint of a series. The panoramas are stored and accessed 

through icons showing their locations on the map. The operator 

can find victims by asynchronously panning through these stored 

panoramas as time becomes available. When a victim is spotted 

the operator uses landmarks from the image and corresponding 

points on the map to record the victim’s location. By changing 

the task from a forced paced one with camera views that must be 

controlled and searched on multiple robots continuously to a self 

paced task in which only navigation needs to be controlled in 

realtime we hoped to provide a control interface that would allow 

more thorough search with lowered mental workload. The 

reductions in bandwidth and communications requirements [1] are 

yet another advantage offered by this approach. 

Although the experimental panoramic interface (Fig. 2) looks 

much the same it behaves quite differently. Robots are again 

selected for control from the colored thumbnails which now lack 

images. Panoramic images are acquired at the terminal point of 

waypoint sequences. Icons conveying the robot’s location and 

orientation at these points are placed on the map for accessing the 

panoramas. The operator can then view stored panoramas by 

selecting an icon and dragging a mouse over the Image Viewer to 

move the image around or using the mouse’s scroll wheel to zoom 

in and out of the image. The associated icon on the Map Data 

Viewer changes orientation in accordance with the part of the 

scene being viewed. 

2.2 Experiment 1 Asynchronous vs. Streaming Video 

2.2.1 Method 

Two equivalent search environments previously used in the 2006 

RoboCup Rescue Virtual Robots competition [1] were selected 

for use in the experiment. Each environment was a maze like hall 

with many rooms and obstacles, such as chairs, desks, cabinets, 

and bricks. Victims were evenly distributed within the 

environments. A third simpler environment was used for training. 

The experiment followed a repeated measures design with 

participants searching for victims using both panorama and 

streaming video modes. Presentation orders for mode were 

counterbalanced. Test environments were presented in a fixed 

order confounding differences between the environments with 

learning effects. Because the environments were closely matched 

we will discuss these differences as transfer of training effects. 

38
2.2.1.1 Participants and Procedure 

21 paid participants, 9 male and 12 female old recruited from the 

University of Pittsburgh community. None had prior experience 

with robot control although most (15) were frequent computer 

users. Six of the participants (28%) reported playing computer 

games for more than one hour per week. 

2.2.1.2 Procedure 

After collecting demographic data the participant read standard 

instructions on how to control robots via MrCS. In the following 

15~20 minute training session, the participant practiced control 

operations for panorama and streaming video modes (both were 

enabled) and tried to find at least one victim in the training 

environment under the guidance of the experimenter. Participants 

then began two testing sessions in which they performed the 

search task using the panorama and streaming video modes. 

2.2.2 Results 

Only one participant failed to find any victims under the most 

lenient criterion of marking the victim within 2 m of the actual 

location. This occurred in the panorama mode on the initial trial. 

Overall participants were successful in searching the environment 

in either mode finding as many as 9 on a trial. The average across 

conditions using the 2 m radius was 4.5 falling to 4.1 for a 1.5 m 

radius, 3.4 at 1 m and 2.7 when they were required to mark 

victims within .75 m. Repeated measures ANOVAs found 

differences in accuracy of location favoring the streaming video 

mode at the 1.5 m radius F(1,19) = 8.038, p=.01), and 2.0 radius 

F(1,19)=9.54, p=.006. Figure 3 shows these differences. 

Victims Found

0

1

2

3

4

5

6

rad .75 rad 1 rad 1.5 rad 2

marking accuracy

panorama

streaming

Figure 3. Effects of display modes 

No significant order effect (learning) was observed. As in earlier 

studies we found a positive relation, F(1,19)=3.86, p=.064, 

between the number of times the operator switched between 

robots and the victims that were found (Figure 4). In accord with 

our hypothesis that this is due to the forced pace of performing 

the task using streaming video no relation was found between the 

frequency of switching and victims for the panorama mode. 

Switching in Streaming mode

0

2

4

6

8

10

12

0 20 40 60 80 100 120

N switches

N victims

Series1

Linear (Series1)

Figure 4. Finding victims was related to switches only in Streaming 

mode 

2.3 Experiment 2 Scaling in N Robots 

2.3.1 Method 

A large USAR environment previously used in the 2006 RoboCup 

Rescue Virtual Robots competition [1] was selected for use in the 

experiment. The environment was a maze like hall with many 

rooms and obstacles, such as chairs, desks, cabinets, and bricks. 

Victims were evenly distributed within the environment. A 

second simpler environment was used for training. The 

experiment followed a repeated measures design with participants 

searching for victims using 4, 8, and finally 12 robots. Robot 

starting points were varied over the three trials. Because our 

primary concern was with changes in performance as N robots 

increased, trials were presented in a fixed order. This design 

confounding learning effects and starting points with N of robots 

was adopted because the randomly selected starting points were 

sufficiently comparable not to bias results and any learning effect 

would attenuate rather than accentuate the expected decrements. 

2.3.1.1 Participants 

15 paid participants, 8 male and 7 female were recruited from the 

University of Pittsburgh community. None had prior experience 

with robot control although most were frequent computer users. 

2.3.1.2 Procedure 

After collecting demographic data the participant read standard 

instructions on how to control robots via MrCS. In the following 

20 minute training session, the participant practiced control 

operations and tried to find at least one victim in the training 

environment under the guidance of the experimenter. Participants 

then began three testing sessions (15 minute each) in which they 

performed the search task using 4, 8, and finally 12 robots. After 

each task, the participants were asked to file the NASA-TXL 

workload survey immediately. 

2.3.2 Results 

Overall participants were successful in searching the 

environment in all conditions finding as many as 12 victims on a 

trial. The average number of victims found was 4.80 using 4 

robots, 7.06 for 8 robots, but only 4.73 when using 12 robots. A 

paired t-test shows that in the 8 robots condition (R8) participants 

explored larger regions, t (15) = -10.44, p = 0.000, while finding 

39
more victims, t (15) = -3.201, p = 0.003, than using a 4 robot team 

(R4). On the other hand, adding four addition robots degraded 

performance with participants in the 8 robot condition (R8) 

exploring larger regions, t (15) = -1.19, p = 0.059, as well as 

finding more victims, t (15) = -3.014, p = 0.005, than they did 

using a 12 robot team (R12). 

Explored Regions

 Median 

 25%-75% 

 Non-Outlier Range R4 R8 R12 0

50

100

150

200

250

300

350

400

450

Figure 5. Explored Regions 

Victims Founded

 Median 

 25%-75% 

 Non-Outlier Range R4 R8 R12 0

2

4

6

8

10

12

14

Figure 6. Victims Found 

Figure 7 shows that as the number of robots is increased, fewer 

victims were found per robot. This measure should remain 

constant if robots were controlled to the same level of 

effectiveness. However, these differences were not significant. 

With increasing numbers of robots operators tended to neglect 

some robots either entirely or after an initial movement as shown 

in Table 2. A paired t-test indicates that participants neglected 

more robots in the 12 robot condition, t (15) = -1.922, p = 0.064, 

than under 4 robots team (R4). 

More robots were neglected after an initial move in the 8 robot 

(R8) condition t (15) = -2.092, p = 0.046, than for 4 robots (R4); 

and still more comparing a 12 robot team (R12) to the 8 robot 

(R8) condition t (15) = -3.761, p = 0.001. 

With increasing numbers of robots operators tended to neglect 

some robots either entirely or after an initial movement as shown 

in Table 2. A paired t-test indicates that participants neglected 

more robots in the 12 robot condition, t (15) = -1.922, p = 0.064, 

than under 4 robots team (R4). 

Victims per Robotic

 Median 

 25%-75% 

 Non-Outlier Range V/R_4 V/R_8 V/R_12

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

Figure 7. Victims Found per Robot 

more robots in the 12 robot condition, t (15) = -1.922, p = 0.064, 

than under 4 robots team (R4). 

More robots were neglected after an initial move in the 8 robot 

(R8) condition t (15) = -2.092, p = 0.046, than for 4 robots (R4); 

and still more comparing a 12 robot team (R12) to the 8 robot 

(R8) condition t (15) = -3.761, p = 0.001. 

Table 1. Neglected Robots 

Number of Robots R4 R8 R12 

Totally 0.00 0.13 0.80 

After the Initial Move 0.00 0.33 1.87 

As in earlier studies we found a positive relation between the 

number of times the operator switched between robots and the 

victims that were found. Higher switching rates are an indicator of 

shortened ITs or more efficient use of NT to service additional 

robots and hence should improve team performance. Figure 6 

shows the number of switches observed under each of the three 

conditions. There were significant differences in number of 

switches between robots for the 4 robot and 8 robot conditions (t= 

-2.914, P<0.007) and the 4 robot and 12 robot conditions (t= -

2.620, P<0.014). Similar results were found for numbers of 

missions (waypoint assignments) between the 4 robot and 8 robot 

condition (t= -3.079, P<0.005) and the 4 robot and 12 robot 

condition (t= -2.118, P<0.043). 

The result of the workload assessment indicates that workload 

increased with increasing numbers of robots to be controlled. 

This difference in workload was significant between the 4 robot 

and 12 robot conditions (P<0.0146). 

Our results show that we have successfully bounded the number 

of directly controllable robots for a realistic USAR task at 

between 8-12. This can be seen for both the number of victims 

found and the regions explored which improve between the four 

robot and eight robot conditions but decline again between 8 and 

12 robots. Determining Fan-out empirically as in [20] the Fan-out 

plateau (point at which performance is no longer improved by 

40
Switch Times

 Median 

 25%-75% 

 Non-Outlier Range S4 S8 S12

10

20

30

40

50

60

70

80

90

Figure 8. Number of Switches 

Workload

 Median 

 25%-75% 

 Non-Outlier Range 

 Outliers R4 R8 R12 20

30

40

50

60

70

80

90

100

110

Figure 9. NASA-TLX Measurement of Mental workload 

adding additional robots) lies somewhere within this region. The 

point at which operator capabilities become saturated can be 

estimated more closely by observing the number of robots that are 

either completely neglected or neglected after the first move. 

This number is approximately 2.7 for the 12 robot condition 

suggesting that the actual limit for this experiment is 

approximately 9 robots. An examination of the number of 

switches between robots supports this estimate because the 

number of switches is essentially the same in both the 8 and 12 

robot conditions. This means that operators have reached their 

limit for interactions and are neglecting the robots for slightly 

longer times to accommodate the additional robot they are 

actively controlling. 

With this initial experiment we are establishing a baseline for 

exploring the effects of robot team size on human performance. 

Even these early results suggest that the navigation component of 

the operator’s task and the perceptual tasks involved in search 

may be somewhat differently impacted by increases in team size. 

We hope to be able to use such results to guide system designers 

in allocating functions statically or dynamically between the 

operator and robot (team) autonomy. 

3. DISCUSSION 

Our original motivation for developing a panorama mode for 

MrCS was to address restrictions posed by a communications 

server added to the 2007 RoboCup Rescue competition to 

simulate bandwidth limitations and drop-outs due to attenuation 

from distance and obstacles. Although the panorama mode was 

designed to drastically reduce bandwidth and allow operation 

despite intermittent communications our system was so effective 

we decided to test it under conditions most favorable to a 

conventional interface. Our first experiment showed that under 

conditions allowing uninterrupted, noise free, streaming video a 

conventional interface lead to somewhat better (5 vs. 4 victims) 

search performance. The switching results, however, suggest that 

asynchronous panoramas do overcome the forced pace switching 

needed to avoid missing unattended targets in realtime interfaces. 

We would expect this advantage to grow as the number of robots 

increases with performance approaching or surpassing streaming 

video at some point. 

The second experiment demonstrates that for this USAR task 

control of four robots lies well within the cognitive capabilities of 

an operator. Our data show that the operators had sufficient 

reserve capacity to effectively control twice as many robots. 

These results suggest that if advantages are to be found for 

panorama-based search they are likely to be found in the 8-12 

robot range. 

It is also important to note that while victims were marked more 

accurately in the streaming video mode, the greater accuracy may 

simply reflect advantages for marking locations rather than actual 

improvement in search performance. Because participants in the 

streaming video mode were able to drive their robots in close 

proximity to victims, their ability to mark locations with greater 

accuracy may have simply resulted from being nearer their targets 

than in the panorama condition where the target must be marked 

from the location at which the panorama had been taken. Just as 

[19] have demonstrated that maps may be better than cameras for 

navigation we hope that asynchronous video and related strategies 

may play a role in improving multirobot search capabilities. 

Coupled with the ability to control robots under poor 

communication conditions such as are expected in USAR and 

other field work we believe that interface innovations of this sort 

have an important role to play in making control of robot teams a 

reality. 

4. ACKNOWLEDGMENTS 

This research has been sponsored in part by AFOSR FA9550- 07-

1-0039, AFOSR FA9620-01-1-0542, ONR Grant N00014-03-1-

0580 and L3-Communications (4500257512) 

5. REFERENCES 

[1] S. Balakirsky, S. Carpin, A. Kleiner, M. Lewis, A. Visser, J. 

Wang, and V. Zipara, “Toward hetereogeneous robot teams 

for disaster mitigation: Results and performance metrics 

from RoboCup Rescue,” Journal of Field Robotics, in press. 

[2] D. J. Bruemmer, D. A. Few, M. C. Walton, R. L. Boring, J. 

L. Marble, C. W. Nielsen, and J. Garner. Turn off the 

television: Real-world robotic exploration experiments with 

a virtual 3-D display. Proc. HICSS, Kona, HI, 2005. 

[3] S. Carpin, T. Stoyanov, Y. Nevatia, M. Lewis and J. Wang. 

Quantitative assessments of USARSim accuracy". 

Proceedings of PerMIS 2006 [ir-13] S. Carpin, J. Wang, M. 

Lewis, A. Birk and A. Jacoff. High fidelity tools for rescue 

robotics: Results and perspectives, Robocup 2005 

Symposium, 2005. 

41
[4] S. Carpin, M. Lewis, J. Wang, S. Balakirsky, C. Scrapper. 

(2006b). Bridging the gap between simulation and reality in 

urban search and rescue. Robocup 2006: Robot Soccer World 

Cup X, Springer, Lecture Notes in Artificial Intelligence, 

2006. 

[5] J. Casper and R. R. Murphy. Human-robot interactions 

during the robot-assisted urban search and rescue response at 

the world trade center. IEEE Transactions on Systems, Man, 

and Cybernetics Part B, 33(3):367–385, June, 2003 

[6] J. W. Crandall, M. A. Goodrich, D. R. Olsen, and C. W. 

Nielsen. Validating human-robot interaction schemes in 

multitasking environments. IEEE Transactions on Systems, 

Man, and Cybernetics, Part A, 35(4):438–449, 2005. 

[7] Cummings, M. and Guerlain, S. An interactive decision 

support tool for real-time in-flight replanning of autonomous 

vehicles, AIAA Unmanned Unlimited Systems, 

Technologies, and Operations, 2004. 

[8] R. Darken, K. Kempster, and B. Peterson, “Effects of 

streaming video quality of service on spatial comprehension 

in a reconnaissance task,” in Proc. Meeting I/ITSEC, 

Orlando, FL, 2001. 

[9] M. Fiala, “Pano-presence for teleoperation,” Proc. Intelligent 

Robots and Systems (IROS 2005), 3798-3802, 2005. 

[10] T. Fong and C. Thorpe, “Vehicle teleoperation interfaces,” 

Autonomous. Robots, no. 11, pp. 9–18, 2001. 

[11] M. Lewis and J. Wang, “Gravity referenced attitude display 

for mobile robots : Making sense of what we see, ” 

Transactions on Systems, Man and Cybernetics Part A, 

37(1), 94-105, 2007. 

[12] M. Lewis, J. Wang, and S. Hughes, “USARsim : Simulation 

for the Study of Human-Robot Interaction,” Journal of 

Cognitive Engineering and Decision Making, 1(1), 98-120, 

2007. 

[13] M. Lewis, S. Hughes, J. Wang, M. Koes, and S. Carpin. 

Validating USARsim for use in HRI research, Proceedings 

of the 49th Annual Meeting of the Human Factors and 

Ergonomics Society, Orlando, FL, 2005, 457-461 

[14] Mathengine, MathEngine Karma User Guide, 

http://udn.epicgames.com/Two/KarmaReference/KarmaUser

Guide.pdf, accessed May 3, 2005. 

[15] D. E. McGovern, “Experiences and Results in Teleoperation 

of Land Vehicles,” Sandia Nat. Labs., Albuquerque, NM, 

Tech. Rep. SAND 90-0299, 1990. 

[16] P. Milgram and J. Ballantyne, “Real world teleoperation via 

virtual environment modeling,” in Proc. Int. Conf. Artif. 

Reality Tele-Existence, Tokyo, 1997. 

[17] Miller, C. Modeling human workload limitations on 

multiple UAV control, Proceedings of the Human Factors 

and Ergonomics Society 47th Annual Meeting, 526-527, 

2004. 

[18] J.R. Murphy, “Application of Panospheric Imaging to a 

Teleoperated Lunar Rover,” in Proceedings of the 1995 

International Conference on Systems, Man, and Cybernetics, 

1995. 

[19] C. Nielsen and M. Goodrich. Comparing the usefulness of 

video and map information in navigation tasks. In 

Proceedings of the 2006 Human-Robot Interaction 

Conference, Salt Lake City, Utah, March 2006. 

[20] D.R Olsen and S.B. Wood, Fan-out: measuring human 

control of multiple robots, in Proceedings of the SIGCHI 

conference on Human factors in computing systems. 2004, 

ACM Press: Vienna, Austria. p. 231-238. 

[21] R. Pausch, M. A. Shackelford, and D. Proffitt, “A user study 

comparing head-mounted and stationary displays,” IEEE 

Symposium on Research Frontiers in Virtual Reality, 

October 25-26, 1993, San Jose, CA. 

[22] C. Pepper, S. Balakirsky, and C. Scrapper. Robot Simulation 

Physics Validation, Proceedings of PerMIS’07, 2007. 

[23] B. W. Ricks, C. W. Nielsen, and M. A. Goodrich. Ecological 

displays for robot interaction: A new perspective. In 

International Conference on Intelligent Robots and Systems 

IEEE/RSJ, Sendai, Japan, 2004. 

[24] P. Scerri, Y. Xu, E. Liao, G. Lai, M. Lewis, and K. Sycara, 

“Coordinating large groups of wide area search munitions,” 

In D. Grundel, R. Murphey, and P. Pandalos (Ed.), Recent 

Developments in Cooperative Control and Optimization, 

Singapore: World Scientific, 451-480. 

[25] N. Shiroma, N. Sato, Y. Chiu, and F. Matsuno, “Study on 

effective camera images for mobile robot teleoperation,” In 

Proceedings of the 2004 IEEE International Workshop on 

Robot and Human Interactive Communication, Kurashiki, 

Okayama Japan, 2004 

[26] D. S. Tan, G. G. Robertson, and M. Czerwinski, “Exploring 

3D navigation: Combining speed-coupled flying with 

orbiting,” in CHI 2001 Conf. Human Factors Comput. Syst., 

Seattle, WA, 2001. 

[27] B. Taylor, S. Balakirsky, E. Messina and R. Quinn. Design 

and Validation of a Whegs Robot in USARSim, Proceedings 

of PerMIS’07, 2007. 

[28] R. Volpe, “Navigation results from desert field tests of the 

Rocky 7 Mars rover prototype,” in The International Journal 

of Robotics Research, 18, pp.669-683, 1999. 

[29] J. Wang, and M. Lewis, “Human control of cooperating 

robot teams”, 2007 Human-Robot Interaction Conference, 

ACM, 2007a. 

[30] J. Wang, and M. Lewis, “Assessing coordination overhead in 

control of robot teams,” Proceedings of the 2007 

International Conference on Systems, Man, and Cybernetics, 

2007b 

[31] C. Wickens and J. Hollands, Engineering Psychology and 

Human Performance, Prentice Hall, 1999. 

[32] H. Yanco, M. Baker, R. Casey, B. Keyes, P. Thoren, J. 

Drury, D. Few, C. Nielsen, D. Bruemmer. “Analysis of 

human-robot interaction for urban search and rescue, 

Proceedings of PERMIS, 2006. 

[33] M. Zaratti, M. Fratarcangeli and L. Iocchi. A 3D Simulator 

of Multiple Legged Robots based on USARSim. Robocup 

2006: Robot Soccer World Cup X, Springer, LNAI, 2006. 

42
The Rat’s Life Benchmark:

Competing Cognitive Robots

Olivier Michel

Cyberbotics Ltd.

PSE C - EPFL

CH-1015 Lausanne, Switzerland

Olivier.Michel@cyberbotics.com

Fabien Rohrer

Cyberbotics Ltd.

PSE C - EPFL

CH-1015 Lausanne, Switzerland

Fabien.Rohrer@cyberbotics.com

ABSTRACT

This paper describes Rat’s Life: a complete cognitive robotics

benchmark that was carefully designed to be easily reproducible in a research lab with limited resources. It relies

on two e-puck robots, some LEGO bricks and the Webots

robot simulation software. This benchmark is a survival

game where two robots compete against each other for resources in an unknown maze. Like the rats in cognitive

animal experimentation, the e-puck robots look for feeders

which allow them to live longer than their opponent. Once a

feeder is reached by a robot, the robot draws energy from it

and the feeder becomes unavailable for a while. Hence, the

robot has to further explore the maze, searching for other

feeders while remembering the way back to the first ones.

This allows them to be able to refuel easily again and again

and hopefully live longer than their opponent.

Keywords

benchmark, SLAM, navigation, autonomy, vision

1. WHY WE NEED COGNITIVE ROBOTICS

BENCHMARKS

1.1 Introduction

Most scientific publications in the area of robotics research

face tremendous challenges: comparing the achieved result

with other similar research results and hence convincing the

reader of the quality of the research work. These challenges

are very difficult because roboticists lack common tools allowing them to evaluate the absolute performance of their

systems or compare their results with others. As a result,

such publications often fail at providing verifiable results,

either because the studied system is unique and difficult to

replicate or they don’t provide enough experimental details

so that the reader could replicate the system accurately.

Nevertheless, some of these publications become the de

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facto state of the art and this makes it extremely difficult to

further explore these research areas, and hence to demonstrate advances in robotics research.

This matter of fact is unfortunately impairing the credibility of robotics research. A number of robotics researchers

proposed to develop series of benchmarks to provide a means

of evaluation and comparison of robotics research results [1,

3, 4, 9, 19].

Although a few robotics benchmarks already exist, the

only robotics benchmarks that are widely known and practiced are implemented as robot competitions.

1.2 Existing Robot Competitions and Benchmarks

Several popular robot competitions are organized on a

regular basis, usually once a year. The Robocup soccer

[6] and FIRA [16] is a robot soccer tournament with several categories (small size league, middle size league, standard platform league, simulation league, etc.). The Robocup

Rescue is based on the Urban Search And Rescue (USAR)

benchmark developed by the NIST [7] where robots have to

search and rescue the victims of a disaster in a urban environment. MicroMouse [11], involves wheeled robots solving

a maze. The FIRST [12], Eurobot [13] and Robolympics

[14] are robot competitions more focused on education than

research in various disciplines (often inspired from sports).

The AAAI Robot Competition [15] proposes different scenarios each year during the AAAI conference, but often lacks

a clear performance metrics. The DARPA Grand Challenge

and Urban Challenge [17] and the European Land-Robot

Trial [18] focus on unmanned ground and sometimes aerial

vehicles racing against each other.

Although some of these competitions clearly focus on education and are more intended to students and children

rather than researchers (FIRST, Eurobot), others competitions (Robocup, FIRA, AAAI) are more intended to researchers. Such competitions are useful as they can provide

elements of comparison between different research results.

However one of the major problem is that the rules often

change across the different editions of the same competition.

Hence it is difficult to compare the progress achieved over

time. Also these competitions are very specific to particular

problems, like Robocup is focused mostly on robot soccer

and has arguably a limited interest for cognitive robotics

[5]. Moreover, in most cases, and especially in the Robocup

case, installing a contest setup is expensive and takes a lot

of resources (many robots, robot environment setup, room,

43
maintenance, controlled lighting conditions, etc.).

1.3 Going Further with Cognitive Robotics Benchmarks

Among all the benchmarks we reviewed which are mostly

robot competitions, none of them provides both stable rules

with advanced cognitive robotics challenges and an easy

setup. This paper proposes a new robotics benchmark called

”Rat’s Life” that addresses a number of cognitive robotics

challenges while being cheap and very easy to setup for any

research lab. The aim of this benchmark is to foster advanced robotics and AI research.

Comparing to soccer playing contests (RoboCup, FIRA),

the Rat’s Life benchmark is more bio-inspired as it focuses

on foraging and survival. Also, it is more likely to contribute to scientific advances in Learning and Self Localization And Mapping (SLAM) as mazes are initially unknown

to the robots. Moreover, it allows the researchers to focus on

a single agent (competiting against another) rather than a

whole team of agents, making the problem somehow simpler

to handle. Finally, it is cheaper.

2. BENCHMARK REQUIREMENTS

In order to be useful a benchmark has to be practiced

by a large number of the best researchers trying to push

further the current state of the art. This can be achieved

by proposing a scientifically and practically appealing series

of benchmarks that will convince researchers to invest their

time with these tools. Hence the Rat’s Life benchmark is

trying to achieve a number of objectives:

2.1 Scientifically appealing

To be scientifically interesting, a benchmark has to address a number of difficult challenges in robotics. The Rat’s

Life benchmark focuses on cognitive robotics and addresses

advanced research topics such as image processing, learning,

navigation in an unknown environment, landmark recognition, SLAM, autonomy management, game strategies, etc.

2.2 Cheap and easy to setup

The benchmark should be easily practicable by any researcher. Hence it has to be cheap and easy to setup. All

the components should be easily available. The Rat’s Life

benchmark costs no more than EUR 2000, for two e-puck

robots and many LEGO components (including a LEGO

NXT unit and four LEGO distance sensors). It requires

only a table to setup a LEGO maze of 114x114 cm.

2.3 Accurate

Accuracy is a very important aspect of a benchmark. The

environment, robots and evaluation rules should be defined

very carefully in an exhaustive manner. This way, the benchmark is accurately replicable and hence different results obtained with different instances of the setup in different research lab can be compared to each others.

2.4 Comparable

Finally, a benchmark is useful if users can compare their

own results to others and thus try to improve the state of

the art. Hence a benchmark should keep a data base of

the solutions contributed by different researchers, including

binary and source code of the robot controller programs.

These different solutions should be ranked using a common

performance metrics, so that we can compare them to each

other.

3. STANDARD COMPONENTS

The Rat’s Life benchmark is based on three standard affordable components: the e-puck mobile robot, LEGO bricks

and the Webots robot simulation software (free version).

3.1 The e-puck mobile robot

Figure 1: The e-puck robot

The e-puck mini mobile robot was originally developed

at the EPFL for teaching purposes by the designers of the

successful Khepera robot. The e-puck hardware and software is fully open source, providing low level access to every

electronic device and offering unlimited extension possibilities. The robot is already equipped with a large number

of sensors and actuators (figure 1). It is well supported by

the Webots simulation software with simulation models, remote control and cross-compilation facilities. The official

e-puck web site [23] gathers a large quantity of information

about the robot, extension modules, software libraries, users

mailing lists, etc. The robot is commercially available from

Cyberbotics [21] for about EUR 570.

3.2 LEGO bricks

The LEGO bricks are used to create an environment for

the e-puck robot. This environment is actually a maze which

contains ”feeder” devices (see next sections) as well as visual

landmarks made up of patterns of colored LEGO brick in

the walls of the maze (see figure 2). These landmarks are

useful hints helping the robot to navigate in the maze. Since

LEGO models are easily demountable, the maze is easily reconfigurable so that the users can create different instances

of the maze according to the specifications of the benchmark.

All the maze, landmarks and the feeder devices are properly

defined in a LEGO CAD file in LXF format using the LEGO

digital designer software freely available from the LEGO factory web site [20]. The corresponding LXF files are freely

available on the Rat’s Life web site [10].

Thanks to the LEGO factory system, users can very easily

order a box containing all the LEGO bricks necessary to

build the environment of the robots.

3.3 The Webots robot simulation software

44
Figure 2: The Rat’s Life maze: LEGO bricks, e-puck

robots and a feeder device (left) and its simulated

counterpart (right)

Webots [8] is a commercial software for fast prototyping

and simulation of mobile robots. It was originally developed

at the Swiss Federal Institute of Technology in Lausanne

(EPFL) from 1996 and has been continuously developed,

documented and supported since 1998 by Cyberbotics Ltd.

Over 500 universities and industrial research centers worldwide are using this software for research and educational

purposes. Webots has already been used to organize robot

programming contests (ALife contest and Roboka contest).

Although Webots is a commercial software, a demo version

is freely available from Cyberbotics’s web site [21]. This

demo version includes the complete Rat’s Life simulation.

So, anyone can download, install and practice the simulation of the Rat’s Life benchmark at no cost.

4. RAT’S LIFE BENCHMARK DESCRIPTION

This paper doesn’t claim to be a technical reference for the

Rat’s Life benchmark. Such a technical reference is available

on the Rat’s Life web site [10].

4.1 Software-only Benchmark

The Rat’s Life benchmark defines precisely all the hardware necessary to run the benchmark (including the robots

and their environment). Hence the users of the benchmarks

don’t have to develop any hardware. Instead, they can focus

on robot control software development only. This is similar to the Robocup standard league where the robot platforms (Aibo robots) and the environment is fully defined and

the competitors are limited to develop control software only.

This has the disadvantage of preventing hardware research

and is constraining the contest to the defined hardware only.

Figure 3: Closeup of the Rat’s Life simulated robots

in Webots (left) and general overview (right)

However, it has the great advantage of letting the users focus on the most challenging part of cognitive robotics, i.e.,

the control software.

4.2 Configuration of the Maze

For each evaluation, the maze is randomly chosen among

a series of 10 different configurations of the maze. In each

configuration, the walls, landmarks and feeder are placed at

different locations to form a different maze. Each configuration also has 10 different possible initial positions and orientations for the two robots. One of them is chosen randomly

as well. This makes 100 possible initial configurations. This

random configuration of the maze prevents the robots from

having a prior knowledge of the maze, and forces them to

discover their environment by exploring it. This yields to

much more interesting robot behaviors. A possible configuration is depicted on figure 3 (right).

4.3 Virtual Ecosystem

The Rat’s Life benchmark is a competition where two epuck robots compete against each other for resources in a

LEGO maze. Resources are actually a simulation of energy

sources implemented as four feeder devices. These feeder

devices are depicted on figure 4. They are made up of LEGO

NXT distance sensors which are controlled by a LEGO NXT

control brick. They display a red light when they are full of

virtual energy. The e-puck robots can see this colored light

through their camera and have to move forward to enter

the detection area of the distance sensor. Once the sensor

detects the robot, it turns its light off to simulate the fact

that the feeder is now empty. Then, the robot is credited

an amount of virtual energy corresponding to the virtual

energy that was stored in the feeder. This virtual energy

will be consumed as the robot is functioning and could be

interpreted as the metabolism of the rat robot. The feeder

will remain empty (i.e., off) for a while. Hence the robot

has to find another feeder with a red light on to get more

45
Figure 4: A full feeder facing an e-puck robot (left)

and an empty one (right)

energy before its energy level reaches 0. When a robot runs

out of virtual energy (i.e., its energy level reaches 0), the

other robot wins.

4.3.1 Biological Comparison

This scenario is comparable to an ecosystem where the

energy is produced by feeders and consumed by robots. The

feeders could be seen as plants, slowy growing from the energy of the sun, water and ground and producing fruits

whereas the robots could be seen as rats, foraging fruits.

Since the fruits produced by a single plant are not sufficient

to feed a rat, the rat has to move around to find more plants.

4.3.2 Electronics Comparison

Although the e-puck robots and feeder devices used in

the Rat’s contest are electronic devices, the energy is actually simulated for convenience reasons. However, it could

be possible to deal with real electrical energy: the feeder

would correspond to photovoltaic solar docking stations accumulating electrical energy over time and the robots could

recharge their actual battery from these stations. However,

such a system would be more complex to setup from a practical and technological point of view. This is why we decided

to use virtual energy instead.

4.4 Robotics and AI Challenges

Solving this benchmark in an efficient way requires the

following cognitive capabilities:

• Recognize a feeder (especially a full one) from a camera

image.

• Navigate to the feeder and dock to it to grab energy.

• Navigate randomly in the maze while avoiding to get

stuck.

• Remember the path to a previously found feeder and

get back to it.

• Optimize energy management.

• Try to prevent the other robot from getting energy.

This translates into a number of control software techniques,

namely image processing, motor control, odometry, landmark based navigation, SLAM, autonomy management, game

theory. Most of these techniques are still open research areas

where new progress will benefit directly to robotics and AI

applications. Both bio-inspired (neural networks, generic algorithms, learning) and traditional approaches (control theory, environment mapping) are concerned as no assumption

is made on the technologies used to implement the controllers. Moreover, because of its similarities with experiments with rodents, the Rat’s Life contest may be a very

interesting benchmark for testing different bio-inspired models, such as place cells, grid cells, spatial learning, conditioning, etc.

The best robots are expected to be able to somehow fully

memorize the maze they explore with the help of the landmarks, to rapidly find their way to the feeders, to maintain

an estimation of the status of every feeder and to develop a

strategy to prevent the opponent from recharging.

4.5 Online Contest

4.5.1 Real World and Simulation

The Rat’s Life contest is defined both as a real environment and a simulation. However, the same control programs, written in C or Java programming language, can

run on both the simulation and the real robots. To run the

control program on the real robots, there are actually two

options. The user can either execute the controller program

on a computer remote controlling the robot or cross-compile

it and execute it on the real robot. In the first case, the

program running on the computer remote controls the real

robot by reading the sensor values from and sending the motor commands to the Bluetooth connection with the robot.

In the second case, the control program is executed directly

on the real robot. All the necessary software tools for remote

control and cross-compilation are integrated within the Webots software, making the transfer from the simulation to

the real robot a very easy process. This way, the same controller program can control both the real and the simulated

robot.

4.5.2 Participation to the Contest

In order to participate in the online contest, the competitors can download the free version of Webots from Cyberbotics’ web site [21]. They can program the simulated epuck robots to perform in the simulated maze. Then, they

have to register a contestant account on the contest’s web

site [10]. Once open, this account allows the competitors to

upload the controller programs they developed with the free

version of Webots. Participation to the contest is totally

free of charge.

46
4.5.3 Ranking System

Every business day (i.e., Monday to Friday) at 12 PM

(GMT) a competition round is started in simulation and

can be watched online from the Rat’s Life web site [10]. A

hall of fame displays a table of all the competitors registered

in the data base and who submitted a robot controller program. If there are N competitors in the hall of fame, then

N − 1 matches are played. The first match of a round opposes the last entry, i.e., number N at the bottom of the hall

of fame, to the last but one entry, i.e., number N − 1. If the

robot number N wins, then the position of these two robots

in the hall of fame are switched. Otherwise no change occurs

in the hall of fame. This procedure is repeated with the new

robot number N − 1 (which may have recently changed due

to the result of the match) and robot number N −2. If robot

number N − 1 wins, then it switches its position with robot

number N − 2, otherwise nothing occurs. This is repeated

with robots number N − 3, N − 4, etc. until robots number

2 and 1, thus totaling a number of N − 1 matches.

This ranking algorithm is similar to the bubble sort. It

makes it possible for a newcomer appearing initially at the

bottom of the ranking, to progress until the top of the ranking in one round. However, any existing entry cannot loose

more than one position in the ranking during one round.

This prevents a rapid elimination of a good competitor (which

could have been caused by a buggy update of the controller

program for example).

4.5.4 And The Winner Is...

The contest is open for a fixed period of time. During this

period of time, new contestants can register and enter the

contest. The contestants can submit new versions of their

controller program any time until the closing date. Once the

closing date is reached, new entry and submissions of new

versions are disabled. Then, seven final rounds are run. The

final ranking for each competitor is computed as the average ranking over these seven final rounds. The competitor

ranked at the top position is declared to be the ”winner of

the simulated Rat’s Life benchmark” and its authors receive

a prize for this: a Webots PRO pack. Moreover the top 3

competitors are selected for a real world series of 3 rounds

(i.e., 6 matches). The winner of these real world rounds

is declared to be the ”winner of the real world Rat’s Life

benchmark” and receives a prize: an e-puck robot.

The real world rounds should however occur during an international conferences or robotics competition to ensure that

a large number of people, including a scientific committee,

attends the event and can check that nobody is cheating the

benchmark.

The contest will run continuously over years so that we can

measure the progress and performances of the robot controllers over a fairly long period of robotics and AI research.

5. EVOLUTION OF THE COMPETITION OVER

TIME

5.1 Movie Database

Observing the evolution of the competition over days was

very interesting and we decided to store all the simulation

movies in a data base to be able to analyse this evolution

afterwards. The movie database contains more than 2500

movies (totalling more than 50 GB of data) and is freely

available online at http://www.cyberbotics.com/ratslife/movies/.

5.2 Participation to the Contest

The competition started on January 7th, 2008 with one,

then two competitors. Table 1 summarizes the evolution of

the participation to the contest over time.

Table 1: Evolution of the participation to the Rat’s

Life contest

Date Number of Competitors

January 31st 6

February 29th 15

March 31st 23

April 30th 26

May 31st 36

June 30th to be completed

5.3 Evolution of Behaviors

The behavior of the robot controllers evolves in a similar

fashion as a genetic algorithm. Competitors are uploading new versions of their robot controller fairly frequently.

Sometimes, a new version brings a significant performance

breakthrough and drives the competitors’ robot on the top

of the hall of fame. This performance breakthough is then

immediately analysed by the other competitors seeing the

simulation movies. They take inspiration from it to improve

their own robot controller and submit their new improved

version to the contest. Rapidly, a large number of competitors can replicate this winning behavior on their robot

and most of the robots in the contest adopt this new efficient behavior. This co-evolution dynamics is similar to

what happens in genetic algoritm where the behavior of efficient individuals spreads rapidly across the population. If we

could plot a fitness function over time, such breakthroughs

would correspond to suddent increase of the fitness value

making steps in the evolutionary process.

5.4 Major breakthroughs

During the contest, several major performance breakthroughs

could be observed simply by analysing the behavior of the

robots in the simulation movies. One could identify five major breakthroughs which happened chronologically one after

the other, bringing each time an improved performance:

5.4.1 Random Walkers

The random walkers came actually from the very first version of the sample source code included with the contest

software development kit, made available to all the competitors. This simple control algorithm similar to Braitenberg

vehicles [2] let the robots move randomly while avoiding the

obstacles. By chance some of them met a feeder from time

time, but this behavior is very inefficient are rely mostly on

luck. Also, this very first version was not very efficient at

navigating and often caused the robot to get stuck in some

unexpected situations, like facing a corner.

5.4.2 Vision-Enabled Random Walkers

47
Figure 5: Rat’s Life Hall Of Fame, on June 6th, 2008

The so called vision-enabled random walkers are an improved version of the original random walker making an extensive use of vision to recognize the feeders and adjust the

trajectory of the robot to reach the feeder instead of simply moving randomly. This results in slightly more efficient

robots who won’t pass in front of a feeder without getting

energy from it. A vision-enabled random walker is included

in the sample code currently distributed to the competitors.

This sample version has however been largely improved by

different competitors over time.

5.4.3 Right Hand Explorers

One of the problems with the random walkers is that a

Braitenberg vehicle behavior is not very efficient at exploring extensively a maze and hence at finding the feeders.

Maze exploration algorithms exist and are much more efficient. The right hand algorithm is one of the simplest

and best known maze exploration algorithms. It consists

in simply following the first wall found on the right hand

side of the robot (this also works with the left hand side of

course). Using this algorithm combined with some vision to

reach efficiently the feeders, a significant performance breakthrough was reached. The first right hand explorer appeared

on February 22nd, with a robot named Tony (which reached

rank #1 of the hall of fame on February 22th very rapidly)

and was rapidly copied by many other competitors as this

behavior is both easy to understand and to re-program.

5.4.4 Energy-aware robots

Getting the energy from the feeder as soon as you find the

feeder is nice, but there is an even better strategy: Once a

robot finds a feeder, it can simply stop and sit in front of

the feeder, thus preventing the other robot from reaching

this feeder. In the meanwhile the robot sitting in front of

the feeder should watch its energy level and decide to move

to the feeder once its energy level reached a very low value,

just enough to make that move to the feeder and refuel.

During this waiting time, the other robot may be struggling

to find a feeder and possibly loose the game if it runs out

of energy. This kind of energy-aware robots appeared on

February 28th, with a robot named Ratchou (which reached

rank #1 thanks to this breakthrough). Similarly to the right

hand explorer, it was rapidly copied by other competitors as

it was easy to understand and to re-program as well.

5.4.5 SLAMers

SLAM stands for Self Localization And Mapping. Comparing to other techniques mentioned above, it involves a

much more complicated algorithm and requires an efficient

image processing. SLAMer robots actually seems to use the

right hand algorithm on a first stage to explore extensively

the maze, but they build dynamically a map of this maze

while exploring it and eventually don’t use the right hand

algorithm at all. Their internal representation of the environment contains the walls, the feeders and likely the landmarks. This map is then used by the robot to get back to

previously found feeders. It turned out to be very efficient

and clearly outperformed the simpler reactive controllers.

The first SLAMer robot is Ratatouille who implemented a

first version of visual SLAM-based navigation on April 6th

and reach rank #1. This first version was however probably not well tuned (or somehow buggy) and it happened to

loose in rare occasions against lucky and efficient right-hand

explorers. However, the author of Ratatouille continued to

improve the performance of his SLAMer robot and finally

sat steadily on the very top of the hall of fame for more than

two months. The other competitors, including Tony among

others, tried hard to implement such an efficient SLAMbased navigation controller, they were not very successful

until June 5th. At this point a competitor with a robot controller named gollum developed a pretty efficient SLAMer

robot able to challenge Ratatouille. Golum reached rank

#2 on June 5th and had a really disputed and very interesting match against Ratatouille, but was not successful.

(to be continued)

5.4.6 Super-SLAMers

The author of Ratatouille actually never stopped from

April 6th to improve his SLAM-based robot controller. A

major improvement was probably the estimation of the status of the feeders, combined with an estimation of the time

needed to travel the maze to reach the feeder. From the most

recent simulation movies, Ratatouille seems to be able to anticipate that a mapped feeder will become available again:

when the feeder is still red, Ratatouille starts to navigate towards this feeder and about one second before it reaches the

feeder, the feeder becomes green again. This makes Ratatouille the most efficient robot controller currently on the

Rat’s Life benchmark (see figure 5). At this point, it is difficult to imagine a better behavior than the one exhibited by

Ratatouille.

48
6. TRANSFER TO THE REAL WORLD

At the time of writting, the competition occured only in

simulation. We plan to run a series of rounds in the real

world, using the same robot controller as the ones used in

simulation for the top three robots. We are currently working to fix wireless communication speed issues to allow a

reliable and real time remote control of real robots allowing

to test the best Rat’s Life controllers in the real world. We

believe that some calibrations of the sensors, motors and image processing algorithms might be necessary to be able to

transfer the best control algorithms from the simulation to

the real world. This issue will be discussed in an upcoming

publication.

7. CONCLUSION

Thanks to the Rat’s Life benchmark, it becomes possible to evaluate the performance of various approaches to

robot control for navigation in an unknown environment,

including various SLAM and bio-inspired models. The performance evaluation allow us to make a ranking between the

different control programs submitted, but also to compare

the progresses achieved over a short period of time of research on this problem. However, this period of time could

be extented and we could, for example, compare the top 5

controller programs developed in 2008 to the top 5 controller

programs developed in 2012 to evaluate how much the state

of the art progressed.

The control program resulting from the best robot controllers could be adapted to real world robotics applications in the areas of surveillance, mobile manipulators, UAV,

cleaning, toys, etc. Also, interesting scientific comparisons

with biological intelligence could be drawn by opposing the

best robot controllers to a real rat (or a rat-controlled robot)

in a similar problem. Similarly, we could also oppose the

best robot controllers to a human (possibly a child) remote

controlling the robot with a joystick and with limited sensory information coming only from the robot sensors (mainly

the camera).

We hope that this initiative is a step towards a more general

usage of benchmarks in robotics research. By its modest

requirements, simplicity, but nevertheless interesting challenges it proposes, the Rat’s Life benchmark has the potential to become a successful reference benchmark in cognitive

robotics and hence open the doors to more complex and

advanced series of cognitive robotics benchmarks.

Acknowledgements

The authors of this paper would like to express their acknowledgments to the IST Cognitive Systems Unit of the

European Commission which funds the ICEA European project

[22] within which the Rat’s Life benchmark and contest were

developed. ICEA stands for Integrating Cognition, Emotion and Autonomy and is focused on brain-inspired cognitive architectures, robotics and embodied cognition, bringing together cognitive scientists, neuroscientists, psychologists, computational modelers, roboticists and control engineers. It aims at developing a cognitive systems architecture integrating cognitive, emotional and bioregulatory

(self-maintenance) processes, based on the architecture and

physiology of the mammalian brain.

8. REFERENCES

[1] Baltes, J.: ”A benchmark suite for mobile robots”,

IROS 2000 conference proceeding (2000), 1101-1106

vol.2, ISBN: 0-7803-6348-5

[2] Braitenberg, V.: ”Vehicles: Experiments in Synthetic

Psychology” Cambridge, MA: MIT Press (1984)

[3] Serri, A.: ”A Lego robot for experimental benchmarking

of robust exploration algorithms”, Circuits and Systems

(2004), iii - 163-6 vol.3, ISBN: 0-7803-8346-X

[4] Eaton, M., Collins, J. J., and Sheehan, L.: ”Toward a

benchmarking framework for research into bio-inspired

hardware-software artefacts”, Artificial Life and

Robotics, Springer Japan, 40-45 Vol.5 number 1 /

March 2001, ISSN: 1433-5298

[5] Collins, J.J., Eaton, M., Mansfield, M., Haskett, D.,

OˆaA ̆ZSullivan, S.: ”Developing a benchmarking  ́

framework for map building paradigms”, Proceedings of

the 9th International Symposium on Artificial Life and

Robotics, January 2004, Oita, Japan, pp. 614-617

[6] Kitano, H., Asada, M., Kuniyoshi, Y., et al: ”RoboCup:

the robot world cup initiative”, IJCAI-95 workshop on

entertainment and AI/ALife (1995)

[7] Jacoff, A., Weiss, B., Messina, E.: ”Evolution of a

Performance Metric for Urban Search and Rescue

Robots”, Proceedings of the 2003 Performance Metrics

for Intelligent Systems (PerMIS) Workshop,

Gaithersburg, MD, September 16-18, 2003

[8] Michel, O. ”Webots: Professional Mobile Robot

Simulation”, Journal of Advanced Robotics Systems,

39-42 Vol.1 number 1 / 2004

http://www.ars-journal.com/International-Journal-ofAdvanced-Robotic-Systems/Volume-1/39-42.pdf

[9] Dillmann, R.: ”Benchmarks for Robotics Research”,

EURON, April 2004.

http://www.cas.kth.se/euron/eurondeliverables/ka1-10-

benchmarking.pdf

[10] Rat’s Life contest. http://www.ratslife.org

[11] Micromouse contest. http://www.micromouseinfo.com

[12] FIRST Robotics competition. http://www.usfirst.org

[13] Eurobot Robotics competition.

http://www.eurobot.org

[14] ROBOlympics. http://www.robolympics.net

[15] AAAI Robot Competition and exhibition.

http://palantir.cs.colby.edu/aaai07

[16] The Federation of International Robot-soccer

Association (FIRA). http://www.fira.net

[17] DARPA Grand Challenge.

http://www.darpa.mil/grandchallenge

[18] European Land-Robot Trial ELROB.

http://www.elrob.org/

[19] EURON Benchmarking Activities.

http://www.euron.org/activities/benchmarks/index.html

[20] LEGO factory. http://factory.lego.com

[21] Cyberbotics Ltd. http://www.cyberbotics.com

[22] ICEA European Project (IST 027819)

http://www.iceaproject.eu

[23] e-puck web site. http://www.e-puck.org

49
The iCub humanoid robot: 

an open platform for research in embodied cognition 

(Special Session on EU-projects) 

Giorgio Metta 

Giulio Sandini 

Italian Institute of Technology and 

University of Genoa 

Via Morego, 30 

16163 Genoa, Italy 

+39 010 71781411 

{giorgio.metta,

giulio.sandini}@iit.it

David Vernon 

Khalifa University 

P.O. Box 573 

Sharjah

david@vernon.eu

Lorenzo Natale 

Francesco Nori 

Italian Institute of Technology 

Via Morego, 30 

16163, Genoa, Italy 

+39 010 71781420 

{lorenzo.natale,

francesco.nori}@iit.it

ABSTRACT

We report about the iCub, a humanoid robot for research in 

embodied cognition. At 104 cm tall, the iCub has the size of a 

three and half year old child. It will be able to crawl on all fours 

and sit up to manipulate objects. Its hands have been designed to 

support sophisticate manipulation skills. The iCub is distributed 

as Open Source following the GPL/FDL licenses. The entire 

design is available for download from the project homepage and 

repository (http://www.robotcub.org). In the following, we will 

concentrate on the description of the hardware and software 

systems. The scientific objectives of the project and its 

philosophical underpinning are described extensively elsewhere 

[1]. 

Categories and Subject Descriptors

I.2.9 [Artificial Intelligence]: Robotics – Commercial robots and 

applications, Kinematics and dynamics, Manipulators, Operator 

interfaces, Sensors. 

General Terms

Experimentation, Standardization. 

Keywords

Humanoid robotics, cognitive systems, open source, software 

modularity. 

1. INTRODUCTION

RobotCub is a collaborative project funded by the European 

Commission under the sixth framework programme (FP6) by Unit 

E5: Cognitive Systems, Interaction and Robotics. It has the twofold goal of: i) creating an open hardware/software humanoid 

robotic platform for research in embodied cognition, and ii) 

advancing our understanding of natural and artificial cognitive 

systems by exploiting this platform in the study of the 

development of cognitive capabilities. 

The RobotCub stance on cognition posits that manipulation plays 

a fundamental role in the development of cognitive capability [1-

4]. As many of these basic skills are not ready-made at birth, but 

developed during ontogenesis [5], RobotCub aims at testing and 

developing this paradigm through the creation of a child-like 

humanoid robot: the iCub. This “baby” robot will act in cognitive 

scenarios, performing tasks useful for learning while interacting 

with the environment and humans. The small (104cm tall), 

compact size (approximately 22kg and fitting within the volume 

of a child) and high number (53) of degrees of freedom combined 

with the Open Source approach distinguish RobotCub from other 

humanoid robotics projects developed worldwide. 

In this paper, we focus on the description of the iCub, both in 

terms of hardware and software. In particular, we will briefly 

discuss the rationale of the hardware design, the modularity and 

reuse of software components, and the consequences of the Open 

Source distribution policy. RobotCub has, in parallel, the goal of 

advancing the science and engineering of cognitive systems. This 

part of the research has been discussed elsewhere in greater detail 

[4, 6] and will not be reported here. 

The hardware of iCub has been specifically optimized and 

designed somewhat holistically: modularity in this case had to be 

traded for functionality and overall size. Software, on the other 

hand, has been designed with modularity and component reuse in 

mind [7]. Both the hardware and software of the iCub have been 

released under the GPL and FDL licenses. The mechanical 

drawings, the electronics, schematics and documentation are 

available from the RobotCub website. The iCub software is 

available as well from the same repository together with a basic 

dynamical simulator of the robot. 

Additional initiatives are aiming at promoting the iCub as the 

platform of choice for research in embodied cognition. Fifteen 

Permission to make digital or hard copies of all or part of this work for 

personal or classroom use is granted without fee provided that copies are 

not made or distributed for profit or commercial advantage and that 

copies bear this notice and the full citation on the first page. To copy 

otherwise, or republish, to post on servers or to redistribute to lists, 

requires prior specific permission and/or a fee. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA.

Copyright 2008 ACM 978-1-60558-293-1...$5.00.

50
robots are expected to be delivered by the end of the project (end 

of 2009) as part of RobotCub and of other EU funded projects. 

2. THE ICUB 

The iCub has been designed to allow manipulation and mobility. 

For this reason 30 degrees of freedom (DOF) have been allocated 

to the upper part of the body. The hands, in particular, have 9 

DOF each with three independent fingers and the fourth and fifth 

to be used for additional stability and support (only one DOF). 

They are tendon driven, with most of the motors located in the 

forearm. The legs have 6 DOF each and are strong enough to 

allow bipedal locomotion. 

From the sensory point of view, the iCub is equipped with digital 

cameras, gyroscopes and accelerometers, microphones, and

force/torque sensors. A distributed sensorized skin is under 

development using capacitive sensor technology. 

Each joint is instrumented with positional sensors, in most cases 

using absolute position encoders. A set of DSP-based control 

cards, designed to fit the iCub, take care of the low-level control 

loop in real-time. The DSPs talk to each other via CAN bus. Four 

CAN bus lines connect the various segments of the robot. 

All sensory and motor-state information is transferred to an 

embedded Pentium based PC104 card that handles acquisition and 

reformatting of the various data streams. Time consuming 

computation is typically carried out externally on a cluster of 

machines. The communication with the robot occurs via a Gbit 

Ethernet connection. 

The overall weight of the iCub is 22kg. The umbilical cord 

contains both an Ethernet cable and power to the robot. At this 

stage there is no plan for making the iCub fully autonomous in 

terms of power supply and computation (e.g. by including 

batteries and/or additional processing power on board). 

The mechanics and electronics were optimized for size, starting 

from an evaluation and estimation of torques in the most 

demanding situations (e.g. crawling). Motors and gears were 

appropriately sized according to the requirements of a set of 

typical tasks. The kinematics was also defined following similar 

criteria. The controllers were designed to fit the available space. 

Figure 5 shows the prototype of the iCub. 

2.1 Mechanics

The kinematic specifications of the body of the iCub, the 

definition of the number of DOF, their actual locations as well 

as the actual size of the limbs and torso were based on 

ergonomic data and x-ray images. 

The possibility of achieving certain motor tasks is favored by a 

suitable kinematics and, in particular, this translates into the 

determination of the range of movement and the number of 

controllable joints (where clearly replicating the human body in 

detail is impossible with current technology). Kinematics is also 

influenced by the overall size of the robot which was imposed a

priori. The size is that of a 3.5 years old child (approximately 

100cm high). This size can be achieved with current technology. 

QRIO1

 is an example of a robot of an even smaller size although 

with less degrees of freedom. In particular, our task 

specifications, especially manipulation, require at least the same 

 

1

 http://www.sony.net/Fun/design/history/product/2000/sdr-4x.html 

kinematics of QRIO with the addition of the hands and moving 

eyes. Also, we considered the workspace and dexterity of the 

arms and thus a three degree of freedom shoulder was included. 

This was elaborated into a proper list of joints, ranges, and 

sensory requirements at the joint level. 

Considering dynamics, the most demanding requirements

appear in the interaction with the environment. Impact forces, 

for instance, have to be considered for locomotion behaviors, 

but also and more importantly, developing cognitive behaviors 

such as manipulation might require exploring the environment 

erratically. As a consequence, it is likely that high impact forces 

need to be sustained by the robot mechanical structure. This 

requires strong joints, gearboxes, and more in general powerful 

actuators and appropriate elasticity (for absorbing impacts). In 

order to evaluate the range of the required forces and stiffness, 

various behaviors were simulated in a dynamical model of the 

robot. These simulations provided the initial data for the design 

of the robot. The simulations were run using Webots2

 and were 

later cross-checked by traditional static analysis. 

At a more general level, we evaluated the available technology, 

compared to the experience within the project consortium and 

the targeted size of the robot: it was decided that electric motors 

were the most suitable technology for the iCub, given also that it 

had to be ready according to the very tight schedule of the 

overall project. Other technologies (e.g. hydraulic, pneumatic) 

were left for a “technology watch” activity and were not 

considered further for the design of the iCub. 

From the kinematic and dynamic analysis, the total number of 

degrees of freedom for the upper body was set to 38 (7 for each 

arm, 9 for each hand, and 6 for the head). For the legs the 

simulations indicated that for crawling, sitting and squatting a 5 

DOF leg is adequate. However, it was decided to incorporate an 

additional DOF at the ankle to support standing and walking. 

Therefore each leg has 6 DOF: these include 3 DOF at the hip, 1 

DOF at the knee and 2 DOF at the ankle (flexion/extension and 

abduction/adduction). The foot twist rotation was not 

implemented. Crawling simulation analysis also showed that for 

effective crawling a 2 DOF waist/torso is adequate. However, to 

support manipulation a 3 DOF waist was incorporated. A 3 DOF 

waist provides increased range and flexibility of motion for the 

upper body resulting in a larger workspace for manipulation 

(e.g. when sitting). 

The neck has a total of 3 DOF and provides full head 

movement. The eyes have further 3 DOF to support both 

tracking and vergence behaviors. 

The actuation solution adopted for the iCub is based on a 

combination of a harmonic drive reduction system (CSD series, 

100:1 ratio for all the major joints) and a brushless frameless 

motor (BLM) from the Kollmorgen frameless RBE series 

(Figure 1). The harmonic drive gears provide zero backlash, 

high reduction ratios on small space with low weight while the 

brushless motors exhibit the desired properties of robustness, 

high power density, and high torque and speed bandwidths 

(especially when compared with conventional DC brushed 

motors). The use of frameless motors permits integration of the 

motor and gears in an endoskeletal structure that minimizes size, 

 

2

 http://www.cyberbotics.com/products/webots/webots5.pdf

51
weight and dimensions. Smaller motors (brushed-DC type) were 

used for the hands and head joints. 

Figure 1: section of the standard brushless motor group of the 

iCub. Positioning of the motor and gears can be noted (as 

indicated). Figure from [8]. Note the compact assembly of the 

frameless motor and harmonic drive gear. 

An example on the use of this structure is depicted in Figure 2, 

which shows the shoulder of the iCub with details of the motor 

enclosure and tendon-driven pulley mechanisms. 

Figure 2: the shoulder of the iCub. Left: CAD schematics. 

Right: the implementation. Note the three DOF of the 

shoulder with intersecting axes of rotation and the placement 

of the actuators in the chest as indicated. 1.75mm steel cables 

join the movement of the motors with the pulleys actuating 

the joints. 

Certain features of the iCub are unique. Tendon driven joints are 

the norm both for the hand and the shoulder, but also in the 

waist and ankle. This reduces the size of the robot but 

introduces elasticity that has to be considered in designing 

control strategies where high forces might be generated.

The hand, for example, is fully tendon-driven. Seven motors are 

placed remotely in the forearm and all tendons are routed 

through the wrist mechanism (a 2 DOF differential joint). The 

thumb, index, and middle finger are driven by a looped tendon 

in the proximal joint. Motion of the fingers is driven by tendons 

routed via idle pulleys on the shafts of the connecting joints. 

The flexing of the fingers is directly controlled by the tendons 

while the extension is based on a spring return mechanism. This 

arrangement saves one cable per finger. The last two fingers are 

coupled together and pulled by a single motor which flexes 6 

joints simultaneously. Two more motors, mounted directly 

inside the hand, are used for adduction/abduction movements of 

the thumb and all fingers except the middle one which is fixed 

with respect to the palm. In summary, eight DOF out of a total 

of nine are allocated to the first three fingers, allowing 

considerable dexterity. The last two fingers provide additional 

support to grasping. 

Joint angles are sensed using a custom designed Hall-effectmagnet pair. In addition room for the electronics and tactile 

sensors has been planned. The tactile sensors are under 

development [9]. 

Figure 3: the hand of the iCub, showing the routing of the 

tendons through the wrist and some of the DOF before full 

assembly is completed (the palm is missing). Tendons are 

made of Teflon-coated cables sliding inside Teflon coated 

flexible steel tubes. 

The overall size of the palm has been restricted to 50mm in 

length; it is 34mm wide at the wrist and 60mm at the fingers. 

The hand is only 25mm thick. 

2.2 Electronics

The generation of motor control signals and sensory data 

acquisition is fully embedded into the iCub electronics. Further 

control layers are implemented externally. The interface 

between the iCub and the outside world occurs through a Gbit 

Ethernet cable. The robot contains motor amplifiers, a set of 

DSP controllers, a PC104-based CPU, and analog to digital 

conversion cards. 

The low-level controller cards are of two types for the brushless 

and the brushed-DC motors respectively. They are based on the 

same DSP (Freescale 56F807). The controller of the brushless 

motors is made of two parts (logic and power) and can deliver a 

current of 6A continuous (20A peak) at 48V. All supply 

voltages are generated internally. The CAN bus is employed to 

communicate with the PC104 CPU. Logic and power are 

52
58x42mm each and can control up to two motors. The power 

stage mounts also a metal heatsink that is then connected to the 

external shell of the robot for dissipation. 

Similarly the controller of the brushed-DC motors is made of 

two parts. One card acts as power supply; the other contains the 

CPU and amplifiers to control up to four motors. In this case the 

maximum continuous current is limited to 1A at 12V. 

Figure 4: the brushless motor control logic and power 

amplifier of the iCub. Transistors and heatsinks are not 

shown. The size of the two PCBs is 58x42mm. 

More development is in progress to interface tactile and 

force/torque sensors as discussed in [8]. 

2.3 Sensors

Given the size of the iCub, sensors were evaluated for 

performance but also weight and interface standards. The 

following table contains the list of available sensors and their 

status of maturity (i.e. integration into the robot hardware): 

Component Model/type Notes 

Cameras PointGrey 

Dragonfly 

2 640x480 

30fps

Firewire cameras, support 

also higher resolution 

Microphones MICRO 

POM2746L

Condenser electrect type 

Inertial

sensors

XSense

MTx

3 gyroscopes, 3 linear 

accelerometers, compass 

Force/torque

sensors

Custom Mechanically compatible with 

the ATI Mini-45 

Position

sensors

AS5045 12bit, absolute magnetic 

encoder

Position

sensors

Faulhaber Integrated position sensing for 

DC motors 

Position

sensors

Honeywell 

SS495A

Finger position sensing 

Tactile

sensors

Custom Based on the AD7147, 

capacitive sensing 

All sensors are fully integrated apart from the force/torque 

sensor whose control electronics is still under development and 

the skin whose entire technology is under testing. More 

information can be found in [8, 9]. 

3. SOFTWARE

The iCub software was developed on top of Yarp [7]. RobotCub 

supported a major overhaul of the Yarp libraries to adapt to a 

more demanding collaborative environment. Better engineered 

software and interface definitions are now available in Yarp. 

Yarp is a set of libraries that support modularity by abstracting 

two common difficulties in robotics: namely, modularity in 

algorithms and in interfacing with the hardware. Robotics is 

perhaps one of the most demanding application environments 

for software recycling where hardware changes often, different 

specialized OSs are typically encountered in a context with a 

strong demand for efficiency. The Yarp libraries assume that an 

appropriate real-time layer is in charge of the low-level control 

of the robot and instead takes care of defining a soft real-time 

communication layer and hardware interface that is suited for 

cluster computation. 

Yarp takes care also of providing independence from the 

operating system and the development environment. The main 

tools in this respect are ACE [10] and CMake3

. The former is an 

OS-independent communication library that hides the quirks of 

interprocess communication across different OSs. CMake is a 

cross-platform make-like description language and tool to 

generate appropriate platform specific project files. 

Yarp abstractions are defined in terms of protocols. The main 

Yarp protocol addresses inter-process communication issues. 

The abstraction is implemented by the port C++ class. Ports

follow the observer pattern by decoupling producers and 

consumers. They can deliver messages of any size, across a 

network using a number of underlying protocols (including 

shared memory when possible). In doing so, ports decouple as 

much as possible (as function of a certain number of userdefined parameters) the behavior of the two sides of the 

communication channels. Ports can be commanded at run time 

to connect and disconnect. 

The second abstraction of Yarp is about hardware devices. The 

Yarp approach is to define interfaces for classes of devices to 

wrap native code APIs (often provided by the hardware 

manufactures). Change in hardware will likely require only a 

change in the API calls (and linking against the appropriate 

library). This easily encapsulates hardware dependencies but 

leaves dependencies in the source code. The latter can be 

removed by providing a “factory” for creating objects at run 

time (on demand). 

The combination of the port and device abstractions leads to 

remotable device drivers which can be accesses across a 

network: e.g. a grabber can send images to a multitude of 

listeners for parallel processing. 

Overall, Yarp’s philosophy is to be lightweight and to be 

“gentle” with existing approaches and libraries. This naturally 

excludes hard real-time issues that have to be necessarily 

addressed elsewhere, likely at the OS level. 

 

3

 http://www.cmake.org 

53
Figure 5: the complete iCub prototype. 

3.1 Yarp example 

For the purposes of YARP, communication takes place through 

connections between named entities called ports. These form a 

directed graph, the YARP Network, where ports are the nodes, 

and connections are the edges. Each port is assigned a unique 

name, such as “/icub/camera/right”. Every port is registered by 

name with a “name server”. The goal is to ensure that if you 

know the name of a port, that is all you need in order to be able 

to communicate with it from any machine. The YARP name 

server converts from symbolic names to all the details necessary 

to make a connection with a specific resource. The YARP name 

server is designed to be easily used by clients who are not 

themselves using the YARP libraries or executables. 

The purpose of ports is to move data from one thread to another 

(or several others) across process and machine boundaries. The 

flow of data can be manipulated and monitored externally (e.g. 

from the command-line) at run-time. It can also be accessed 

without using the YARP libraries or executables, since the 

relevant protocols are documented. 

A port can send data to any number of other ports. A port can 

receive data from any number of other ports. Connections 

between ports can be freely added or removed, and may use 

different underlying transports. The use of several different 

transports and protocols allows us to exploit their best 

characteristics. TCP is reliable; it can be used to guarantee the 

reception of a message. UDP can be faster than TCP, but 

without guarantees. Multicast is efficient for distributing the 

same information to large numbers of targets. Shared memory 

can be employed for local connections. 

Figure 6 shows a very simple network of ports for a visual 

tracking application. Machine 1, in this example, grabs images 

which are sent to another application (the tracker proper). The 

output of the tracker consists of two parts: the image coordinates 

of the tracked object and an image with a graphic overlay 

showing how good the tracker is doing. The output is sent to a 

control process on another machine (Machine 2) and for 

visualization to yet another machine. Different protocols can be 

used for reasons of efficiency. 

Figure 6: example of a YARP network for a simple visual 

control loop. 

4. OPEN SOURCE ROBOTICS 

RobotCub is Open Source both for software and hardware. While 

the phrase “Open Source software – OSS” is clear, “Open Source 

hardware” might sound strange, but in fact it is a plain transfer of 

the open source philosophy to the entire design of the RobotCub 

platform. The design of the robot started from the preparation of 

specifications (e.g. estimation of torque, speed, etc.), a typical 3D 

CAD modeling, and eventually in the preparation of the executive 

files which are used to fabricate parts and for assembly. Without 

good documentation it is very complicated to build and assemble 

a full robot. This means that documentation (as for software) is 

particularly important. 

The CAD files, in some sense, can be seen as the source code, 

since they are the “preferred form of the work for making 

modifications to it”, in the language of the GPL. They get 

“compiled” into 2D drawings which represent the executive 

drawings that can be used by any professional and reasonably 

well-equipped machine shop either to program CNC machines or 

to manually prepare the mechanical parts. This compilation 

process is not fully automated and requires substantial human 

intervention. There is a clear dependency of the 2D drawings on 

the original 3D CAD model. To enable the same type of virtuous 

development cycle as occurs in open source software, the 3D 

CAD is required, since changes happen in 3D first and get 

propagated to 2D later. In addition, assembly diagrams, part lists, 

and all the material produced during the design stage should be 

included to guarantee that the same information is available to 

new developers. 

One difference between software and the hardware design is that 

there are currently no effective formats for interchange of 3D 

models. Proprietary systems such as SolidWorks and Pro/E can 

import and export a range of formats, but going from one to 

another is lossy, destroying the information needed for production 

54
and leaving just the basic geometrical shape. So in practice, 

designs are tied to tools produced by a particular vendor, and 

interoperability between hardware design tools is limited. In 

RobotCub we were forced to choose a specific set of tools for 

mechanical and electronic CAD and future upgrades will have to 

strictly adhere to these standards. Due to the absence of open 

source professional design tools, RobotCub uses proprietary 

products. This is an unfortunate situation, but there is no practical 

alternative at the moment. The “C++” and “gcc” of CAD do not 

exist yet. 

As a practical matter, the simple duplication of RobotCub parts 

does not require the use of any of these tools since we provide all 

executive drawings and production files (e.g. Gerber files for the 

PCBs). For modification, the design tools are somewhat 

expensive (although educational discounts or educational releases 

exist). Free of charge viewers are currently available for all file 

types in question. 

For RobotCub, we decided to license all the CAD sources under 

the GPL which seems appropriate given their nature. Associated 

documentation will be licensed under the FDL. These will be 

made available through the usual source code distribution 

channels (e.g. repositories, websites). 

5. CONCLUSION

The design process of RobotCub has been a distributed effort as 

for many open source projects. Various groups developed various 

subcomponents and contributed in different ways to the design of 

the robot including mechanics, electronics, sensors, etc. In 

particular, a whole design cycle was carried out for the subparts 

(e.g. head, hand, legs) and the prototypes that have been built and 

debugged. The final CAD and 2D drawings were discussed and 

then moved to the integration stage. Clearly, communication was 

crucial at the initial design stage to guarantee a uniform design 

and a global optimization. 

The distributed design broke down at the integration stage where 

the industrial partner (Telerobot Srl. – Genoa) stepped in to carry 

out integration, verification and consistency checks. The design 

and fabrication of the control electronics was also subcontracted 

to a specialized company. It is important to stress the 

collaboration with industry for a project of this size and with these 

goals and requirements. For many reasons building a complete 

platform involves techniques and management that is better 

executed following industrial standards. One example that applies 

to RobotCub is the standardization of the documentation. 

A further strategy used in RobotCub is that of building early. 

Each subsystem was built and copied as soon as possible. In 

several cases debugging happened either because the copies of the 

robot did not work as expected or because easy-to-fix problems 

were spotted. Sometimes the documentation had to be improved. 

Unfortunately, this strategy was applied less extensively to some 

of the subparts which are or were still under design and 

debugging. The design stage will be completed with the 

realization of the fifteen copies of the iCub. 

This will further test the documentation and in general the 

reliability of the overall platform including software, debugging 

tools, electronics, etc. The first release of the iCub will be 

consolidated after this final fabrication stage. 

The actual design of the robot had to incorporate manipulation by 

providing sophisticated hands, a flexible oculomotor system, and 

a reasonable bimanual workspace. On top of this, the robot has to 

support global body movements such as crawling, sitting, etc. 

These many constraints were considered in preparing the 

specifications of the robot and later on during the whole design 

process.

Both the iCub design and its software architecture are distributed 

as Open Source. This is not enough to guarantee success. 

Additional initiatives are required. RobotCub is giving away six 

copies of the iCub to the winners of an Open Call for proposals to 

use the iCub (recently concluded). In addition a structure called 

the Research and Training Site (RTS) has being created to support 

visiting researchers to work on the iCub prototypes in Genoa. 

6. ACKNOWLEDGMENTS

The authors would like to thank the RobotCub Consortium. The 

authors were supported by European Union grant RobotCub (IST2004-004370) and by euCognition (FP6 Project 26408). Paul 

Fitzpatrick is gratefully acknowledged for the continuous support 

to Yarp. 

7. REFERENCES

[1] L. Fadiga, L. Craighero, and E. Olivier, "Human motor 

cortex excitability during the perception of others' 

action," Current Biology, vol. 14 pp. 331-333, 2005. 

[2] L. Fadiga, L. Craighero, G. Buccino, and G. Rizzolatti, 

"Speech listening specifically modulates the excitability 

of tongue muscles: a TMS study," European Journal of 

Neuroscience, vol. 15, pp. 399-402, 2002. 

[3] G. Rizzolatti and L. Fadiga, "Grasping objects and 

grasping action meanings: the dual role of monkey 

rostroventral premotor cortex (area F5)," in Sensory

Guidance of Movement, Novartis Foundation 

Symposium, G. R. Bock and J. A. Goode, Eds. 

Chichester: John Wiley and Sons, 1998, pp. 81-103. 

[4] D. Vernon, G. Metta, and G. Sandini, "A Survey of 

Cognition and Cognitive Architectures: Implications for 

the Autonomous Development of Mental Capabilities in 

Computational Systems," IEEE Transactions on 

Evolutionary Computation, special issue on AMD, vol. 

11, 2007. 

[5] C. von Hofsten, "On the development of perception and 

action," in Handbook of Developmental Psychology, J. 

Valsiner and K. J. Connolly, Eds. London: Sage, 2003, 

pp. 114-140. 

[6] G. Sandini, G. Metta, and D. Vernon, "RobotCub: An 

Open Framework for Research in Embodied 

Cognition," presented at IEEE-RAS/RJS International 

Conference on Humanoid Robotics, Santa Monica, CA, 

2004.

[7] P. Fitzpatrick, G. Metta, and L. Natale, "Towards LongLived Robot Genes," Journal of Robotics and 

Autonomous Systems, Special Issue on Humanoid 

Technologies, vol. 56, 2008. 

[8] N. G. Tsagarakis, G. Metta, G. Sandini, D. Vernon, R. 

Beira, F. Becchi, L. Righetti, J. Santos-Victor, A. J. 

Ijspeert, M. C. Carrozza, and D. G. Caldwell, "iCub – 

The Design and Realization of an Open Humanoid 

55
Platform for Cognitive and Neuroscience Research," 

Advanced Robotics, vol. 21, 2007. 

[9] M. Maggiali, G. Cannata, P. Maiolino, G. Metta, M. 

Randazzo, and G. Sandini, "Embedded Distributed 

Capacitive Tactile Sensor," presented at The 11th 

Mechatronics Forum Biennial International Conference 

2008, University of Limerick, Ireland, 2008. 

[10] S. D. Huston, J. C. E. Johnson, and U. Syyid, The ACE 

Programmer's Guide: Addison-Wesley, 2003. 

56
An Open-Source Simulator for Cognitive Robotics 

Research: The Prototype of the iCub Humanoid Robot 

Simulator 

V. Tikhanoff, A. Cangelosi 

University of Plymouth 

Plymouth PL4 8AA 

UK 

vadim.tikhanoff@plymouth.ac.u

k; acangelosi@plymouth.ac.uk 

P. Fitzpatrick 

Lira-lab University of Genova 

Viale F. Causa, 13 

Genova Italy 

paulfitz@liralab.it 

G. Metta, L. Natale, F. Nori 

Italian Institute of Technology 

Via Morego 30 

Genova Italy 

giorgio.metta@iit.it 

lorenzo.natale@iit.it 

francesco.nori@iit.it 

ABSTRACT

This paper presents the prototype of a new computer simulator for 

the humanoid robot iCub. The iCub is a new open-source 

humanoid robot developed as a result of the “RobotCub” project, 

a collaborative European project aiming at developing a new 

open-source cognitive robotics platform. The iCub simulator has 

been developed as part of a joint effort with the European project 

“ITALK” on the integration and transfer of action and language 

knowledge in cognitive robots. This is available open-source to all 

researchers interested in cognitive robotics experiments with the 

iCub humanoid platform. 

Keywords

Open-Source, Simulator, iCub humanoid robot, cognitive 

robotics. 

1. INTRODUCTION 

Computer simulations play an important role in robotics research. 

Despite the fact that the use of a simulation might not provide a 

full model of the complexity present in the real environment and 

might not assure a fully reliable transferability of the controller 

from the simulation environment to the real one, robotic 

simulations are of great interest for cognitive scientists [18]. 

There are several advantages of robotics simulations for 

researchers in cognitive sciences. The first is that simulating 

robots with realistic physical interactions permit to study the 

behavior of several types of embodied agents without facing the 

problem of building in advance, and maintaining, a complex 

hardware device. The computer simulator can be used as a tool for 

testing algorithms in order to quickly check for any major 

problems prior to use of the physical robot. Moreover, simulators 

also allow researchers to experiment with robots with varying 

morphological characteristics without the need to necessarily 

develop the corresponding features in hardware [1]. This 

advantage, in turn, permits the discovery of properties of the 

behavior of an agent that emerges from the interaction between 

the robot’s controller, its body and the environment. Another 

advantage is that robotic simulations make it possible to apply 

particular algorithms for creating robots’ controllers, such as 

evolutionary or reinforcement learning algorithms [12]. The use 

of robotics simulation permits to drastically reduce the time of the 

experiments such as in evolutionary robotics. In addition, it makes 

it possible to explore research topics like the co-evolution of the 

morphology and the control system [1]. A simulator for the iCub 

robot magnifies the value a research group can extract from the 

physical robot, by making it more practical to share a single robot 

between several researchers. The fact that the simulator is free and 

open makes it a simple way for people interested in the robot to 

begin learning about its capabilities and design, with an easy 

"upgrade" path to the actual robot due to the protocol-level 

compatibility of the simulator and the physical robot. And for 

those without the means to purchase or build a humanoid robot, 

such small laboratories or hobbyists, the simulator at least opens a 

door to participation in this area of research. 

The iCub simulator is currently being used by both the RobotCub 

and the ITALK project partners for preliminary experiments on 

the simulator robot, and subsequent testing with the physical 

robots. 

2. ICUB SIMULATOR DEVELOPMENT 

The iCub simulator has been designed to reproduce, as accurately 

as possible, the physics and the dynamics of the robot and its 

environment. The simulated iCub robot is composed of multiple 

rigid bodies connected via joint structures. It has been constructed 

collecting data directly from the robot design specifications in 

order to achieve an exact replication (e.g. height, mass, Degrees of 

Freedom) of the first iCub prototype developed at the Italian 

Institute of Technology in Genoa. The environment parameters on 

gravity, objects mass, friction and joints are based on known 

environment conditions. 

2.1 Open-Source Approach 

The iCub simulator presented here has been created using open 

source libraries in order to make it possible to distribute the 

Permission to make digital or hard copies of all or part of this work for 

personal or classroom use is granted without fee provided that copies 

are not made or distributed for profit or commercial advantage and that 

copies bear this notice and the full citation on the first page. To copy 

otherwise, or republish, to post on servers or to redistribute to lists, 

requires prior specific permission and/or a fee. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA. 

Copyright 2008 ACM 978-1-60558-293-1...$5.00. 

57
simulator freely to any researcher without requesting the purchase 

of restricted or expensive proprietary licenses. 

The very first iCub simulator prototype was developed using the 

commercial Webots package [10,17], a professional robotic 

simulator which is widely used in academia and research. The 

Webots package is primarily designed for industrial simulations 

but used as a reliable tool for robotic research. Although a 

powerful software, the main disadvantages of the Webots package 

are its price, the computational heaviness of the package itself and 

the fact that, depending on the type of license, there are 

limitations on the source code available in order to modify some 

properties of the actual simulator. Therefore the potential open 

source distribution of such a first prototype was quite limited. 

Other open source simulators suitable for robotics research also 

exist. Amongst others we can find the Player/Gazebo project [6, 

7], Simbad [16], Darwin2K [8], EvoRobot [4,12] and the 

OpenSim [14]. The Simbad, Darwin2K and Evorobot simulators 

have a strong focus on evolutionary algorithms and they have 

been mainly developed for scientific educational purposes. They 

are built to study AI algorithms and machine learning for multirobot platforms. Gazebo is a powerful and complex multi-robot 

simulation in a 3D environment. OpenSim is a general multi-robot 

platform built in a similar way as the Gazebo package. However 

such systems use the same third party software and libraries. 

Although the proposed iCub simulator is not the only open source 

robotics platform, it is one of the few that attempts to create a 3D 

dynamic robot environment capable of recreating complex worlds 

and fully based on non-proprietary open source libraries. 

2.2 Physics Engine 

The iCub simulator uses ODE [13] (Open Dynamic Engine) for 

simulating rigid bodies and the collision detection algorithms to 

compute the physical interaction with objects. The same physics 

library was used for the Gazebo project and the Webots 

commercial package. ODE is a widely used physics engine in the 

open source community, whether for research, authoring tools, 

gaming etc. It consists of a high performance library for 

simulating rigid body dynamics using a simple C/C++ API. ODE 

was selected as the preferred open source library for the iCub 

simulator because of the availability of many advanced joint 

types, rigid bodies (with many parameters such as mass, friction, 

sensors...), terrains and meshes for complex object creation. 

2.3 Rendering Engine 

Although ODE is a good and reliable physics engine, computing 

all the physical interaction of a complex system can take a good 

deal of processing power. Since ODE uses a simple rendering 

engine based on OpenGL, it has limitations for the rendering of 

complex environments comprising many objects and bodies. This 

can significantly affect the simulation speed of complex robotic 

simulation experiments. It was therefore decided to use OpenGL 

directly combined with SDL [15], an open source cross platform 

multimedia library. This makes it possible to render the scene with 

much more ease and to carry out computationally-efficient 

simulation experiments. 

2.4 YARP Protocol 

As the aim was to create an exact replica of the physical iCub 

robot, the same software infrastructure and inter-process 

communication will have to be used as those used to control the 

physical robot. iCub uses YARP [5, 9] (Yet Another Robot 

Platform) as its software architecture. YARP is an open-source 

software tool for applications that are real-time, computationintensive, and involve interfacing with diverse and changing 

hardware. The simulator and the actual robot have the same 

interface either when viewed via the device API or across network 

and are interchangeable from a user perspective. The simulator, 

like the real robot, can be controlled directly via sockets and a 

simple text-mode protocol; use of the YARP library is not a 

requirement. This can provide a starting point for integrating the 

simulator with existing controllers in esoteric languages or 

complicated environments. 

2.5 Architecture 

Figure 1. This figure shows the architecture of the simulator 

with YARP support. The User code can send and receive 

information to both the simulated robot itself 

(motors/sensors/cameras) and the world (manipulate the 

world). Network wrappers allow device remotization. The 

Network Wrapper exports the YARP interface so that it can 

be accessed remotely by another machine. 

2.6 iCub Body Model 

The iCub simulator has been created using the data from the 

physical robot in order to have an exact replica of it. As for the 

physical iCub, the total height is around 105cm, weighs 

approximately 20.3kg and has a total of 53 degrees of freedom 

(DoF). These include 12 controlled DoFs for the legs, 3 controlled 

DoFs for the torso, 32 for the arms and six for the head. 

The robot body model consists of multiple rigid bodies attached 

through a number of different joints. All the sensors were 

implemented in the simulation on the actual body, such as touch 

sensors and force/torque sensors. As many factors impact on the 

torque values during manipulations, the simulator might not 

guarantee to be perfectly correct. However the simulated robot 

torque parameters and their verification in static or motion are a 

good basis and can be proven to be reliable [11]. 

58
(a) (b) 

(c) (d) 

Figure 2. Photo of real iCub (a), of simulated iCub and the 

binocular view (b) The simulated iCub moving all four limbs 

as part of a demo (c) and the simulated iCub looking at and 

manipulating an object in its environment.(d) 

All the commands sent to and from the robot are based on YARP 

instructions. For the vision we use cameras located at the eyes of 

the robot which in turn can be sent to any workstation using 

YARP in order to do develop vision analysis algorithms. 

The system has full interaction with the world/environment. The 

objects within this world can be dynamically created, modified 

and queried by simple instruction resembling those that YARP 

uses in order to control the robot. 

3. ICUB SIMULATOR AND COGNITIVE 

ROBOTICS RESEARCH PROJECTS 

This section presents a research initiative on embodied cognition 

and developmental cognitive robotics based on the two EU 

projects RobotCub (robotcub.org) and ITALK (italkproject.org). 

Various robotics experiments in these two projects will rely on the 

use of the iCub simulator. 

The RobotCub project aims at the development of an open 

humanoid robotic platform (iCub) and simultaneously the 

advancement of our understanding of cognitive systems by 

exploiting this platform in the study of the development of 

cognitive capabilities in humanoid robots. The idea is that, by 

creating a common platform, this will enable many laboratories to 

join this effort without having to invest themselves in developing 

yet another robotic platform. The second aim of RobotCub is to 

investigate the development of these cognitive skills in natural 

and artificial cognitive systems. The project will carry out a plan 

of empirical research including neuroscience, developmental 

psychology, and robotics. This plan is centered on manipulation 

behavior, ranging from the direct aspects of reaching and grasping 

for objects to the use of gestures for communication. Aspects that 

will be touched along the way are—for instance—looking and 

overt attention, reaching, the detection and discovery of 

affordances, learning through imitation, and interaction. The 

emergent approach naturally encompasses the study of ontogenic 

development and, in fact, a comparatively large effort will be 

devoted to its study. The RobotCub project roadmap for this 

investigation includes the study of the starting point in terms of 

core abilities, the motivation of the system to explore and gather 

data, and new studies on a few research areas such as looking, 

reaching and manipulation, posture, locomotion, and social 

interaction. For each of these areas, issues of prospective use of 

information, motivation, and the mechanisms of exploration have 

to be experimentally investigated. The RobotCub agenda aims at 

covering—through targeted empirical investigation—most if not 

all of these issues. 

The ITALK project intends to develop cognitive robotic agents, 

based among others on the iCub humanoid platform, that learn to 

handle and manipulate objects and tools autonomously, to 

cooperate and communicate with other robots and humans, and to 

adapt their abilities to changing internal, environmental, and 

social conditions. The main theoretical hypothesis behind the 

project is that the parallel development of action, 

conceptualisation and social interaction permits the bootstrapping 

of language capabilities, which on their part enhance cognitive 

development. This is possible through the integration and transfer 

of knowledge and cognitive processes involved in sensorimotor 

learning and the construction of action categories, imitation and 

other forms of social learning, the acquisition of grounded 

conceptual representations and the development of the 

grammatical structure of language. 

The undergoing research falls into five main research themes: (i) 

action development, (ii) conceptualisation, (iii) social interaction, 

(iv) language emergence, and (v) integration and bootstrapping of 

cognition. 

The study of the development of complex action manipulation 

capabilities will –in contrast to existing approaches– be based on 

synchronous development of motor, social and linguistic skills. 

For this it is fundamental to identify the characteristics of action 

development that are compatible with this scenario and reject 

those that are mere engineering solutions. Two core properties of 

biological motor control systems will be considered: 

compositionality, the construction of hierarchically ordered 

gesturing and manipulation, and generalization. We will study 

how action development can be guided by individual exploration 

by the robot and by imitating humans. 

A fundamental skill of any cognitive system is the ability to 

produce a variety of behaviours and to display the behaviour that 

is appropriate to the current individual, social, cultural and 

environmental circumstances. This will require agents (1) to 

reason about past, present and future events, (2) to mediate their 

motor actions based on this reasoning process and (3) to 

communicate using a communication system that shares 

59
properties with natural language. For this agents will need to 

develop and maintain internal categorical states, i.e. ways to store 

and classify sensory information. We term such internal states 

embodied concepts and we understand them as representations 

grounded in sensory-motor experiences that identify crucial 

aspects of the environment and/or of the agent/environmental 

interaction. 

Another essential component of the ITALK research project is to 

look at the role of social learning and social interaction to support 

the development of a shared linguistic communication system. In 

particular, new research will consider (i) the role of imitation and 

human-robot interaction for the acquisition of shared 

communication systems based on deixis, gestures and reference, 

(ii) the role of users’ expectation in human-robot interaction and 

(iii) the emulation of actions and gestures in the learning of 

multimodal task-oriented behavior. Such research will be based 

on a series of human-robot interaction (HRI) experiments and on 

observational studies on parent-child dyads which will inform 

robot-robot and human-robot experiments. We expect to extend 

the expertise and methodologies in dialog systems for HRI studies 

to new studies on social interaction and communication where the 

robot’s linguistic communication system develops through 

interaction with its environment and other robots and humans. 

The ITALK project will follow a cognitive linguistics approach. 

As it is centred on the interaction between action and language 

development, it provides the ideal testbed to investigate the 

emergence of linguistic constructions in close interaction with the 

development of action, social and grounded conceptual 

capabilities. We will focus on the emergence of linguistic 

structure. Among the research issues include (i) generalisation as 

the basis of the emergence of symbolic systems, (ii) the role of 

speech and “acoustic packaging”: speech or sound signals which 

serve as a cue to aid the learning of action sequences, (iii) the role 

of constructional grounding: the acquisition of linguistic 

construction and how one construction become favoured over 

another, (iv) the ontogenetic emergence of compositional 

lexicons, and (v) evolutionary studies on language emergence. 

In the coming years the ITALK project aims to achieve a series of 

scientific and technological objectives such as providing new 

scientific explanations of the integration of action, social and 

linguistic skills and in particular on the hypothesis that action, 

social and linguistic knowledge co-develop and further bootstrap 

cognitive development. Another main aim deals with developing 

sets of methods for analyzing the interaction of language, action 

and cognition in humans and artificial cognitive agents using 

robot learning experiments, computer simulations, cognitive 

linguistic analysis, and experimental investigations from 

developmental linguistics, the neuroscience of language and 

action, and human-robot interaction experiments. Furthermore the 

project will develop innovative and cognitively plausible 

engineering principles, techniques and approaches for the design 

of communicative and linguistic capabilities in cognitive robots 

able to interact with their physical and social world and to 

manipulate entities, artefacts and other agents including humans. 

All of the above aims would be demonstrated through the use of 

robotic experiments on the acquisition of object manipulation, 

social skills and linguistic capabilities in simulated and physical 

cognitive robots. In particular, robotic agents will be able to (a) 

acquire complex object manipulation capabilities through social 

interaction; (b) develop an ability to create and use embodied 

concepts; (c) develop social skills that allow flexible interaction 

with other agents or people; (d) develop linguistic abilities to 

communicate about their interaction with the world. 

4. CONCLUSION 

The current version of the iCub simulator has been used for 

preliminary testing by partners in the RobotCub and ITALK 

projects. In addition to being used for experiments on the 

development of controllers for the iCub robot, some groups have 

used the simulator to create a mental model [2] used by the robot 

to represent the current state of the environment. 

Future plans on the simulator development will mostly involve the 

design of functionalities to model and interact with the physical 

environment. For example, this will allow the users to modify the 

objects in the world where the iCub resides, in order to allow 

different types of experiments. Finally, further work will focus on 

the systematic testing and replication of simulation studies with 

the physical robot. 

5. ACKNOWLEDGEMENTS 

This work was supported by the European Commission FP6 

Project RobotCub (IST-004370) and FP7 Project ITALK (ICT214668) within the Cognitive Systems and Robotics unit (FP7 

ICT Challenge 2). The authors also acknowledge the support of 

the FP6 euCognition Coordinated Action project funded under the 

same Cognitive Systems and Robotics unit. 

6. REFERENCES 

[1] J.C. Bongard & R. Pfeifer (2003). Evolving complete agents 

using artificial ontogeny. In Hara, F. & R. Pfeifer, Eds., 

Morpho-functional Machines: The New Species (Designing 

Embodied Intelligence) Springer-Verlag, pp. 237-258 

[2] PF Dominey (2007) Sharing Intentional Plans for Imitation 

and Cooperation: Integrating Clues from Child 

Developments and Neurophysiology into Robotics, 

 Proceedings of the AISB 2007 Workshop on Imitation. 

[3] European commission, unit e5, home page. 

http://cordis.europa.eu/ist/cognition/index.html, 2007. 

[4] Evorobot http://laral.istc.cnr.it/evorobot/simulator.html 

[5] P. Fitzpatrick, G. Metta, L. Natale: Towards Long-lived 

Robot Genes, Robotics and Autonomous Systems, 56(1):29-

45, 2008 

[6] B. Gerkey, R. T. Vaughan and A. Howard. The Player/Stage 

Project: Tools for Multi-Robot and Distributed Sensor 

Systems. Proceedings of the 11th International Conference 

on Advanced Robotics, 2003. 

[7] N. Koenig and A. Howard. Design and Use Paradigms for 

Gazebo, An Open-Source Multi-Robot Simulator. 

IEEE/RSJ International Conference on Intelligent Robots 

and Systems (IROS), Sendai, Japan, 2004. 

[8] C. Leger, Darwin2K: An Evolutionary Approach to 

Automated Design for Robotics. Kluwer Academic 

Publishers, Aug 2000. 

60
[9] G. Metta, P. Fitzpatrick & L. Natale. YARP: Yet Another 

Robot Platform. International Journal on Advanced 

Robotics Systems, 3(1):43–48, 2006. 

[10] O. Michel, “Webots: Professional mobile robot simulation,” 

International Journal of Advanced Robotic Systems, vol. 1, 

no. 1, pp.39–42, 2004. 

[11] N. Nava,V. Tikhanoff, G. Metta, G Sandini, Kinematic and 

Dynamic Simulations for The Design of RoboCub UpperBody Structure ESDA 2008 

[12] S. Nolfi & D. Floreano (2000). Evolutionary Robotics: The 

Biology, Intelligence and Technology of Self-Organizing 

Machines Cambridge, MA: MIT Press/Bradford Books 

[13] Open Dynamics Engine http://opende.sourceforge.net/. 

[14 OpenSim Simulator http://opensimulator.sourceforge.net/. 

[15 SDL – Simple DirectMedia Layer http://www.libsdl.org/ 

[16] Simbad Simulator - http://simbad.sourceforge.net 

[17] Webots - http://www.cyberbotics.com/ 

[18] Ziemke T. (2003). On the role of robot simulations in 

embodied cognitive science, AISB Journal, 1(4), 389-99 

61
Symbiotic Robot Organisms:

REPLICATOR and SYMBRION Projects

Special Session on EU-projects

Serge Kernbach∗

Eugen Meister

Florian

Schlachter

Kristof Jebens

University of Stuttgart

Universitätsstr. 38,

D-70569 Stuttgart,

Germany

Marc Szymanski

Jens Liedke

Davide Laneri

Lutz Winkler

University of

Karlsruhe

Engler-Bunte-Ring 8

D-76131 Karlsruhe,

Germany

Thomas Schmickl

Ronald Thenius

Karl-FranzensUniversity

Graz

Universitatsplatz 2

A-8010 Graz, Austria

Paolo Corradi

Leonardo Ricotti

Scuola Superiore

Sant’Anna

Viale Rinaldo Piaggio

34

56025 - Pontedera

(PI), Italy

ABSTRACT

Cooperation and competition among stand - alone swarm

agents can increase the collective fitness of the whole system.

An interesting form of collective system is demonstrated by

some bacteria and fungi, which can build symbiotic organisms. Symbiotic communities can enable new functional capabilities which allow all members to survive better in their

environment. In this article we show an overview of two

large European projects dealing with new collective robotic

systems which utilize principles derived from natural symbiosis. The paper provides also an overview of typical hardware, software and methodological challenges arose along

these projects, as well as some prototypes and on-going experiments available on this stage.

Keywords: collective robotics, swarms, artificial evolution, reconfigurable systems

1. INTRODUCTION

Nature shows several interesting examples for cooperation

of individuals. Most prominent examples of cooperation are

found in social insects [1], where specialized reproductive

schemes (in most cases just a few out of thousands of colony

members are able to reproduce) and the close relationships

of colony members favoured the emergence of highly cooperative behaviours [2]. However, also non-eusocial forms of

cooperative communities evolved, like the collective hunting in predatory mamals [3] (e.g., lions, whales, ...) or the

trophallactic altruism in vampire bats. Such cooperative be-

∗Corresp. author: Serge.Kernbach@ipvs.uni-stuttgart.de

Permission to make digital or hard copies of all or part of this work for

personal or classroom use is granted without fee provided that copies are

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bear this notice and the full citation on the first page. To copy otherwise, to

republish, to post on servers or to redistribute to lists, requires prior specific

permission and/or a fee.

PerMIS 08, August 19-21, 2008, Gaithersburg, MD, USA

Copyright 2008 ACM 978-1-60558-293-1 ...$5.00.

haviours are mostly explained by reciprocal advantages due

to the cooperative behaviours and/or by the close relationship among the community members. In contrast to that,

cooperation sometimes arises also among individuals that

are not just very distant in a gene pool, sometimes they do

not even share the same gene pool: Cooperative behaviours

between members of different species is called ’Symbiosis’.

A non-exhaustive list of prominent examples are the pollination of plants by flying insects (or birds), the cooperation

between ants and aphids. Also lichens, which are a close

integration of fungi and algae and the cooperation between

plant roods and fungi represent symbiotic interactions.

A common pattern in all these above-mentioned forms of

cooperation is that single individuals perform behaviours,

which - on the first sight - are more supportive for the collective of the group than for themselves. However, as these behaviours have emerged through natural selection, we can assume that these cooperative behaviours have their ultimate

reasoning in a sometimes delayed and often non-obvious individual egoistic advantage.

Symbiotic forms of organization emerge new functional capabilities which allow aggregated organisms to achieve better fitness in the environment. When the need of aggregation

is over, symbiotic organism can dis-aggregate and exists further as stand-alone agents, thus an adaptive and dynamical

form of cooperation is often advantageous.

Lately, technical systems mimic natural collective systems

in improving functionality of artificial swarm agents. Collective, networked or swarm robotics are scientific domains,

dealing with a cooperation in robotics [4]. Current research

in these domains is mostly concentrated on cooperation and

competition among stand-alone robots to increase their common fitness [5]. However, robots can build a principally new

kind of collective systems, when to allow them to aggregate

into a multi-robot organism-like-forms. This ”robot organism” can perform such activities that cannot be achieved

by other kind of robotic systems and so to achieve better

functional fitness.

To demonstrate this idea, we consider a collective energy foraging scenario for micro-robots Jasmine [6]. Swarm

robots can autonomously find an energy source and recharge.

62
The clever collective strategy can essentially improve the efficiency of energy foraging, but nevertheless a functional fitness of a swarm is limited. For instance, if the recharging

station is separated from a working area by a small barrier,

robots can never reach the energy source. However, if robots

aggregate into more complex high-level organism which can

pass the barrier, they will reach the docking station. In

this way a cooperative organization of robotic system allows an essential increase of functional capabilities for the

whole group. The large integrated project ”REPLICATOR”

(www.replicatores.eu), funded by the European commission,

within the work programme ”Cognitive systems, interaction

and robotics”, deals with such issues as reconfigurability of

sensors and actuators, adaptive control and learning strategies as well as working in real environments.

The cooperative (swarm-based or symbiotic) organization

of the robotic system provides essential plasticity of used

hardware and software platforms. The robot organism will

be capable of continuously changing its own structure and

functionality. Such an evolve-ability opens many questions

about principles and aspects of long- and short-term artificial evolution and controllability of artificial evolutionary processes. The large integrated project ”SYMBRION”

(www.symbrion.eu), funded by European commission, within

the work programme ”Future and Emergent Technologies”,

is focused on evolve-ability, dependability and artificial evolution for such robot organisms based on bio-inspired and

computational paradigms. Both projects are open-science

and open-source.

Both projects, consortia and the European commission

are closely cooperating to achieve the targeted goals. It is

expected that results of both projects create new technology

for making artificial robotic organisms self-configured, selfhealing, self-optimizing and self-protecting from a hardware

and software point of view. This leads not only to extremely

adaptive, evolve-able and scalable robotic systems, but also

enables the robot organisms to reprogram themselves without human supervision, to develop their own cognitive structures and, finally, to allow new functionalities to emerge.

The rest of this paper is organized in the following way:

In Section 2 we discuss a new paradigm of symbiotic systems. Section 3 gives an example of the energy foraging

scenario. Sections 4 and 5 briefly mention the hardware and

software challenges, where as Section 6 introduces several

ideas towards evolve-ability of the robot organisms. Finally,

in Section 7 we conclude this work.

2. NEW PARADIGM IN COLLECTIVE

ROBOTIC SYSTEMS

Collective intelligence is often associated with macroscopic

capabilities of coordination among robots, collective decision

making, labor division and tasks allocation in the group [7].

The main idea behind this is that robots are achieving better

performance when working collectively and so are capable

of performing such activities which are not possible for individual robots. The background of collective intelligence is

related to the capability of swarm agents to interact jointly

in one medium. There are three different cases of such interactions:

1. In the first case agents communicate through a digital

channel, capable for semantic messages exchange. Due to

information exchange, agents build different types of common knowledge [8]. This common knowledge in fact underlie

collective intelligence.

2. The second case appears when macroscopic capabilities

are defined by environmental feedback. The system builds a

closed macroscopic feedback-loop, which works in a collective way as a distributed control mechanisms. In this case

there is no need of complex communication, agents interact only by kinetic means. This case if interaction is often

denoted as a spatial reasoning, or spatial computing.

3. The third case of interactions we encounter in nature, when some bacteria and fungi (e.g. dictyostelium discoideum) can aggregate into a multi-cellular organism when

this provides better chances of survival [9]. In this way,

they interact not only through information exchange or spatial interactions, they build the closest physical, chemical

and mechanical interconnections, through the agents still

remain independent from each other.

The first two cases of interactions are objects of extensive

research in many domains: robotics, multi-agents systems,

bio-inspired and adaptive community and so on. However

the practical research in the last case represents essential

technological difficulties and therefore is not investigated

enough. Despite the similarities between a robot swarm and

multi-robot organism, such as a large number of robots, focus on collective/emergent behavior, a transition between

them is a quite difficult step due to mechanical, electrical

and, primarily, conceptual issues [10]. In the following sections we introduces corresponding challenges in more detail.

Now, we believe that research around the third case of

interactions is concentrated on four important questions:

1. Reconfigurability, adaptability and learn-ability of the

symbiotic systems. These issues include flexible and multifunctional sensors and actuators, distributed computation,

scalability, modelling, control and other issues, which are

closely related to the reconfigurable robotic research. The

REPLICATOR project is focused on these points.

2. Evolve-ability of the symbiotic systems, which includes

principles and aspects of long- and short-term artificial evolution and adaptivity as well as exploring and analogies to

biological systems. The SYMBRION project is focused on

these points.

3, 4 Embodiment of evolutionary systems for different environments and medias as well as investigation of information properties of such systems. These points are covered by

other research initiatives and projects.

In this way, the next step in a further research within

the collective robotic community can consist in investigation multi-robot organisms or, in other words, a transition

from robot swarm to a multi-robot organisms. All further

sections are devoted to demonstrate diverse aspects of such

a transition.

3. EXAMPLE: ENERGY FORAGING SCENARIO

In this section we will demonstrate the advantages of symbiotic organization of autonomous robotic systems. We choose

for this purpose an example of energy homeostasis, because

it is applicable to both living and robotic organisms and so

we can draw several analogies between them.

The distinctive property of any living organism is the energy homeostasis and, closely connected, foraging behavior and strategies [3]. The robots, equipped with on-board

63
recharging electronics, can also possess its own energy homeostasis. In this way, when swarm robots get ”hungry”, they

can collectively look for energy resources and execute different strategies in a cooperative energy foraging [11]. In

critical cases robots can even decide to perform individual

foraging, competing with other robots for resources.

The need of energy is a perfect example of natural fitness. If robots that are performing individual strategies find

enough energy, they can survive in the environment. In

turn, this means that these strategies were sufficient enough

to balance these robots energetic budgets. Simultaneously,

other energetically die if their behavioral strategy was poor.

Based on such energy foraging, many of evolutionary approaches for different robotic species can be developed, compared and tested.

However, if there are many robots foraging in the environment, several undesired effects can emerge: (1) the docking

station can become a ”bottleneck” resource that essentially

decreases the swarm efficiency; (2) robots with a high-energy

level can occupy the docking station and block low-energetic

robots. These robots can energetically die (and so decrease

the swarm efficiency); (3) many robots can create a ”crowd”

around a docking station and essentially hinder a docking

approach. This can increase the total recharging time and

makes worse the energetic balance of the whole swarm.

Robots, in pursuing their energetic homeostasis, have only

two possible decisions to make: (1) to execute a current

collective task or (2) to move for recharging. In balancing

these two behaviours, a cooperative strategy may find the

right timing and the right combination between these individual decisions of all robots. Lately, several strategies of

energy foraging for a robot swarm up to 70 swarm agents are

implemented, see Fig. 1. These cover different bio-inspired

approaches [12], [13] and hand-coded strategies [14].

In one of these experiments, a few robots died close to

the docking station and blocked the recharge area (we ”simulated” this in the Fig. 1(b)). Robots that were in front

of this barrier (away from the docking station) finally also

died. This is the limit of functional fitness of swarm robots.

There is no strategy, that allow swarm robots to overpass the

barrier. Only when swarm robots would collectively emerge

new functionality, like ”pass the barrier”, they would solve

the ”barrier problem”.

Thus, an ideal solution for the ”barrier problem” can be

the aggregation of many single robots into one cooperative

multi-robot organism. This way, they can reach the docking

stations by ”growing legs” and stepping over the barrier. In

that case, the robots are helping each other in a cooperative

manner, see Fig. 1(c).

Obviously, such a robotic behaviour is extremely challenging from many viewpoints: Cooperative (symbiotic) robot

systems have many similarities with known robotic research

as e.g. mechanical self-assembling [15] or reconfigurable

robotics [16]. However, the symbiotic form, show in Fig. 1,

essentially differs from this robotic research, namely: (1)

Robots should be capable for autonomous aggregation and disaggregation; (2) Robots in the disaggregate state should possess individual locomotion; (3)

There is no central control neither for disaggregated

state (swarm) nor for the aggregate state (organism); (4) Stand-alone robots should profit from the

aggregation into organism.

The swarm-based approaches, which is underlying the ag-

(a)

(b)

(c)

Figure 1: (a) Docking of a few robots for recharging. Shown is the two-line approach: the first line -

recharging robots, the second line - robots waiting

for recharging; (b) The ”barrier problem” - robots

are separated form docking stations by a barrier; (c)

A possible solution to the ”barrier problem”: swarm

robots form a symbiotic multi-robot organism and

collective pass the barrier.

64
gregation processes, differs primarily from aggregated systems which are studied in the field of ”reconfigurable robotics”.

In the following we consider on-going work with aggregated

(symbiotic) robot organisms.

4. HARDWARE CHALLENGES

The main feature of a modular robot consists in being

composed of several potentially independent modules, with

limited complexity and capabilities, which are able to connect to each other in different configurations, in order to

form a robot with greater capabilities. The global knowledge and the functionalities of the assembled robot generate

by sharing of information and of resources between modules

and by the fundamental capability of self-reconfiguration,

in order to meet the demands of different tasks or different

working environments. As a consequence, the overall functionalities and capabilities of a robotic modular organism

are deeply related to the hardware structure and functions

of its basic composing modules.

At the current stage of development of the projects (both

projects started in 2008), the development of the hardware

represents one of the hardest issues. In general, the concept

of hardware design is as follows:

1. Independence for separate robots, this includes capabilities for communication, computation and sensing as a

stand-alone robot, as well as individual locomotion and energy management.

2. Large computational power of the organism, required

for performing on-line and on-board evolutionary approaches.

3. Heterogeneity of individual robots, which allows their

later specialization within the organism.

4. Rich sensing and communication capabilities of the

organism. The more robots are joined in the organism, the

more functional diversity the organism can demonstrate.

5. Possible higher independency from human in term of

energy, support and maintenance.

The consortia considered many state-of-the-art reconfigurable solutions, such as superBot [17], M-Tran [18], PolyBot [19], molecube [20], HYDRA/ATRON [21] and others, even visited some of these labs for exchange of experience. Currently, we follow three different developmental

lines, which will be later fused into one or two first prototypes.

4.1 Mechanical Challenges

The mechanical design of a robot, which is working together with other robots inside a swarm, differs in several

points from the design of a robot being a part of an organism.

In the first case, criteria like small size, simple kinematics,

simple casing, high mobility and low price define the design

of the robot. On the other hand, a robot inside of a selfreconfigurable organism needs docking elements, high-power

motors to produce enough torque, depending on the design

of the organism one or more independent degrees of freedom and a casing with high stiffness to handle reaction between robots. Within the REPLICATOR and SYMBRION

projects, one of the challenges will be to combine the characteristics of both kinds of robots into one.

In the beginning, there seems to be a few major problems that need to be solved. First of all the robot must

have a docking element capable of handling the stress of several robots docked to it while applying all their forces (e.g.

gravity, reaction, inertia force). Additionally, the docking

element needs to assure the automatic coupling of several

electric contacts needed for information exchange and power

distribution between the robots inside an organism. Beside

technical requirements the docking element should support

the self aggregation of the robots. No matter how the position of two robots to each other is, the docking procedure

should work. Therefore the docking element needs to balance misalignment and displacement to a certain degree. To

increase the amount of possible structures for the organism

and to simplify docking for the robots, all docking elements

will be unisex and there will be at least four docking elements on each robot. Another problem is the mobility of

the robot requested by the swarm based requirements. In

order to guarantee local communication between robots, a

reasonable velocity (i.e. a contacting rate) is needed. The

kind of suitable locomotion is under evaluation.

The general approach in the state of art of modular robotics

is the development of ”cube-like” robotic modules with internal motors, batteries and control. The docking ports are

usually placed on the sides and both locomotion and lifting

abilities are provided mechanically separating the module in

two blocks, able to bend reciprocally. This bending allows

the lifting of attached modules, but often represents the only

locomotion strategy for the robot, that can be quite slow and

complex to control in accuracy and resolution of movement.

Hence, as a new feature in modular robotics, we are currently considering to introduce higher locomotion capabilities, for instance integrating wheels in the modules, giving

more independency to each module. The aim is to fabricate

modules that are firstly conceived as independent robots

rather than ”just” modules to be assembled in a robotic organism. The increase in independency for what concerns

locomotion allows in this way single modules, now robotic

units, to move and explore the environment, rapidly acquiring information about the environment. Subsequently, they

can rapidly reach their neighbours and, as a last process,

engage assembly. Furthermore, wheeled modules could be

used by the robotic organism as ”wheeled feet” in order to

have a faster global locomotion. As advanced feature, the

wheels themselves could be an actuation mechanism (i.e., a

rotational degree of freedom), considering to integrate into

the wheels the docking mechanism. A wheeled-locomotion

approach is characterized by a very high-energy efficiency

on smooth surfaces, but it could show limitation on sandy

or pebbly surfaces and even in facing small obstacles (like

electrical cables, grass, etc.). The first concept in order to

solve this issue consists in moving from a basic mini-rover

configuration with four wheels to a caterpillar-based robotic

unit, able to provide locomotion even on challenging surfaces

and environments.

A differential drive is easy to implement and to control.

However, not every movement is possible. The docking of

two robots in the orientation of their wheel axis is only possible with a non trivial motion sequence. A non-holonomic

drive is capable of positioning the robot everywhere and in

any orientation to another robot, but is difficult to implement in design as well as in control. With at least two

degrees of freedom a movement by crawling is also possible. Unfortunately, this is done by use of the main actuators which consume a lot of power. The optimal solution

depends therefore on the scenario for the robots. At the moment, a crawling like locomotion is likely for the replicator

robot while a mixture between non-holonomic and differen65
tial drive is more suitable for the SYMBRION robot.

These are only two challenges out of many which need

to be solved within the REPLICATOR and SYMBRION

projects, but in the end we will know much more about

suitable design of self aggregating robots.

4.2 Electronic Challenges

The electronic design is a huge challenge due to strong

restrictions of the size of the robot and the complexity of

the hardware design. Each stand-alone robot is equipped

with two processors, one main microcontroller (MCU) and

one shadow microprocessor (CPU, see Fig. 2). The breakdown in microcontroller and microprocessor was deliberately

intended to separate computational tasks within the single

cell.

Core

MCU

Shadow

CPU

RAM+Flash

Sensors/PC/Camera

Upper board

cells CAN cells

I2C

USB

(SPI)

Embedded Linux,

Evolutionary Algorithms,

ANN...

RTOS, Sensor pre-processing,

AIS...

SPI

I2C

SPI

Sensors/PC/ZigBee

USB

Upper board

CELL

HDD

Figure 2: Functional electronic design of modules.

The core microcontroller performs basic functionality (e.g.

sensor pre-processing, running artificial immune system) and

keeps the robot alive. The shadow microprocessor is mainly

responsible for bio-inspired approaches like the genetic algorithms, sensor fusion, ANNs etc. and is more powerful

in comparison to the core processor. Due to higher computational power results in higher energy consumption, the

shadow processor is able to run at different power-down

modes when computational power isn’t needed.

One of the biggest challenges during the electronic design

is the development of the shadow processor module in a

tiny size as well as finding solutions for shared resources like

memory, power and communication capabilities.

5. SOFTWARE CHALLENGES

Beside the hardware challenges, the project is faced with

many software requirements. Because robots can either run

independently, as a swarm, as an organism, or even as a

swarm of organisms, the interaction has to be managed in

an organized and efficient way.

The different layers of software development are shown in

Fig. 3. On the bottom layer there are two different processors, which are able to communicate with each other and

have to be coordinated at the robot level. To cope with

the additional difficulties a swarm or an organism causes, a

middleware-like system is necessary. On top of this abstraction layer high-level control mechanisms and distributed applications can be integrated.

Figure 3: Different layers for software development.

5.1 Robot OS

On the robot level it is necessary to adopt mechanisms

to coordinate data and data flow in a suitable way, and at

the same time it is essential to predict and organize the behaviour of the multitasking system. It is also critical for

the project to deal with the event driven architecture of

the robot especially in respect to the real-time sensor system. For this reason a Real-Time Operating System (RTOS)

builds the base of the software structure. The software architecture of the robot is modular and provides basic functionalities such as creation and termination of tasks and

threads, inter-task communication, inter-processor communication, external event management, and memory allocation. Additionally the robot runtime system has to provide

the middleware system with appropriate interfaces.

5.2 Middleware

Once the robots are aggregated into a more advanced

multi-cellular organism it is essential to have an efficient controlling and coordinating mechanism. Therefore a middleware layer is introduced which defines unified interfaces and

communication services according to the individual robot

capabilities. The distributed middleware controls synchronization processes between nodes, configures and handle the

communication bus (CAN) and manages distributed memory and energy resources. Furthermore it has to provide the

robots with an abstraction layer between the operational

system functions and the high-level controller domain.

5.3 High-level control concepts

Our projects will evaluate and test a variety of different

control-concepts for the single robots as well as for the aggregated high-level robotic organism. Example can be given by

artificial immune and artificial neuronal networks, different

learning mechanisms as well as classical model-based controllers. In the following we describe one of these controllers

- a bio-inspired controller concept which we call ”HormoneDriven Robot Controller” (HDRC). A data-structure that

will hold configuration information for the robot, especially

for the used software controllers of the robotic node, is called

”Genome”in our constortia’s terminology. This Genome will

contain also a set of rules that link the degradation and the

secretion of hormones to the local levels of other hormones.

The secretion of hormones can be triggered by other hormones or by receptors that get activated by receiving environmental stimuli. Hormones can alter the sensitivity of

receptors, trigger activities, modulate certain controllers or

even activate/deactivate whole (sub-)controllers. This way

we expect that a variety of systems can easily evolve:

1. Homeostatic systems: These hormone systems can

66
allow the organism to regulate a variety of internal properties around a homeostatic set point. For example, an robot

”hungry” for light but located in the dark, can increase its

motion level, thus will increase its chance to find a light spot.

2. Adaptive behaviours: Hormones can reflect a change

of state of the environment, thus they can modulate controllers to respond to these environmental changes.

3. Target-oriented behaviours: Hormones with very

fast dynamics (short-term acting hormones) can be even

used to steer robots autonomously towards certain targets

or to actively avoid areas or objects. This can be used in

the previously mentioned foraging-for-energy scenarios.

3. Signal propagation and timing: As hormones are

passed also among the robotic nodes in an aggregated organism, hormones can be used for signal propagation along

the body of this organism. In nature, such systems show

frequently the ability to perform rather well working timing tasks (see for example the synchronization of fireflies

in [2]). We can expect to evolve such signal-propagation

mechanisms also in our aggregated robotic organisms, possibly synchronizing the movement patterns of legs or other

body parts.

To allow the HDRC to evolve the above-mentioned tasks

and to evolve the needed functionality to perform such tasks,

we have to implement a separate hormone controller. This

controller is created from the evolved information in the

Genome and frequently simulates hormone secretions (additions), degradations and diffusion within each robotic node.

Using the available communication capabilities of the robots,

the hormones are exchanged also between the robotic nodes,

thus allowing a diffusion of virtual hormones within the

whole higher-level organism.

Fig. 4 shows two distinct ways how the HDRC can be used

in two different swarm states:

State 1: Fig. 4a shows that each robot is contains several

virtual compartments, which associated with different real

robot ”body parts”. In the case depicted here, each robot

contains 2 lateral, one frontal and one terminal compartment. In the center, there is a fifth (central) compartment

located. Sensors can trigger excretion of hormones into their

corresponding local compartment and actuators can be modulated/affected only by hormone concentrations which are

present in their corresponding compartment. Hormones are

diffused to neighboring compartments and to to the central

compartment. In the depicted case, a light sensor senses an

obstacle to the left of the robot. It triggers the secretion

(addition) of a hormone into this segment, which enhances

the speed of the associated left motor. By diffusion, the

same hormone reaches also the right compartment, where

it can decrease the rotation speed of the right motor: The

robot turns to the right. A central luminance sensor (central

compartment) can trigger the secretion of another hormone,

which generally increases motor speed on both sides: The

robot drives (forages) faster in brighter illuminated areas.

State 2: Fig. 4b shows a totally different usage of the

HDRC: One robot started to call other robots for aggregation. It secrets a specific ”head-marking” hormone. This

hormone is secreted only in the first robot that starts the

aggregation. Due to the diffusion process and the increasing

chain length, the concentration of this hormone decreases,

as the robotic organism gets larger. By using this gradient

as a source of information for the ”tail robots”, the organism

can be limited to certain sizes and there is always a gradient

Figure 4: (a) Schematic drawing of a hormonedriven robot controller (HDRC) performing an

obstacle-avoidance behaviour. Receptors can trigger hormone secretions. these hormones can differ

through several virtual body compartments inside of

a single robot. Hormones can switch on or off actuators, modulate actuator function or interfere with

other hormones; (b) Several robotic nodes are coupled together to a higher-level organism. Simulated

hormones are floating through the ”body”, forming hormone gradients. In the picture, a dedicated

”head”-hormone is shown. These hormone gradients

can support the formation of aggregated organisms

out from the ”fuzzy” swarm state, which is formed

by many free-driving or free-walking robots.

inside of the organism that points towards the ”head”. This

gradient information can also be important for coordinating

body movements.

5.4 Simulation Framework

To test, compare and verify different robot designs, different organism configuration and the controllers in a quick

and cheap way, a simulation environment needs to be implemented. The simulation should offer an easy and fast

way to create a test environment and to design some basic

robot architectures to test the availabilities the robot might

have. Later the simulation can be used to test different organism configurations and to verify the different controllers.

Furthermore, the simulation can be applied in long term scenarios to explore biologic mechanisms like evolutionary and

genetic algorithms, collective and symbiotic behaviour and

neuronal networks.

In the REPLICATOR and SYMBRION projects we will

use Delta-3D for the simulation framework, see Fig. 5. It offers lots of interfaces and has already successfully been used

in other simulations. The aim is to simulate the physics of

the single robots, as well as that one of a whole organism.

67
Figure 5: Screenshot of the Simulation Environment

Using Delta 3D.

3D-models from CAD-programs can easily be loaded into

the environment and without any effort a robot model can

be created in the simulation. Different robot configurations

like form, size and the position and orientation of the joints

of the robot can be easily created and tested within the environment. Additionally the simulation needs to integrate the

controller into the environment without modifying it with

the aim that the robot will behave in the simulation nearly

the same as in the real environment. Therefore a hardware

abstraction layer (HAL) needs to be strictly specified, which

will offer the same functionality for the actual robot and the

simulated one. A robot controller will only use the functionality of the HAL, so that a robot, developed in a simulation

environment, will run on a real robot and vice versa.

As the requirements to the simulation will grow with the

complexity of the controller, running the simulation on just

one computer or even just on a single core won’t be sufficient enough. Therefore a distributed simulation will be

mandatory. For this purpose Delta-3D offers an interface to

the High Level Architecture (HLA), a general purpose architecture for distributed computing. Using this architecture

the simulation can be executed on several computers having

different platforms located within a local area network or

connected through the internet as well.

6. TOWARDS EVOLVE-ABILITY OF THE

ROBOT ORGANISM

Within the projects, the creation of evolvable or otherwise

adaptive software and hardware is the main focus. However,

from the conceptual point of view, achievement of evolveability for the robot organism is planned in two complementary ways, which we call bio-inspired (or bio-mimicking) and

engendering-based approaches.

6.1 Bio-inspired/bio-mimicking approach

Any bio-inspired approach is based on analogies to living

organisms and is carried out by the biological partners in

our consortia. Our bio-inspired control algorithms use neither any global point of information nor any form of complex

knowledge. Our algorithms are stable to a wide range of environmental conditions and are extremely robust. Therefore,

the bio-inspired strategies in projects are going to draw advantage from the well-known robustness/simplicity as well

as from the plasticity/adaptability derived from natural systems. Our goal is to create stable, robust and adaptable

robotic organisms. Here we will investigate a variety of concepts, such as:

1. Genome: All robotic organisms will carry one or

several Genomes. A Genome is a collection of genes, which

carry information about controller structure and controller

dynamics. A gene can be a simple part of a blueprint, which

”depicts” a part of the final controller. But a gene can also

work as a rule, which is used to ”construct” parts of the

final controller. In the latter case, there can be interferences

between different genes, thus competition or cooperation can

arise also on the genetic level. A self-organized process can

be established which will be able to create a flexible, but

robust controller structure.

2. Controller: We will investigate several controller

types, ranging from rules-based controllers, to Evolvable

Artificial Neural Networks (EANN), to hormone-based controllers and to even hand-coded controllers that execute handoptimized (modular) parts of the whole organism’s behavioural

repertoire.

3. Sexuality/Reproduction: We plan to enhance and

to speed-up the dynamics of artificial evolution by implementing virtual-reproduction of robots. A separate process

will allow to remove controllers from the least fit robots and

to re-initialize them with mixtures (interbreeds) of the controllers of more fit robots. We will also investigate the advantages of sexual reproduction in such scenarios.

4. Embryology: To allow well-ordered controllers to

emerge from the information stored in the Genome, we will

mimic embryological processes, driven by a virtual hormone

system.

6.2 Engineering-based approach

The engineering-based approach is complementary to the

bio-inspired one and focuses in such issues as learning, distributed decision making, navigation and so on. Generally,

consortium focuses on three following approaches (these approaches are closely connected so that finally it will be a

kind of hybrid framework):

1. On-line learning. On-line learning is based on the

behavior level and uses automatically generated feedback.

The feedback comes from internal, external and virtual sensors. Some direct feedback can be sensed through visionbased subsystem, by using FRID-based identification or localization technologies, by using smart laser scanner, sound,

light, humidity, temperature, internal energy sensor and other

sensors. It is intended to use middleware and sensor-fusion

approach to generate complex non-direct feedbacks through

virtual sensors. Since off-line mechanisms can hardly be applied to real robots, the challenge of the proposed approach

is to perform non-supervised learning without any off-line

mechanisms (or at least with a minimum of them). This

can be achieved by combining evolving computation with

rewards/feedback/fitness calculated on-line. Therefore the

whole approach can be named ”on-line learning”.

2. Evolutionary computation. High computational

power of the system allows running on-line and on-board

such well-known approaches as genetic programming (GP)

(e.g. [22]), Genetic Algorithms (GA) (e.g. [23]). To avoid

the problems posed by a huge search space, we intend to

integrate limitations, originating from hardware platform.

Another set of problems we are aware of are the fitness

functions required for these algorithms. These fitness functions are very difficult to calculate based only on local sensor

68
data. Moreover these functions are evaluated extremely delayed because the organism mostly assess their fitness after

accomplishing the task.

3. Approaches from the domain of Distributed

Artificial Intelligence (DAI). On-line learning as well as

GA/GP include diverse aspects of DAI such as a distributed

knowledge management, semantic information processing,

navigation and actuation in the environment, planning, sensor fusion and others. Development and implementation of

these approaches is an important step towards evolve-ability

of the robot organisms.

7. CONCLUSION

In this short paper we made on overview of two large

European projects, dealing with a new paradigm in collective systems, where the swarm robots get capable of selfassembling into a single symbiotic multi-robot organism. We

introduced an energy foraging scenario for both robot species

and demonstrated that a transition between collective and

symbiotic robot forms represents a very hard problem. It involves not only hardware and software issues, but also very

basic questions being also open not only in biological but also

in engineering sense. We demonstrated the main hardware

and software challenges and the road-map how to achieve

the evolve-ability of the robot organisms.

8. ACKNOWLEDGEMENT

REPLICATOR and SYMBRION projects are funded by

European Commission within the 7th framework programm.

We want to thank ”euCognition”1 for supporting your involvement in the conference.

9. REFERENCES

[1] E. Bonabeau, M. Dorigo, and G. Theraulaz. Swarm

intelligence: from natural to artificial systems. Oxford

University Press, New York, 1999.

[2] S. Camazine, J-L. Deneubourg, N.R. Franks, J. Sneyd,

G. Theraulaz, and E. Bonabeau. Self-Organization in

Biological Systems. Princeton University Press,

Princeton, NJ, USA, 2003.

[3] D.W. Stephens and J.R. Krebs. Foraging Theory.

Princeton University Press, 1987.

[4] E. Sahin. Swarm Robotics: From sources of inspiration

to domains of application. Springer-Verlag,

Heidelberg, Germany, 2004.

[5] S. Kornienko, R. Thenius, O. Kornienko, and

T. Schmickl. Re-embodiment of honeybee aggregation

behavior in artificial micro-robotic system. Adaptive

Behavior (accepted for publication).

[6] S. Kornienko, O. Kornienko, and P. Levi. Ir-based

communication and perception in microrobotic

swarms. In Proc. of the IROS 2005, Edmonton,

Canada, 2005.

[7] G. Weiss. Multiagent systems. A modern approach to

distributed artificial intelligence. MIT Press, 1999.

[8] J.Y. Halpern and Y. Mosesi. Knowledge and common

knowledge in a distributed environment. J. of the

Association for Computer Machinery, 37(3):549–587,

1990.

1http://cordis.europa.eu/ist/cognition/index.html

[9] H. Haken. Synergetics: An introduction, third edition.

Springer-Verlag, New York, 1983.

[10] S. Kornienko, O. Kornienko, A. Nagarathinam, and

P. Levi. From real robot swarm to evolutionary

multi-robot organism. In Proc. of the CEC2007,

Singapure, 2007.

[11] S. Kornienko and O. Kornienko. Collective energy

homeostasis in a large-scale micro-robotic. Robotics

and Autonomous Systems (under resubmitting).

[12] D. H ̈abe. Bio-inspired approach towards collective

decision making in robotic swarms. Master Thesis,

University of Stuttgart, Germany, 2007.

[13] T. Kancheva. Adaptive role dynamics in energy

foraging behavior of a real micro-robotic swarm.

Master Thesis, University of Stuttgart, Germany,

2007.

[14] A. Attarzadeh. Development of advanced power

management for autonomous micro-robots. Master

Thesis, University of Stuttgart, Germany, 2006.

[15] A. Ishiguro and T. Maegawa. Self-assembly through

the interplay between control and mechanical systems.

In Proc. of IEEE/RSJ06 Int. Conf. on Intelligent

Robots and Systems, pages 631–638, Beijing, China,

2006. IEEE.

[16] S. Murata, K. Kakomura, and H. Kurokawa. Docking

experiments of a modular robot by visual feedback. In

Proc. of IEEE/RSJ06 Int. Conf. on Intelligent Robots

and Systems, pages 625–630, Beijing, China, 2006.

IEEE.

[17] Wei-Min Shen, Maks Krivokon, Harris Chiu, Jacob

Everist, Michael Rubenstein, and Jagadesh Venkatesh.

Multimode locomotion for reconfigurable robots.

Autonomous Robots, 20(2):165–177, 2006.

[18] Haruhisa Kurokawa, Kohji Tomita, Akiya Kamimura,

Shigeru Kokaji, Takashi Hasuo, and Satoshi Murata.

Distributed self-reconfiguration of m-tran iii modular

robotic system. Int. J. Rob. Res., 27(3-4):373–386,

2008.

[19] Alex Golovinsky, Mark Yim, Ying Zhang, Craig

Eldershaw, and David Duff. Polybot and

polykinetic/spl trade/ system: a modular robotic

platform for education. In ICRA, pages 1381–1386.

IEEE, 2004.

[20] V. Zykov, E. Mytilinaios, B. Adams, and H. Lipson.

Self-reproducing machines. Nature, 435(7039):163–164,

2005.

[21] David Johan Christensen, Esben Hallundbok

Ostergaard, and Henrik Hautop Lund. Metamodule

control for the atron self-reconfigurable robotic

system. In Proc. of the IAS-8, pages 685–692,

Amsterdam, 2004.

[22] J. Koza. Genetic programming: on the programming of

computers by means of natural selection. MIT Press,

Cambridge, Massacgusetts, London, England, 1992.

[23] M. Srinivas and Lalit M. Patnaik. Genetic algorithms:

A survey. Computer, 27(6):17–26, 1994.

69
Virtual Agent Modeling in the RASCALLI Platform

(Special Session on EU-projects)

Christian Eis

Research Studios Austria

Vienna, Austria

christian.eis@

researchstudio.at

Marcin Skowron

Austrian Research Institute for

Artificial Intelligence

Vienna, Austria

marcin.skowron@ofai.at

Brigitte Krenn

Austrian Research Institute for

Artificial Intelligence,

Research Studios Austria

Vienna, Austria

brigitte.krenn@ofai.at

ABSTRACT

The RASCALLI platform is both a runtime and a development environment for virtual systems augmented with cognition. It provides a framework for the implementation and

execution of modular software agents. Due to the underlying software architecture and the modularity of the agents,

it allows the parallel execution and evaluation of multiple

agents. These agents might be all of the same kind or of

vastly different kinds or they might differ only in specific

(cognitive) aspects, so that the performance of these aspects

can be effectively compared and evaluated.

Categories and Subject Descriptors

I.2.11 [Distributed Artificial Intelligence]: Intelligent

agents; D.2.11 [Software Architectures]: Domain-specific

architectures; K.6.3 [Software Management]: Software

development

General Terms

Design, Experimentation, Measurement

Keywords

Cognitive agents, Agent modeling, Agent evaluation, Open

source software

1. INTRODUCTION

This paper gives an overview of the architecture and functionality of the RASCALLI platform, developed as part of

the RASCALLI project1. In this project, the platform is

used as the underlying software environment for the development and execution of so called RASCALLI (Responsive

Artificial Situated Cognitive Agents that Live and Learn on

the Internet). It provides the facilities for user-agent and

1European Commission Cognitive Systems Project FP6-

IST-027596-2004 RASCALLI.

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personal or classroom use is granted without fee provided that copies are

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bear this notice and the full citation on the first page. To copy otherwise, to

republish, to post on servers or to redistribute to lists, requires prior specific

permission and/or a fee.

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA.

Copyright 2008 ACM 978-1-60558-293-1 ...$5.00.

agent-agent communication and serves as a testbed for the

evaluation of various incarnations of the agents that use different sets of action-perception tools, action selection mechanisms and knowledge resources. The platform supports

a modular development style, where agents are assembled

from small re-usable building blocks. Agents of different

kinds and configurations can run simultaneously within a

single platform environment. This enables the evaluation

and comparison of different agents as well as the evaluation

of whole agent communities.

The paper is organized as follows: Section 2 describes the

general objectives of the RASCALLI project to the extent

that they are relevant for the design and implementation of

the RASCALLI platform. Section 3 gives a brief overview

of related platforms and methodologies. The RASCALLI

platform itself is then described in section 4, and section 5

gives an overview of the agent components implemented in

the RASCALLI project. Finally, section 6 explains how the

RASCALLI platform can be used for agent evaluation.

2. PROJECT OBJECTIVES

The project RASCALLI aims at the development of virtual agents that perform tasks related to accessing and processing information from the Internet and domain-specific

knowledge bases. RASCALLI agents, further referred to

as Rascalli, represent a growing class of cooperative agents

that do not have a physical presence, but nevertheless are

equipped with major ingredients of cognition including situated correlates of physical embodiment to become adaptive, cooperative and self improving in a virtual environment, given certain tasks.

The project objectives cover the following topics: development of a computational framework for the realization

of cognitive agents providing intelligent assistance capabilities; cognitive architecture and modeling; perception and

action; reasoning; learning; communication; agent-to-agent

and agent-to-user interfaces. The Rascalli answer questions

of their users, learn the users’ preferences and interests, and

use this knowledge to present the users with new, interesting information. The agents exist in an environment consisting of external knowledge sources on the Internet, such

as search engines and RSS feeds, and domain-specific knowledge bases. They communicate with their users as well as

with other Rascalli.

Rascalli are developed in a modular fashion, which allows

individual agents to be built from different sets of components. This enables e.g. the creation of agents which are “ex70
perts” in different knowledge domains. During its life-time,

each agent adapts to its user’s interests and thus further specializes in a certain sub-domain and evolves in accordance

with the user’s preferences. This results in a community of

specialized agents, which can communicate with each other

to provide requested information to their users.

The modular approach enables the evaluation and comparison of different sets of components, including different

cognitive aspects (e.g. different learning strategies) by executing multiple Rascalli in the same environment and evaluating their performance (e.g. by means of user tests).

For the realization of these objectives, system integration

turned out to be a major roadblock, due to the following

reasons:

• Even though Java was chosen as the main implementation language for the project, some project partners

have no or little experience with Java development.

• In order to avoid re-implementation, we had to integrate existing components from previous projects.

These components are based on a wide range of technologies, such as different programming languages (e.g.

Perl, Java, Lisp) and even native binaries for different

operating sytems (Linux and Windows).

• Initial attempts at providing a development environment that integrates all of these components and can

be replicated on each developer’s machine proved to

be difficult to use and keep up-to-date.

Based on the project objectives and constraints outlined

above, we arrived at the following set of requirements for

our software platform:

• Support the execution of various agents, belonging to

different users.

• Support agent-to-agent and agent-to-user communication.

• Allow developers to implement diverse agents based on

shared components (this also means that multiple versions of each component can exist at the same time).

• Integrate external and legacy components with minimal effort.

• Build agents in a modular, component-based fashion.

• Build the platform itself in a component-based, extensible fashion.

3. RELATED WORK

Research into related work has been conducted in multiple directions, including multi-agent platforms, as well as

platforms and development methodologies for cognitive systems. While many such platforms and methodologies exist,

none of them meets the requirements set for the RASCALLI

platform.

3.1 Multi-Agent Platforms

We have investigated FIPA2 compliant agent platforms,

such as JADE3 [1], which is a Java-based middleware for

multi-agent systems. However, these systems mostly focus

on distributed systems and communication issues. Also, the

RASCALLI platform is not a multi-agent system in the traditional sense, where agents are independent components

of a larger application, working for a common goal. Instead, Rascalli are complete individual entities that simply

happen to share the same environment and may communicate with each other, if they wish. Furthermore, none of

the investigated agent platforms supports the development

style targeted by the RASCALLI platform, where multiple

agent architectures and agent definitions, as well as multiple

versions of agent components co-exist in a single platform

instance.

It might be interesting future work to implement or integrate some of the FIPA standards (such as the Agent Communication Language) with the RASCALLI platform.

3.2 Agent Development Methodologies and

Frameworks

As an example of an agent development methodology, Behavior Oriented Design (BOD)4 [2] supports the implementation of agents based on an iterative development process

and a modular design. However, it does not provide much

of a runtime environment. Therefore, BOD does not really compare to the RASCALLI platform, even though both

advocate a modular approach. It would, however, be interesting to implement an agent architecture based on BOD

within the RASCALLI platform and thus use the platform

as a runtime environment for BOD agents.

As for development frameworks, AKIRA5 [7] aims to create a C++ development framework to build cognitive architectures and complex artificial intelligent agents. However,

like the FIPA multi-agent platforms, it targets different requirements than the RASCALLI platform. It might be interesting to consider exploiting some of AKIRA’s concepts

within the RASCALLI platform.

4. RASCALLI PLATFORM

This section provides an overview of the RASCALLI platform. We start with a set of features supported by the platform in order to fulfill the requirements listed above. Then

we describe the software architecture of the platform and

explain how this architecture supports the various platform

features.

4.1 Platform Features

Multi-Agent: The platform supports the concurrent execution of multiple agents, including agents of the same

kind, as well as agent of different kinds, ranging from

very similar to vastly different.

Multi-User: Each agent has a single user (but one user

may have several agents).

2http://www.fipa.org/

3http://jade.tilab.com/

4http://www.cs.bath.ac.uk/ai/AmonI-sw.html

5https://sourceforge.net/projects/a-k-i-r-a/

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Figure 1: Platform Layers

Communication: Agent-to-agent communication can be

implemented on the Java level, since all agents run

within a single runtime environment. Alternatively,

agents can communicate via instant messaging (this

opens the possibility to use multiple, distributed platform instances). Several channels for agent-to-user

communication have been implemented (currently a

proprietary protocol for the 3D client interface, Jabber instant messaging and email).

Component-Based Architecture: All the parts that are

required to set up a specific agent are developed in a

component-based fashion so that individual Rascalli

can be assembled from these components in a Legolike manner.

Extensibility: The platform itself is built in a componentbased fashion and can therefore be easily extended,

even at runtime.

Distributed, Concurrent Development: A single platform instance is shared by all developers for implementing different agents, with minimal interference between individual developers.

Multi-Version: In order to support the concurrent development of different kinds of agents based on shared

components, the platform supports the execution of

multiple versions of the same components at the same

time.

System Integration: External (and possibly legacy) components need to be integrated only once and are then

available to all agents running in the platform in an

easy-to-use manner. Since only one instance of the

platform is required, there is no need to duplicate the

entire software environment on multiple developer machines.

4.2 Platform Architecture

The RASCALLI platform is implemented as a layered architecture (Fig. 1).

4.2.1 Infrastructure Layer

The Infrastructure Layer contains basic tools and components used in the RASCALLI project. Specifically, these are

Java, Maven6 and OSGi7. In addition, this layer contains

custom-made development and administration tools for the

RASCALLI platform, such as user interfaces for agent configuration and deployment tools.

The most important feature of this layer is the use of

OSGi, which implements a dynamic component model on

top of Java. This means that components can be installed,

6http://maven.apache.org/

7http://www.osgi.org/

Figure 2: Agent Layer

started, stopped and uninstalled at runtime. Furthermore,

dependencies between components are managed by OSGi in

a fashion that allows the execution of multiple versions of a

single component at the same time. Finally, OSGi provides a

framework for service-based architectures, where each component can provide services to other components, based on

Java interface specifications.

The use of OSGi thus enables the platform features ’multiversion’ and ’extensibility’, and supports the implementation of a ’component-based architecture’ in the upper two

platform layers.

’Distributed, concurrent development’ is enabled by Maven and some custom-made components on this layer.

4.2.2 Framework Layer

The Framework Layer comprises general platform services

and utilities employed by the Rascalli, including communication (user to agent, agent to agent), event handling, RDF

handling, technology integration (Perl, web services, etc.),

and various other platform services.

The services on this layer implement the ’multi-agent’,

’multi-user’ and ’communication’ features of the platform.

Furthermore, this is the place where ’system integration’

takes place. External components are integrated and made

available to the components of the Agent Layer as OSGi

services, which can then be accessed on the Java level.

4.2.3 Agent Layer

The Agent Layer is the application layer of the platform

and contains the implementation of the actual agents. It

is designed to support the development and execution of

multiple agents of different kinds as required by the project

objectives. This layer consists of the following sub-layers:

Agent Architecture Layer: An agent architecture is a

blueprint defining the architectural core of a particular type of Rascalli. More precisely, it sets the roles

of agent components and provides means for defining

and assembling a specific agent. The architecture can

also contain implementations of common components

shared by all agent definitions.

Agent Component Layer: Contains implementations of

the roles defined on the Agent Architecture Layer.

Agent Definition Layer: An agent definition is an assembly of specific components of the Agent Component

72
Figure 3: MBE agent architecture

Layer of a specific agent architecture. Different agent

definitions for the same agent architecture might contain different components for certain roles.

Agent Instance Layer: Contains the individual agent instances. Each Rascallo is an instantiation of a specific

agent definition.

Fig. 2 gives a (simplified) example of an agent architecture (the Mind-Body-Environment architecture, see section

5). The Agent Architecture Layer defines two roles, Mind

and Tool, and implements an agent component (Action Dispatcher) shared by all agent definitions. The Agent Component Layer contains two implementations of the Mind role,

as well as two Tools. Based on this architecture, two agent

definitions combine each of the Mind implementations with

the available Tools and the Action Dispatcher into different

kinds of agents. Finally, a number of agent instances are

shown on the Agent Instance Layer.

5. AGENT COMPONENTS

This section gives an overview of the agent components

which have been implemented in the RASCALLI project

(for more detailed information see [10]). RASCALLI agents

are currently based on a reactive agent architecture with

a perception-action loop. This agent architecture is called

Mind-Body-Environment architecture, because each agent

has a central control unit (Mind), which perceives and acts

on the Environment via a set of sensor and effector tools

(Body), as shown in Fig. 3.

The Environment comprises the agent’s user, other agents,

Internet services and domain-specific knowledge bases. The

agent perceives its environment (via a set of perception sensors, implemented as software tools) as a set of virtual entities with their own characteristics and properties. These

include strings of written language originating from the user

or extracted from HTML documents, markup tags, information about the accessibility of various Internet and local

tools and resources, user feedback, etc. Therefore, the agent

has to deal with a dynamic environment i.e. evolving content of the websites, permanent or temporary inaccessibility

of Internet services, appearance of new content or services,

changes in the user preferences and interests, as well as the

natural language input from the user and the web-pages.

Similarly, all actions of an agent in its environment are performed on the above introduced set of entities.

The Body contains components called Tools, which serve

as sensors (Perception Layer) and effectors (Actuator Layer).

A specific agent definition may contain an arbitrary subset

of the available Tools, but of course, the chosen Mind component must be able to deal with the selected Tools. Some

of the available Tools are:

• T-IP4Dual, T-IP4Simple and T-IP4Adaptive,

Input Processing Tools transform natural language and

user feedback inputs into categorized information useable by the respective Mind components, and serve as

a Perception Layer of an agent.

• T-MMG, for generating multi-modal output to the

user. The Multi-Modal Generation Component provides a middle-ware functionality between generated

agent output and the user interfaces. The generation

component implements a template-based approach (in

form of Velocity templates) by encoding vocabulary,

phrases, gestures etc., which can be combined with

the output of the RASCALLI Tools and context data.

The use of Velocity8, a template generation engine, allows templates to be designed and refined separately

from the application code.

• T-QA, a general purpose open-domain question answering system (based on the work described in [8],

[9]) is used in the RASCALLI platform to provide answers to the user factoid-type questions expressed in

natural language.

• T-Nalqi, a natural language database query interface.

The Tool is used in the RASCALLI platform for querying the databases accessible to the Rascalli, in a search

for instances and concepts that can provide answers to

the user questions. The component analyses natural

language questions posed by the user and retrieves answers from the system’s domain-specific databases.

• T-RSS, provides a mechanism for Rascalli to retrieve

current information that might be of interest for the

user.

• T-Wikipedia, an interface and analysis Tool for Wikipedia.

The Mind component performs action selection, based on

the current input from the environment and the agent internal state. It can also make use of supporting services, for

example a user/agent modeling service. The following Mind

components are being developed in the RASCALLI project:

• Simple Mind, which performs action selection with

a simple rule-based mechanism. These rules match to

specific cues in the input data arriving from sensor

channels. ’Simple Mind’ extracts relevant information

and passes this information on to the appropriate effector tool. Even though seemingly non-trivial behavior

can be accomplished through a series of interactions of

the Simple Mind and the available tools, the Simple

Mind does not contain any cognitive aspects such as

memory or learning.

8http://velocity.apache.org

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• DUAL Mind, which incorporates the DUAL/AMBR

([5], [6]) cognitive architecture for action selection. It

includes a long term memory (LTM) where general

and episodic knowledge is stored, and a working memory (WM) constituted by the active part of LTM, perceptual input and goals. The DUAL mind operates

only on represented knowledge and has only a mediated connection to the body and the environment.

Thus it contains a partial, selected representation of

the environment at an abstract conceptual level and

experiential memories related to specific episodes like

organization of the interaction of an agent with its environment.

• Adaptive Mind, a machine learning based classification driven action selection mechanism. Based on

the available knowledge, including the perception of

an input situation, the agent finds a set of actions

that can be applied to a given input situation. The

selection of a particular action is based on the similarities with other actions the agent had successfully

performed in the past, i.e. received positive feedback

from the user. The action selection classifiers are implemented as Maximum Entropy models [4]. The data

used for training the classifiers represents an input situation in terms of entities from the environment perceived by the agent, an action applied to this situation

and the feedback obtained from the user.

RASCALLI agents come with a variety of user interfaces

comprising a 3D client featuring an embodied conversational

character [3] (ECA-UI, see Fig. 4 and 5), a Jabber instant

messaging integration, a web-based user interface (Web-UI)

and two domain-specific, special purpose interfaces which

allow the user the explore in a playful way the domainspecific knowledgebases accessible to the currently implemented Rascalli. The Web-UI9 mainly serves for user registration, download of the 3D-client and specification of Internet resources (URLs and RSS-feeds) that are considered

by the user as important to be monitored by the agent.

The agents use the Web-UI to present list-like information

to the user, and more generally all information not well

suited for presentation by means of synthesized speech. The

ECA-UI, on the contrary, specializes on virtual human-tohuman dialogue. In order to avoid the bottelneck imposed

by speech recognition, user input is restrained to utterances

typed into a small text window and to pressing buttons in

order to praise or scold the agent. The user is expected

to ask domain-specific questions but may also engage in a

chatterbot-type of conversation with the ECA. To do this

the Rascalli make use of ALICE chat bot technology.10

The knowledge sources are a music database featuring

songs and albums of more than 60,000 singers/musicians

and a database providing background information on musical artists such as their family relations, religion, track

record, band membership etc.11

Based on these components, multiple agent definitions

have been conceptualized and developed, including the initial implementation of an agent with a basic set of tools

9http://intralife.researchstudio.at/rascalli/ 10http://www.alicebot.org/downloads/programs.html 11See http://rascalli.researchstudio.at/ and

http://rascalli.dfki.de/ontology/ for browsing the data.

(sandbox for testing the system components and their integration), an agent utilizing an implementation of the DUAL

cognitive architecture as central control unit, and a Smart

Music Companion. Using those various incarnations of the

agents implemented in the RASCALLI platform the performance (in terms of user satisfaction) can be compared and

evaluated.

6. AGENT EVALUATION

In the following, we first give an overview of evaluation

scenarios supported by the RASCALLI platform in general

and the currently implemented Rascalli in particular. We

then give a more detailed account of an evaluation scenario

the goal of which is to investigate how the use of cognitive

aspects in an agent can improve the user experience.

6.1 Evaluation Scenarios

We distinguish three kinds of scenarios:

1. Automated performance measures: The high modularity of the platform eases the integration of automated

performance measures with existing and future agent

architectures. For example, one could easily measure

the time an agent needs to fulfill a given task, as well

as the accuracy with which an agent performs certain

tasks.

2. Data mining from user activity logs: All user activities

are logged in the platform including user id, agent id,

timestamp and activity type. These data can then be

evaluated employing data mining techniques and other

quantitative evaluation methods, in order to identify

prevalent usage patterns of individual users and across

different users, as well as different kinds of agents.

3. User testing: We distinguish two kinds of user testings. The one are studies where users interact with

an agent for a short time to fulfill a certain, narrowly

defined task. The other one are studies where users

interact with their agents more freely for a longer period of time. While with the former the focus lies on

testing specific aspects of the system and the related

human-computer interaction, the latter address more

general questions about what makes an agent a suitable companion for its user, which interfaces support

which tasks and how the interaction of the user with

the agent and his/her attitude towards, his/her liking and understanding of the companion changes over

time.

As there are currently no automated performance measures built into the RASCALLI platform, and the platform

has not yet been made accessible to a broader public and

thus we still lack suffient amounts of usage data for applying

data mining techniques, we will concentrate in the following

on user testing. Due to its modularity, the platform allows

us to experiment with agents being placed in the same environment, but assembled from different internal building

blocks and therefore are equipped with different perception

and action capabilities as well as decision making strategies.

A male (Fig. 4) and a female (Fig. 5), human-like version

of the 3D character have been implemented. Both characters are built on the basis of the same body model and are

equipped with a similar set of gestures and facial expressions.

74
Figure 4: ECA user interface (male)

Figure 5: ECA user interface (female)

They are also comparable as regards their appearance, both

are designed to fit a pop-rock scenario. The identity of the

characters except for gender related optical features allows

us to study effects that may be attributed to different perception of gender by simply switching between the male and

female character whereas all other parameters in the system are kept the same. The RASCALLI system enables us,

without further programming, to experiment with all kinds

of settings where we let a user interact with or train his/her

agent making use of either the male or the female version of

the 3D character and then switch to the opposite sex.

The availability of two conceptually different, complementary UIs for user-agent communication, i.e., the Web-UI for

standard windows and menu-based human-computer interaction and the ECA-UI for interaction closely related to human multimodal dialogue, is a valuable prerequisite to investigate user preferences for different modes of interaction

and social implications of human-computer interfaces.

At the time of writing two user studies are completed: the

one (S1) concerning the liking and evaluation of individual

users engaging in a prescripted question-answer communication with the male Rascalli character, the other one (S2)

is a study concerning the usability of the interface to the

music data. Two further user studies are under preparation. The one (S3) is a replication of the question-answer

study employing the female character instead of the male

one. Whereas the previously mentioned studies are all onetime encounters with the system, the second one (S4) of

the studies under preparation is a longer-term study where

the users interact with and train their agents over a longer

period of time, with user assessments at the beginning, at

several intermediate stages and at the end of the agent-user

collaboration period. Amongst others, we are interested in

changes over time of the users’ liking of their agents, their

expectations on the performance of their agents, their accounts of trust, and their strategies to adapt to their agents

in order to achieve/satisfy their information requirements in

collaboration with their agents.

In particular, we prepare two variants (narrow and broad)

of the longer-term study. In the narrow study (S4.1), the

task is to train the agent as good as possible to monitor

RSS-feeds for a specific topic of interest. To do so, the users

are asked to identifiy and sharpen a topic of interest such

as artist, group, genre, song, album etc. by exploring the

music-related knowledge of their agent utilizing the agent’s

domain-specific interfaces. In addition, they are asked to

inform the agent about preferred Internet sources by specifying respective RSS feeds through the Web-UI. The agent

will then monitor the feeds and alert the user when encountering relevant information making use of a Jabber client.

In the broad study (S4.2) the users are left much more unguided. Other than in S4.1 where the users are confined to

the two domain-specific interfaces and the Web-UI, in S4.2

they have access to all UIs. The users are more generally

informed that the agents have some domian-specific knowledge about popular music and besides can access the Internet. Depending on what information the users frequently

access, which Internet sources they specify, and which feedback (praise, scolding) they give to their agents, the agents

will adapt to the users’ interests and aim at providing more

related information. The more effort the users invest in

training their agents, the better the agents should become

in providing the users with new information relevant to the

users’ interests.

6.2 Evaluation Example: Use of Cognitive Aspects in an RSS Feed Filtering Scenario

We make use of a simple scenario for RSS feed filtering to

illustrate the platform’s capability to augment the agents’

abilities by incorporating cognitive aspects into processing.

Since the different agents can exist at the same time in the

same environment and thus be subject to the same external

influences, they can be reliably compared and evaluated.

Recall: In the RSS Feed Filtering scenario, the agents’

task is to provide their users with (potentially) interesting

information gathered from music-related RSS feeds on the

Internet. The users train their agents according to their

interests, thus creating an agent profile containing relevant

keywords such as artist names, song names and genre names.

The users also provide RSS feed URLs to their agents, which

the agents then query for new information.

The research question for this simple scenario is whether

certain properties of an agent improve the overall user satisfaction (as measured by the rate of false positives and negatives). Therefore, in addition to the basic keyword-based

filtering of RSS feeds, the following elements can be added

to a particular agent:

• The ability to find similar agents (agents with a similar

75
agent profile) and consider those agents’ RSS feeds in

addition to the ones provided by its own user. This

essentially extends the agent’s search space.

• The ability to find items (artists, songs, etc.) similar

to the ones specified in the agent profile. These items

are then added to the filter keywords, thus extending

the agent’s search criteria.

The services required to perform these tasks (finding similar agents, finding similar artists, etc.) are provided by the

RASCALLI framework and made available to the agents as

additional Tools in the action and perception layers.

This setup allows us to create and compare four agent definitions, containing neither of the two features, one of them,

or both. For the evaluation, different users are equipped

with one of the available types of agents. The users can

then identify false positives and negatives.

Obviously, this example could be implemented without a

complex system such as the RASCALLI platform. However,

even in this simple case the platform has some advantages

to offer:

• Components can be shared between agents. For example, the service to find similar agents is an external web

service, which is made available within the platform as

a simple OSGi/Java service.

• The platform provides a single runtime environment

for all the agents (there would be multiple agents of

each kind), so that inter-agent communication (for exchanging RSS feed URLs) can be easily implemented.

7. CONCLUSIONS

The RASCALLI platform meets a unique set of requirements, that is not targeted by any of the investigated platforms or methodologies. In particular, it supports the development and execution of multiple agents of different kinds.

Furthermore, it supports the evaluation and comparison of

such different agents within a single environment.

Future work includes the completion of the development

environment (e.g. the integration with development tools

such as the Eclipse IDE), as well as the possible integration

of certain aspects of other projects, such as BOD, AKIRA

or JADE.

The RASCALLI platform and selected system components will be made available to the research community by

the end of 2008 via the project homepage.12 In particular, the project partners Research Studios Austria (SAT)

and the Austrian Research Institute for Artificial Intelligence (OFAI) will provide an open source version of the

platform and Tools, respectively. In addition, SAT will make

available their other system components and user interfaces

as managed services with limited support and data volume

free of charge for the research community. The German Research Center for Artificial Intelligence (DFKI) will make

available their data sources via an open research license and

provide their system components as webservices. The companies Ontotext and Radon Labs will make available their

SwiftOWLIM semantic repository and the 3D client, respectively. The New Bulgarian University (NBU) will conribute

their DUAL-inspired implementation of an agent’s mind.

12http://www.ofai.at/rascalli

8. ACKNOWLEDGMENTS

This research is supported by the EC Cognitive Systems

Project FP6-IST-027596-2004 RASCALLI, by the national

FFG program ’Advanced Knowledge Technologies: Grounding, Fusion, Applications’ (project SELP), and by the Federal Ministry of Economics and Labour of the Republic of

Austria. The work presented here builds on joint work

within the RASCALLI project. In particular the authors

would like to thank our collegues from the following institutions: SAT, OFAI, Radon, NBU, Ontotext and DFKI. Finally, our participation in the PerMIS’08 workshop is supported by the European Network for the Advancement of

Artificial Cognitive Systems (euCognition, European Commission, Unit E5 - Cognition, FP6 Project 26408).

9. REFERENCES

[1] F. Bellifemine, A. Poggi, and G. Rimassa. JADE: a

FIPA2000 compliant agent development environment.

In AGENTS ’01: Proceedings of the fifth international

conference on Autonomous agents, pages 216–217,

New York, NY, USA, 2001. ACM.

[2] J. Bryson. Intelligence by Design: Principles of

Modularity and Coordination for Engineering Complex

Adaptive Agents. PhD thesis, MIT, Department of

EECS, Cambridge, MA, 2001. AI Technical Report

2001-003.

[3] J. Cassell, J. Sullivan, S. Prevost, and E. Churchill,

editors. Embodied Conversational Agents. MIT Press,

2000.

[4] E. Jaynes. Information theory and statistical

mechanics. Physical Review, 106(4):620–630, 1957.

[5] B. Kokinov. A hybrid model of reasoning by analogy.

In K. Holyoak and J. Barnden, editors, Analogical

Connections, volume 2 of Advances in Connectionist

and Neural Computation Theory, pages 247–320.

Ablex, 1994.

[6] B. Kokinov and A. Petrov. Integration of memory and

reasoning in analogy-making: the AMBR model. In

D. Gentner, K. Holyoak, and B. Kokinov, editors,

Analogy: Perspectives from Cognitive Science. MIT

Press, in press.

[7] G. Pezzulo and G. Calvi. Designing modular

architectures in the framework AKIRA. Multiagent

Grid Syst., 3(1):65–86, 2007.

[8] M. Skowron. A Web Based Approach to Factoid and

Commonsense Knowledge Retrieval. PhD thesis,

Hokkaido University, Sapporo, Japan, 2005.

[9] M. Skowron and K. Araki. Effectiveness of combined

features for machine learning based question

classification. Special Issue of the Journal of the

Natural Language Processing Society Japan on

Question Answering and Automatic Summarization,

12(6):63–83, 2005.

[10] M. Skowron, J. Irran, and B. Krenn. Computational

framework for and the realization of cognitive agents

providing intelligent assistance capabilities. In

Proceedings of the Cognitive Robotics Workshop at the

18th European Conference on Artificial Intelligence,

2008.

76
Evaluation Criteria for Human-Automation Performance 

Metrics 

Birsen Donmez 

MIT 

Dept. of Aero-Astro 

Cambridge, MA, USA 

1(617)258-5046 

bdonmez@mit.edu 

Patricia E. Pina 

MIT 

Dept. of Aero-Astro 

Cambridge, MA, USA 

1(617)258-5046 

ppina@mit.edu 

M. L. Cummings 

MIT 

Dept. of Aero-Astro 

Cambridge, MA, USA 

1(617)252-1512 

missyc@mit.edu 

ABSTRACT

Previous research has identified broad metric classes for humanautomation performance to facilitate metric selection, as well as 

understanding and comparison of research results. However, there 

is still lack of an objective method for selecting the most efficient 

set of metrics. This research identifies and presents a list of 

evaluation criteria that can help determine the quality of a metric 

in terms of experimental constraints, comprehensive 

understanding, construct validity, statistical efficiency, and 

measurement technique efficiency. Future research will build on 

these evaluation criteria and existing generic metric classes to 

develop a cost-benefit analysis approach that can be used for 

metric selection. 

Categories and Subject Descriptors

C.4 [Performance of Systems]: Measurement Techniques 

J.7 [Computers in Other Systems] 

General Terms

Measurement, Performance, Experimentation, Human Factors, 

Standardization, Theory. 

Keywords

Metric Quality, Human Supervisory Control, Validity, Statistics, 

Experiments. 

1. INTRODUCTION 

Human-automation teams are common in many domains, such as 

military operations, process control, and medicine. With 

intelligent automation, these teams operate under a supervisory 

control paradigm. “Supervisory control means that one or more 

human operators are intermittently programming and continually 

receiving information from a computer that itself closes an 

autonomous control loop through artificial effectors and sensors 

to the controlled process or task environment [1].” Example 

applications include robotics for surgery, rock sampling for 

geology research, and military surveillance with unmanned 

vehicles. 

A popular metric used to evaluate human-automation 

performance in supervisory control is mission effectiveness [2, 3]. 

Mission effectiveness focuses on performance as it relates to the 

final output produced by the human-automation team. However, 

this metric fails to provide insights into the process that leads to 

the final mission-related output. A suboptimal process can lead to 

a successful completion of a mission, e.g., when humans adapt to 

compensate for design deficiencies. Hence, focusing on just the 

mission effectiveness makes it difficult to extract information to 

detect design flaws and to design systems that can consistently 

support successful mission completion. 

Measuring multiple human-computer system aspects, such as the 

situational awareness of the human, can be valuable in diagnosing 

performance successes and failures, and identifying effective 

training and design interventions. However, choosing an efficient 

set of metrics for a given experiment still remains a challenge. 

Many researchers select their metrics based on their past 

experience. Another approach to metric selection is to collect as 

many measures as possible to supposedly gain a comprehensive 

understanding of the human-automation team performance. These 

methods can lead to insufficient metrics, expensive 

experimentation and analysis, and the possibility of inflated type I 

errors. There appears to be a lack of a principled approach to 

evaluate and select the most efficient set of metrics among the 

large number of available metrics. 

Different frameworks of metric classes are found in the literature 

in terms of human-autonomous vehicle interaction [4-7]. These 

frameworks define metric taxonomies and categorize existing 

metrics into high level metric classes that assess different aspects 

of the human-automation team performance and are generalizable 

across different missions. Such frameworks can help 

experimenters identify system aspects that are relevant to 

measure. However, these frameworks do not include evaluation 

criteria to select specific metrics from different classes. Each 

metric set has advantages, limitations, and costs, thus the added 

value of different sets for a given context needs to be assessed to 

select the set that maximizes value and minimizes cost. Permission to make digital or hard copies of all or part of this work for 

personal or classroom use is granted without fee provided that copies are 

not made or distributed for profit or commercial advantage and that 

copies bear this notice and the full citation on the first page. To copy 

otherwise, or republish, to post on servers or to redistribute to lists, 

requires prior specific permission and/or a fee. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA. 

Copyright 2008 ACM 978-1-60558-293-1...$5.00. 

77
Automation

Behavior

Human 

Behavior 

Precursors 

HUMAN 1

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Figure 1. Conceptual model of human-supervisory control (modified from Pina et al. [5]). 

This paper presents a brief overview of existing generalizable 

metric frameworks and then defines a set of evaluation criteria for 

metric selection. These criteria and the generic metric classes 

constitute the basis for the future development of a cost-benefit 

methodology to select supervisory control metrics. 

2. GENERALIZABLE METRIC CLASSES 

For human-autonomous vehicle interaction, different frameworks 

of metric classes have been developed by researchers to facilitate 

metric selection, and understanding and comparison of research 

results. Olsen and Goodrich proposed four metric classes to 

measure the effectiveness of robots: task efficiency, neglect 

tolerance, robot attention demand, and interaction effort [4]. This 

set of metrics measures the individual performance of a robot, but 

fails to explicitly measure human performance. 

Human cognitive limitations often constitute a primary bottleneck 

for human-automation team performance [8]. Therefore, a metric 

framework that can be generalized across different missions 

conducted by human-automation teams should include cognitive 

metrics to understand what drives human behavior and cognition. 

In line with the idea of integrating human and automation 

performance metrics, Steinfeld et al. suggested identifying 

common metrics in terms of three aspects: human, robot, and the 

system [7]. Regarding human performance, the authors discussed 

three main metric categories: situation awareness, workload, and 

accuracy of mental models of device operations. This work 

constitutes an important effort towards developing a metric 

toolkit; however, this framework suffers from a lack of metrics to 

evaluate collaboration effectiveness among humans and among 

robots. 

Pina et al. [5] defined a more comprehensive framework for 

human-automation team performance based on a high-level 

conceptual model of human supervisory control. Figure 1 

represents this conceptual model for a team of two humans 

collaborating, with each controlling an autonomous platform. The 

platforms also collaborate autonomously. These collaboration 

layers are depicted by arrows between each collaborating unit. 

The operators receive feedback about automation and mission 

performance, and adjust automation behavior through controls if 

required. The automation interacts with the real world through 

actuators and collects feedback about mission performance 

through sensors. 

Based on this model, Pina et al. [5] defined five generalizable 

metric classes: mission effectiveness, automation behavior 

efficiency, human behavior efficiency, human behavior 

precursors, and collaborative metrics (Table 1). Mission 

effectiveness includes the popular metrics and measures 

concerning how well the mission goals are achieved. Automation 

and human behavior efficiency measure the actions and decisions 

made by the individual components of the team. Human behavior 

precursors measure a human’s initial state, including attitudes and 

cognitive constructs that can be the cause of and can influence a 

given behavior. Collaborative metrics address three different 

aspects of team collaboration: collaboration between the human 

and the automation collaboration between the humans that are in 

the team, and autonomous collaboration between different 

platforms. 

These metric classes can help researchers select metrics that can 

result in a comprehensive understanding of the human-automation 

performance, covering issues ranging from automation 

capabilities to human cognitive abilities. However, there still is a 

lack of an objective methodology to select a collection of metrics 

78
that most efficiently measure a system’s human-automation 

performance. The following section presents a preliminary list of 

evaluation criteria that can help researchers evaluate the quality of 

a set of metrics. 

Table 1. Human supervisory control metric classes and 

subclasses [9] 

3. METRIC EVALUATION CRITERIA 

The proposed metric evaluation criteria for human supervisory 

control systems consist of five general categories that are listed in 

Table 2. These categories focus both on the metrics, which are 

constructs, and on the associated measures, which are 

mechanisms for expressing construct sizes. There can be multiple 

ways of measuring a metric. For example, situational awareness, 

which is a metric, can be measured based on objective or 

subjective measures [10]. Different measures for the same metric 

can generate different benefits and costs. Therefore, the criteria 

presented in this section evaluate a metric set by considering the 

metrics (e.g., situational awareness), the associated measures 

(e.g., subjective responses), and the measuring techniques (e.g., 

questionnaires given at the end of experimentation). 

These proposed criteria target human supervisory control systems, 

with influence from the fields of systems engineering, statistics, 

human factors, and psychology. These fields have their own 

flavors of experimental metric selection including formal design 

of experiment approaches such as response surface methods and 

factor analyses, but often which metric to select and how many 

are left to heuristics developed through experience. 

Table 2. Metric evaluation criteria 

1) Experimental Constraints (e.g., time required to 

analyze a metric) 

2) Comprehensive Understanding (e.g., causal relations 

with other metrics) 

3) Construct Validity (e.g., power to discriminate 

between similar constructs) 

4) Statistical Efficiency (e.g., effect size) 

5) Measurement Technique Efficiency (e.g., intrusiveness 

to subjects)

1) Mission Effectiveness (e.g., key mission 

performance parameters) 

2) Automation Behavior Efficiency (e.g., usability, 

adequacy, autonomy, reliability) 

3) Human Behavior Efficiency

a) Attention allocation efficiency (e.g., scan patterns, 

prioritization) 

b) Information processing efficiency (e.g., decision 

making) 

4) Human Behavior Precursors

a) Cognitive precursors (e.g., situational awareness, 

mental workload) 

b) Physiological precursors (e.g., physical comfort, 

fatigue) 

5) Collaborative Metrics

a) Human/automation collaboration (e.g., trust, 

mental models) 

b) Human/human collaboration (e.g., coordination 

efficiency, team mental model) 

c) Automation/automation collaboration (e.g., 

platforms’ reaction time to situational events that 

require autonomous collaboration) 

3.1 Experimental Constraints 

Time and monetary cost associated with measuring and analyzing 

a specific metric constitute the main practical considerations for 

metric selection. Time allocated for gathering and analyzing a 

metric also comes with a monetary cost due to man-hours, such as 

time allocated for test bed configurations. Availability of 

temporary and monetary resources depends on the individual 

project; however, resources will always be a limiting factor in all 

projects. 

The stage of system development and the testing environment are 

additional factors that can guide metric selection. Early phases of 

system development require more controlled experimentation in 

order to evaluate theoretical concepts that can guide system 

design. Later phases of system development require a less 

controlled evaluation of the system in actual operation. For 

example, research in early phases of development can assess 

human behavior for different automation levels, whereas research 

in later phases can assess the human behavior in actual operation 

in response to the implemented automation level. 

The type of testing environment depends on available resources, 

safety considerations, and the stage of research development. For 

example, simulation environments can enable researchers to have 

high experimental control, and manipulate and evaluate different 

system design concepts accordingly. In simulation environments, 

researchers can create off-nominal situations and measure 

operator responses to such situations without exposing them to 

risk. However, simulation creates an artificial setting and field 

testing is required to assess system performance in actual use. The 

types of measures that can be collected are constrained by the 

testing environment. For example, the responses to rare events are 

more applicable for research conducted in simulated 

environments, whereas observational measures can provide better 

value in field testing. 

3.2 Comprehensive Understanding 

It is important to maximize the understanding gained from a 

research study. However, due to the limited resources available, it 

is not possible to collect all required metrics. Therefore, each 

metric should be evaluated based on how much it explains the 

phenomenon of interest and how much it helps explain the 

underlying reasons for what other metrics measure. 

The most important aspect of a study is finding an answer to the 

primary research question. The proximity of a metric to 

answering the primary research question defines the importance 

of that metric. For example, a workload metric may not tell much 

79
without a mission effectiveness metric. However, this does not 

mean that the workload metric fails to provide additional insights 

into the human-automation performance. Another characteristic of 

a metric that is important to consider is the amount of additional 

understanding gained using a specific metric when a set of metrics 

are already collected. For example, rather than having two metrics 

that measure mission effectiveness, having one metric that 

measures mission effectiveness and another metric that measures 

human behavior can provide a better understanding on the team 

performance. 

In addition to providing additional understanding, another desired 

metric quality is its causal relations with other metrics. A better 

understanding can be gained, if a metric can help explain the 

underlying reasons to what the other metrics measure. For 

example, operator response to an event, hence human behavior, 

will often be dependent on the conditions and/or operator’s state 

when the event occurs. The response to an event can be described 

in terms of three set of variables [11]: a pre-event phase that 

defines how the operator adapts to the environment; an eventresponse phase that describes the operator’s behavior in 

accommodating the event; and an outcome phase that describes 

the outcome of the response process. The underlying reasons for 

the operator’s behavior and the final outcome for an event can be 

better understood if the initial conditions and operator’s state 

when the event occurs is also measured. When used as covariates 

in statistical analysis, the initial conditions of the environment and 

the operator can help explain the variability in other metrics of 

interest. Thus, in addition to human behavior, experimenters are 

encouraged to measure human behavior precursors and 

automation behavior in order to assess the operator state and 

environmental conditions which may influence human behavior. 

3.3 Construct Validity 

Construct validity refers to how well the associated measure 

captures the metric or construct of interest. For example, 

subjective measures for situational awareness ask subjects to rate 

the amount of situational awareness they had on a given scenario 

or task. These measures are proposed to help in understanding 

subjects’ situational awareness [10, 12]. However, self-ratings 

assess meta-comprehension rather than comprehension of the 

situation: it is unclear whether or not operators are aware of their 

lack of situational awareness. Therefore, subjective responses on 

situational awareness are not valid to assess the actual situational 

awareness but rather the awareness of lack of situational 

awareness. 

Good construct validity requires a measure to have high 

sensitivity to changes in the targeted construct. That is, the 

measure should reflect the change as the construct moves from 

low to high levels [13]. For example, the primary task 

performance starts to break down only when the workload reaches 

higher levels [13, 14]. Therefore, primary task performance 

measures are not sensitive to changes in the workload at lower 

workload levels, since with sufficient spare processing capacity 

the operators are able to compensate for the increase in workload. 

A measure with high construct validity should also be able to 

discriminate between similar constructs. The power to 

discriminate between similar constructs is especially important for 

abstract constructs that are hard to measure and difficult to define, 

such as human workload or attentiveness. An example measure 

that fails to discriminate two related metrics is galvanic skin 

response. Galvanic skin response is the change in electrical 

conductance of the skin attributable to the stimulation of the 

sympathetic nervous system and the production of sweat. 

Perspiration causes an increase in skin conductance, thus galvanic 

skin response has been proposed and used to measure workload 

and stress levels (e.g., Levin et al. [15]). However, even if 

workload and stress are related, they still are two separate metrics. 

Therefore, galvanic skin response cannot alone suggest a change 

in workload. 

Good construct validity also requires the selected measure to have 

high inter- and intra-subject reliability. Inter-subject reliability 

requires the measure to assess the same construct for every 

subject, whereas intra-subject reliability requires the measure to 

assess the same construct if the measure were repeatedly collected 

from the same subject under identical conditions. 

Intra- and inter-subject reliability is especially of concern for 

subjective measures. For example, self-ratings are widely utilized 

for mental workload assessment [16, 17]. This technique requires 

operators to rate the workload or effort experienced while 

performing a task or a mission. Self-ratings are easy to 

administer, non-intrusive, and not expensive. However, different 

individuals may have different interpretations of workload, 

leading to decreased inter-subject reliability. For example, some 

participants may not be able to separate mental workload from 

physical workload [18], and some participants may report their 

peak workload whereas others may report their average workload. 

Another example of low inter-subject reliability is for subjective 

measures of situational awareness. Vidulich & Hughes [10] found 

that about half of their participants rated situational awareness by 

gauging the amount of information to which they attended; while 

the other half of the participants rated their SA by gauging the 

amount of information they thought they had overlooked. 

Participants may also have recall problems if the subjective 

ratings are collected at the end of a test period, raising concerns 

on the intra-subject reliability of subjective measures. 

High correlation between different measures, even if they are 

intended to assess different metrics, is another limiting factor for 

metric selection. A high correlation can be indicative of the fact 

that multiple measures assess the same metric or the same 

phenomenon. Hence, including multiple measures that are highly 

correlated with each other can result in wasted resources. 

3.4 Statistical Efficiency 

There are three metric qualities that should be considered to 

ensure statistical efficiency: total number of measures collected, 

frequency of observations, and effect size. 

Analyzing multiple measures that are correlated with each other 

would inflate type I error. That is, as more dependent variables 

are analyzed, finding a significant effect when there is none 

becomes more likely. The inflation of type I error due to multiple 

dependent variables can be handled with multivariate analysis 

techniques, such as Multivariate Analysis of Variance 

(MANOVA) [19]. It should be noted that multivariate analyses 

are harder to conduct as researchers are more prone to include 

irrelevant variables in multivariate analyses, possibly hiding the 

few significant differences among many insignificant ones. The 

best way to avoid failure to identify significant differences is to 

80
design an effective experiment with the most parsimonious 

metric/measure set that is expected to produce differences, and 

excluding others that are not expected to show differences among 

many treatments. 

Another metric characteristic that needs to be considered is the 

number of observations required for statistical analysis. 

Supervisory control applications require humans to be monitors of 

automated systems, with intermittent interaction. Because humans 

are poor monitors by nature [20], human monitoring efficiency is 

an important metric to measure in many applications. The 

problem with assessing monitoring efficiency is that, in most 

domains, errors or critical signals are very rare, and operators can 

go through an entire career without encountering them. For that 

reason, in order to have a realistic experiment, such rare events 

cannot be included in a study with sufficient frequency. 

Therefore, if a metric requires response to rare events, the 

associated number of observations may not enable the researchers 

to extract meaningful information from this metric. Moreover, 

small frequency of observed events cannot be statistically 

analyzed unless data is obtained from a very large number of 

subjects, such as in medical studies on rare diseases. Conducting 

such large scale supervisory control experiments is generally costprohibitive. 

The number of subjects recruited for a study is especially limited 

when participants are domain experts such as pilots. The power to 

identify a significant difference, when there is one, depends on 

the differences in the means of factor levels and the standard 

errors of these means. Standard errors of the means are 

determined by the number of subjects. One way to compensate for 

limited number of subjects in a study is to use more sensitive 

measures that will provide a large separation between different 

conditions, that is, a high effect size. Experimental power can also 

be increased by reducing error variance by collecting repeated 

measures on subjects, focusing on sub-populations (e.g., 

experienced pilots), and/or increasing the magnitude of 

manipulation for independent variables (low and high intensity 

rather than low and medium intensity). However, it should also be 

noted that increased control on the experiment, such as using subpopulations, can lead to less generalizable results, and there is a 

tradeoff between the two. 

3.5 Measurement Technique Efficiency 

The data collection technique associated with a specific metric 

should not be intrusive to the subjects or to the nature of the task. 

For example, eye trackers are used for capturing operator’s visual 

attention [21, 22]. In particular, head-mounted eye trackers can be 

uncomfortable for the subjects, and hence influence their 

responses. Wearing an eye-tracker can also lead to an unrealistic 

situation that is not representative of the task performed in the real 

world. 

Eye trackers are an example of how a measurement instrument 

can interfere with the nature of the task. The measuring technique 

itself can also interfere with the realism of the study. For example, 

off-line query methods are used to measure operator’s situational 

awareness [23]. These methods are based on briefly halting the 

experiment at randomly selected intervals, blanking the displays, 

and administering a battery of queries to the operators. This 

situational awareness measure then assesses global situational 

awareness metric by calculating the accuracy of operator’s 

responses. The collection of the measure requires the interruption 

of the task in a way that is unrepresentative of the reality 

generating an artificial setting. The interruption may also interfere 

with other metrics such as operator’s performance and workload, 

as well as other temporal-based metrics. 

4. DISCUSSION 

Supervisory control of automation is a complex phenomenon with 

high levels of uncertainty, time-pressure, and a dynamicallychanging environment. The performance of human-automation 

teams depend on multiple components such as human behavior, 

automation behavior, human cognitive and physical capabilities, 

team interactions, etc. Because of the complex nature of 

supervisory control, there are many different metrics that can be 

utilized to assess performance. However, it is not feasible to 

collect all possible metrics. Moreover, collecting multiple metrics 

that are correlated can lead to statistical problems such as inflated 

type I errors. 

This paper presented a preliminary list of evaluation criteria for 

determining a set of metrics for a given research question. These 

criteria were populated under five major headings: experimental 

constraints, comprehensive understanding, construct validity, 

statistical efficiency, and measurement technique efficiency. It 

should be noted that there are interactions between these major 

categories. For example, the intrusiveness of a given measuring 

technique can affect the construct validity for a different metric. 

In one such case, if the situational awareness is measured by 

halting the experiment and querying the operator, then the 

construct validity for the mission effectiveness or human behavior 

metrics become questionable. Therefore, the evaluation criteria 

presented in this paper should be applied to a collection of metrics 

rather than each individual metric alone, taking the interactions 

between different metrics into consideration. The list of 

evaluation criteria presented in this paper is a guideline for metric 

selection. It should be noted that there is not a single set of 

metrics that are the most efficient across all applications. The 

specific research aspects such as available resources and the 

questions of interest will ultimately determine the relative metric 

quality. Future research will identify a methodology based on a 

cost-benefit analysis approach, which will objectively identify the 

best set of metrics for classifications of research studies. 

5. ACKNOWLEDGMENTS 

This research is funded by the US Army Aberdeen Test Center. 

6. REFERENCES 

[1] Sheridan, T.B., Telerobotics, automation, and human 

supervisory control. 1992, Cambridge, MA: The MIT Press. 

[2] Scholtz, J., et al., Evaluation of human-robot interaction 

awareness in search and rescue, in Proceedings of the IEEE 

International Conference on Robotics and Automation 

(ICRA). 2004: New Orleans. 

[3] Cooke, N.J., et al., Advances in measuring team cognition, in 

Team cognition: understanding the factors that drive process 

and performance, E. Salas and S.M. Fiore, Editors. 2004, 

American Psychological Association: Washington, D. C. p. 

83-106. 

[4] Olsen, R.O. and M.A. Goodrich, Metrics for evaluating 

human-robot interactions, in Proceedings of NIST 

81
Performance Metrics for Intelligent Systems Workshop. 

2003. 

[5] Pina, P.E., et al., Identifying generalizable metric classes to 

evaluate human-robot teams, in Proceedings of Metrics for 

Human-Robot Interaction Workshop at the 3rd Annual 

Conference on Human-Robot Interaction. 2008: Amsterdam, 

The Netherlands. 

[6] Crandall, J.W. and M.L. Cummings, Identifying predictive 

metrics for supervisory control of multiple robots. IEEE 

Transactions on Robotics - Special Issue on Human-Robot 

Interaction, 2007. 23(5): p. 942-951. 

[7] Steinfeld, A., et al., Common metrics for human-robot 

interaction, in Proceedings of the 1st Annual IEEE/ACM 

Conference on Human Robot Interaction (Salt Lake City, 

Utah). 2006, ACM Press: New York, NY. 

[8] Wickens, C.D., et al., An Introduction to Human Factors 

Engineering. 2nd ed. 2004, Upper Saddle River, New Jersey: 

Pearson Education, Inc. 

[9] Pina, P.E., B. Donmez, and M.L. Cummings, Selecting 

metrics to evaluate human supervisory control applications. 

2008, MIT Humans and Automation Laboratory: Cambridge, 

MA. 

[10] Vidulich, M.A. and E.R. Hughes, Testing a subjective metric 

of situation awareness, in Proceedings of the Human Factors 

Society 35th Annual Meeting. 1991, The Human Factors and 

Ergonomics Society: Santa Monica, CA. p. 1307-1311. 

[11] Donmez, B., L. Boyle, and J.D. Lee, The impact of 

distraction mitigation strategies on driving performance.

Human Factors, 2006. 48(4): p. 785-804. 

[12] Taylor, R.M., Situational awareness rating technique 

(SART): the development of a tool for aircrew systems 

design, in Proceedings of the NATO Advisory Group for 

Aerospace Research and Development (AGARD) Situational 

Awareness in Aerospace Operations Symposium (AGARDCP-478). 1989. p. 17. 

[13] Eggemeier, F.T., C.A. Shingledecker, and M.S. Crabtree, 

Workload measurement in system design and evalution, in 

Proceeding of the Human Factors Society 29th Annual 

Meeting. 1985: Baltimore, MD. p. 215-219. 

[14] Eggemeier, F.T., M.S. Crabtree, and P.A. LaPoint, The effect 

of delayed report on subjective ratings of mental workload, 

in Proceedings of the Human Factors Society 27th Annual 

Meeting. 1983: Norfolk, VA. p. 139-143. 

[15] Levin, S., et al., Tracking workload in the emergency 

department. Human Factors, 2006. 48(3): p. 526-539. 

[16] Wierwille, W.W. and J.G. Casali, A validated rating scale 

for global mental workload measurement applications, in 

Proceedings of the Human Factors Society 27th Annual 

Meeting. 1983: Santa Monica, CA. p. 129-133. 

[17] Hart, S.G. and L.E. Staveland, The subjective workload 

assessment technique: a scaling procedure for measuring 

mental workload, in Human Mental Workload, P. Hancock 

and N. Meshkati, Editors. 1988, North Holland B. V.: 

Amsterdam, The Netherlands. p. 139-183. 

[18] O'Donnell, R.D. and F.T. Eggemeier, Workload assessment 

methodology, in Handbook of perception and human 

performance: vol. II. Cognitive processes and performance, 

K.R. Boff, L. Kaufmann, and J.P. Thomas, Editors. 1986, 

Wiley Interscience: New York. p. 42-1 - 42-49. 

[19] Johnson, R.A. and D.W. Wichern, Applied multivariate 

statistical analysis. Fifth ed. 2002, NJ: Pearson Education. 

[20] Sheridan, T.B., Humans and automation: system design and 

research issues. 2002, New York, NY: John Wiley & Sons 

Inc. 

[21] Janzen, M.E. and K.J. Vicente, Attention allocation within 

the abstraction hierarchy. International Journal of HumanComputer Studies, 1998. 48: p. 521-545. 

[22] Donmez, B., L. Boyle, and J.D. Lee, Safety implications of 

providing real-time feedback to distracted drivers. Accident 

Analysis & Prevention, 2007. 39(3): p. 581-590. 

[23] Endsley, M.R., B. Bolte, and D.G. Jones, Designing for 

situation awareness: an approach to user-centered design. 

2003, Boca Raton, FL: CRC Press, Taylor & Francis Group. 

82
Assessing Measures of Coordination Demand Based 

on Interaction Durations 

Michael Lewis 

School of Information Sciences

University of Pittsburgh

Pittsburgh, PA 15260 USA 

ml@sis.pitt.edu 

Jijun Wang 

Quantum Leap Innovations, Inc. 3 Innovation Way, Suite 100

Newark, DE 19711 USA 

jijunwang.cn@gmail.co

ABSTRACT 

Controlling multiple robots substantially increases the complexity of 

the operator’s task because attention must constantly be shifted 

among robots in order to maintain situation awareness (SA) and exert 

control. In the simplest case an operator controls multiple 

independent robots interacting with each as needed. Control 

performance at such tasks can be characterized by the average 

demand of each robot on human attention. In this paper we present 

several approaches to measuring, coordination demand, CD, the 

added difficulty posed by having to coordinate as well as operate 

multiple robots. Our initial experiment compares “equivalent” 

conditions with and without coordination. Two subsequent 

experiments attempt to manipulate and measure coordination 

demand directly using an extension of the Neglect Tolerance model. 

Categories and Subject Descriptors

I.2.9 [Artificial Intelligence]: Robotics—operator interfaces

General Terms

Human Factors, Measurement, Experimentation 

Keywords

Human-robot interaction, metrics, evaluation, multi-robot 

System 

1. INTRODUCTION

Borrowing concepts and notation from computational complexity, 

control of robots by issuing waypoints, could be considered O(n) 

because demand increases linearly with the number of robots to be 

serviced. Another form of control such as designating a search 

region by drawing a box on a GUI (Graphical User Interface), being 

independent of the number of robots, would be O(1). From this 

perspective the most complex tasks faced in controlling teams are 

likely to be those that involve choosing and coordinating subgroups 

of robots. Simply choosing a subteam to perform a task (the 

 

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iterated role assignment problem), for example, has been shown to be 

O(mn) [6]. The three experiments presented in this paper develop 

methods to assess the operator effort required to coordinate robots in 

tasks representative of expected application areas. 

1.1 Coordination Demand 

Despite the apparent analogy between command complexity and the 

workload imposed by a command task there is no guarantee that 

human operators will experience difficulty in the same way. The 

performance of human-robot teams is complex and multifaceted 

reflecting the capabilities of the robots, the operator(s), and the 

quality of their interactions. Recent efforts to define common 

metrics for human-robot interaction [11] have favored sets of metric 

classes to measure the effectiveness of the system’s constituents and 

their interactions as well as the system’s overall performance. In 

this paper we present new measures of the demand coordination 

places on operators of multirobot systems and three experiments 

evaluating our approach and the usefulness of these measures. 

Controlling multiple robots substantially increases the complexity of 

the operator’s task because attention must constantly be shifted 

among robots in order to maintain situation awareness (SA) and exert 

control. In the simplest case an operator controls multiple 

independent robots interacting with each as needed. A search task in 

which each robot searches its own region would be of this category 

although minimal coordination might be required to avoid overlaps 

and prevent gaps in coverage. Control performance at such tasks 

can be characterized by the average demand of each robot on human 

attention [5]. Under these conditions increasing robot autonomy 

should allow robots to be neglected for longer periods of time 

making it possible for a single operator to control more robots. 

For more strongly cooperative tasks and larger teams, individual 

autonomy alone is unlikely to suffice. The round-robin control 

strategy used for controlling individual robots would force an 

operator to plan and predict actions needed for multiple joint 

activities and be highly susceptible to errors in prediction, 

synchronization or execution. Estimating the cost of this 

coordination, however, proves a difficult problem. Established 

methods of estimating multirobot system, MRS, control difficulty, 

neglect tolerance, and fan-out [5] are predicated on the independence 

of robots and tasks. In neglect tolerance, the period following the 

end of human intervention but preceding a decline in performance 

below a threshold is considered time during which the operator is 

free to perform other tasks. If the operator services other robots 

over this period, the measure provides an estimate of the number of 

robots that might be controlled. Fan-out, when measured 

83
empirically, works from the opposite direction, adding robots and 

measuring performance until a plateau without further improvement 

is reached. Both approaches presume that operating an additional 

robot imposes an additive demand. These measures are particularly 

attractive because they are based on readily observable aspects of 

behavior: the time an operator is engaged controlling the robot, 

interaction time (IT), and the time an operator is not engaged in 

controlling the robot, neglect time (NT). 

2. COORDINATION DEMAND

To separate coordination demand (CD) from the demands of 

interacting with independent robots we have extended Crandall et 

al.’s (2005) neglect tolerance model by introducing the notion of 

occupied time (OT) as illustrated in Figure 1. 

The neglect tolerance model describes an operator’s interaction with 

multiple robots as a sequence of control episodes in which an 

operator interacts with a robot for period IT raising its performance 

above some upper threshold after which the robot is neglected for the 

period NT until its performance deteriorates below a lower threshold 

when the operator must again interact with it. To accommodate 

 

NT IT 

FT OT FT 

NT: Neglect Time; IT: Interaction Time; 

FT: Free Time, time off task; OT: Occupied Time 

IT+OT: time on task 

Time

Team Effectiveness 

Figure 1. Extended neglect tolerance model

dependent tasks we introduce occupied time, OT, to describe the 

time spent controlling other robots in order to synchronize their 

actions with those of the target robot. The episode depicted in Figure 

1 starts just after the first robot is serviced. The ensuing free time 

( FT ) preceding the interaction with a second dependent robot, the 

OT for robot-1 (that would contribute to IT for robot-2), and the FT 

following interaction with robot-2 but preceding the next interaction 

with robot-1 together constitute the neglect time for robot-1. 

Coordination demand, CD, is then defined as:

 

 NT

OT

NT

FT

CD ¦ ¦ 1 (1) 

Where, CD for a robot is the ratio between the time required to 

control cooperating robots and the time still available after 

controlling the target robot, i.e.; the portion of a robot’s free time that 

must be devoted to controlling cooperating robots. Note that OTn

associated with robotn is less than or equal to NTn because OTn

covers only that portion of NTn needed for synchronization. 

Most MRS research has investigated homogeneous robot teams 

where additional robots provide redundant (independent) capabilities. 

Differences in capabilities such as mobility or payload, however, 

may lead to more advantageous opportunities for cooperation among 

heterogeneous robots. These differences among robots in roles and 

other characteristics affecting IT, NT, and OT introduce additional 

complexity to assessing CD. Where tight cooperation is required as 

in box-pushing, task requirements dictate both the choice of robots 

and the interdependence of their actions. In the more general case 

requirements for cooperation can be relaxed allowing the operator to 

choose the subteams of robots to be operated in a cooperative manner 

as well as the next robot to be operated. This general case of 

heterogeneous robots cooperating as needed characterizes the types 

of field applications our research is intended to support. To 

accommodate this more general case, the Neglect Tolerance model 

must be further extended to measure coordination between different 

robot types and for particular patterns of activity. 

The resulting expression [13] measures the way in which the team’s 

capabilities or resources are combined to accomplish the task without 

reference to the operation or neglect of particular robots. So, for 

example, it would not distinguish between a situation in which one 

robot of type, X, was never operated while another was used 

frequently from a situation in which both robots of type, X, were 

used more evenly. The incorporation of action patterns further 

extends the generality of the approach to accommodate patterns of 

cooperation that occur in episodes such as dependencies between 

loading and transporting robots. When an empty transporter arrives, 

its brief IT would lead to extended OTs as the loaders do their work. 

When the transporter has been filled the dependency would be 

reversed. 

3. SIMULATION ENVIRONMENT

The reported experiments were performed using the USARSim 

robotic simulation with 2-6 simulated robots performing Urban 

Search and Rescue (USAR), experiments 1 & 3, or box pushing 

(experiment 2) tasks. USARSim is a high-fidelity simulation of 

USAR robots and environments developed as a research tool for the 

study of Human Robot Interaction (HRI) and multi-robot 

coordination. Validation studies showing agreement for a variety of 

feature extraction techniques between USARSim images and camera 

video are reported in [3], showing close agreement in detection of 

walls and associated Hough transforms for a simulated Hokuyo laser 

range finder [2] and close agreement in behavior between USARSim 

models and the robots being modeled [4,8,9,12,15]. 

3.1 MrCS – The Multirobot Control System 

A multirobot control system (MrCS) was developed to conduct these 

experiments. The system was designed to be scalable to allow of 

control different numbers of robots, reconfigurable to accommodate 

different human-robot interfaces, and reusable to facilitate testing 

different control algorithms. 

The user interface of MrCS is shown in Figure 2. The interface is 

reconfigurable to allow the user to resize the components or change 

the layout. Shown in the figure is a configuration that used in the 

RoboCup 2006 competition in which a single operator controls six 

robots. On the upper and center portions of the left-hand side are the 

robot list and team map panels, which show the operator an overview 

of the team. The destination of each of robot is displayed on the map 

to help the user keep track of current plans. Using this display, the 

operator is also able to control regional priorities by drawing 

rectangles on the map. On the center and lower portions of the 

right-hand side are the camera view and mission control panels, 

84
which allow the operator to maintain situation awareness of an 

individual robot and to edit its exploration plan. On the mission panel, 

the map and all nearby robots and their destinations are represented 

to provide partial team awareness so that the operator can switch 

between contexts while moving control from one robot to another. 

The lower portion of the left-hand side is a teleoperation panel that 

allows the operator to teleoperate a robot. 

3.2 Experiments 

One approach to investigating coordination demand is to design 

experiments that allow comparisons between “equivalent” conditions 

Figure 2. MrCS GUI 

with and without coordination demands. The first experiment and 

one comparison within the third experiment follow this approach. 

The first experiment compares search performance between a team 

of autonomously coordinating robots, manually (waypoint) 

controlled robots, and mixed initiative teams with autonomously 

coordinated robots that accepted operator inputs. The impact of 

coordination demand was observable through the difference in 

performance between the manually controlled teams and the mixed 

initiative ones. The fully automated teams provided a control 

ensuring that the benefits in the mixed initiative condition were not 

due solely to the superior performance of the automation. 

While experiment 1 examines coordination demand indirectly by 

comparing performance between conditions in which it was filled 

either manually or through automation, experiments 2 & 3 attempt to 

manipulate and measure coordination demand directly. In 

experiment 2 robots perform a box pushing task in which CD is 

varied by control mode and robot heterogeneity. By making the 

actions of each robot entirely dependent on the other, this choice of 

task eliminates the problem of distinguishing between interactions 

intended to control a target robot and those needed to coordinate with 

another. The third experiment attempts to manipulate coordination 

demand in a loosely coordinated task by varying the proximity 

needed to perform a joint task in two conditions and by automating 

coordination within subteams in the third. Because robots must 

cooperate in pairs and interaction for control needs to be 

distinguished from interaction for coordination for this task, CD is 

computed between robot types (equation 2) rather than directly 

between robots (equation 1) as done in experiment 2. 

All three experiments used paid participants from the University of 

Pittsburgh and lasted approximately one and a half hours. All used 

repeated measures designs and followed a standard sequence starting 

with collection of demographic data. Standard instructions for the 

experiment were presented followed by a 10 minute training session 

during which the participant was allowed to practice using the MrCS. 

Participants then began their first trial followed by a second with a 

short break in between. Experiments 2 and 3 included a third trial 

with break. At the conclusion of the experiment participants 

completed a questionnaire. 

4. EXPERIMENT 1 

Participants were asked to control 3 P2DX robots simulated in 

USARsim to search for victims in a damaged building. Each robot 

was equipped with a pan-tilt camera with 45 degrees Field of View 

(FOV) and a front laser scanner with 180 degree FOV and resolution 

of 1 degree. When a victim was identified, the participant marked its 

location on NIST Reference Test Arena, Yellow Arena [7]. Two 

similar testing arenas were built using the same elements with 

different layouts. In each arena, 14 victims were evenly distributed in 

the world. We added mirrors, blinds, curtains, semitransparent 

boards, and wire grid to add difficulty in situation perception. Bricks, 

pipes, a ramp, chairs, and other debris were put in the arena to 

challenge mobility and SA in robot control. 

Presentation of mixed initiative and manual conditions were 

counterbalanced. Under mixed initiative, the robots analyzed their 

laser range data to find possible exploration paths. They cooperated 

with one another to choose execution paths that avoided duplicating 

efforts. While the robots autonomously explored the world, the 

operator was free to intervene with any individual robot by issuing 

new waypoints, teleoperating, or panning/tilting its camera. The 

robot returned back to auto mode once the operator’s command was 

completed or stopped. While under manual control robots could not 

autonomously generate paths and there was no cooperation among 

robots. The operator controlled a robot by giving it a series of 

waypoints, directly teleoperating it, or panning/tilting its camera. As 

a control for the effects of autonomy on performance we conducted 

“full autonomy” testing as well. Because MrCS doesn’t support 

victim recognition, based on our observation of the participants’ 

victim identification behaviors, we defined detection to have 

occurred for victims that appeared on camera for at least 2 seconds 

and occupied at least 1/9 of the thumbnail view. Because of the high 

fidelity of the simulation, and the randomness of paths picked 

through the cooperation algorithms, robots explored different regions 

on every test. Additional variations in performance occurred due to 

mishaps such as a robot getting stuck in a corner or bumping into an 

obstacle causing its camera to point to the ceiling so no victims could 

be found. Sixteen trials were conducted in each area to collect data 

comparable to that obtained from human participants. 

4.1 Results 

All 14 participants found at least 5 of a possible 14 (36%) victims in 

each of the arenas. These data indicate that participants exploring 

less than 90% of the area consistently discovered 5 to 8 victims while 

those covering greater than 90% discovered between half (7) and all 

(14) of the victims. Within participant comparisons found wider 

regions were explored in mixed-initiative mode, t(13) = 3.50, p 

< .004, as well as a marginal advantage for mixed-initiative mode, 

t(13) = 1.85, p = .088, in number of victims found. Comparing with 

85
“full autonomy”, under mixed-initiative conditions two-tailed t-tests 

found no difference (p = 0.58) in the explored regions. 

No difference was found between area explored in autonomous or 

mixed initiative searches, however, autonomously coordinating 

robots explored significantly, t(44) = 4.27, p < .001, more regions 

than under the manual control condition (see Figure 3). Participants 

found more victims under both mixed-initiative and manual control 

conditions than under full autonomy with t(44) = 6.66, p < .001, and 

t(44) = 4.14, p < .001, respectively (see Figure 8). The median 

number of victims found under full autonomy was five. Comparing 

the mixed-initiative with the manual control, most participants (79%) 

rated team autonomy as providing either significant or minor help. 

Human Interactions 

Participants intervened to control the robots by switching focus to an 

individual robot and then issuing commands. Measuring the 

distribution of attention among robots as the standard deviation of 

the total time spent with each robot, no difference (p = .232) was 

found between mixed initiative and manual control modes. However, 

we found that under mixed initiative, the same participant switched 

robots significantly more often than under manual mode (p = .027). 

Across participants, the frequency of shifting control among robots 

explained a significant proportion of the variance in number of 

victims found for both mixed initiative, R2 =.54, F (1, 11) = 12.98, p 

= .004, and manual, R2

 = .37, F (1, 11) = 6.37, p < .03, modes. 

Figure 3. Victims Found and Regions Explored 

In this experiment, cooperation was limited to deconfliction of plans 

so that robots did not re-explore the same regions or interfere with 

one another. The experiment found that even this limited degree of 

autonomous cooperation helped in the control of multiple robots. The 

results showed that cooperative autonomy among robots helped the 

operators explore more areas and find more victims. The fully 

autonomous control condition demonstrates that this improvement 

was not due solely to autonomous task performance as found in [10] 

but rather resulted from mixed initiative cooperation with the robotic 

team. 

5. EXPERIMENT 2 

Finding a metric for cooperation demand (CD) is difficult because 

there is no widely accepted standard. In this experiment, we 

investigated CD (as defined in Section II) by comparing performance 

across three conditions selected to differ substantially in their 

coordination demands. When an operator teleoperates the robots one 

by one to push the box forward, he must continuously interact with 

one of the robots because neglecting both would immediately stop 

the box. Because the task allows no free time (FT) we expect CD to 

be 1. However, when the user is able to issue waypoints to both 

robots, the operator may have FT before she must coordinate these 

robots again because the robots can be instructed to move 

simultaneously. In this case CD should be less than 1. 

Intermediate levels of CD should be found in comparing control of 

homogeneous robots with heterogeneous robots. Higher CD should 

be found in the heterogeneous group since the unbalanced pushes 

from the robots would require more frequent coordination. In the 

present experiment, we compared computed CDs between these three 

conditions.

Figure 4. Box pushing task 

Figure 4 shows our experiment setting simulated in USARSim [7]. 

The controlled robots were either two Pioneer P2AT robots or one 

Pioneer P2AT and one less capable three wheeled Pioneer P2DX 

robot. Each robot was equipped with a GPS, a laser scanner, and a 

RFID reader. On the box, we mounted two RFID tags to enable the 

robots to sense the box’s position and orientation. When a robot 

pushes the box, both the box and robot’s orientation and speed will 

change. Furthermore, because of irregularities in initial conditions 

and accuracy of the physical simulation the robot and box are 

unlikely to move precisely as the operator expected. In addition, 

delays in receiving sensor data and executing commands were 

modeled presenting participants with a problem very similar to 

coordinating physical robots. 

We introduced a simple matching task as a secondary task to allow 

us to estimate the FT available to the operator. Participants were 

86
asked to perform this secondary task as possible when they were not 

occupied controlling a robot. Every operator action and periodic 

timestamped samples of the box’s moving speed were recorded for 

computing CD . 

A within subject design was used to control for individual 

differences in operators’ control skills and ability to use the interface. 

To avoid having abnormal control behavior, such as a robot 

bypassing the box bias the CD comparison, we added safeguards to 

the control system to stop the robot when it tilted the box. 

5.1 Participants and Procedure

14 paid participants, 18-57 years old were recruited from the 

University of Pittsburgh community. None had prior experience with 

robot control although most were frequent computer users. 

Participants performed three testing sessions in counterbalanced 

order. In two of the sessions, the participants controlled two P2AT 

robots using teleoperation alone or a mixture of teleoperation and 

waypoint control. In the third session, the participants were asked to 

control heterogeneous robots (one P2AT and one P2DX) using a 

mixture of teleoperation and waypoint control. The participants were 

allowed eight minutes to push the box to the destination in each 

session. At the conclusion of the experiment participants completed a 

questionnaire. 

5.2 Results 

Figure 5 shows a time distribution of robot control commands 

recorded in the experiment. As we expected no free time was 

recorded for robots in the teleoperation condition and the longest free 

times were found in controlling homogeneous robots with waypoints. 

The box speed shown on Figure 5 is the moving speed along the 

hallway that reflects the interaction effectiveness (IE) of the control 

mode. The IE curves in this picture show the delay effect and the 

frequent bumping that occurred in controlling heterogeneous robots 

revealing the poorest cooperation performance. 

None of the 14 participants were able to perform the secondary task 

while teleoperating the robots. Hence, we uniformly find TAD=1 and 

CD=1 for both robots under this condition. Within participants 

comparison found that under waypoint control the team attention 

demand in heterogeneous robots is significantly higher than the 

demand in controlling homogeneous robots, t(13)=2.213, p=0.045 

(Figure 5). No significant differences were found between the 

homogeneous P2AT robots in terms of the individual cooperation 

demand (P=0.2). Since the robots are identical, we compared the 

average CD of the left and right robots with the CDs measured under 

heterogeneous condition. Two-tailed t-test shows that when a 

participant controlled a P2AT robot, lower CD was required in 

homogeneous condition than in the heterogeneous condition, 

t(13)=-2.365. p=0.034. The CD required in controlling the P2DX 

under heterogeneous demand (CD) condition is marginally higher 

than the CD required in controlling homogenous P2ATs, 

t(13)=-1.868, p=0.084 (Figure 5). Surprisingly, no significant 

difference was found in CDs between controlling P2AT and P2DX 

under heterogeneous condition (p=0.79). This can be explained by 

the three observed robot control strategies: 1) the participant always 

issued new waypoints to both robots when adjusting the box’s 

movement, therefore similar CDs were found between the robots; 2) 

the participant tried to give short paths to the faster robot (P2DX) to 

balance the different speeds of the two robots, thus we found higher 

CD in P2AT; 3) the participant gave the same length paths to both 

robots and the slower robot needed more interactions because it 

trended to lag behind the faster robot, so lower CD for the P2AT was 

found for the participant. Among the 14 participants, 5 of them 

(36%) showed higher CD for the P2DX contrary to our expectations. 

Figure 5 The time distribution curves for teleoperation (upper) 

and waypoint control (middle) for homogeneous robots, and 

waypoint control (bottom) for heterogeneous robots 

6. EXPERIMENT 3 

To test the usefulness of the extended CD measureme for a weakly 

cooperative MRS, we conducted an experiment assessing 

coordination demand using an Urban Search And Rescue (USAR) 

task requiring high human involvement and of a complexity suitable 

to exercise heterogeneous robot control. In the experiment, 

participants were asked to control explorer robots equipped with a 

laser range finder but no camera and inspector robots with only 

cameras. Finding and marking a victim required using the 

inspector’s camera to find a victim to be marked on the map 

generated by the explorer. The capability of the robots and the 

cooperation autonomy level were used to adjust the coordination 

demand of the task.. 

6.1 Experimental design 

Three simulated Pioneer P2AT robots and 3 Zergs [1], a small 

experimental robot were used. Each P2AT was equipped with a front 

laser scanner with 180 degree FOV and resolution of 1 degree. The 

Zerg was mounted with a pan-tilt camera with 45 degree FOV. The 

robots were capable of localization and able to communicate with 

other robots and control station. The P2AT served as an explorer to 

build the map while the Zerg could be used as an inspector to find 

victims using its camera. To accomplish the task the participant must 

coordinate these two types robot to ensure that when an inspector 

robot finds a victim, it is within a region mapped by an explorer 

robot so the position can be marked. 

Three conditions were designed to vary the coordination demand on 

the operator. Under condition 1, the explorer had 20 meters detection 

range allowing inspector robots considerable latitude in their search. 

Under condition 2, scanner range was reduced to 5 meters requiring 

closer proximity to keep the inspector within mapped areas. Under 

condition 3, explorer and inspector robots were paired as subteams in 

which the explorer robot with a sensor range of 5 meters followed its 

inspector robot to map areas being searched. We hypothesized 

that CDs for explorer and inspector robots would be more even 

distributed under condition-2 (short range sensor) because explorers 

would need to move more frequently in response to inspectors’ 

searches than in condition-1 in which CD should be more 

asymmetric with explorers exerting greater demand on inspectors. 

87
We also hypothesized that lower CD would lead to higher team 

performance. Three equivalent damaged buildings were constructed 

from the same elements using different layouts. Each environment 

was a maze like building with obstacles, such as chairs, desks, 

cabinets, and bricks with 10 evenly distributed victims. A fourth 

environment was constructed for training. Figure 6 shows the 

simulated robots and environment. A within subjects design with 

counterbalanced presentation was used to compare the cooperative 

performance across the three conditions. 

6.2 Results 

Overall performance was measured by the number of victims found, 

the explored areas, and the participants’ self-assessments. To 

examine cooperative behavior in finer detail, CDs were computed 

from logged data for each type robot under the three conditions. We 

compared the measured CDs between condition 1 (20 meters sensing 

range) and condition 2 (5 meters sensing range), as well as condition 

2 and condition 3 (subteam). To further analyze the cooperation 

behaviors, we evaluated the total attention demand in robot control 

and control action pattern as well. Finally, we introduce control 

episodes showing how CDs can be used to identify and diagnose 

abnormal control behaviors. 

6.2.1 Overall performance 

Examination of data showed two participants failed to perform the 

task satisfactorily. One commented during debriefing that she 

thought she was supposed to mark inspector robots rather than 

victims. After removing these participants a paired t-test shows that 

in condition-1 (20 meters range scanner) participants explored more 

regions, t(16) = 3.097, p = 0.007, as well as found more victims, 

t(16) = 3.364, p = 0.004, than under condition-2 (short range 

scanner). In condition-3 (automated subteam) participants found 

marginally more victims, t(16) = 1.944, p = 0.07, than in condition-2 

(controlled cooperation) but no difference was found for the extent of 

regions explored. In the posttest survey, 12 of the 19 (63%) 

participants reported they were able to control the robots although 

they had problems in handling some interface components, 6 of the 

19 (32%) participants thought they used the interface very well, and 

only one participant reported it being hard to handle all the 

components on the user interface but still maintained 

Figure 6 Scout and Explorer robots 

she was able to control the robots. Most participants (74%) thought 

it was easier to coordinate inspectors with explorers with long range 

scanner. 12 of the 19 (63%) participants rated auto-cooperation 

between inspector and explorer (the subteam condition) as improving 

their performance, and 5 (26%) participants though auto-cooperation 

made no difference. Only 2 (11%) participants judged team 

autonomy to make things worse. 

6.2.2 Coordination effort

During the experiment we logged all the control operations with 

timestamps. From the log file CDs were computed for each type 

robot according to equation 2 in section 2. Figure 7 shows a typical 

(IT,FT) distribution under condition 1 (20 meters sensing range) in 

the experiment with a calculated CD for the explorer of 0.185, a CD 

for the inspector of 0.06. The low CDs reflect that in trying to control 

6 robots the participant ignored some robots while attending to others. 

The CD for explorers is roughly twice the CD for inspectors. After 

the participant controlled an explorer, he needed to control an 

inspector multiple times or multiple inspectors since the explorer has 

a long detection range and large FOV. In contrast, after controlling 

an inspector, the participant needed less effort to coordinate 

explorers. 

Figure 8 shows the mean of measured CDs. We predicted that when 

the explorer has a longer detection range, operators would need to 

control the inspectors more frequently to cover the mapped area. 

Therefore a longer detection range should lead to higher CD for 

explorers. This was confirmed by a two tailed t-test that found higher 

coordination demand, t(18) = 2.476, p = 0.023, when participants 

controlled explorers with large (20 meters) sensing range. 

We did not find a corresponding difference, t(18)=.149, p=0.884, 

between long and short detection range conditions for the CD for 

inspectors. This may have occurred because under these two 

conditions the inspectors have exactly the same capabilities and the 

difference in explorer detection range was not large enough to impact 

inspectors’ CD for explorers. Under the subteam condition, the 

automatic cooperation within a subteam decreased or eliminated the 

coordination requirement when a participant controlled an inspector. 

Within participant comparisons shows that the measured CD of 

inspectors under this condition is significantly lower than the CD 

under condition 2 (independent control with 5 meters detection 

range), t(18) = 6.957, p < 0.001. Because the explorer always tries to 

automatically follow an inspector, we do not report CD of explorers 

in this condition. 

As auxiliary parameters, we evaluated the total attention demand, i.e. 

the occupation rate of total interaction time in the whole control 

period, and the action pattern, the ratio of control times between 

inspector and explorer, as well. Paired t-test shows that under long 

sensing conditions, participants interacted with robots more times 

than under short sensing 

IT distribution

0 200 400 600 800 1000

Time (s)

R13 R22 R12 R21 R13 R23

Figure 7 Typical (IT,FT) distribution (higher line indicates the 

interactions of explorers). 

88
which implies that more robot interactions occurred. The mean 

action patterns under long and short range scanner conditions are 

2.31 and 1.9 respectively. This means that with 20 and 5 meters 

scanning ranges, participants controlled inspectors 2.31 and 1.9 times 

respectively after an explorer interaction. Within participant 

comparisons shows that the ratio is significantly larger under long 

sensing condition than under short range scanner condition, t(18) = 

2.193, p = 0.042. 

&'H[S0 &'LQV0 &'H[S0 &'LQV0 &'LQVVXEWHDP











0HDQ

(UURUEDUV&,

Figure 8 CDs for each robot type 

6.2.3 Analyzing Performance 

As an example of applying CDs to analyze coordination behavior, 

the performance over explorer CD and total attention demand under 

the 20 meters sensing range condition reveals three abnormal cases A, 

B, and C low on both CD and TAD. Associating these cases with 

recorded map snapshots, we observed that in case A, one robot was 

entangled by a desk and stuck for a long time, for case B, two robots 

were controlled in the first 5 minutes and afterwards ignored, and in 

case C, the participant ignored two inspectors throughout the entire 

trial. 

7. CONCLUSIONS

We proposed an extended Neglect Tolerance model to allow us to 

evaluate coordination demand in applications where an operator must 

coordinate multiple robots to perform dependent tasks. Results 

from the first experiment that required tight coordination conformed 

closely to our hypotheses with the teleoperation condition producing 

CD=1 as predicted and heterogeneous teams exerting greater demand 

than homogenous ones. The CD measure proved useful in 

identifying abnormal control behavior revealing inefficient control 

by one participant through irregular time distributions and close CDs 

for P2ATs under homogeneous and heterogeneous conditions (0.23 

and 0.22), a mistake with extended recovery time (41 sec) in another, 

and a shift to asatisficing strategy between homogeneous and 

heterogeneous conditions revealed by a drop in CD (0.17 to 0.11) in 

a third. 

As most target applications such as construction or search and rescue 

require weaker cooperation among heterogeneous platforms the 

second experiment extended NT methodology to such conditions. 

Results in this more complex domain were mixed. Our findings of 

increased CD for long sensor range may seem counter intuitive. 

Our data show, however, that this effect is not substantial and 

provide an argument for focused metrics of this sort which measure 

constituents of the human-robot system directly. Moreover, this 

experiment also shows how CD can be used to guide us to identify 

and analyze aberrant control behaviors. 

We anticipated a correlation between performance (found victims) 

and process (measured CDs) measures. However, we did not find the 

expected relationship in this experiment. From observation of 

participants during the experiment we believe that high level 

strategies, such as choosing areas to be searched and path planning, 

had a significant impact on the overall performance. The participants 

had few problems in learning to jointly control explorers and 

inspectors but needed time to figure out effective strategies for 

performing the task. Because CD measures control behaviors not 

strategies these effects were not captured. These experiments have 

demonstrated the utility of measuring the process of human-robot 

interaction as well as outcomes to diagnosing operator performance 

and identifying aspects of the task, particularly for multiple robots, 

that might benefit from automation. While our approach to 

measuring CD was supported in the last two experiments the third 

experiment suggests the need for more sophisticated measures that 

can take into account strategies and patterns of actions as well as 

their durations. 

8. ACKNOWLEDGEMENTS

This work was supported in part by the Air Force Office of 

Scientific Research under Grant FA9550-07-1-0039 and Office 

of Naval Research Grant N00014-03-1-0580. 

9. REFERENCES

[1] Balakirsky, S., Carpin, S., Kleiner, A., Lewis, M., Visser, A., 

Wang, J., and Zipara, V. Toward hetereogeneous robot teams for 

disaster mitigation: Results and performance metrics from 

RoboCup Rescue, Journal of Field Robotics, 2007, 24(11-12): p. 

943-967. 

[2] Carpin, S., Wang, J., Lewis, M., Birk, A., and Jacoff, A. (2005). 

High fidelity tools for rescue robotics: Results and perspectives, 

Robocup 2005 Symposium. 

[3] S. Carpin, T. Stoyanov, Y. Nevatia, M. Lewis, M.,J. Wang, 

(2006a). Quantitative assessments of USARSim accuracy". 

Proceedings of PerMIS 2006 

[4] Carpin, S., Lewis, M., Wang, J., Balakirsky, S., Scrapper, C. 

(2006b). Bridging the gap between simulation and reality in 

urban search and rescue. Robocup 2006: Robot Soccer World 

Cup X, Springer, Lecture Notes in Artificial Intelligence 

[5] J. W. Crandall, M. A. Goodrich, D. R. Olsen, and C. W. Nielsen. 

Validating human-robot interaction schemes in multitasking 

environments. IEEE Transactions on Systems, Man, and 

Cybernetics, Part A, 35(4):438–449, 2005 

[6] B. Gerkey and M. Mataric. A formal framework for the study of 

task allocation in multi-robot systems. International Journal of 

Robotics Research, 23(9):939–954, 2004. 

[7] A. Jacoff, E. Messina and J. Evans, Experiences in deploying 

test arenas for autonomous mobile robots. In Proceedings of the 

2001 Performance Metrics for Intelligent Systems (PerMIS) 

Workshop, Mexico City, Mexico, September 2001. 

[8] M. Lewis, S. Hughes, J. Wang, M. Koes and S. Carpin, 

Validating USARsim for use in HRI research, Proceedings of 

the 49th Annual Meeting of the Human Factors and Ergonomics 

Society, Orlando, FL, 457-461, 2005. 

[9] C. Pepper, S. Balakirsky and C. Scrapper. Robot Simulation 

Physics Validation, Proceedings of PerMIS’07, 2007. 

[10] N. Schurr, J. Marecki, M. Tambe, P. Scerri, N. Kasinadhuni, and 

J. Lewis, The future of disaster response: Humans working 

with multiagent teams using DEFACTO, In AAAI Spring 

Symposium on AI Technologies for Homeland Security, 2005. 

[11] A. Steinfeld, T. Fong, D. Kaber, M. Lewis, J. Scholtz, A. 

Schultz and M. Goodrich, M. (2006). Common Metrics for 

Human-Robot Interaction, 2006 Human-Robot Interaction 

Conference, ACM, March, 2006. 

89
[12] B. Taylor, S. Balakirsky, E. Messina and R. Quinn. Design and 

Validation of a Whegs Robot in USARSim, Proceedings of 

PerMIS’07. 

[13] Wang, J. Human Control of Cooperating Robots, dissertation, 

University of Pittsburgh, 

http://etd.library.pitt.edu/ETD/available/etd 

-01072008-135804/unrestricted/Wang_EDC_2007-final2.pdf 

(accessed 7/22/2008), 2007. 

[14] J. Wang and M. Lewis (2007) Human control of cooperating 

robot teams, 2007 Human-Robot Interaction Conference, ACM. 

[15] M. Zaratti, M. Fratarcangeli and L. Iocchi. A 3D Simulator of 

Multiple Legged Robots based on USARSim. Robocup 2006: 

Robot Soccer World Cup X, Springer, LNAI, 2006. 

90
The Gestural Joystick and the Efficacy of the Path 

Tortuosity Metric for Human/Robot Interaction 

Richard Voyles 

University of Denver 

2390 S. York Street 

Denver, CO USA 

1 (303) 871-2481 

rvoyles@du.edu 

Jaewook Bae 

Samsung Corp. 

1st 75 W. Plumeria Drive 

San Jose, CA USA 

baex0021@umn.edu 

Roy Godzdanker 

University of Denver 

2390 S. York Street 

Denver, CO USA 

roygod@gmail.com 

ABSTRACT

This paper describes the design and evaluation of the “gestural 

joystick,” a wearable 2-D pointing controller for mobile robots in 

hazardous environments that uses hand gestures. Hazardous 

environments, such as that of a collapsed building search, require 

operators to wear a significant amount of protective clothing. This 

protective clothing, which may include hard hats, suits, gloves, 

goggles, etc., reduces comfort, mobility, dexterity, load capacity, 

and ability to interact with conventional computer input devices. 

The gestural joystick, which is embedded in protective clothing, 

mitigates some of these impacts, but at the cost of lesser 

familiarity for the user and, therefore, potentially lesser 

performance. Effective performance metrics are required to 

evaluate this interface mechanism. Path tortuosity has been 

proposed as a performance metric for the evaluation of 

teleoperation of a robot, but has not been proven to be distinct 

from time-to-complete metrics. By injecting controlled 

uncertainty between the user and robot, we show, for the first 

time, that path tortuosity is a useful and distinct metric for the 

evaluation of robot teleoperation. 

Categories and Subject Descriptors

B.4.2 [Input/Output Devices]

General Terms

Human Factors 

Keywords

Human/robot interaction, path tortuosity, gestures. 

1. INTRODUCTION 

Urban search and rescue (USAR) has received much 

interest, recently, from robotics researchers around the 

world. Robots have a great deal to offer in that they are 

more expendable than humans, can be made smaller than 

humans to enter confined spaces, and can tolerate harsher 

conditions. Robots are routinely deployed during 

emergency response exercises and are increasingly being 

deployed during actual emergencies. For instance, after the 

September 11th attack on the World Trade Center, robot 

scientists contributed to USAR teams to search for trapped 

victims [1]. USAR robots are currently controlled 

exclusively via teleoperation but traditional input devices 

have proven inappropriate due to the protective clothing 

required [2]. Traditional human/computer interaction (HCI) 

devices are hampered by protective clothing including 

safety glasses, hard hats, respirators, and, most importantly, 

gloves. Gloves have been found to reduce operator 

effectiveness in many tasks [3]. Since emergency 

responders are required to wear heavy gloves to insulate 

themselves from the hazardous environment, we have been 

investigating ways to embed wearable human/robot 

interfaces into the bulky clothing itself -- exploiting it as an 

asset, rather then a liability. 

The prototype wearable glove-based input interface was 

Permission to make digital or hard copies of all or part of this work for 

personal or classroom use is granted without fee provided that copies are 

not made or distributed for profit or commercial advantage and that 

copies bear this notice and the full citation on the first page. To copy 

otherwise, or republish, to post on servers or to redistribute to lists, 

requires prior specific permission and/or a fee. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA.

Copyright 2008 ACM 978-1-60558-293-1...$5.00. 

Figure 1: Using the Gestural Joystick to operate a 

commercial Inuktun robot. 

91
presented in [13] (and shown in Figure 1) for our USAR 

robot, TerminatorBot [4], which is a miniature robot for 

core-bored inspection tasks. This interface paradigm grew 

from the burdens of providing an intuitive interface and 

controller for the TerminatorBot with conventional 

interaction devices (Figure 2). Conventional input devices, 

such as touch screen, mouse, keyboard and joystick, are 

cumbersome to operators wearing safety gears, even 

though they are small enough to carry conveniently. 

Conventional glove-based interfaces, such as the Power 

Glove, CyberGlove, MIT LED glove and others [5], have 

shown to be highly accurate for the recognition of various 

hand gestures [6], [7], [8], [9]. However, these glove 

interfaces require complex and fragile sensor structures and 

wires and are not suitable for use in rugged environments. 

We are developing a new paradigm of gestural joysticking 

for USAR tasks that reduces encumbrances, yet remains 

intuitive to non-technical operators. Evaluating novel 

paradigms is challenging, however, and requires great care. 

1.1 HRI Performance Metrics 

In the evaluation of user efficacy, metrics are necessary to 

measure how well a rescuer can control the robot under 

specified tasks [10], [11]. The development of metrics for 

USAR robots is still in its infancy, though the standard 

“time-to-complete” metric is commonplace. Steinfeld [11] 

tried to generalize common metrics for task-oriented HRI 

and built a standardized framework in HRI. However, the 

framework is difficult to apply to such a specific domain as 

that represented by USAR and development is still in 

progress. 

The time required to complete a specified, closed-ended 

task is a common metric for the efficacy of user interfaces. 

This metric is simple to implement, it results in a single, 

quantitative value that is easily compared, and it applies to 

many types of tasks and interfaces. If one interface requires 

the user to spend more time in completing a standardized, 

relevant task than another interface, it is reasonable to 

conclude that the former interface is inferior to the latter. 

More recently, researchers have begun to examine other 

metrics that relate more specifically to the robot 

teleoperation task. It has been suggested that the degree of 

smoothness of resulting motion of a human-directed robot 

control task is a good indicator of the quality of the 

human/robot interface [10]. Voshell et al termed this metric 

“path tortuosity” [10] and quantified it through fractal 

dimension [12]. They used the 2-D projection of a mobile 

robot’s motion on the ground to show that path tortuosity 

correlated well with user subjective opinions and time-tocomplete. However, to our knowledge, nobody has clearly 

demonstrated that path tortuosity is actually distinct from 

time-to-complete. Until now, the question has been left 

unanswered as to whether or not path tortuosity adds 

information or merely confirms time-to-complete 

measurements (which are easier to gather). In fact, path 

tortuosity often provides similar results to the easier to 

measure time-to-complete metric. 

In this paper, we employ two different metrics to evaluate 

the human/robot interface for a specific task: time-tocomplete and path tortuosity. In a test of non-technical 

users, we introduced varying degrees of uncertainty 

between the operator console and the robot, unknown to 

the operator. In effect, we were varying the quality of 

control they had over the robot in a controlled way, 

independent of the interface device. Our results provide 

evidence that path tortuosity is distinct from time-tocomplete and provides a complimentary measure of 

efficacy in human/robot interaction. 

Figure 2: The initial PDA-based interface for the 2. SYSTEM CONFIGURATION 

TerminatorBot is too confusing for non-technical users. The gestural input system (see Figure 3), which we call 

“WRIST” for Wearable Responder Interface for Search 

Tasks, forgoes the complex gestural capabilities of other 

glove interfaces, but also eliminates the encumbrances of 

these other interfaces such as wires, batteries, and active 

components. By simplifying the interface to only the 

pointing task, a robust, wearable, wire-free solution results 

that is suitable for hazardous environments with none of 

the difficulties of a complex alphabet to memorize. Based 

on permanent magnets and sensitive Giant 

Magnetoresistive (GMR) detectors, analog 

forward/backward and right/left gestures are encoded into 

commands that can be relayed to a robot, personal 

computer, or other device requiring pointing information. 

Calibration of the sensitive but highly nonlinear GMR 

detectors is described in [15]. User evaluation tests are 

presented below for a simulated search and rescue task to 

compare controllability to a conventional joystick. These 

92
tests employ not only the standard metric of time-tocomplete, but add a metric for path tortuosity based on the 

fractal dimension of the robot's traced path. Possibly for the 

first time, we demonstrate the independence of the path 

tortuosity metric from the time-to-complete metric for 

pointing controllability. 

WRIST provides unencumbered wearability that can be 

easily equipped on many styles of traditional gloves with 

minimal modifications. Moreover, the hardware structure 

of the system should permit intuitive and robust operation. 

The embedded rare-earth permanent magnets (Figure 4) 

have relatively small size and consume no power. The 

sensor pad is integrated with eight GMR sensors and is 

worn on the wrist or embedded in the fringe of the sleeve. 

The magnets and sensors interact with no interconnecting 

wires allowing the glove to be easily removed. 

The signal strength of each magnetic sensor changes with 

wrist motion. The redundant sensor signals are continually 

monitored by the CPU where they are translated into the 

four directional components as described later. The sensor 

pad contains 8 GMR sensors (AA004, NVE Co., Eden 

Prairie, Minnesota, USA) and 8 op-amps on a flexible 

printed circuit board (PCB). The sensor pad can be 

completely wrapped around the wrist. The PCB is about the 

thickness of a piece of paper making it easy to embed into a 

sleeve. 

The CPU module is built around the Atmel Corporation's 

8-bit AtMega128 RISC microprocessor. Its Analog/Digital 

converters can process eight analog signals from the eight 

magnetic sensors. Each Analog/Digital converts a signal 

into a 10-bit digital output. The glove of WRIST includes 

nothing but four rare-earth magnets. Therefore, it is 

washable and virtually unbreakable. 

Figure 3: The WRIST system consists of an array of 

magnets on the glove, an array of sensors on the sleeve, and 

a data processor. 

Figure 5: Usability tests based on the NIST gate model. 

Top is a virtual robot driven through a single gate to a goal 

position. Bottom is the trace of a physical Inuktun robot 

Figure 4: Configuration of the magnets and GMR sensors. driven through a single gate to a goal position. 

93
3. USABILITY EVALUATION 

A variety of usability tests were developed to test operator 

performance with WRIST in comparison to a conventional 

joystick and a mouse in two different modes (position and 

velocity mode). Fitz’ Law tests were performed as well as 

physical mobility tests and virtual and physical robot 

control tests based on the NIST “gate” model. The focus of 

this paper will be on the virtual and physical robot control 

tests. 

In the NIST gate model, a single robot is teleoperated to 

navigate through a narrow gate, as shown in Figure 5. 

While the tests by NIST have used multiple gates, we use 

only one, for simplicity. 

While the path tortuosity metric has been proposed before 

[10], it has not been proven to provide information that is 

independent of the time-to-complete metric. Although it is 

intuitive to use such a metric, many tests show close 

correspondence between the two. For example, in Figure 6, 

we show the results of five separate trials for the WRIST 

system and a conventional joystick. (Time to complete is 

on the top while fractal dimension is on the bottom.) Both 

metrics trend downward as gap width increases, meaning 

that the quality of control increases (task time gets shorter 

and the path gets smoother) for each interface device as the 

course gets easier. This is the expected result and shows 

that path tortuosity is consistent with intuition and time-tocomplete, but it does not demonstrate path tortuosity is 

actually providing new information. 

3.1 Verification of the Uniqueness of Path 

Tortuosity 

In an effort to validate the independence of the metric, we 

deliberately introduced random error into the control 

software of certain test subjects without the test subject's 

knowledge. This error manifested itself in the form of a 

random angular offset in the motion direction of the cursor 

commanded by the user. In effect, this error controlled the 

degree of inaccuracy with which the user could control the 

cursor for the devices tested. 

The distribution of the angular error was Gaussian and we 

made no modification to the commanded magnitude. For 

our operator pool, we used over one hundred nonengineering undergraduate students in a laboratory class 

that introduces them to technology. The task was explained 

to them and they were given one practice trial with each of 

five different interface devices. The interface devices 

included the WRIST system, a joystick, a trackball, a 

mouse in position mode and a mouse in velocity mode. 

Only a small subset of the data is presented here. 

In comparing these "perturbed" runs to normal runs across 

several users, we found that time-to-complete was not 

reliably correlated with the actual inaccuracy of the trial, 

which is assumed to be dictated by the introduced error. 

The path tortuosity, as computed through Fractal 

Figure 6: Top set of plots show the time-to-complete metric for five trials each of the WRIST and a conventional joystick as gate 

width increases. The bottom set of plots show path tortuosity for the same devices and gate tasks. The two metrics trend the 

94
dimension, was a more reliable predictor of the introduced 

error. 

The data are difficult to interpret as a pronounced learning 

effect is evident in the results (Figure 7). The subjects are 

not particularly tech savvy so many of the interface devices 

were new to them and they were only given one practice 

trial. As they moved through the five trials with each 

device, negative slopes are apparent as time-to-complete 

and path tortuosity both decrease with practice. 

Furthermore, the gate width was varied for many of the test 

subjects, which varies the difficulty of the task. This 

introduces a negative or positive slope depending on 

whether the width is increasing or decreasing. 

Group 1: Normal then Noise - Shrinking Gap

0

5000

10000

15000

20000

25000

1 2 3 4 5 6 7 8 9 10

Time (ms)

0.88

0.9

0.92

0.94

0.96

0.98

1

1.02

1.04

Fractal Dimension

21072 Time 23058 Time 24085 Time

21072 Frac Dim 23058 FD 24085 FD

Group 2: Noise then Normal - Shrinking Gap

0

5000

10000

15000

20000

25000

30000

1 2 3 4 5 6 7 8 9 10

Time (ms)

0.82

0.84

0.86

0.88

0.9

0.92

0.94

0.96

0.98

1

1.02

1.04

Fractal Dimension

22075 Time 24062 Time 25090 Time

22075 FD 24062 FD 25090 FD

Figure 7: Group 1, top, and Group 2, bottom, indicating the 

trend over two devices and noise conditions for both time-tocomplete metric and path tortuosity. Test subjects are denoted 

by number. 

To counteract these effects, we look at complementary test 

suites that reverse the effects. For example, we took two 

groups of test subjects and had them use devices in the 

same order; in this case, mouse in velocity mode followed 

by the joystick. (Five trials with each device are 

completed.) Over the five trials, the gate width is gradually 

reduced, making the task more difficult and offsetting the 

learning effect. The complementary tests groups had noise 

injected at different times, however. By examining the 

slope and intercept of the trends, we can spot significant 

artifacts in the metrics. 

Group 1 had noise introduced into the mouse tasks but not 

the joystick tasks while group 2 had noise introduced into 

the joystick tasks but not the mouse tasks. With the 

offsetting effects of learning and increasing difficulty, the 

slopes are near zero. 

With the slope near zero, we can focus on the intercept to 

see which is higher or lower in relation to the device and 

noise. The intercepts are tabulated below and we see that 

path tortuosity is a more reliable predictor of the introduced 

noise than time-to-complete. (Erroneous cases are 

highlighted in Table 1.) 

Table 1: Regression statistics of groups of user data. 

Group Device/Noise Time 

Intercept 

Fractal 

Dimension 

Intercept 

Group 1 Mouse/No 17310 0.988 

Group 1 Joystick/Yes 20150 0.979 

Group 1 Mouse/No 18680 0.992 

Group 1 Joystick/Yes 22220 1.000 

Group 1 Mouse/No 13960 0.942 

Group 1 Joystick/Yes 18790 0.966 

Group 2 Mouse/Yes 18950 0.964 

Group 2 Joystick/No 22830 0.919 

Group 2 Mouse/Yes 22810 0.945 

Group 2 Joystick/No 18070 0.919 

Group 2 Mouse/Yes 12790 0.959 

Group 2 Joystick/No 14620 0.938 

MouseVel Joystick 

MouseVel Joystick 

To further demonstrate the independence of path tortuosity, 

we gathered another set consisting of two groups of data: a 

"Noisy" group of 6 test subjects with random error 

introduced and a "Normal" group of 22 test subjects. Since 

it is meaningless to directly compare the performance of 

individual test subjects, we exhaustively compared the 

average performance (both time-to-complete and path 

tortuosity) of every subgroup of four test subjects from 

each group. This resulted in 15 Noisy subgroups (6

C4 – 6-

choose-4) and 7315 Normal subgroups (22C4). 

Comparing every Noisy subgroup to every other Normal 

subgroup involved over 100,000 comparisons. Of these 

comparisons, the fractal dimension of the noisy subgroup 

was greater than the fractal dimension of the normal 

95
subgroup 99.5% of the time while the time-to-completion 

of the noisy subgroup was greater than the time-tocompletion of the normal subgroup 49.4% of the time 

(essentially chance). 

Figure 8: Random sampling of group comparisons with 

time-to-complete, top, and path tortuosity, bottom, for robot 

teleoperation tasks with and without noise introduced. 

4. CONCLUSION 

A large number of tests have been conducted on both 

technical and non-technical users to determine the 

usefulness of the WRIST system in human/robot 

interaction. Over 120 users were tested with various input 

devices, including the WRIST system, a mouse, a joystick, 

and a trackball on both simulated robots and physical 

robots. We gathered both quantitative results and 

qualitative results. Our quantitative user test results indicate 

users were not as proficient, in either time-to-complete or 

path tortuosity, in using the WRIST as compared to the 

joystick or mouse. This is not surprising as nearly all users 

had some familiarity with these devices. In fact, learning 

rates were extrapolated from the data and the WRIST, 

indeed, shows a much higher improvement rate over the 

trials. In qualitative evaluations from non-technical users 

who had little prior exposure to use of a joystick, users 

preferred the WRIST system for its more intuitive nature. 

Coupling this result with the portability of the device and 

other unmeasured benefits of its wire-free nature leads us 

to believe it will be a successful interface when fully 

developed. 

The discrimination between the time-to-complete and path 

tortuosity metrics is highly meaningful. It seems intuitive 

that the two metrics would be distinct, but we believe this 

is the first result that demonstrates they are, in fact, distinct 

and separably valuable. 

5. ACKNOWLEDGMENTS 

Partial funding for this work was provided by the NSF 

Safety, Security and Rescue Research Center and by NSF 

through grant 0719306. Thanks to Robin Murphy and the 

NSF R4 program for the loan of the Inuktun robot. 

6. REFERENCES 

[1] R. Murphy, “Human-robot interaction in rescue robotics,” 

IEEE Systems, Man and Cybernetics, vol. 34, no. 2, May 

2004. 

[2] K. Newman, “The open interface: Beyond keyboards and 

mice,” e.nz Magazine, May 2002. 

[3] G. I. of Technology, “Real-time cooperative behavior for 

tactical mobile robot teams,” Georgia Tech College of 

Computing and Georgia tech research Institute: Final Report, 

vol. A003, 2001. 

[4] R. M. Voyles, A. C. Larson, M. Lapoint, and J. Bae, “Corebored search and rescue applications for an agile limbed 

robot,” in Proceedings of the 2004 IEEE/RSJ International 

Conference on Intelligent Robots and Systems, vol. 1, 2004, 

pp. 58–66. 

[5] D. Sturman and D. Zeltzer, “A survey of glove-based input,” 

in IEEE Computer graphics and Applications, 1994. 

[6] G. Kessler, L. Hodges, and N. Walker, “Evaluation of the 

cyberglove as a whole-hand input device,” in ACM 

Transactions on Computer-Human Interaction, vol. 2, no. 4, 

1995, pp. 263–283. 

[7] B. H. Thomas and W. Piekarski, “Glove based user 

interaction techniques for augmented reality in an outdoor 

environment,” Virtual Reality, vol. 6, pp. 167–180, 2002. 

[8] B. Thomas and W. Piekarski, “Glove based user interaction 

techniques for augmented reality in an outdoor 

environment,” Virtual Reality, vol. 6, no. 3, pp. 167–180, 

2002. 

[9] R. Voyles and P. Khosla, “A multi-agent system for 

programming robots by human demonstration,” Integrated 

Computer-Aided Engineering, vol. 8, no. 1, pp. 59–67, 2001. 

[10] M. Voshell, D. Woods, and F. Phillips, “Overcoming the 

keyhole in human-robot coordination: simulation and 

evaluation,” in Proceedings of the Human Factors and 

Ergonomics Society, pp. 26–30, 2005. 

[11] A. Steinfeld, T. Fong, D. Kaber, M. Lewis, J. Scholtz, A. 

Schultz, and M. Goodrich, “Common metrics for humanrobot interaction,” in Human-Robot Interaction Conference, 

March 2006. 

96
[12] Mandelbrot, B., “How Long is the Coast of Britain? 

Statistical Self-Similarity and Fractional Dimension,” 

Science, v. 156, n. 3775, pp. 636-638, 1967. 

[13] J. Bae and R. Voyles, “Wearable joystick for gloves-on 

human/computer interaction,” in Proceedings of the SPIE 

Defense and Security Symposium, Orlando, FL, April 2006. 

[14] M. Goldstein, D. Chincholle, and M. Backstrom, “Assessing 

two new wearable input paradigms: The finger-joint-gesture 

palm-keypad glove and the invisible phone clock.” Personal 

and Ubiquitous Computing, vol. 4, no. 2/3, 2000. 

[15] J. Bae, A. Larson, R.M. Voyles, R. Godzdanker, J. Pearce, 

"Development and User Testing of the Gestural Joystick for 

Gloves-On Hazardous Environments," in Proc. of the IEEE 

Intl. Symp. on Robot & Human Interactive Communication, 

Jeju, Korea, Aug. 2007, pp. 1096-1101. 

97
Modeling of Thoughtful Behavior with Dynamic 

Expert System

Vadim Stefanuk 

Institute for Information Transmission Problems, 

Russian Academy of Science, 

Bolshoy Karetny per. 19

127051 Moscow, Russia 

7 495 6504679 

stefanuk@iitp.ru 

ABSTRACT 

The concept of Dynamic Expert System, used in this paper to cope 

with changing data and knowledge, was introduced at the start of 

1990th. 

Implemented via a quasi-static approach, the Dynamic Expert 

System presents a certain step forward in the modeling of 

intelligent behavior, which reminds that of human beings. There 

are two reasons for such a claim. First, in general case Dynamic 

Expert System never interrupts its activity, occasionally 

interrogating the user if it suspects that some of the previously 

entered data are obsolete or become unsatisfactory in some other 

way. This mode reminds the behavior of an alive, as it was 

discussed in a number of our previous publications. 

The present paper considers a second important reason. It shows 

that Dynamic Expert System in certain sense resolves the Frame 

Problems of AI, demonstrating the level of reasoning, which is 

very close to that of human beings. A simple example of a 

rule-based traffic light control illustrates this property. 

Keywords

Dynamic Expert System, Frame Problem, Artificial alive 

creature, Thoughtful Behavior, traffic lights. 

1. INTRODUCTION 

Recently there was a new wave of interest to the AI systems 

working in realistic surroundings as the ideas of data 

accumulation and the knowledge evolution were recognized 

as their important characteristics. In this paper it is proposed 

to treat corresponding problems via the concept of Dynamic 

Expert System. This term and the concept were introduced 

at the start of 1990th when a quasi-static approach to the 

system dynamics has been proposed [5]. The quasi-static 

approach provides a smooth combination of static and 

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not made or distributed for profit or commercial advantage and that copies 

bear this notice and the full citation on the first page. To copy otherwise, or 

republish, to post on servers or to redistribute to lists, requires prior specific 

permission and/or a fee. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA. 

Copyright 2008 ACM 978-1-60558-293-1 $5.00. 

change, when during certain time the knowledge used 

considered to be stable allowing for an inference to be made. 

However over larger time intervals some drastic 

modifications of the knowledge are allowed. 

The implemented system found its first application in the 

seismology domain [5-7]. The Dynamic Expert System in 

this application never stops reacting to any new information 

on the various seismic predecessors arriving to the system. 

From time to time the system itself interrogates the user if it 

suspects that previously entered data are obsolete. In this 

respect the system behaves itself as an alive. In the present 

paper we will try to develop further this observation and to 

show that its behavior may be considered also as a 

thoughtful one. 

The results of this paper supplement the paper [8], where it 

was shown that the concept of Dynamic Expert System is 

tightly related to the area of Empirical Bayesian Schemes 

and to the modern area of Modeling Field Theory Dynamic 

[4]. 

2. CLASSIC FRAME PROBLEM 

The proposed concept of Dynamic Expert System is not 

only useful in applications as described in [6]. There are 

some grounds to expect it may be a new step in the 

development of the whole area of Artificial Intelligence as it 

leads to the design of an artifact system, which is alive and 

has the intellectual behavior in a real sense of the word. 

The reason for so ambitious statement lies in the fact that our 

Dynamic Expert System resolves the Frame Problems first 

mentioned by J.McCarthy and P.Heyes in [3], which was 

considered to be the main obstacle on the way of further 

progress in Artificial Intelligence. 

The original formulation of the problem is the following one. 

Let in the situational calculus [3] it is asserted that 

Holds (Situation_0, Black (Block A)) 

Holds (Situation_0, Separate (Block A)) 

Holds (Situation_0, Separate (Block B)) 

 98
Is the following statement correct? 

Holds (Result (Put-on (Block A, Block B), Situation_O), 

Black (Block A)) 

In other words if one puts the Block A on the Block B, is it 

true that the color of the Block A would remain black? It 

turned out that rather obvious for a human being positive 

answer is not automatically obtainable in the Situation 

Calculus Certain additional statements have to be made to 

arrive to such an answer, like the following one [3]: 

Holds (Situation_O, Black(Block A)) 

à Result (Put_On(Block A, Block B), Situation_0), 

Black(Block A)) ,

which explicitly shows that the Block A does not change its 

color. 

The Frame Problem became a tough problem for AI due to 

the fact that the number of additional frame statements may 

be enormous one to be realistic in applications. There were 

many attempts to overcome the problem by the proper 

choice of logic formalisms, which have created actually 

some other equivalent problems (see the information on 

WWW). 

One practical solution was to use ‘a natural law of inertia’ or 

‘do not touch sleeping dog’ which roughly admits that 

things do not change if the change was not mentioned 

explicitly in the system. The Frame Problem was solved to 

some extend in the system STRIPS to control a robot, where 

the objects to be moved were real things shifted around 

research laboratory, which obviously ‘do not change their 

colors’. 

The other important side of the Frame Problem was stressed 

by Marvin Minsky: it is not clear at all how to find and 

remove from the memory of a robot all the consequences of 

an action if the situation changed and this action was not 

performed (see also [1]). 

Such situations are quite natural for a human, who has to 

reconsider his actions many times a day when he comes 

across with new situations. He understands clearly, what has 

preserved and what changed in transition form one situation 

to another. It looks like the problem does not really exist for 

a human being. 

 It must be especially difficult for an intelligent computer 

controlled robot due to the fact that even if some data and 

knowledge were fixed initially, the inferences from those 

may combine with the inferences obtained from the 

knowledge, which is modifiable, and the total result of the 

inferences becomes unclear. 

3. PHILOSOPHICAL ASPECTS 

For the purpose of our paper it is important to note that the 

Frame Problem obtained also a philosophical interpretation, 

which demonstrates that this problem distinguishes the 

behavior of an alive from that of an ordinary computer 

program. In other words, if one finds an adequate solution 

for the Frame Problem he probably deals with an artificial 

creature, which may be referred to as an alive. 

Dannett in [1] formulated an Epistemological Frame 

Problem, how ‘a cognitive creature ... with many beliefs 

about the world” can update those beliefs when it performs 

an act so that they remain “roughly faithful to the world” ’? 

Fodor puts a similar question [2]: ‘How does the machine's 

program determine which beliefs the robot ought to 

re-evaluate given that it has embarked upon some or other 

course of action?’ 

Almost the same is said in the publication [9], where an 

importance of limited time and adaptation to changes are 

stressed: ‘A more intricate problem in the notion of 

adaptiveness, how can we expect to reuse results from 

earlier proofs when the circumstances change? The author 

plans to investigate these questions for the particular 

application domain of intelligent help’. 

Concluding the paragraph we have to say that the logic is 

‘quite correct’ at this point: the color of a block may change 

when the situation changes, for example due to a subtle 

change in the illumination or something similar. The Frame 

Problem should not be resolved by changing the logical 

formalism used. It is the problem that must be recognized 

and taken into account in the design of an advanced 

computer system. For us it is important to note that the 

system taking this problem into consideration should be 

recognized as a new step in creation of artificial intellectual 

entity, similar to the intelligent things existing in Nature. 

In our Dynamic Expert System some modification of any 

property is possible only when a certain rule in the 

Knowledge Base admits such a modification or the rule 

being brought into the system by the user from outside. 

Then, it is the responsibility of our system to modify 

accordingly the believes, which currently exist in the system. 

Thus, the Dynamic Expert System resolves the Frame 

Problem in a way it is done by a human. 

4. QUASI-STATIC ARCHITECTURE 

The quasi-static mode we described in [5,6] and elsewhere. 

It results from a certain modification of our static ES 

ZNATOK and a recursive use of this shell during one 

session of interaction with the user. At each recursive step 

practically all the data and all involved rules may be 

modified. Of course, if there are reasons for such 

modifications in the original KB or they are forced by the 

interaction with the system user. 

 99
 

Our quasi-static architecture resolves the classic problem – 

how to remove all the consequences, which follows from a 

certain fact if the fact is not true any more. At least it is 

achieved in “a pure ES shell” with only pure rules [6]. 

When the static shell ZNATOK is used in the dynamic mode, 

the Knowledge Engineer should take special care for the 

possible side effects in order to obtain an appropriate 

behavior of the system. This requires from the Knowledge 

Engineer a deep understanding both system architecture and 

the problem domain. 

By the way, as it was mentioned in [6], the total number of 

possible side effects is doubled in a quasi-static mode with 

respect to the static mode. For each relative side effect, 

created by the form F1 for form F2 in static case, in the 

dynamic mode one has to consider the possibility to have a 

side effect of the form F2 for the Form F1. However, the 

side effects are the most powerful way to achieve a 

flexibility and effectiveness of the system performance and 

we want to keep them. 

One of the important tasks for the Knowledge Engineer is to 

achieve an operational coherence when the side effects are 

used. Partially, operational coherence may be tested if one 

tries the shell in a number of static environments. 

To achieve the operational coherence and the effectiveness 

the types for the system attributes were introduced in the 

system such as dynamic, static, fuzzy, and etc. The dynamic 

type restricts the number of attributes that may be 

reconsidered. The fuzzy type reduces the required 

computational efforts by distinguishing ordinary attributes 

from the fuzzy ones [7]. 

5. TRAFFIC LIGHTS CONTROL 

Our Dynamic Expert System, which is originally “tuned to” 

modification of the data and rules of the system on the run, 

naturally solves the Frame Problem in this application. 

In this application the data considered are to be either of 

static or dynamic type. Based on the Dynamic Expert 

System Shell “Seismo” [5,7] the traffic system is designed 

in such a way that new dynamic value automatically causes 

a proper change to all other values involved in the inference. 

Due to this and other important properties we avoid the 

difficulty that was referred to as the Frame Problem. 

This property will be illustrated here with an example of the 

traffic light control, which looks a bit more practical in 

comparison to the Block Word models of AI. 

In case of pedestrian controlled traffic light, if the variable 

color is announced to be static one the light would behave 

itself incorrectly. Either it would not change the color, or the 

color would change itself accordance with a rule stored in 

the Knowledge Base of the Dynamic Expert System. If the 

type of the variable color were said to be dynamic one, the 

pedestrian traffic light would work quite correctly. 

Indeed, normally the pedestrian controlled traffic light will 

be in the state of ‘green‘ towards approaching cars, thus 

creating no obstacle for the traffic. It changes its color for 

the yellow and then for the red one, if a person wants to 

cross the street and pushes the corresponding button. 

6. CONCLUSION 

The Dynamic Expert System presents a certain step forward 

in the modeling of intelligent behavior, which reminds that 

of human beings. There are several reasons for such a claim. 

In the present paper it is shown that Dynamic Expert System 

resolves the Frame Problems of AI in a certain sense, thus 

demonstrating the level of reasoning, which is very close to 

that of a human. A simple example of a rule-based traffic 

light control illustrates this property. In this example the 

Dynamics of our system becomes quite essential. 

7. ACKNOWLEDGEMENTS 

This research was partially supported by the Russian Fond 

for Basic Research and with the Fundamental research 

program by Presidium of Russian Academy of Science.

8. REFERENCES 

[1] Dennett, D. Brainstorms. Cambridge, MIT Press, 1978. 

[2] Fodor, J.A. The Modularity of Mind. Cambridge, MIT Press, 

1983. 

[3] McCarthy, J. & Hayes, P.J. “Some Philosophical Problems 

from the Standpoint of Artificial Intelligence”, in Machine 

Intelligence 4, ed. D.Michie and B.Meltzer, Edinburgh: Edinburgh 

University Press, pp. 463-502, 1969. 

[4] Perlovsky L.I., Neural networks and intellect: Using model 

based concepts, Oxford University Press, New York (2001). 

[5] Stefanuk V.L. The Behavior of Quasi-static Shell in Changing 

Fuzzy Environment, The Proceedings of the IY National Artificial 

Intelligence conference KII'94, Rybinsk, V.1, pp.199-203, 1994, 

(in Russian) 

[6] Stefanuk V.L., Dynamic expert systems. KYBERNETES, 

The International Journal of Systems & Cybernetics. V.29, Issue 5, 

pp. 702-709, MCB University Press: 2000. 

[7] Stefanuk V., Intellectual Performance using Dynamical Expert 

Knowledge in Seismic Environment. Proceedings of the Workshop 

“Performance Metrics for Intelligent Systems (PerMIS'06)”, 

http://www.isd.mel.nist.gov/PerMIS_2006/proceedings/ 

PerMIS_Program.pdf

[8] Stefanuk V.. Dynamic Knowledge Processing – Practical 

Approach. In Proceedings of 2007 International Conference on 

Integration of Knowledge Intensive Multi-Agent Systems 

(KIMAS’07), Copyright © IEEE, Prining House, Inc., Stoughton: 

2007, pp. 22-27. 

[9] Wern, A., Reactive Abduction. Proceedings of ECAI-92, 

pp.159-163. 

100
Ontological Perspectives for Autonomy Performance 

Hui-Min Huang, Elena Messina, Tsai-Hong Hong, Craig Schlenoff 

National Institute of Standards and Technology (NIST) 

100 Bureau Drive, MS 8230 Gaithersburg, Maryland 20899 USA 

+1.301.975. { 3427, 3510, 3444, 3456 } 

{ hui-min.huang, elena.messina, tsai-hong.hong, craig.schlenoff }.nist.gov 

ABSTRACT 

Goals must be assigned for any unmanned system’s (UMS) 

operation before the system’s autonomous performance can be 

measured. This paper reports the early results of construction of 

an ontology for mission goals that could serve as a template for 

stating the goal. The Autonomy Levels for Unmanned Systems 

(ALFUS) Framework is a key element in the ontology. In other 

words, we design the goal ontology in terms of mission, 

environment, and operator interaction aspects. We also leverage a 

collection of related efforts to further evolve the goal ontology, 

including the Urban Search and Rescue (US&R) robots 

requirements set, the Perception System for Dynamic 

Manufacturing, and an extension to the NIST-participated 

Defense Advanced Research Projects Agency (DARPA) Spoken 

Language Communication and Translation System for Tactical 

Use (TRANSTAC) project. 

Categories and Subject Descriptors

J.2 [physical sciences and engineering] ontology, unmanned 

systems performance 

General Terms

Measurement, Performance, Design, Human Factors, 

Standardization, Verification 

Keywords

ALFUS, communication, environment, goal, manufacturing, 

metrics, mobility, ontology, sensor, terminology, urban search and 

rescue (US&R) 

1. INTRODUCTION 

Unmanned systems (UMSs) have been playing increasingly 

important roles in many aspects of the society. In a broad sense, 

UMS includes the unmanned vehicles that aid military operations, 

the robots that aid bomb disposal tasks, the robots that help the 

search and rescue operations, and the automation machine 

systems that perform the part manufacturing and assembly tasks. 

It is vital for practitioners to be able to model the systems and 

measure their performances. 

We propose to develop an ontology for a generic UMS. The 

ontology should provide a comprehensive and structural 

organization for the UMS knowledge, including the hardware, 

software, interfaces, performance, etc. Figure 1 provides an 

overview. All the aspects must be defined and formally related. 

Typically, a UMS is to perform goals that the operator assigns. 

Many issues need to be addressed, including how to acquire a 

UMS that fits the needs, how to state the goals to allow precise 

execution, how to evaluate the performance, etc. We envision the 

ontology to be able to provide all these features for practitioners. 

Figure 1: High Level View of the Ontology 

The development effort is underway. This paper describes the 

first increment of results from this effort. 

1.1 Scope of the Ontology 

This paper describes the development of a particular subset of the 

ontology, the UMS goal. Given the fact that UMSs may be 

commanded to perform different types of tasks, it is important to 

devise a sound approach to knowledge acquisition and 

organization. Our plan is to develop a structure such that the 

generic aspects can be instantiated and applied to different 

applications. We also describe how performance metrics are 

included in the ontology and are measured by comparing the 

metrics and the goal.

1.2 Aspects of the Ontology 

In the area of information technology, we define ontology as a 

rigorous or formal model that encompasses a collection of 

concepts and their relationships for the topic of interest [1, 2, 3, 

4, 5, 6, 7]. As such, we propose that ontology should cover the 

following aspects: 

x Terminology and definitions 

This paper is authored by employees of the United States 

Government and is in the public domain. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA. 

ACM ISBN 978-1-60558-293-1/08/08.

x Requirements/capability attributes 

x Performance metrics 

101
x Engineering specifications 

x Standards 

In other words, to develop an ontology for a topic, the engineer 

should: 

x identify the key concepts from the terms and definitions 

used in the domain, 

x identify the user, capability, and performance 

requirements for the program, and 

x utilize engineering specifications and applicable 

standards for the UMS and its subsystems and 

components. 

In this first increment for development of a UMS ontology, we 

begin with the terminology, metrics, and requirements aspects and 

leave the others for future development. 

1.3 Performance Metrics—ALFUS 

Framework Overview 

The performance of UMS must be measured in terms of the 

assigned goals. It is desirable to have a generic and standard 

structure for stating the goal. There are multiple concerns in the 

goal statement, including operation (or mission), environment, 

and operator interactions. These lead us to apply the Autonomy 

Levels for Unmanned Systems (ALFUS) Framework that NIST 

has been developing [8]. The ALFUS Framework describes that 

the autonomy of a UMS can be characterized with Contextual 

Autonomous Capability (CAC). The CAC model is composed of 

the following three aspects (or axes), Mission Complexity (MC), 

Environmental Complexity (EC), and Human Independence (HI), 

as shown in Figure 2. Each axis is further decomposed into a set 

of performance metrics. 

Figure 2: The ALFUS Framework 

The ALFUS Framework was developed originally by the ad hoc 

ALFUS Working Group (WG) that was lead by NIST. The group 

has later joined the Society for Automotive Engineers (SAE), a 

standards development organization, as the UMS Performance 

Measures Subcommittee. 

During the first ALFUS workshop, it was determined that the first 

objective of the group should be terminology [9]. This is because 

the ALFUS WG decided to take a definition-based approach. The 

fundamental terms, including autonomy and UMS were defined. 

The key words and their relationships were further developed into 

additional terms, sub-relationships, as well as metrics. This fits 

well with the ontology concept. Figure 3 illustrates this construct. 

The MC metrics correspond to, among other aspects, the accuracy 

and repeatability aspects of a goal. The EC metrics correspond to 

the spatial and temporal aspects of the goal statement. Human 

interaction may be critical in assisting the robot to reach a safe 

state or to reach the goal. 

Figure 3: ALFUS Framework Structure 

1.4 The Involved Use Cases and Concepts 

In the three project activities that we use to further evolve this 

ontology, the US&R robots project has generated a 

comprehensive requirements set through intense interactions with 

the user community. The perception system for dynamic 

manufacturing project also derived a set of requirements from a 

workshop attended by the industry. We use these results to iterate 

the goal ontology. The TRANSTAC project uses a System, 

Component, and Operationally-Relevant Evaluation (SCORE) 

approach to evaluate the candidate systems. We began to apply 

some of the key concepts of SCORE in formulating the ontology 

[10, 11]. 

2. PERFORMANCE CHARACTERISTICS 

AND REQUIREMENTS 

The performance characteristics or requirements of various UMS 

systems were analyzed and pertinent elements were extracted for 

the development of the ontology, namely, the ontological model 

of the mission goal for UMS. The following described two use 

cases. 

2.1 Teleoperation Requirements for US&R 

Federal Emergency Management Agency (FEMA) US&R Task 

Force personnel would be among the users who would teleoperate 

the robots for search and rescue operations. Figure 4 provides an 

example of the types of terrain which the US&R robots might 

have to traverse [11, 12]. 

The users conveyed to the NIST project team how they anticipate 

the robotic technology could help them. This typifies the 

interaction between users and technologists who may be 

implementing the requirements. The entire set of the requirements 

can be seen in [13]. The existent ontology work in this area 

includes [14, 15]. 

102
Figure 4: Rubble Pile that Robots Might have to Traverse 

For this development effort, we examine a subset of the 

requirements and attempt to restructure them to facilitate the 

ontology implementation. We also apply engineering disciplines 

to attempt to explore further details of Requirements. Table 1 

illustrates our analysis effort, with the left column stating a subset 

of the Requirements and the right column listing the robotic 

functions or subsystems that are involved to fulfill the 

requirements. The intent is to organize the robotic knowledge 

through the ontology. 

Requirement Involved UMS 

Functions 

To project remote situational awareness 

(SA), beyond line of sight, into 

compromised or collapsed structures or 

to convey other types of information; or 

be able to operate around corners of 

buildings; as such, SA for near, far, and 

field of view are required 

Video, command and 

control signals in 

tight space 

To enable use of video in confined 

spaces and for short-range object 

identification, which can wash out from 

excessive illumination of the scene; 

therefore, adjustability is required 

Variable illumination 

To support the SA, the robot should be 

able to ingress a specified number of 

meters into the worst case collapse, a 

reinforced steel structure 

Maneuver within 

tight space 

To use this system in sensitive public 

situations where maintaining control of 

remote systems is imperative and 

limiting access to video images and 

other communications to authorized 

personnel is prudent; should be shielded 

from jamming interference and 

encrypted for security 

Security 

To project remote situational awareness 

or to convey other types of information 

down range within line of sight 

Video, command and 

control over long 

range 

Table 1: Mapping of Requirements to US&R UMS Functions 

Beyond this example, we reviewed several other Requirements 

observing that, overall, the following features are keys to the 

US&R robotic operations: 

x Situation awareness facilitation 

x Maneuvering in tight space 

x Radio link for video and command and control data 

x Usability to the operator 

x Minimum training 

x System monitoring 

x Sufficient power supply 

x Compatible with current logistics system 

These are to be reflected in the ontology work. 

2.2 Requirements for Next Generation 

Manufacturing 

An impediment to advancing manufacturing to its next level is 

lack of adequate sensors and perception systems, because the 

involving environments would be dynamic and unstructured. 

Therefore, dynamic metrology is a key technology. Those 

perception systems must be comprehensive, pervasive and 

providing redundancy. In scenarios such as a robot grasping a 

moving part off an assembly line, a single, narrowly focused 

sensor will not be sufficient. The sensor may fail, may not be 

robust enough for the task, may not sense other objects that could 

become obstacles, or may not be able to adequately sense humans 

in the workspace to prevent accidents. Perception for such 

scenarios would require sensor fusion and control logic to 

facilitate arbitrations among multiple subsystems. 

 

To further discuss the roles and requirements of advanced sensor 

and perception for the future manufacturing, a workshop was held 

in October, 2007, which brought together people from 

Government, industry and academia [16]. A number of the 

participants indicated that the ability to measure the positions and 

orientations (6DOF) of components in dynamic environment 

would result in considerable cost savings in applications such as 

automobile manufacturing. The installations with more intelligent 

combinations of sensing and automation will better enable US 

manufacturers to compete globally. They also called for reference 

standards, as those would assist the community in establishing 

clear performance metrics for systems and algorithms. 

All these requirements were collected and will be incorporated 

into a comprehensive robotic ontology. One section of the 

ontology deals with sensors. A generic sensor includes major 

attributes of sensing function, sensing target, and sensor 

specification. Figure 5 provides an illustration of this model using 

the Protégé tool1

. Each of the attributes is further elaborated. For 

example, sensing targets include the properties of spatial-

 

1 Disclaimer: Certain trade names and company products are mentioned in 

the text or identified in certain illustrations to facilitate communication. 

In no case does such an identification imply recommendation or 

endorsement by the NIST, nor does it imply that the products are 

necessarily the best available for the purpose

103
temporal, chemical, climate, kinematic, etc. This effect is 

illustrated in Figure 6, using the same tool. Specifications may 

include speed, drift, resolution, etc. The generic structure, as 

represented in an ontology, allows the information for specific 

sensors to be recorded. This ontology will serve as a knowledge 

base or as a tool for a sensory requirements analysis. It will also 

be useful in standardizing terminology for robots and sensors and 

in understanding the application of metrics and standards. 

Figure 5: Ontological Model for Sensor Definition 

Figure 6: Ontological Model for Sensing Targets 

3. ONTOLOGY: ELEMENTARY 

FEATURES 

The previous sections have described the project requirements and 

the metrics model. Now we will focus on developing the 

ontology that encompasses those aspects. We first defined sets of 

fundamental references and relationships that are used to develop 

the UMS ontology. 

3.1 Relationships 

Two types of fundamental relationships are defined to associate 

the ontological entities. These relationships are further subtyped 

and instantiated to form hierarchical structures.

x Part-whole: partOf

This relationship can be further instantiated to specific 

needs. The following are two subsets: 

Physical Subtypes: enclosedBy, boundedBy, 

composedOf

Logical Subtypes: controlledBy, integratedIn, 

boundedBy, composedOf 

These can be further instantiated for particular 

applications. There are also issues of mapping of 

numbers (a car is composed of auto parts), 

complementary active and passive relationships 

(composedOf and consistOf). 

x Peer: associatedWith

Physical Subtypes: connectedWith 

Logical Subtypes: interfaceWith, integratedWith 

x Generalization/specialization: typeOf

x Requirement: required, optional; and, or

3.2 Spatial Aspect 

3.2.1 References 

x distance, pose, area, tolerance typeOf spatial_feature 

o position partOf pose 

o orientation partOf pose 

 coordinate partOf position 

 angle partOf orientation 

o coordinate partOf area 

x range typeOf distance 

3.2.2 Environmental Features 

x object_class typeOf spatial_feature 

o ground_ object_class typeOf object_class 

o maritime_object_class typeOf object_class 

o aerial_ object_class typeOf object_class 

3.3 Temporal Aspect x time, tolerance typeOf temporal_feature 

x duration typeOf temporal_feature 

3.4 Spatial and Temporal x speed typeOf temporal_feature and spatial_feature 

x acceleration typeOf temporal_feature and spatial_feature 

4. GOAL FOR UMS 

We began to generate an ontology for the concept of mission goal 

for the UMS. The identification of the goal attributes is facilitated 

through the project requirements as described in Section 3. The 

hierarchical layout of the section headings reflects the structure of 

the ontology. The mission goal is composed of the subgoals for 

the subsystems. The subgoals cover operational, environmental, 

and operator aspects. 

Given the fact that UMSs may be commanded to perform vastly 

different types of tasks, our bottom-up approach is to develop a 

structure and ontological attributes that might be generic to certain 

applications. As such, the following subsections describe what is 

equivalent to an illustrative goal ontology suitable for a particular 

104
set of applications. Different types of applications may need 

separate sets of the ontology. 

4.1 Subgoal for Mobility Subsystem 

A UMS includes a mobility system. Therefore, the following is 

modeled: 

mobility subsystem integratedWith UMS 

The subsystem’s goal can be modeled as: 

x mobility_goal partOf UMS_goal 

o pose partOf mobility_goal 

o object_class partOf mobility_goal 

o time partOf mobility_goal 

o duration partOf mobility_goal 

o speed partOf mobility_goal 

o acceleration partOf mobility_goal 

o mobility_goal boundedBy tolerance 

4.2 Subgoal for Sensor Subsystem 

A UMS typically includes a sensor system. Therefore, the 

following is modeled: 

sensor subsystem integratedWith UMS 

The subsystem’s goal can be modeled as:

x sensory_goal partOf UMS_goal 

o range partOf sensory_goal 

o frequency partOf sensory_goal 

4.3 Subgoal for Communication Subsystem 

A UMS typically includes a communication system. Therefore, 

the following is modeled: 

communication subsystem integratedWith UMS 

The subsystem’s goal can be modeled as: 

x comm_goal partOf UMS_goal

o cover_range partOf comm_goal 

o set_bandwidth partOf comm_goal 

o receive_send_line_of_sight partOf comm_goal 

4.4 Subgoal for Power Subsystem 

A UMS typically includes a power system. Therefore, the 

following is modeled: 

power subsystem integratedWith UMS 

The subsystem’s goal can be modeled as: 

x power_subgoal partOf UMS_goal 

o set_peak_power_output partOf power_subgoal 

o save_min_power partOf power_subgoal 

4.5 Subgoal for Mission Package Subsystem 

A robot typically carries additional subsystems beyond the 

platform. They may be manipulators, tools, special sensors, 

weapon, etc. Subgoals must be developed for them. 

mission package integratedWith UMS 

The subsystem’s goal can be modeled as:

x mission_subgoal partOf UMS_goal 

o identify_victim partOf mission_subgoal 

o assemble_door partOf mission_subgoal 

o establish_observation_post partOf mission_subgoal 

o translate_text partOf mission_subgoal 

4.6 Subgoal for Chassis Subsystem 

A UMS includes a chassis system. Therefore, the following is 

modeled: 

chassis subsystem integratedWith UMS 

The subsystem’s goal can be modeled as:

x chassis_goal partOf UMS_goal 

o set_illumination_intensity partOf chassis_goal 

4.7 Subgoal for Human-Robot Interaction 

(HRI) Subsystem 

A UMS includes a HRI system. Therefore, the following is 

modeled: 

HRI subsystem integratedWith UMS 

The subsystem’s goal can be modeled as: 

x HRI_goal partOf UMS_goal

o sound_alarm partOf HRI_goal

o display_health_status partOf HRI_goal

4.8 Collaboration 

A UMS goal may be to collaborate with other systems. The 

subsystems of a UMS may need to collaborate among themselves. 

x collaboration_subgoal partOf UMS_goal

The subsystem’s goal can be modeled as:

o wait_until partOf collaboration_subgoal

o synchronize_with partOf collaboration_subgoal

Note that the performance metrics for the collaboration will be 

described later in this paper. 

4.9 Prioritization and Management 

 The UMS entities may be given multiple goals. The entities may 

receive multiple goals from their collaborators. 

x manage_goals partOf UMS_goal 

o multi-tasking partOf manage_goals 

o prioritize_goals partOf manage_goals 

105
 

 value partOf prioritize_goals 

o costs partOf prioritize_goals 

Note that being able to prioritize the goals would enhance the 

autonomous performance of the UMS. 

4.10 Additional Subgoals 

Additional subsystems may be employed and the subgoals should 

be identified. 

5. ALFUS METRICS 

As described earlier, the definition of performance metrics is an 

important aspect of the UMS knowledge and, therefore, it is a part 

of the ontology. We have developed the autonomous 

performance of UMS using the ALFUS metrics. 

x Autonomy_performance partOf UMS_performance

o MC partOf Autonomy_performance

 { subtasks_structure, precision, repeatability, 

uncertainty, safety_level, risk_level } partOf MC

 { control_echelon, interoperability, 

knowledge_shared } partOf MC

 { situation_analysis, replans } partOf MC

 { perception } partOf MC

o EC partOf Autonomy_performance

 solution ratios partOf EC

 Scale: No impediment, one impediment out of 

N possibilities, (N-1) out of N, n out of N, N out 

of N 

 solution_difficulty_levels partOf EC

 { energy consumption levels, computation load 

levels, look-ahead ability } partOf

solution_difficulty_levels 

o HI partOf autonomy_performance

 { % of plan generated by UMS, % of plan pregenerated, % of plan execution that operator is 

involved, % of robot vs. operator initiated 

interactions, required training, workload } 

partOf HI

6. GOAL STATE-METRICS 

ASSOCIATIONS 

Various aspects of the ontology should be related. In this section, 

we illustrate how the requirements, goal, and autonomous 

performance aspects fit together, focusing on the US&R 

application example. 

x The goal model is driven by the Requirements, which state 

that the robot “should be able to ingress a specified 

number of meters into the worst case collapse” and 

“project remote situational awareness or to convey other 

types of information down range.” These are reflected in 

the mobility and communication subgoals in the ontology. 

x The US&R Requirements call for the operator control unit 

(OCU) displays to be clear and legible in outdoor 

situations and under ambient light conditions. This is to 

facilitate UMS control and to reduce the stress level of the 

user, one of the autonomous performance metrics in the 

ALFUS Framework. 

x The US&R Requirements further call for “enable use of 

video in confined spaces and for short-range object

identification.” This corresponds to the solution_difficulty 

and situation_analysis metrics in ALFUS. 

7. SUMMARY 

An ontological approach is used to model certain aspects of UMS. 

The objective is to facilitate the investigation of the performance 

of UMSs. In particular, we represented the goal of a UMS in the 

ontology, followed by representing the autonomous performance. 

We further identified several cases illustrating that the two are 

integrated. Our ultimate goal is to expand on this work for a 

broad scope ontology that can be helpful to a large audience in the 

community. 

8. REFERENCES 

[1] Vujasinovic, M., “An Industrial Validation of a Semantic 

Mediation Architecture,” IEEE Internet Computing, October 

2007 

[2] Fiorentini, X. et al., “An Ontology for Assembly 

Representation,” NIST Interagency/Internal Report (NISTIR) 

7436, Gaithersburg, MD, July 2007 

[3] Obrst, L., et al., “The 2006 Upper Ontology Summit Joint 

Communique,” Applied Ontology Journal 2006 

[4] Deshayes, L. et al., “An Ontology Architecture for Standards 

Integration and Conformance in Manufacturing,” 

Proceedings of the IDMME 2006 Grenoble, France, May 17-

19, 2006 

[5] Schlenoff, C. I., et al., “ An Intelligent Ground Vehicle 

Ontology for Multi-Agent System Integration,” Proceedings 

of the 2005 Knowledge Intensive Multi-Agent Systems 

(KIMAS) Conference, Waltham, MA, April 18-21, 2005 

[6] Schlenoff, C. I., et al., “A Standard Intelligent System 

Ontology,” 2005 SPIE Defense and Security Symposium, 

March 2005, Florida 

[7] Schenk, J.R. and Wade, R.L., “Robotic Systems Technical 

and Operational Metrics Correlation,” PerMIS’08 Workshop, 

Gaithersburg, Maryland, October 2008 

[8] Autonomy Levels for Unmanned Systems (ALFUS) 

Framework, Volume II: Framework Models Version 1.0, 

NIST Special Publication 1011-II-1.0, Huang, H. et al., Ed., 

National Institute of Standards and Technology, 

Gaithersburg, MD, December 2007 

[9] Autonomy Levels for Unmanned Systems Framework, 

Volume I: Terminology, Version 1.1, Huang, H. Ed., NIST 

106
 

Special Publication 1011, National Institute of Standards and 

Technology, Gaithersburg, MD, September 2004 

[10] Weiss, B.A. and Schlenoff, C., “Evolution of the SCORE 

Framework to Enhance Field-Based Performance 

Evaluations of Emerging Technologies,” PerMIS’08, 

Gaithersburg, MD, October 2008 

[11] Schlenoff C, et al., Applying SCORE to Field-Based 

Performance Evaluations of Soldier Worn Sensor 

Technologies. Journal of Field Robotics 2007 

September;24(8/9):671-98 

[12] Messina, E., Jacoff, A., “Performance Standards for Urban 

Search and Rescue Robots,” Proceedings of the SPIE 

Defense and Security Symposium, Orlando, FL, April 2006 

[13] Messina, E. R., et al., Statement of Requirements for Urban 

Search and Rescue Robot Performance Standards, NIST 

Draft Report, May 2005 

[14] Schlenoff, C. I., et al., “ Test Methods and Knowledge 

Representation for Urban Search and Rescue Robots,” 

Chapter in the Climbing and Walking Robots Book, August 

2007 

[15] Schlenoff, C. I. and Messina, E. R., “A Robot Ontology for 

Urban Search and Rescue,” 2005 CIKM Conference: 

Workshop on Research in Knowledge Representation for 

Autonomous Systems, Bremen, Germany, October 2005 

 [16] Draft Proceedings of the Dynamic Measurement and 

Control for Autonomous Manufacturing Workshop, To Be 

Published as a NIST Internal Report, Gaithersburg, MD, 

October 2008 

107
Robotic Systems Technical and Operational Metrics 

Correlation

Jason R. Schenk, Ph.D. DeVivo AST 

2225 Drake Ave Suite 2

Huntsville Al 35805 

256-489-4614

jasonschenk@devivoast.com 

Robert L. Wade

US Army Aviation and Missile Research, 

Development and Engineering Center 

Software Engineering Directorate (SED) 

Redstone Arsenal, AL 35898

256-842-6174

robert.l.wade@us.army.mil 

ABSTRACT 

As unmanned systems become more prevalent, so does the 

emphasis on quantifying their performance using standard

measures. Several research efforts have attempted to elicit 

important attributes associated with unmanned systems 

performance, with limited applicability and success. We

identify several reasons for this, including the lack of

adherence to a strict ontology and taxonomy, the use of

means-based rather than goal-based tests, and the lack of a 

clear correlation between tests and predicted performance. 

This paper provides a conceptual framework for the 

development of correlations between technical 

characteristics and operational performance. These

correlations provide a foundation for generating predictive 

performance test standards. 

Categories and Subject Descriptors 

B.8.2 [Hardware]: Performance and Reliability –

performance analysis and design aids

General Terms

Algorithms, Measurement, Performance, , Human Factors, 

Standardization

Key Words 

Analytic Hierarchy Process (AHP), Explosive Ordinance 

Disposal (EOD), unmanned systems, correlation, 

performance metrics 

1. Introduction

A multiplicity of technical performance measures have 

been developed for requirements documents, system

performance specifications, and research analysis of current

Department of Defense (DoD) robotic systems. None are 

standardized or widely accepted. Furthermore, their

correlation to operational performance is not known or

well-understood within the robotics community. In fact, 

operational performance and technical characteristics are

often ill-defined, mixed, or applied inconsistently. The 

establishment of a set of consistent normative technical and

operational metrics based on a strict and logical ontology is 

critical to informing the design, comparison, and selection

of unmanned systems [1]. 

The Robotic Systems Technical and Operational Metrics

Correlation (RSTOMC) project aims to develop a 

methodology for establishing testable quantitative measures 

that correlate with unmanned systems performance. This 

project is sponsored by the United States Army and the 

Joint Robotics Ground Enterprise (JGRE), Office the 

Undersecretary of Defense (OUSD). Explosive ordinance 

disposal (EOD) is a current pressing need for the Army, so 

the focus of the current RSTOMC project is on teleoperated EOD platform domain analysis. This focus adds 

the benefit of working systems and operators with a 

significant historical experience. The RSTOMC project 

will develop a preliminary model for technical to 

operational correlation using quantitative and qualitative

information from this domain. Based on these correlations, 

the project allows for the development of a method for

selecting a set of technical performance tests and metrics

for evaluating systems. 

Standardized robotic system metrics will enable the DoD to

define, specify, distinguish, evaluate, and test robotic 

systems in a more systematic manner. This project will

attempt to derive more reliable correlations between the

technical and operational characteristics of robotic systems. 

This correlation has the potential to simplify and reduce the 

cost of analysis. Successful execution of this effort will 

provide the foundation for a project manager or user to 

objectively predict the impact of technical changes on 

operational performance, or the operational performance of 

a proposed system, to an accuracy of 80% by performing a 

set of low cost technical tests. While the creation of

specific tests may be left to future work, the RSTOMC

effort will produce a model for predicting operational 

performance based on a set of technical measures. We

will refine the model based on the data available from

within the EOD robotics community and develop a 

software based system that allows for the continued

maturation of the model as well as the incorporation of

108

that this contribution was authored or co-authored by a contractor or

affiliate of the U.S. Government. As such, the Government retains a

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additional domains. Finally, we propose a method for test 

creation and near-optimal set selection. 

2. RSTOMC Plan 

The overall goal for this project is to improve the ability to

objectively assess robotic systems by developing a tool

that, through simple tests and measures, can predict the 

mission-specific operational performance to at least 80%

accuracy. To reach this goal, a methodology for robotic 

systems performance measurement will be developed to

identify and assess both technical measures and the 

operational performance of the systems in application 

specific usage scenarios. Technical measures are defined

here as a quantitative assessment of a characteristic in a

controlled environment. A technical characteristic is a 

physical ability of a system. This is different from

operational performance measures, which are defined

relative to mission goals or tasks. Correlations between the 

technical and performance measures will be determined.

The resulting correlations will be captured in a software 

tool to be distributed to appropriate agencies. The 

RSTOMC project consists of the following tasks: 

Task 1) Collect and Analyze Operational Scenario.

Subtask 1) Select the method of analysis.

Subtask 2) Select the data source and domain. 

Task 2) Define Technical Performance Characteristics. 

Subtask 3) Identify relevant technical

characteristics (TC) of EOD systems. 

Task 3) Define Operational Score (Os). This task may

include defining mission-specific criteria which we 

call operational measures (Om). 

Subtask 4) Identify operational requirements and

their relative importance for successful EOD 

system performance. 

Task 4) Establish Correlations between Operational 

Performance and TC. Operational performance may 

be defined as the Os or Om. 

Subtask 5) Identify the correlation between TC 

and operational performance. 

Subtask 6) (Future work) Design technical 

performance metrics. and measures (TPM), 

validating results where possible.

Subtask 7) (Future work) Create a method for 

selecting a near-optimal set of tests. Incorporate

and document the results within a software

product. 

2.1 Subtask 1: Select Method 

Broadly speaking, efforts to measure robotic systems 

quality fall into two main categories. The first is based on

task decomposition, such as [2], where each missionspecific task is broken down into its most fundamental 

subtasks and the physical requirements or resources

required to accomplish them. The overall performance is 

assumed to be the sum of a systems ability to complete 

each subtask. These efforts generally start with subject

matter experts listing tasks or functions that a system must

perform, and their frequency or importance. Such 

decomposition is often limited by experts’ ability to 

quantify the relative relationships of functions to

performance. This becomes difficult or impossible in high 

complexity systems with multiple interaction effects and

high order dependencies [3]. Further, such analyses risk

focusing on means rather than ends, limiting its relevance 

back to overall system performance. 

One effort based on task decomposition to create a set of 

prioritized and measureable requirements for urban search 

and rescue robot performance comes from the National 

Institute of Standards and Technology (NIST) [4]. The

study used subject matter experts to identify 103

requirements across 13 robotic platform categories from 

aerial to land to aquatic. There were 21 requirements that 

were most widely applicable across the 13 robot categories. 

Tests and measures were developed for each of these 

requirements, such as “communication range – beyond line 

of sight”. 

The National Institute of Justice has also used task 

decomposition to determine metrics for assessing 

unmanned system in law enforcement [5]. In their study,

they used a focus group to obtain nine key attributes critical 

to system selection. These attributes were: purchase cost, 

platform speed, ability to complete its mission, minimal 

weight, minimal down time, minimal maintenance cost and

maintenance requirements, manipulator lift capacity, and

operating range. A survey was then conducted to

determine acceptable values for each. 

An effort by the Air Force Research Laboratory (AFRL)

attempts to link technical measures to operational

requirements for explosive ordinance disposal (EOD) 

robotic vehicles [6][7]. This project used Quality Function

Deployment (QFD) to elicit requirements from subject

matter experts, as well as one-on-one interviews to gain 

detailed insight into requirements. The results of their most 

recent project are used in the current research, and are 

discussed in greater detail in the following sections. 

Task decomposition allows for a complete enumeration of

expected task requirements. However, decomposition is 

platform and strategy dependent, meaning different designs 

or solution strategies cannot be tested as effectively or

without bias. Secondly, decomposition of tasks does not

test interaction effects, unless explicitly enumerated during

the decomposition. Unmanned systems are complex and as

such have complex interactions between component parts

or capabilities. These interactions may form the basis for 

important emergent behaviors or qualities that allow the 

system to function or fail in surprising ways [8]. 

A second class of research efforts takes a gestalt approach, 

starting with the systems-level requirements of a system. 

The assumption is that complex systems have complex, 

inseparable interactions that produce emergent behavior. 

These emergent properties cannot be captured except by

looking at the system as a whole. For example, Steinfeld et 

al. list five features that are required of a task-oriented 

human-robot system [9]. These are: navigation,

manipulation, perception, management, and social, which

are further broken down into more specific measurable 

109
tasks. These tasks remain relatively generic and mission

independent. It is again up to the subject matter expert to

determine the relative importance of each of these tasks to 

the specific mission profile. Cummings et al. generated

five sets of metrics classes using a separate ontological 

framework, based on human robot interaction (HRI) theory

[10]. These classes are human behavior efficiency, human

behavior precursors, Unmanned Vehicle (UV) behavior

efficiency, collaboration, and mission effectiveness. 

Systems-level approaches are useful in that they include the

complex and emergent properties of a system in its 

analysis. However, it is often difficult to create a set of 

technical tests to measure the top-level requirements a 

system. Additionally, such tests do not provide much 

specific information about a system. On the other hand, 

they are much more goal oriented, allowing for fair

comparison of different platform designs or solution

strategies. Such high-level tests are often very expensive, 

approaching the cost and complexity of full-blown field

trials. Finally, the authors are not aware of any top-down 

approach that has generated specific weights for the 

importance of each of the proposed high-level requirements 

to overall performance. 

Another distinction one must consider is the ontology used

in the approach. Two common ontologies are illustrated by

the Architecture Framework for Unmanned Systems

(AFUS), which standardizes a set of terms, definitions, and 

attributes common across all domains of unmanned 

systems [11]. The two ontologies are the Conceptual View

(means-oriented) and the Capabilities View (goal-oriented). 

The Conceptual View describes unmanned systems in 

terms of component structure, knowledge store, and gross 

actions. The Capabilities describes capabilities and

behaviors a system is able to perform. For example, a laser

range-finder is a concept used to describe the composition 

of a system, while object-detection and tracking (which 

may use a laser range-finder) is a capability of the 

platform. The ontology chosen drives the development of 

the criteria, tests, and measures that are chosen to predict

system performance. 

2.1.1 Analytic Hierarchy Process 

Ideally, technical as well as operational performance data 

would be available from rigorous lab and field

experimentation, and real-world observation across a wide

range of platforms. Due to cost and logistics limitations, it 

is often more practical to obtain data through the elicitation

of expert opinions. There are several ways in which to

accomplish this, including Quality Function Deployment

(QFD) and Analytic Hierarchy Process (AHP). The 

fundamental mathematics of the RSTOMC project comes 

from the AHP, which provides a systematic approach to

correlating low level features with high level system

requirements [12]. The raw data comes from a QFD and 

interviews performed by AFRL. The following is a brief

description of the proposed mathematical relationships. 

These equations represent an idealized, hierarchical, and 

theoretical model of the relationships. The actual manifest

structure of our analysis will depend on the specifics of the 

data. 

Figure 2 Conceptual hierarchy of EOD unmanned 

systems analysis 

Operational requirements, Om, include all the important

criteria that may arise during an EOD mission. Examples

might include probability of successful disarming or

average time to disarm. In addition, their frequency or

relative importance to the completion of the mission 

provides the basis for weighting. The weighted sum of

these requirements yields the operational performance 

score of the system, Os. 

࢙ࡻ ൌ ሾࢃሿሾ࢓ࡻሿ (1) 

Technical characteristics refer to the physical systems and

their interactions, such as end-effector lift capacity or

screen resolution. These characteristics each have a unique

impact on the set of operational requirements. The nature 

of this impact provides the weighting factors: 

ሾܱ௠ሿ ൌ ሾࢃ૚ሿሾܶܥሿ (2) 

To further complicate matters, available metrics and 

derived tests may not correspond 1:1 to technical 

characteristics, which would require another set of weights, 

ࢃ૛. However, if a 1:1 correspondence can be established

(that is, each test measures only one technical 

characteristic), then this weighting matrix is equal to the 

identity, I. These tests and metrics, which we call technical

performance metrics, or TPM, may be related back to the 

operational performance score, in the following manner: 

ܱ௦ ൌ ሾܹሿሾࢃ૚ሿሾࢃ૛ሿିଵሾܶܲܯሿ (3) 

As an alternative, TPM may be directly related to 

operational requirements, or even operational performance 

scores, using weights derived from a separate survey. In 

this way, only one set of weights are needed, indifferent to

the relationship of operational requirements and technical 

characteristics:

ܱ௦ ൌ ൣ ෡ܹ൧ሾܶܲܯሿ (4) 

W2

W1

Os

W

Om Om

TC TC TC TC 

TPM 

... 

... 

TPM ... 

110
This holds true only if the TPM are a minimum necessary 

and sufficient measure of the operational score (no zero

rows or columns in the weighting matrix, ࢃ(૛. In either

case, the relationship is linear. Therefore, there are no 

interaction terms between TPM. This assumption is 

unlikely for complex systems, especially if each TPM 

corresponds to about one TC. For example, it would be

difficult to design a TPM measuring manipulator reach and

a TPM measuring lift capacity that are independent of one 

another, since lift capacity is relative to the extension of the

arm. We are motivated to develop TPM based on some 

other criteria besides decomposition to the most

fundamental tasks. 

2.2 Subtask 2: Select Data Source and 

Domain

We chose the AFRL analysis to provide the raw data for

the project, because it is one of the few analyses that

quantify the relationships between characteristics and

performance. The analysis uses Quality Function 

Deployment and significant domain expert input to 

formulate operational requirements, technical

characteristics, and their relationship to one another. The 

inclusion of this relational data makes it ideal for our 

analysis. 

This analysis draws from interviews and focus groups with 

270 DOD unit-level EOD technicians from 45 different 

organizations across the four United States armed forces 

services. The goal of the analysis was to generate 

requirements for the combat variant of the Next Generation 

EOD Remote Control Vehicle (NGEODRCV). The report 

identified and ranked, using QFD, 67 “technical 

characteristics” based on 79 “customer needs.” The expert

interviews provided details to the technical characteristics,

breaking them down further into approximately 271 stated 

needs, preferences, tasks, design elements, features, etc.

The set of roughly 271 failure modes, design preferences, 

tasks, features, specifications, and customer requirements 

that make up the responses do not represent a clear and

consistent ontology for use in our analysis. In order to be 

applicable to the RSTOMC project, they must be organized

in such a way that a small set of valid technical metrics can

be derived to be predictive of operational performance. By

creating a set of technical tests and metrics, and using a set 

of weights derived from the domain expert interviews, we 

can use the AHP methodology to generate a first order 

linear model of operational performance. 

2.3 Subtask 3: Identify TC 

Technical characteristics were established by the TSWG 

NGEODRCV Common Systems Architecture dated 14 

January 2003. These characteristics were placed in a threetiered hierarchy. For example, Navigation is broken into

“path planning” and “path execution”. Each of these is 

further broken down. For example, path execution is

broken down into “obstacle detection” and “obstacle 

avoidance”. 

Table 2 Sample of Technical Characteristics from the 

QFD

Navigation Payload

Path Planning 

Path

Execution

Sensor

Integration

Tool

Integration

 Position capability (D-1-a)  Mapping capability (D-1-b)  Waypoint navigation (D-1-c) Obstacle avoidance (D-2-a) Obstacle Detection (D-2-b) Logical (E-1-a) Electrical (E-1-b)  Physical (E-1-c)  Electrical (E-2-b)  Physical (E-2-c) 

These characteristics were further broken down and defined

in surveys. For example, “Tether Durability” was 

described as the ability to resist being run over by the 

platform (51%), resist tensile forces (25%), resist rough 

terrain (9%), and resist both rough terrain and being run 

over (15%). In a QFD, these characteristics are of the same

level of scope, type, and fidelity. In other words, the 

ontology should be consistent. Typically, these are 

measurable characteristics with a possible range, such as 

“battery life: 0-24 hours”. However, in the present QFD, 

characteristics are a mixture of resistance to failure modes 

(e.g. tether resistance against being run over, prevention of

dirt clogging treads), design modality preferences (e.g. 

joystick vs. keyboard), tasks (e.g. ability to place countermeasures on a vehicle, ability to reach into a 55-gal drum),

typical customer requirements (e.g. fine/smooth motor

control, “observability” of platform orientation), 

specifications (e.g. 12-hour battery life, maximum arm lift 

of 25-50 lbs.), and features (e.g. rangefinder). The experts’

reasoning generally appears within the interview responses.

Therefore, this feature of the analysis may be addressed by

(and provides further motivation for) goal-based tests. 

As a result of trying to fit all of the needs into the predetermined hierarchy, several of the 271 needs are the same 

under multiple headings (e.g. depth perception appears

under Visual (B-2-a) as well as Displays (C-2-d)). 

Therefore, the ranked list may be skewed, since some

important needs may be diffused among multiple technical 

characteristics, while other characteristics represent

aggregates of several important needs that could be brokenup further. 

In an effort to tighten the taxonomy, we re-sort and reclassify the needs into new technical characteristics 

categories. Each listed need maintains its constituent 

weight (the weight of the characteristic it belonged to times 

the percent of respondents citing it for that characteristic). 

The result is a list of approximately twenty-five new

technical characteristics categories. Under each of these 

categories, the same 271 TC remain (condensed to 96 by

combining duplicate and redundant TC), only in a more

useful way for the RSTOMC project. 

111
2.4 Subtask 4: Identify Operational 

Requirements

In a QFD, user requirements in the form of qualities are 

listed along the left side of the table [13][14][15]. These 

requirements might include general qualities such as “ease 

of deployment” or “mobility”. Note that the emphasis is on 

general goals, rather than specific means or tactics. In the 

present case, the requirements represented possible tasks 

that a system would need to perform during operations, as

determined by a joint service focus group of combat 

experienced EOD technicians. These included tasks such 

as “offload robot” and “negotiate terrain”, along with the 

subtasks required to accomplish these. The subtasks were 

weighted via survey as to their importance to the overall 

mission. As discussed previously, tests based on task 

decomposition methods tend to dictate the solution 

strategy, limiting its ability to compare innovative design or 

operational strategies [16]. More general goal-oriented

requirements allow comparison of disparate designs over

ordinal measures. At the least, the sum total of these 

requirements provides Os. The derivation of a more goalfocused set of operational measures, Om, may result from a 

separate survey. The formulation of tests based on these 

results will be discussed further in section 2.6. 

Table 1 Sample of User Requirements from the QFD 

Requirement

Off-load Robot 

Unsecure robot 

Power-up robot 

Remove robot from vehicle 

Pick up robot 

Drive robot off vehicle 

Off-load OCU

Remove OCU from vehicle 

Set up OCU

Attach tether to OCU 

2.5 Subtask 5: Identify the correlation The body of the QFD matrix represents the correlation

between customer requirements and technical 

characteristics. Since we are reorganizing the data, the 

correlations must be carried along with the lowest level TC

as they move to our new taxonometric structure. Since the 

operational analysis interview results cite the rationale and 

the relative number of respondents citing each rationale, we 

are able to carry that response over to the new parent 

category without losing that response’s relative 

contribution to overall system performance. 

2.6 Subtask 6: Generate TPM Tests 

This section details the important considerations associated

with test selection. Although this and the following section

are identified as future works, it is important to mention 

here. This is because the present work is intended to 

ultimately facilitate the creation of standard tests, so 

preliminary work must be cognizant of this goal. 

The level of testing selected is based on cost, resources, the 

desired number and complexity of tests, and the required

level of specificity and “predictiveness” of tests. Since 

each TC has its own weighting, tests may be devised that

measure the each independently, collectively, across

categories, or some variation of the three. The type of tests

selected depends on 4 factors: 

1. The natural grouping of the technical requirements. 

Some sets of requirements are coupled or difficult to

segregate. Interactions and emergent properties may

also exist that cannot be measured if TC are measured 

in isolation. A solid taxonomy and ontology will 

facilitate this.

2. Cost or difficulty of the test. A set of tests that 

measure individual components separately may be

more or less difficult or expensive than a single 

aggregate test. Cost is also impacted by interaction

effects, as it may be more difficult to isolate TC that

are naturally coupled.

3. The “informativeness” of the test. More atomic tests

provide more specific information, while aggregate 

tests may be more predictive of actual operational 

performance, due to interaction effects and their goal 

rather than means focus.

4. The number of tests. A smaller set of tests are 

preferable to a large battery of tests. 

Overall, the goal is to provide a small set of informative 

tests that together predict performance to the highest 

accuracy possible. Below are three levels of tests along the 

spectrum of aggregation. The weights included in the 

tables are estimated from the results of the operational

analysis and our effort to re-sort the results for our purpose. 

2.6.1 Atomic tests 

A large number of very specific “atomic” tests designed to

measure each TC separately provide very specific

information about a given platform. It provides clear

evidence of what specific features or abilities are strong or

weak in a platform, but the correlation to real world

operational performance may not be as high. This is 

because individual tests would only provide for a first order

linear model where interactions between components are 

ignored. 

Also, specific tests of “means” dictate a solution strategy 

and limit the possibility for innovation. For example, if

system performance for a hypothetical mission is defined as 

the ability to cross a bridge, then tests of waypoint sensors,

the drive train, stability, distance sensors and obstacle 

avoidance might be devised to see if the robot could cross 

the bridge. However, a system designed to bypass the 

bridge altogether and fjord the river might accomplish the

112
mission objective equally well, but score poorly on these 

atomic, “means” tests. Further, due to unmeasured 

interactions, the system that scores well on such tests might

still be unable to accomplish the mission objectives, for

example if its extra features make it too heavy or wide to

cross the bridge.

Table 5 Examples of "atomic" level tests 

Test Details ࢝ෝ

Light 

board 

Tests the manual dexterity of the 

robot, the controllability of the 

system, and the visual feedback of the 

device 

~4% 

Lift

strength

Tests the strength of arm, effector,

and the stability of the platform

~4% 

Reach Tests the range of motion (solid angle 

or volume) of the arm 

~3% 

Climb Tests the maximum grade of stairs, 

curbs, and slopes scalable 

~3% 

2.6.2 Aggregate tests 

Alternatively, higher level “aggregate” tests are designed to

measure sets of technical characteristics that are naturally

coupled. These types of tests tend to be fewer in number, 

but more complex. As a result, interactions are captured 

and the subsequent model can be more predictive of 

operational performance. The tradeoff is that the 

information provided by the results of tests is less specific. 

The determination of specific deficiencies in the platform

requires follow-up analysis. Using our river-crossing

example, the test would measure how well (quickly, 

reliably, etc.) the robot could cross a bridge, rather than the 

individual systems that provide that affordance. As with

the atomic tests, this level still risks measuring means 

rather than goals.

Table 6 Examples of "aggregate" level tests 

Test Details ࢝ෝ

Advanced 

Visual 

Acuity 

Tests the ability to detect various 

types and levels of signals 

~15% 

Signal 

Strength

Tests the ability to maintain a

strong signal across distance and 

with physical and electronic 

interference 

~23% 

Manual 

dexterity 

Tests the ability to access and 

manipulate objects of various 

types, sizes despite possible 

obstructions 

~15% 

2.6.3 Task level tests 

A third design philosophy might be to create tests that are 

“task” or “goal” based. These tests are also very aggregate

in that they test many components and the interactions in 

concert. The overall performance on a task represents a

system-level emergent capability, thereby allowing for

multiple robot design types or strategies to be compared. 

Task outcomes (such as the ability to get to the other side 

of a river) are measured rather than means (bridge crossing, 

swimming, etc.). This method has the potential for being 

the most predictive of operational performance and best 

able to compare disparate robotic systems, because its tests 

more closely approximate the real world. As with all more 

aggregate tests, however, insight into specifics require post 

hoc analysis. In addition, the results of these tests will 

most likely not be independent, so the sum weightings may 

not be equal to 1. Finally, the resource and time costs

associated with these tests approach those of full-blown 

field trials, the current method with which this effort is 

intended to improve upon. 

Table 7 Examples of "task" level tests 

Test Details ࢝ෝ

Retrieve Enter a room and retrieve an object. 

There may be other objects in room, 

doors, stairs/slopes, and other 

obstacles, variable lighting, target 

object may be obstructed, buried, or

inside a container, object may be 

large, small, fragile, slippery, or 

heavy.

~25-

75% 

Arrange Move objects to a predetermined 

arrangement. Specific tasks might 

include stacking, clearing an area, 

manipulating small objects (Chess, 

Perfection, Toy Ball), etc.

~25-

75% 

Regardless of the level of testing, tests must be correlated 

back to overall operational performance. The AFRL study 

provides a basis for this, as the previous section detailed. 

Verification may be conducted through additional surveys

or interviews, using AHP or another method. 

2.7 Subtask 7: TPM Test Set Selection 

Given the sheer number of alternative performance test 

combinations, an empirical method of test selection should 

be derived. This method is fundamentally a combination of 

two classical problems. First, it is a cost benefit-analysis. 

Each proposed test has a unique cost associated with it, in 

terms of resource requirements, time requirements, and 

costs associated with the difficulty of testing and

measurement. The goal is to find a set of tests that can 

predict with the requisite level of accuracy at the minimum

cost. To achieve this accuracy, the set of tests must span 

the relevant system characteristics that correlate with 

overall performance. This is a set covering problem. The 

solution must cover characteristics that account for at least 

80% of the variability. In other words the overall test 

selection problem becomes: minimize the cost of the 

selected tests, such that the sum of ݓෝ of the TC covered by

the selected tests  80%. This problem is NP-hard, and

therefore we propose future work use a solution derived

113
from a heuristic, such as a greedy algorithm or evolutionary

computation.

3. Preliminary Findings 

The present work and review of similar efforts has 

produced the following findings, representing common 

themes that appear throughout the literature and research. 

These findings represent principles that must be addressed 

in order to adequately represent the problem and provide a 

useful solution: 

1. Taxonomy must be hierarchical – taxonomy, or the 

hierarchical categorization of a set of concepts, must

be well-formed. This means that at each level of 

abstraction, categories must be distinct (exclusive), of

the same level (scope), and of the same disciminant 

(type). 

2. Ontology is critical – without a solid ontology,

analyses become confused, where customer 

requirements are confused with subtasks and 

strategies, which are in turn confused with technical 

characteristics. A good ontology to develop tests will 

identify requirements based on the goals of the 

deployment, and tests based on the ability to achieve 

goals, regardless of method or strategy of the 

platform. 

3. Characteristics are coupled – it is difficult to

separate some characteristics from one another,

because they are interrelated. For example, usability,

of either the input or output sub-system, is difficult to 

exclude from the sensory or motor sub-systems of a 

platform, respectively.

4. Weighting is variable – each platform design may

employ a different strategy to accomplish goals,

meaning that there is an interaction between platform 

and the importance (weights) of test scores, if those 

are based on technical characteristics rather than 

goals. For example, one platform might rely more

heavily on its strength to clear obstacles, while a 

second platform uses its robust drive system to scale 

most obstacles, and a third uses its small size and 

superior environmental awareness to circumnavigate 

obstacles. The weight of associated tests would be 

different in each case.

5. Ends over means – tests based on technical 

characteristics specify the solution strategy. By

focusing on technical characteristics rather than goals,

tests are biased towards a preconceived solution

strategy. This biases tests against innovation, and 

potentially forces systems to maintain “vestigial” 

features in order to satisfy test requirements.

6. Performance over characteristics – the goal of 

metrics is to inform acquisition decisions based on 

performance under intended use. Goal-based

assessments are preferable to characteristics that, 

although interesting, are not directly predictive of 

performance. 

7. Roles change goals and means – designs are 

optimized towards their roles. Platforms designed for 

one role cannot be compared to those designed for a 

different role, except relative to its in-class

performance. For example, a tank cannot be 

compared to a fighter aircraft, except through 

comparing how good the tank is at its role versus how 

good the fighter is at its role. 

8. Expertise variability valuable to measuring 

learning curve – by using pairs of operators matched 

based on observed covariates, expertise levels can be

controlled for (neutralized). Also, main effects plots 

on expertise will show the learning curve for each

platform [17]. 

4. Summary

The AFRL study provides the basis for a set of operational 

requirements, Om, and their relative importance to the 

overall operational performance Os. A second set of Om

that are more mission and goal targeted may be derived

from a separate survey. Subject matter experts interviewed

in the study related the technical characteristics, TC, to the 

operational requirements. By testing these characteristics,

one can determine technical performance metrics, TPM, 

that use these relationships to measure the operational 

performance objectively. Each test may measure technical

characteristics either individually or in logical aggregate 

groups. 

This process will provide a methodology for generating and 

weighting technical performance tests and metrics that

inform design and selection decisions for EOD robotic 

systems as well as other unmanned systems in a 

standardized way. The successful completion of the project 

will see the following deliverables: a set of TC and 

weights that can predict 80% of the operational

performance of a tele-operated EOD robotic system, insight 

into the critical design characteristics of a tele-operated

EOD robotic system, and a methodology for the 

construction of an objective, quantifiable, reliable, and

empirically valid testing standard for predicting unmanned 

systems performance. 

5. References

[1] van Rees, R. 2003. Clarity in the Usage of the 

Terms Ontology, Taxonomy and Classification.

Construction Infomatics Digital Library. 

http://itc.scix.net/paperw78-2003-432.content

(accessed 7/1/08). 

[2] Mitchell, D.K. 2005. Soldier Workload Analysis 

of the Mounted Combat System (MCS) Platoon’s 

Use of Unmanned Assets. Technical Report, 

ARL-TR-3476, U.S. Army Research Laboratory,

Aberdeen Proving Ground, MD. 

[3] Woods, D.D. and Hollnagel, E. 2006. Joint 

Cognitive Systems: Patterns in Cognitive

Systems Engineering. CRC Press, Boca Raton. 

[4] Messina, E., Jacoff, A., Scholtz, J., Schlenoff, C., 

Huang, H., Lytle, A., & Blitch, J. 2005. 

Statement of Requirements for Urban Search and

Rescue Robot Performance Standards 

(Preliminary Report). Department of Homeland

Security Science and Technology Directorate and

National Institute of Standards and Technology. 

114
http://www.isd.mel.nist.gov/US&R_Robot_Stand

ards/Requirements%20Report%20(prelim).pdf

(accessed 7/1/08). 

[5] National Institute of Justice. 2000. Final Report 

on Law Enforcement Robot Technology 

Assessment. TSWG Task T-150B2. 

http://www.nlectc.org/jpsg/robotassessment/robot

assessment.html (accessed 7/1/08). 

[6] AFRL. 2006. Next Generation EOD Remote 

Controlled Vehicle: Military Combat 

Operational Analysis (DRAFT). Combating

Terrorism Technology Support Office Technical 

Support Working Group. 

[7] AFRL. 2003. Next Generation EOD Remote 

Controlled Vehicle: Operational Analysis. 

Combating Terrorism Technology Support Office 

Technical Support Working Group. 

[8] Hollnagel, E., Woods, D.D., & Leveson, N. 

2006. Resilience Engineering: Concepts and 

Precepts. Ashgate; Burlington, VT. 

[9] Steinfeld, A., Fong, T., Kaber, D., Lewis, M., 

Scholtz, J., Schultz, A., and Goodrich, M. 2006. 

Common metrics for human-robot interaction. In

Proceedings of the 1st ACM SIGCHI/SIGART 

Conference on Human-Robot interaction (Salt 

Lake City, Utah, USA, March 02 - 03, 2006). 

HRI '06. ACM, New York, NY, 33-40. 

[10] Donmez, B., Pina, P., & Cummings, M. 2008. 

Evaluation Criteria for Human-Automation 

Performance Metrics. PerMIS conferece 

proceedings; August 19-21, 2008, Gaithersburg. 

[11] Society of Automotive Engineers AS-4A. 2008. 

Architecture Framework for Unmanned Systems. 

Architecture Framework Subcommittee, Society 

of Automotive Engineers. 

[12] Saaty, T.L. 1980. The Analytic Hierarchy 

Process. McGraw-Hill, New York, NY. 

[13] Kolarik, W.J. 1999. Creating Quality. McGrawHill, Boston. 

[14] Kusiak, A. 1999. Engineering Design – 

Products, Processes, and Systems. Academic 

Press, San Diego. 

[15] Lowe, A.J. 2000. QFD-HOQ tutorial. 

http://www.gsm.mq.edu.au/cmit/qfd-hoqtutorial.swf (accessed 5/5/08). 

[16] Saaty, T.L. 1999. Fundamentals of the Analytic 

Network Process. ISAHP; August 12-14, Kobe, 

Japan. 

[17] Allen, T.T. 2006. Introduction to Engineering 

Statistics and Six Sigma: Statistical Quality

Control and Design of Experiments and Systems. 

Springer-Verlag, London. 

115
Survey of Domain-Specific Performance Measures in

Assistive Robotic Technology

Katherine M. Tsui and Holly A. Yanco

University of Massachusetts Lowell

Department of Computer Science

1 University Avenue

Lowell, MA, USA

{ktsui, holly}@cs.uml.edu

David J. Feil-Seifer and Maja J. Mataric ́ University of Southern California

Department of Computer Science

941 West 37th Place

Los Angeles, CA, USA

{dfseifer, mataric}@usc.edu

ABSTRACT

Assistive robotics have been developed for several domains,

including autism, eldercare, intelligent wheelchairs, assistive

robotic arms, external limb prostheses, and stroke rehabilitation. Work in assistive robotics can be divided into two

larger research areas: technology development, where new

devices, software, and interfaces are created; and clinical

application, where assistive technology is applied to a given

end-user population. Moving from technology development

towards clinical applications is a significant challenge. Developing performance metrics for assistive robots can unveil

a larger set of challenges. For example, what well established

performance measures should be used for evaluation to lend

credence to a particular assistive robotic technology from a

clinician’s perspective? In this paper, we survey several areas of assistive robotic technology in order to demonstrate

domain-specific means for evaluating the performance of an

assistive robot system.

Categories and Subject Descriptors

A.1 [Introductory and Survey]

General Terms

Performance measures

Keywords

Assistive technology, human-robot interaction, robotics, enduser evaluation

1. INTRODUCTION

Assistive robotics may have therapeutic benefits in domains ranging from autism to post-stroke rehabilitation to

eldercare. However, it can be challenging to transition an

assistive device developed in the lab to the target domain.

This problem can occur even when the device was designed

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with a specific end user in mind. R ̈omer et al. provided

guidelines for compiling a technical file for an assistive device for transfer from academic development to manufacturing [52]. Their guidelines state that documentation of

an assistive device must include its “intended use, design

specifications, design considerations, design methods, design

calculations, risk analysis, verification of the specifications,

validation information of performance of its intended use,

and compliance to application standards” [52]. Academic

and industrial research labs are the piloting grounds for new

concepts. However, due to the institutional separation between the research environment and end-users, special care

must be taken so that a finished project properly addresses

the needs of end-users. As such, it is imperative for the

development of assistive robotic technologies to involve the

end-user in the design and evaluations [28]. These end-user

evaluations, with the proper performance measures, can provide the basis for performance validation needed to begin the

transition from research pilot to end product.

Does there exist a ubiquitous set of performance measures for the evaluation of assistive robotic technologies?

Time to task completion or time on task are common measures. R ̈omer et al. propose an absolute measure for time to

task completion, where the time is normalized with an ablebodied person’s performance [52]. Task completion time fits

many robotic applications, such as retrieving an object with

a robotic manipulator. However, it may not suit other applications, such as a range of motion exercise in the rehabilitation of an upper limb. R ̈omer et al. also acknowledge other

factors in determining performance measures, namely “user

friendliness, ease of operation, [and] effectiveness of input

device” [52].

Aside from the very general metrics described above, should

there even be a ubiquitous set of performance metrics? This

lack of a ubiquitous set has occurred in part because each domain has very specific needs in terms of performance. Most

metrics do not translate well between domains or even subdomains. The field of assistive robotics technology has used

a wide variety of performance measures specific to domains

for end-user evaluations. However, there are observable similarities between various employed metrics and how they are

devised. In order to evaluate an assistive robotic technology

within a particular domain, clinical performance measures

are needed to lend validity to the device.

Clinical evaluation is the mechanism used to determine

the clinical, biological, or psychological effects of an evaluated intervention. Clinical evaluations use The Good Clin116
ical Practice Protocol, which requires clearly stated objectives, checkpoints, and types and frequency of measurement

[68]. Well established domains can have well established

performance measures. For example, the Fugl-Meyer motor

assessment, created in 1975 [25], is commonly used when

evaluating upper limb rehabilitation for patients post-stroke.

FIM [42] is popular when measuring the function independence of a person with respect to activities of daily living

(ADLs). The two evaluations have little correlation, if any,

to each other because they are domain-specific. However,

they are both used for studying potential end-users that do

not use assistive technology, and can serve as an effective

method for assessing performance relative to the established

baseline.

In this paper, we explore contemporary end-user evaluations and the performance measures used in evaluating assistive robotic technology. We detail the performance measures

and discuss for which evaluations and contexts they would

be appropriate.

2. ASSISTIVE ROBOTIC TECHNOLOGIES

Haigh and Yanco surveyed assistive robotics in 2002 [30].

A historical survey of rehabilitation robotics through 2003

can be found in Hillman [32]. Simpson surveyed intelligent

wheelchairs through 2004 [57]. We present a contemporary

survey of assistive technologies that have been evaluated by

end-users. We believe that the primary focus of end-user

evaluations should be on the human performance measurements, and secondarily on the performance of the robot.

This section highlights six areas of assistive technology development: autism; eldercare; intelligent wheelchairs, assistive robotic arms; prosthetic limbs; and post-stroke rehabilitation. For each area, we describe a few examples of

performance metrics and how they are employed/applied.

2.1 Autism Spectrum Disorder

An increasing number of research institutions are investigating the use of robots as a means of interaction with

children with autism spectrum disorder (ASD), including

the National Institute of Information and Communications

Technology [37], University of Hertfordshire [49, 50, 48],

Universit ́e de Sherbrooke [43, 53], University of Southern

California [21], University of Washington [60], and Yale University [55, 56]. The goal of these systems is to use robots as

a means of affecting the social and communicative behavior

of children with autism for either assessment or therapeutic

purposes.

2.1.1 End-user Evaluations

The University of Hertfordshire has conducted several observation studies with children with ASD [49]. In one study,

four children interacted with Robota, a robot doll, over a period of several months. Post-hoc analysis of video footage of

interaction sessions yielded eye gaze, touch, imitation, and

proximity categories. Performance measures included frequency of the occurrence of the categories. Another study

used the hesitation and duration of a drumming session as a

task-specific measure of engagement with a drumming robot

[50]. In addition, measures for observing social behavior

were taken from existing work from the autism research

community regarding methods for using video coding for

observing social behavior [64] to determine if a robot was an

isolator or mediator for children with autism [48].

The Universit ́e of Sherbrooke conducted an observation

study of four children with autism spectrum disorder over

seven weeks [43]. The children interacted with Tito, a humancharacter robot, three times per week for five minutes. Video

was collected during the interactions. In post-hoc analysis, the interactions were categorized into shared attention,

shared conventions, and absence of shared attention or conventions; all video data were coded using twelve-second windows. Performance measures included frequency of the occurrence of categories. Other work involved the use of automated interaction logs in order to model a user’s play behavior with the robot [53]. Performance measures included

correlation of recognized play with observed behavior.

The National Institute of Information and Communications Technology (NICT) conducted a longitudinal observation study in a day-care setting [37]. Groups of children

interacted with a simple character robot, Keepon, in twenty

five three-hour sessions over five months. Each session was

a free-play scenario that was part of the regular day-care

schedule. Children were given the opportunity to interact

with the robot, or not, and children were allowed to interact

with the robot in groups. Video of these interactions was

recorded and analyzed in a qualitative fashion. In particular, they observed changes in dyadic interaction between the

child, the robot, and peers.

The University of Southern California (USC) conducted a

study with children with autism interacting with a bubbleblowing robot [20]. This research uses a repeated-measures

study to compare two types of robot behavior, contingent

(the robot responds to the child’s actions) and random (the

robot executes an action after a random amount of time has

passed). The scenario involved the child, the robot, and

a parent observed for forty-five minutes. Post-hoc analysis

of video data was used to identify joint-attention, vocalizations, social orienting, and other forms of social interaction,

identified by target (parent, robot, or none). These behaviors were taken from a diagnostic exam, the Autism Diagnostic Observation Schedule (ADOS) [40], which uses a similar

scenario to the one used in the experiment, providing a key

for identifying relevant evaluative behavior. Results from

this work supported the hypothesis that a robot behaving

contingently provoked more social behavior than a robot behaving randomly. Performance measures included frequency

and richness of the interaction observed between sessions.

The University of Washington developed a study that

compared a robot dog, AIBO, to a simple mechanical stuffed

dog [60]. After a brief introductory period, the participants,

parent and child, interacted with the one of the artifacts for a

period of thirty minutes. The sessions were videotaped, and

coded for behavior. The behavior coding included verbal

engagement, affection, animating artifact, reciprocal interaction, and authentic interaction. The data were compared

between sessions with each dog. The performance measure

used was the amount of coded social behavior observed.

Yale University has been developing robots for diagnostic and therapeutic applications for children with autism.

Specifically, they are developing passive sensing techniques

along with robots designed to exhibit social “presses” in order to provoke and observe the behavior of children with

autism [55]. One example of this approach was the use

of observing gaze behavior as a means for providing diagnostic information [56]. In one study, children were outfitted with eye-tracking equipment and their gaze was tracked

117
with various visual and auditory stimuli. This experiment

tested both children with autism and typically developing

children. The performance measure for this study was to

determine if the gaze tracker could identify significant differences between the gaze patterns of children with autism

and typically developing children. Another study compared

affective prosody given from either a human or robot speech

therapist [36].

2.1.2 Analysis

One common technique for measuring performance in the

ASD domain is coding, followed by a post-hoc analysis to

create keywords, phrases, or categories from video data [51].

Categories and definitions are defined from these units. The

data, such as open ended responses to questions or recorded,

can be annotated with the categories. To ensure reliability, multiple coders are trained on the units and definitions.

When multiple coders are used, inter-rater reliability needs

to be established, usually assessed using Cohen’s kappa [12].

However, in each case, the basic unit of time for behavior

data could be vastly different, ranging from tenths of a second [49], to twelve seconds [43], to assessments of the entire

session [37]. The resulting performance measures use the

number of occurrences within the categories.

While these assessments are in most cases driven by existing tools used in developmental or autism-specific settings,

there is little evidence shown so far that the measures used

translate well to real-world improvements in learning, social

skill development, and psychosocial behavior. It is important to note that autism is considered a spectrum disorder

and that there is a great deal of heterogeneity to the population [24]. While studies can show effects for a small subgroup

of children, it is important to analyze how generalizable the

results are. One strategy for ensuring that the observed

data are somewhat grounded in the field of autism research

is to draw the analysis metrics from existing communities

[51, 20].

2.2 Eldercare

Studies show that the elderly population is growing worldwide [6]. Roboticists from research institutions, such as

NICT [70], USC [63], and University of Missouri [72] are

investigating robots for use as minders, guides, and companions.

2.2.1 End-user Evaluations

The University of Missouri in conjunction with TigerPlace, an eldercare facility, studied assistive technology for

aging in place [72], where residents who would otherwise be

required to have full-time nursing-home care are able to live

in their current residence and have health services brought to

them instead. As part of this effort, they developed a fuzzylogic augmentation of an existing day-to-day evaluation, the

Short Physical Performance Battery (SPPB) [29]. This test

measures the performance for balance, gait, strength, and

endurance.

NICT conducted a five-week study of twenty three elderly

women interacting with Paro, the therapeutic care robot

seal, in an eldercare facility. Interaction occurred one to

threes times per week [70]. Performance measures included

self assessment of the participant’s mood (pictorial Likert

scale [39] of 1 (happy) to 20 (sad)) before and after the

interaction with Paro; questions from the Profile of Mood

States questionnaire [41] to evaluate anxiety, depression, and

vigor (Likert scale of 0 (none) to 4 (extremely)); and urinary

specimens to measure stress.

Researchers at the USC are currently developing a robot

for exercise therapy in adults suffering from dementia [63].

Exercise therapy was part of the regular care regiment provided by the staff at the nursing home location of the experiment, but keeping the elders engaged in the task was

a challenge for the staff. The experiment scenario involves

using a robot to demonstrate, coach, and monitor exercises.

The real-world performance measure for success is compliance to the exercise regimen, measured by time on task (from

recorded video data post-hoc), or overall health of the residents. Initial studies involved using a focus group to assess resident’s reactions to the robot. For the focus group

interaction, performance was measured by the number of

residents showing willingness to interact with the robot.

2.2.2 Analysis

Most of the above systems are currently at the feasibility

stage of implementation, an important stage of evaluation

for determining if the technology is ready for deployment

in a real-world environment. User and behavior studies of

eldercare systems, such as with Paro, serve to describe the

effects that such systems have on users and their environment. By emphasizing social interaction and fitness, these

performance measures implicitly measure changes in quality

of life (QoL).

Current evaluations of eldercare systems occur over a period of days or weeks. As these systems become more permanent fixtures in eldercare environments, the assessment

of QoL becomes more important. There exist standardized

questionnaires for observing QoL at multiple points of time.

Therefore, QoL can be a good method of observing the longterm effectiveness of a change in the eldercare environment

[76]. For example, the SF-36 survey [1] is used to assess

health-related QoL, while the 15-D [59] survey is used to

measure QoL along several elements of a subject’s lifestyle.

2.3 Intelligent Wheelchairs

Intelligent wheelchairs can potentially improve the quality of life for people with disabilities. Research has focused

on autonomous and semi-autonomous collision-free navigation and human-robot interaction (i.e., novel input devices

and intention recognition) and has been conducted by both

research institutions and companies.

2.3.1 End-user Evaluations

In 2005, MobileRobots (formerly ActivMedia) and the

University of Massachusetts Lowell evaluated the Independence – Enhancing Wheelchair (IEW) [45, 46] with several

end-users at a rehabilitation center. The original testing design planned to use of a maze-like obstacle course made of

cardboard boxes. However, this scenario did not work well

with the participants. They were frustrated by a maze that

was not like their regular driving environments and viewed

boxes as moveable objects.

Instead, the participants operated the IEW as they would

typically use a wheelchair in their everyday lives (e.g., going

to class which entailed moving through corridors with other

people and passing through doorways). The performance

measure, number of hits/near misses and time on task, was

not modified. The results have not yet been published.

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End-user trials have also been completed by intelligent

wheelchair companies, such as DEKA [16] and CALL Centre

[8], seeking government approval to prove the safety of these

systems. The University of Pittsburgh has conducted an

evaluation of DEKA’s iBOT with end-users [13].

2.3.2 Analysis

In the domain of intelligent wheelchairs, the majority of

user testing has been in the form of feasibility studies with

able-bodied participants. As noted in Yanco [77], able-bodied

participants are more easily able to vocalize any discomforts

and stop a trial quickly. These pilot experiments pave the

way for end-user trials.

One barrier to end-user trials of robotic wheelchair systems is the need for the use of a participant’s seating on

the prototype system. While seating can be moved from the

participant’s wheelchair to the prototype system (if compatible) and back, this seating switch can take thirty to sixty

minutes in each direction, making multiple testing sessions

prohibitive.

We discuss performance measures commonly used thus far

in feasibility studies. One of the most common tests of an

autonomous intelligent wheelchair is passing through a doorway [58]. Passing through a doorway without collision is one

of seven “environmental negotiations” that a person must

perform in order to be prescribed a power wheelchair for

mobility [67]. Other tasks include changing speed to accommodate the environment (e.g., cluttered = slow), stopping

at closed doors and drop offs (e.g., stairs and curbs), and

navigating a hallway with dynamic and stationary objects

(e.g., people and furniture).

In the case of these power mobility skills, the user is rated

based on his/her ability to safely complete the task. In

contrast, robotic performance measures are not binary. Performance measures include time to completion (i.e., time

to pass through the doorway), number of interactions, and

number of collisions. Recent performance measures include

accuracy, legibility, and gracefulness of the motion used to

pass through the doorway [9, 62].

2.4 Assistive Robotic Arms

Robotic arms can improve the quality of life by aiding

in activities of daily living (ADLs), such as self-care and

pick-and-place tasks. Robotic arms can be used in fixed

workstations, placed on mobile platforms, or mounted to

wheelchairs. Research focuses both on building robot arms

and the design of human-robot interaction. One topic of interest is retrieving an object from a shelf or floor (i.e., pickand-place task), one of the most common ADLs [61]. Institutions investigating assistive robotic arms include Clarkson

University [26], Delft University [65], Stanford University

[71], University of Massachusetts Lowell [66], University of

Pittsburgh [11], and TNO Science & Industry [65].

2.4.1 End-user Evaluations

Stanford University conducted an experiment with twelve

spinal cord injury patients on two user interfaces for ProVAR,

a vocational workstation [71]. After using each interface,

each participant answered an evaluation questionnaire. Performance measures included open-ended responses to positive and negative questions on the robot’s appearance, navigation, ease of use, error messages, complexity, usefulness,

and functionality, and also on the participant’s satisfaction.

The University of Pittsburgh evaluated the effects of a

Raptor arm, a commercially available wheelchair-mounted

robotic arm, on the independence of eleven spinal cord injury patients [11]. Participants first completed sixteen ADLs

without the Raptor arm, then again after initial training,

and once more after thirteen hours of use. At each session,

the participants were timed to task completion and classified

as dependent, needs assistance, or independent.

Clarkson University evaluated eight multiple sclerosis patients over five ADLs with and without the Raptor arm [26].

The participants in this study all required assistance with

self-care ADLs. Participants were evaluated before and after training on the Raptor arm. At each session, the participants were timed to task completion and interviewed. They

also rated the level of difficulty of task performance and

the Psychosocial Impact of Assistive Devices Scale (PIADS)

[15].

University of Massachusetts Lowell conducted an experiment of a new visual human-robot interface for the Manus

Assistive Robotic Manipulator (ARM), a commercially available European robot arm. Eight individuals who used wheelchairs and had cognitive impairments participated in an

eight week controlled experiment to control the robot arm in

a pick-and-place task. Performance measures included time

to task completion (i.e., object selection time), level of attention, level of prompting (based on measurement of functional

independence [42]), and survey responses (i.e., preference of

interface, improvements).

TNO Science & Industry and Delft University conducted

a four person case study [65]. The end-users were people who use power wheelchairs and have weak upper limb

strength and intact cognition. TNO Science & Industry

evaluated their alternative graphical user interface for the

Manus ARM. The performance measures included number

of mode switches, task time, Rating Scale of Mental Effort

(RSME) [78], and survey responses.

2.4.2 Analysis

As demonstrated by Tsui et al. [66], Tijsma et al. [65],

and Fulk et al. [26], it is also important to account for

the user’s experience with respect to cognitive workload and

mental and emotional state. The basis for the user’s experience performance measure must be derived or adapted from

an existing clinical measure.

In Tsui et al. [66] and Tijsma et al. [65], the participants were rated or rated themselves with respect to cognitive workload. In Tsui et al. [66], the level of prompting

during a trial was a cognitive measure based on FIM, which

is a scale that measures functional independence [42]. A person is rated on a Likert scale (1 = needs total assistance to

7 = has complete independence) on a variety of ADLs. FIM

may also be applied as a cognitive measure to activities such

as “comprehension, expression, social interaction, problem

solving, and memory” [42]. In Tijsma et al. [65], RSME was

used as a cognitive performance measure. RSME is a 150

point scale measuring the mental effort needed to complete

a task, where 0 = no effort and 150 = extreme effort. The

Standardized Mini-Mental State Examination [47] is another

cognitive performance measures used in older adults.

In Fulk et al. [26], participants explicitly ranked the perceived difficulty of the task and their mental and emotional

state were recorded using PIADS. PIADS is a twenty six

item questionnaire in which a person rates their perceived

119
experience after completing a task with an assistive technology device [14]. It measures the person’s feelings of competence, willingness to try new things, and emotional state.

PIADS is well established and significantly used in the US

and Canada [14]. An alternative emotional performance

measure is the Profile of Mood States [41] used in Wada

et al. [70].

2.5 External Limb Prostheses

Robotic prostheses can serve as limb replacements. Research institutions, such as Hong Kong Polytechnic University [38], Massachusetts Institute of Technology [3], Northwestern University [44], and the Rehabilitation Institute of

Chicago [44], have investigated creating new robotic prosthetics and control strategies.

2.5.1 End-user Evaluations

The Rehabilitation Institute of Chicago (RIC) and Northwestern University conducted a clinical evaluation of six

individuals who underwent targeted muscle reinnervation

surgery [44]. After the upper limb prosthetic device was optimally configured for each patient’s electromyography signals (EMG), functional testing occurred after the first month,

third month, and sixth month. The functional testing was

comprised of a series of standard tests: box and blocks,

clothespin relocation, Assessment of Motor and Process Skills

(AMPS) [23], and the University of New Brunswick prosthetic function [54]. Performance measures included time to

complete task, accuracy, and AMPS score.

Researchers at the Massachusetts Institute of Technology conducted a clinical evaluation with three unilateral,

transtibial amputees [3]. Data collection included oxygen

consumption, carbon dioxide generation, joint torque, and

joint angle. Kinematic and kinetic data were collected using

a motion capture system for the ankle-foot prosthesis and

unaffected leg. The resulting performance measures were

metabolic cost of transport (using oxygen consumption as a

parameter), gait symmetry between the legs, vertical ground

reaction forces, and external work done at the center of mass

of each leg.

Hong Kong Polytechnic University conducted a clinical

evaluation with four transtibial amputees over the course of

three consecutive days [38]. Data collected included motion

capture and open-ended responses about the participant’s

comfort and the prosthesis’ stability, ease of use, perceived

flexibility, and weight. Stance time, swing time, step length,

vertical trunk motion, and average velocity were derived

from the motion capture data. Performance measures included ranking of the prostheses used (with respect to comfort, stability, ease of use, perceived flexibility, and weight),

gait symmetry, and ground force reactions.

2.5.2 Analysis

Performance measures involving ADLs can be used in

evaluating prostheses because ADLs include functions such

a locomotion and self-care activities. Locomotion includes

walking and climbing stairs, and self-care activities involve

a high level of dexterity. Heinemann et al. [31] proposed the

Orthotics and Prosthetics Users’ Survey (OPUS). Burger et

al. [7] in turn evaluated the Upper Extremity Functional

Status of OPUS with sixty one users with unilateral, upper limb amputations and found that the scale was suitable

for the measuring functionality of the population. The Upper Extremity Function Status is comprised of twenty three

ADLs, rated in a Likert scale fashion (0 = unable to complete, 3 = very easy to complete. Similarly, AMPS is also

comprised of ADLs but in a more flexible fashion; there

are eighteen categories of ADLs with up to eleven choices

within a category [2]. Another measure of quality of life is

FIM, which is comprised of eighteen ADLs.

2.6 Stroke Rehabilitation

Robots are being investigated for gait training at Arizona State University [73], upper-limb recovery at RIC and

Northwestern University [33], and wrist rehabilitation at

Hong Kong Polytechnic University [34]. It is well documented that stroke patients regain most of their mobility

through repetitions of task training [35]. Many researchers

are investigating the use of robots as a way to augment current rehabilitation strategies for post-stroke patients.

2.6.1 End-user Evaluations

An example of a typical rehabilitation robot study using

stroke patients was conducted by RIC and Northwestern

University of the Therapy Wilmington Robotic Exoskeleton (T-WREX). The team conducted a clinical evaluation of

twenty three stroke survivors over sixteen weeks comparing

robot-assisted therapy to a traditional rehabilitation therapy regimen [33]. The researchers observed functional arm

movement, quality of affected arm use, range of motion, grip

strength, a survey of patient satisfaction of therapy, and

the use of the affected arm in the home when not undergoing therapy. Performance assessments with or without the

robot included Fugl-Meyer [25] and Rancho Functional Test

for Upper Extremity [74] to measure ability to use the arm.

In addition, they measured use of the arm outside of the experimental setting by using the Motor Activity Log [69], a

self-report, to determine how the arm was used in the home.

Finally, to assess the costs of using the robot, they measured

the amount of time that the user needed assistance in order

to use the T-WREX.

The early stages of rehabilitation robot development involves evaluations of the performance of the robot in a pilot

setting. Some evaluations are users studies, where the robot

is used with small number of users to determine what needs

to be altered [73]. Performance measures used involve satisfaction surveys, measures of robustness, and analyses of the

quantifiability of sensor data for clinical purposes. These

measures are specific to the robot being evaluated, and in

general cannot be used in the field in general.

The primary assessment of post-stroke rehabilitative robotics involves the use of clinical assessments of patient function. Discussed above was the Fugl-Meyer and Rancho Functional Test. However, there are many others used. At at

Northwestern University and RIC, Ellis et al. [18] supplemented the Fugl-Meyer with several other measures, including the Chedokee McMaster Stroke Assessment, the Reaching Performance Scale, and the Stroke Impact Scale. At

Hong Kong Polytechnic University, Hu et al. [34] used four

other measures: the Motor Status Score (MSS, used to assess

shoulder function) [22], the Modified Ashworth Scale (MAS,

used to measure of increase of muscle tone) [4], the Action

Research Arm Test (ARAT, used to assess grasp, grip, pinch,

and gross movement) [17], and FIM (used to asses functionality in ADLs) [42]. These performance measures provide

the picture of the clinical definition of effectiveness.

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2.6.2 Analysis

Stroke rehabilitation is an established medical domain.

Thus, the evaluations of these experiments use relevant clinical evaluations to determine the effectiveness of the robotaugmented therapy. The scope of rehabilitative robotics for

patients post-stroke is quite large, ranging from upper-limb

recovery to gait training and wrist rehabilitation. Even

within a domain, the specific performance measures differ

depending on the therapy and may not translate well to

another sub-domain. For example, the MSS is applicable

to the T-WREX [33] upper-arm rehabilitative aid, but not

evaluating gait rehabilitation.

Functional evaluations, such as the Fugl-Meyer [27] and

Wolf Motor Function [75], are crucial to comparing the effectiveness of robot-augmented therapies to one another in

addition to comparing them with non-robot augmentations

for current therapies. It is through these comparisons that

robots can truly be evaluated as a rehabilitative device.

3. CONCLUSIONS

We believe that performance measures should be specific

to the domain and relevant to the task. Domains with clear,

well-established medical or therapeutic analogs can leverage

existing clinical performance measures. For example, the

Fugl-Meyer motor assessment, founded in 1975 [25], is popular when evaluating upper limb rehabilitation of post-stroke

patients. Domains without strong therapeutic analogs can

appropriately borrow clinical performance measures. Alternatively, they may draw inspiration from a clinical performance measure to create a new one or augment an existing

one if none of the existing measures are appropriate [29].

Further, we believe that evaluations conducted with endusers should focus at least as highly on human performance

measures as they do on system performance measures. By

placing the emphasis on human performance, it becomes

possible to correlate system performance with human performance. Celik et al. has taken the important first steps

for stroke-rehabilitation by examining trajectory error and

smoothness of motion with respect to Fugl-Meyer [10]. Similarly, Brewer et al. has used machine learning techniques

on sensor data to predict the score of a person with Parkinson’s disease on the Unified Parkinson Disease Rating Scale

(UPDRS) [5, 19].

Existing performance measures for most of assistive robotic

technologies do not provide sufficient detail for experimental

and clinical evaluations. We provide a summary of performance measures used (see Table 1) and offer guidelines as

to choosing appropriate and meaningful performance measures:

• Consult a clinician who specializes in the particular

domain, if possible.

• Choose an appropriate clinical measure for the domain.

A domain’s “gold standard” will provide the best validity to clinicians.

• Choose an appropriate method to capture a participant’s emotional and mental state.

• Consider an appropriate quality of life measurement.

• Administer the human performance measures at least

before and after the experiment.

• Consider coding open ended responses, comments,

and/or video.

• Concretely define each enumeration in a Likert scale.

By choosing meaningful performance measures, robotics researchers provide a common ground for interpretation and

acceptance by the clinical community. In addition, the researchers of a given system are also given clear guidelines for

how to observe and define performance of a given system.

Through this survey, we seek other well-established performance measures to apply to assistive robotic technologies.

Common performance measurements will allow researchers

to both compare the state of the art approaches within specific domains and also to compare against the state of the

practice within the field outside of the robotics community.

4. ACKNOWLEDGMENTS

This work is funded in part by the National Science Foundation (IIS-0534364, CNS-0709296) and the Nancy Laurie

Marks Family Foundation.

5. REFERENCES

[1] N. K. Aaronson, C. Acquadro, J. Alonso, G. Apolone,

D. Bucquet, M. Bullinger, K. Bungay, S. Fukuhara,

B. Gandek, S. Keller, D. Razavi, R. Sanson-Fisher,

M. Sullivan, S. Wood-Dauphinee, A. Wagner, and J. E.

Ware Jr. Intl. Quality of Life Assessment (IQOLA) Project.

Quality of Life Research, 1(5):349–351, 2004.

[2] AMPS.com. Assess of Motor and Process Skills. In

http://www.ampsintl.com/tasks.htm, 2008.

[3] S. Au. Powered Ankle-Foot Prosthesis for the Improvement

of Amputee Walking Economy. PhD thesis, MIT, 2007.

[4] R. Bohannon and M. Smith. Interrater reliability of a

modified Ashworth scale of muscle spasticity. Physical

Therapy, 67(2):206–7, 1987.

[5] B. R. Brewer, S. Pradhan, G. Carvell, P. Sparto,

D. Josbeno, and A. Delitto. Application of Machine

Learning to the Development of a Quantitative Clinical

Biomarker for the Progression of Parkinson’s Disease. In

Rehab. Eng. Society of North America Conf., 2008.

[6] J. Brody. Prospects for an ageing population. Nature,

315(6019):463–466, 1985.

[7] H. Burger, F. Franchignoni, A. Heinemann, S. Kotnik, and

A. Giordano. Validation of the orthotics and prosthetics

user survey upper extremity functional status module in

people with unilateral upper limb amputation. J. of Rehab.

Medicine, 40(5):393–399, 2008.

[8] CALL Centre. Smart wheelchair. In http://callcentre.edu

cation.ed.ac.uk/Smart WheelCh/smart wheelch.html, 2008.

[9] T. Carlson and Y. Demiris. Human-wheelchair

collaboration through prediction of intention and adaptive

assistance. In IEEE Intl. Conf. on Robotics and

Automation, 2008.

[10] O. Celik, M. K. O’Malley, C. Boake, H. Levin, S. Fischer,

and T. Reistetter. Comparison of robotic and clinical motor

function improvement measures for sub-acute stroke

patients. In IEEE Intl. Conf. on Robotics and Automation,

2008.

[11] E. Chaves, A. Koontz, S. Garber, R. Cooper, and

A. Williams. Clinical evaluation of a wheelchair mounted

robotic arm. Technical report, Univ. of Pittsburgh, 2003.

[12] J. A. Cohen. A coefficient of agreement for nominal scales.

Educational and Psychological Measurement, 20:37–46,

1960.

[13] R. Cooper, M. Boninger, R. Cooper, A. Dobson, J. Kessler,

M. Schmeler, and S. Fitzgerald. Use of the Independence

3000 IBOT Transporter at home and in the community. J.

of Spinal Cord Medicine, 26(1):79–85, 2003.

121
Table 1: Summary of Performance Measures Used in Assistive Robotic Technology Domains

Domain Performance Measures Used

Autism Behavior coding, correlate sensor modeling of behavior to human-rated behavior

Eldercare Activities of daily living (SBBP, etc.), mood, stress (Standardized Mini-Mental State), quality of

life (SF-36, 15-D, etc.)

Intelligent Wheelchairs Number of hits/near misses, time on task, accuracy, gracefulness

Assistive Robotic Arms Activities of daily living, time to task completion, mental state (RSME, Profile of Mood States),

attention, level of prompting

Prostheses Functional tests (AMPS, OPUS, FIM, etc.), measures of effort (oxygen consumption, etc.), accuracy,

time to complete task, comfort, ease of use

Post-Stroke Rehabilitation Functional measures (Fugl-Meyer, MSS, ARAT, FIM, Chedokee McMaster, Reaching Performance

Scale, MAS, Wolf Motor, etc.), use of affected limb in home (Motor Activity Log, etc.)

[14] H. Day and J. Jutai. Piads in the world. In

http://www.piads.ca/worldmapshtm/worldmap.asp, 2008.

[15] H. Day, J. Jutai, and K. Campbell. Development of a scale

to measure the psychosocial impact of assistive devices:

lessons learned and the road ahead. Disability and Rehab.,

24(1–3):31–37, 2002.

[16] DEKA Research and Development Corporation. DEKA

Evolved Thinking. In http://www.dekaresearch.com, 2008.

[17] W. DeWeerdt and M. Harrison. Measuring recovery of

arm-hand function in stroke patients: a comparison of the

Brunnstrom-Fugl-Meyer test and the Action Research Arm

Test. Physiother Can, 37(2):65–70, 1985.

[18] M. D. Ellis, T. Sukal, T. DeMott, and J. P. A. Dewald.

ACT3D exercise targets gravity-induced discoordination

and improves reaching work area in individuals with stroke.

In IEEE Intl. Conf. on Rehab. Robotics, 2007.

[19] S. Fahn, R. Elton, et al. Unified Parkinson’s Disease Rating

Scale. Recent developments in Parkinson’s disease,

2:153–163, 1987.

[20] D. J. Feil-Seifer and M. J. Matari ́c. Robot-assisted therapy

for children with autism spectrum disorders. In Conf. on

Interaction Design for Children: Children with Special

Needs, 2008.

[21] D. J. Feil-Seifer and M. J. Matari ́c. Toward socially

assistive robotics for augmenting interventions for children

with autism spectrum disorders. In Intl. Symposium on

Experimental Robotics, 2008.

[22] M. Ferraro, J. Demaio, J. Krol, C. Trudell, K. Rannekleiv,

L. Edelstein, P. Christos, M. Aisen, J. England, and

S. Fasoli. Assessing the Motor Status Score: A Scale for the

Evaluation of Upper Limb Motor Outcomes in Patients

after Stroke. Neurorehabilitation and Neural Repair,

16(3):283, 2002.

[23] A. Fisher. AMPS: Assessment of Motor and Process Skills

Volume 1: Development, Standardisation, and

Administration Manual. Ft Collins, CO: Three Star Press

Inc, 2003.

[24] B. Freeman. Guidelines for Evaluating Intervention

Programs for Children with Autism. J. of Autism and

Developmental Disorders, 27(6):641–651, 1997.

[25] A. Fugl-Meyer, L. Jaasko, I. Leyman, S. Olsson, and

S. Steglind. The post-stroke hemiplegic patient. 1. a

method for evaluation of physical performance.

Scandinavian J. of Rehab. Medicine, 7(1):13–31, 1975.

[26] G. Fulk, M. Frick, A. Behal, and M. Ludwig. A wheelchair

mounted robotic arm for individuals with multiple sclerosis.

Technical report, Clarkson Univ., 2005.

[27] D. Gladstone, C. Danells, and S. Black. The Fugl-Meyer

Assessment of Motor Recovery after Stroke: A Critical

Review of Its Measurement Properties. Neurorehabilitation

and Neural Repair, 16(3):232, 2002.

[28] D. Greenwood, W. Whyte, and I. Harkavy. Participatory

Action Research as a Process and as a Goal. Human

Relations, 46(2):175–192, 1993.

[29] J. Guralnik, E. Simonsick, L. Ferrucci, R. Glynn,

L. Berkman, D. Blazer, P. Scherr, and R. Wallace. A short

physical performance battery assessing lower extremity

function: association with self-reported disability and

prediction of mortality and nursing home admission. J. of

Gerontology, 49(2):M85–94, 1994.

[30] K. Haigh and H. A. Yanco. Automation as caregiver: A

survey of issues and technologies. In AAAI-2002 Workshop

on Automation as Caregiver: The Role of Intelligent

Technology in Elder Care, 2002.

[31] A. W. Heinemann, R. K. Bode, and C. O’Reilly.

Development and measurement properties of the orthotics

and prosthetics users’ survey (opus): a comprehensive set

of clinical outcome instruments. Prosthetics and Orthotics

Intl., 27(3):191–206, 2003.

[32] M. Hillman. Rehabilitation robotics from past to present -

a historical perspective. In IEEE 8th Intl. Conf. on Rehab.

Robotics, 2003.

[33] S. J. Housman, V. Le, T. Rahman, R. J. Sanchez, and D. J.

Reinkensmeyer. Arm-training with t-wrex after chronic

stroke: Preliminary results of a randomized controlled trial.

In IEEE Intl. Conf. on Rehab. Robotics, 2007.

[34] X. L. Hu, K. Y. Tong, R. Song, X. j. Zheng, I. F. Lo, and

K. H. Lui. Myoelectrically controlled robotic systems that

provide voluntary mechanical help for persons after stroke.

In IEEE Intl. Conf. on Rehab. Robotics, 2007.

[35] W. Jenkins and M. Merzenich. Reorganization of

neocortical representations after brain injury: a

neurophysiological model of the bases of recovery from

stroke. Progress in Brain Research, 71:249–66, 1987.

[36] E. S. Kim, E. Newland, R. Paul, and B. Scassellati. A

Robotic Therapist For Positive, Affective Prosody in

High-Functioning Autistic Children. In Poster Pres. at the

Intl. Meeting for Autism Research, 2008.

[37] H. Kozima and C. Nakagawa. Longitudinal child-robot

interaction at preschool. In AAAI Spring Symposium on

Multidisciplinary Collaboration for Socially Assistive

Robotics, pages 27–32, 2007.

[38] W. Lee, M. Zhang, P. Chan, and D. Boone. Gait Analysis

of Low-Cost Flexible-Shank Trans-Tibial Prostheses. IEEE

122
Trans. on Neural Systems and Rehab. Eng., 14(3):370–377,

2006.

[39] R. Likert. A technique for the measurement of attitudes.

Archives of Psychology, 140(5):1–55, 1932.

[40] C. Lord, S. Risi, L. Lambrecht, E. H. C. Jr., B. L.

Leventhal, P. C. DiLavore, A. Pickles, and M. Rutter. The

autism diagnostic observation schedule-generic: A standard

measure of social and communication deficits associated

with the spectrum of autism. J. of Autism and

Developmental Disorders, 30(3):205–223, 2000.

[41] D. M. McNair, M. Lorr, and L. F. Droppleman. Profile of

mood states. In Educational and Industrial Testing Service,

1992.

[42] MedFriendly.com. Functional independence measure. In

http://www.medfriendly.com/

functionalindependencemeasure.html, 2007.

[43] F. Michaud, T. Salter, A. Duquette, H. Mercier, M. Lauria,

H. Larouche, and F. Larose. Assistive technologies and

child-robot interaction. In AAAI Spring Symposium on

Multidisciplinary Collaboration for Socially Assistive

Robotics, 2007.

[44] L. Miller, K. Stubblefield, R. Lipschutz, B. Lock, and

T. Kuiken. Improved Myoelectric Prosthesis Control Using

Targeted Reinnervation Surgery: A Case Series. IEEE

Trans. on Neural Systems and Rehab. Eng., 16(1):46–50,

2008.

[45] MobileRobots Inc. Independence-enhaning wheelchair. In

http://www.activrobots.com/RESEARCH/wheelchair.html,

2008.

[46] MobileRobots Inc. Robotic chariot. In

http://activrobots.com/robots/robochariot.html, 2008.

[47] D. Molloy and T. Standish. A Guide to the Standardized

Mini-Mental State Examination. Intl. Psychogeriatrics,

9(S1):87–94, 2005.

[48] B. Robins, K. Dautenhahn, and J. Dubowsky. Robots as

Isolators or Mediators for Children with Autism? A

Cautionary Tale. In AISB05: Social Intelligence and

Interaction in Animals, Robots and Agents, 2005.

[49] B. Robins, K. Dautenhahn, R. te Boekhorst, and

A. Billard. Robots as assistive technology – does

appearance matter? In IEEE Int. Workshop on Robot and

Human Interactive Communication, 2004.

[50] B. Robins, K. Dautenhahn, R. te Boekhorst, and

C. Nehaniv. Behaviour Delay and Robot Expressiveness in

Child-Robot Interactions: A User Study on Interaction

Kinesics. In Intl. Conf. on Human-Robot Interaction, 2008.

[51] R. Robins, C. Fraley, and R. Krueger. Handbook of

Research Methods in Personality Psychology. Guilford

Press, 2007.

[52] G. R ̈omer and H. Stuyt. Compiling a Medical Device File

and a Proposal for an Intl. Standard for Rehabilitation

Robots. IEEE Intl. Conf. on Rehab. Robotics, pages

489–496, 2007.

[53] T. Salter, F. Michaud, D. L ́etourneau, D. Lee, and

I. Werry. Using proprioceptive sensors for categorizing

interactions. In Human-Robot Interaction, 2007.

[54] E. Sanderson and R. Scott. UNB test of prosthetic function:

a test for unilateral amputees [test manual]. Fredericton,

New Brunswick, Canada, Univ. of New Brunswick, 1985.

[55] B. Scassellati. How Social Robots Will Help Us to Diagnose,

Treat, and Understand Autism. Robotics Research: Results

of the 12th Intl. Symposium ISRR, 28:552–563, 2007.

[56] F. Shic, B. Scassellati, D. Lin, and K. Chawarska.

Measuring context: The gaze patterns of children with

autism evaluated from the bottom-up. Intl. Conf. on

Development and Learning, pages 70–75, 2007.

[57] R. Simpson. Smart wheelchairs: A literature review. J. of

Rehab. Research Development, 42(4):423–36, 2005.

[58] R. C. Simpson. Improved automatic adaption through the

combination of multiple information sources. PhD thesis,

Univ. of Michigan, Ann Arbor, 1997.

[59] H. Sintonen. The 15-d measure of health related quality of

life: Reliability, validity and sensitivity of its health state

descriptive system. Working Paper 41, Center for Health

Program Evaluation, 1994.

[60] C. Stanton, P. Kahn, R. Severson, J. Ruckert, and B. Gill.

Robotic animals might aid in the social development of

children with autism. In Intl. Conf. on Human Robot

Interaction, pages 271–278, 2008.

[61] C. Stranger, C. Anglin, W. S. Harwin, and D. Romilly.

Devices for assisting manipulation: A summary of user task

priorities. IEEE Trans. on Rehab. Eng., 4(2):256–265, 1994.

[62] T. Taha, J. V. Mir ́o, and G. Dissanayake. Pompdp-based

long-term user intention prediction for wheelchair

navigation. In IEEE Intl. Conf. on Robotics and

Automation, 2008.

[63] A. Tapus, J. Fasola, and M. J. Matari ́c. Socially assistive

robots for individuals suffering from dementia. In

Human-Robot Interaction Intl. Conf., Workshop on

Robotic Helpers: User Interaction, Interfaces and

Companions in Assistive and Therapy Robotics, 2008.

[64] C. Tardif, M. Plumet, J. Beaudichon, D. Waller,

M. Bouvard, and M. Leboyer. Micro-analysis of social

interactions between autistic children and normal adults in

semi-structured play situations. Intl. J. of Behavioral

Development, 18(4):727–747, 1995.

[65] H. Tijsma, F. Liefhebber, and J. Herder. Evaluation of new

user interface features for the manus robot arm. In IEEE

Intl. Conf. on Rehab. Robotics, pages 258–263, 2005.

[66] K. Tsui, H. Yanco, D. Kontak, and L. Beliveau.

Development and evaluation of a flexible interface for a

wheelchair mounted robotic arm. In Intl. Conf. on Human

Robot Interaction, 2008.

[67] Univ. of Illinois Chicago. Power mobility skills checklist. In

http://internet.dscc.uic.edu/forms/0534.pdf, 2008.

[68] US Food and Drug Administration. Guidance for industry,

E6 good clinical practice: consolidated guidance. Federal

Register, 10:691–709, 1997.

[69] G. Uswatte, E. Taub, D. Morris, K. Light, and

P. Thompson. The Motor Activity Log-28: Assessing daily

use of the hemiparetic arm after stroke. Neurology,

67(7):1189, 2006.

[70] K. Wada, T. Shibata, T. Saito, and K. Tanie. Effects of

robot-assisted activity for elderly people and nurses at a

day service center. IEEE, 92(11):1780–1788, 2004.

[71] J. Wagner and H. Van der Loos. Training strategies for the

user interface of vocational assistive robots. Intl. Conf. on

Eng. in Medicine and Biology Society, EMBC, 2, 2004.

[72] S. Wang, J. Keller, K. Burks, M. Skubic, and H. Tyrer.

Assessing Physical Performance of Elders Using Fuzzy

Logic. IEEE Intl. Conf. on Fuzzy Systems, pages

2998–3003, 2006.

[73] J. A. Ward, S. Balasubramanian, T. Sugar, and J. He.

Robotic gait trainer reliability and stroke patient case

study. In IEEE Intl. Conf. on Rehab. Robotics, 2007.

[74] D. Wilson, L. Baker, and J. Craddock. Functional test for

the hemiparetic upper extremity. American J. of

Occupational Therapy, 38(3):159–64, 1984.

[75] S. Wolf, P. Thompson, D. Morris, D. Rose, C. Winstein,

E. Taub, C. Giuliani, and S. Pearson. The EXCITE Trial:

Attributes of the Wolf Motor Function Test in Patients

with Subacute Stroke. Neurorehabilitation and Neural

Repair, 19(3):194, 2005.

[76] S. Wood-Dauphinee. Assessing quality of life in clinical

research: From where have we come and where are we

going? J. of Clinical Epidemiology, 52(4):355–363, 1999.

[77] H. Yanco. Evaluating the performance of assistive robotic

systems. Performance Metrics for Intelligent Systems

(PerMIS) Workshop, pages 21–25, 2002.

[78] F. Zijlstra. Efficiency in work behaviour: A design

approach for modern tools. PhD thesis, Delft Univ., 1993.

123
Refining the Cognitive Decathlon 

Robert L. Simpson, Jr. 

Applied Systems Intelligence, Inc. 

3650 Brookside Parkway, Suite 500 

Alpharetta, Georgia, USA 

bsimpson@asinc.com 

Charles R. Twardy 

OnLine Star, Inc. 

2515 Red Cedar Dr. 

Bowie, Maryland, USA 

ctwardy@onlinestarinc.com 

ABSTRACT

We argue that cognitive tests of intelligent agents should use 

modern intelligence theory to help ensure the test battery covers 

key aspects of cognition and decomposes them as diagnostically 

as possible. To this end we assess the recent BICA cognitive 

decathlon proposal [15] on the Cattel-Horn-Carrol (CHC) factor 

model of human intelligence [11], and suggest tests to fill the 

gaps. Some of those tests come from cognitive performance 

software developed by NTI [17 & 18]. Appealing again to CHC 

theory, we note remaining gaps and suggest known tests which 

can fill them. 

Categories and Subject Descriptors

I.2.0 [Artificial Intelligence]: General – cognitive simulation

General Terms

Measurement, Performance, Experimentation, Human Factors 

Keywords

Cognitive decathlon, Integrated cognitive agents, Intelligence 

theory, Cattel-Horn-Carrol Model (CHC), BICA 

1. INTRODUCTION 

The idea of a cognitive decathlon dates back at least to the early 

1990s when: “Vere proposed creating a “Cognitive Decathlon” to 

create a sociological environment in which work on integrated 

cognitive systems can prosper. Systems entering the Cognitive 

Decathlon are judged, perhaps figuratively, based on a cumulative 

score of their performance in each cognitive “event.” The 

contestants do not have to beat all of the narrower systems in their 

one specialty event, but compete against other well-rounded 

cognitive systems.” [23, p. 460]. In Newell [16] as well as 

Anderson and Lebiere [1], the goal is to resist specialization, and 

return AI to a broad vision of integrated intelligence. Anderson 

and Lebiere said their article could be viewed as a proposal for 

events in the decathlon, with initial scores provided by ACT-R 

and classical connectionism. Recognizing that goal, DARPA’s 

Information Processing Technology Office (IPTO) has been 

looking for a “Cognitive Grand Challenge” to rival the highlysuccessful vehicle Grand Challenge. In January 2005, IPTO held 

a Grand Challenge workshop. They commissioned MITRE to 

prepare a report [2] detailing why previous Grand Challenge 

proposals had failed. Participants at the workshop were given 

copies of the report. It concluded that a Grand Challenge must 

meet these criteria: 

x Clear and compelling demonstration of cognition

x Clear and simple measurement

x Decomposable and diagnostic

x Ambitious and visionary, but not unrealistic

x Compelling to the general public

x Motivating for researchers

These in turn were explained in some detail. For example, to be 

“clear and compelling”: 

a. The test should be a proxy for a range of problems 

requiring cognitive capabilities. 

b. The test should not be “game-able” or solvable by 

“cheap tricks” 

c. It should not be solvable by brute force computation, 

alone, and it should not lend itself to idiot savant solutions. 

d. It should require integration of multiple cognitive 

capabilities. 

 The best general categories were “Physical Activity”, like 

RoboCup, and “Take a Test”. The MITRE review placed a 

Cognitive Decathlon into the “Take a Test” camp. But what sort 

of test? 

2. RIGHT IDEA, WRONG TEST 

RPI’s Selmer Bringsjord [2, 4 &5] proposed that AI agents simply 

be given the Wechsler Adult Intelligence Scale (WAIS), a popular 

IQ test. Others proposed the New York Regent’s exams, or the 

California STAR tests, which are performance tests, not aptitude 

tests. Bringsjord calls the general approach “Psychometric AI”. 

Unlike the all-or-none Turing Test, failure on a broad test like 

WAIS is diagnostic – the pattern of successes and failures on the 

questions will tell us what the agent does well and poorly. 

Furthermore, intelligence tests have been used for clinical 

diagnosis, opening up intriguing possibilities for “diagnosing” 

agents – which we expect will show a great many deficits when 

compared with humans, perhaps in characteristic patterns. For 

example, Paul Harrison [12] argues that statistical methods based 

on the Gaussian distribution react “autistically” to outliers. 

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copies bear this notice and the full citation on the first page. To copy 

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requires prior specific permission and/or a fee. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA. 

Copyright 2008 ACM 978-1-60558-293-1...$5.00.

However, the choice of test matters. WAIS and other standard 

tests are deficient because they cover mainly memory and 

attention, things which computers are very good at [9]. Indeed, 

124
Sanghi and Dowe [21] claim to have written a simple 960-line 

Perl program that gets average human scores on various IQ tests1

, 

which is clearly a reductio for those tests, since the program earns 

its scores on arithmetic, logical, and pattern questions, not 

language or semantic ones. 

We argue that this is a problem with the particular tests, not the 

general idea. As we discuss in the next section, modern CHC 

theory holds that human intelligence factors into at least 10 broad 

aptitudes, only 2 or 3 of which are exercised by standard IQ tests. 

Flanagan et al. [10, p.54] claim, “The Wechsler verbal/nonverbal 

model does not represent a theoretically or empirically supported 

model of the structure of intelligence.” Our proposal, in a nutshell, 

is to make sure that all are covered. We want the individual tasks 

to map fairly cleanly onto cognitive “modules” – cohesive units 

of cognitive function. So we need to know what those units are. 

3. CHC: MODERN PSYCHOMETRIC 

THEORY 

The underlying model of intelligence has changed in the hundred 

years since psychometric testing began. 

Flanagan et al. [10 & 11] describe the progression of intelligence 

theories & tests from single-factor theories to modern theories. 

They argue that the most well-supported theory of cognitive 

factors is “modern Gf-Gc” theory. Their version is CHC theory, 

so called because it merges Carroll’s 8-factor model based on an 

exhaustive review of the factor analysis literature2

 with the HornCattell 10-factor model. CHC theory has 10 broad cognitive 

abilities, each of which subsumes between 2 and 14 more narrow 

abilities. 

The most common intelligence tests (Stanford-Binet, and the 

Wechsler tests, including WAIS) do not match up with modern 

CHC theory. They were originally designed for single-factor or 

dichotomous theories of intelligence, and later revisions – the 

SB:IV and WISC-III or WAIS-III – have only been slightly 

updated: they do not correspond to the current consensus on the 

most likely cognitive factor/ability boundaries. Indeed, according 

to a new study, the recently-updated WISC-IV “measures [only] 

crystallized ability (Gc), visual processing (Gv), fluid reasoning 

(Gf), short-term memory (Gsm), and processing speed (Gs); some 

abilities are well-measured, others are not” [13]. 

3.1 The CHC Factors 

The factors are [17], pp.30-31, 42-45): 

Gf – fluid intelligence: what we use when faced with a novel task; 

inductive and deductive reasoning. 

Gc – crystallized intelligence: acquired knowledge; “the sage” 

Gq – quantitative knowledge, esp. arithmetical 

 

 

1 They did not attempt the Wechsler tests or the Stanford-Binet tests, 

presumably because they are not publicly available. Nor should we 

expect their program to do well on them. As we see later, those tests 

have heavy language and semantic components. Sanghi and Dowe used 

the ACE, Eysenck tests 1—8, I.Q. Test Labs, test Testedich.de, and an 

I.Q. test from Norway. They scored poorly on the last 3 (59, 84, and 60) 

respectively. See their Table 1 (p.4) and references.

2 Carroll reviewed 1500 studies covering 461 data sets.

Grw – reading/writing ability; basic written comprehension & 

expression 

Gsm – short-term memory; storage for a few seconds; working 

memory 

Gv – visual processing: including spatial orientation 

Ga – auditory processing: “the ability to perceive, analyze, and 

synthesize patterns among auditory stimuli, and discriminate 

subtle nuances in patterns of sound” (p.42) 

Glr – long-term storage and retrieval: long-term memory 

performance (not content) 

Gs – processing speed: “attentive speediness”; on the order of 2-3 

minutes (p.44) 

Gt – decision/reaction time or speed: on the order of seconds or 

parts thereof 

To get a good measure of human cognitive abilities, CHC theory 

suggests at least two independent tests for each of these 10 broad 

abilities, preferably using relatively unrelated “narrow” abilities 

from within the broad ability. For example, a measure of Fluid 

Intelligence, Gf, might include a test on “General Sequential 

Reasoning” and on “Induction”. 

Mueller et al. [15] present a cognitive decathlon they designed for 

DARPA’s Biologically Inspired Cognitive Architecture program, 

BICA. BICA sought to “develop comprehensive biological 

embodied cognitive agents that could learn and be taught like a 

human.” Mueller et al. developed three complex Challenge 

Scenarios, 23 Cognitive Decathlon3

 tasks, and a Biovalidity 

Assessment. We are concerned with the Decathlon tasks. 

In Table 1, we have labeled the BICA decathlon tests according to 

the CHC abilities we think they measure. Unsurprisingly, the 

Visual tests measure Visual Processing, Gv. Some of the more 

challenging ones may also measure long-term memory, Glr, given 

that they involve remembering and recognizing places previously 

visited. Likewise, the advanced Search tasks involve Processing 

Speed (Gs), Memory (Glr & Gsm), and possibly some Fluid 

Intelligence (Gf ) when the agent must learn hiding patterns. 

Language and Knowledge areas test long-term memory (Glr) and 

Crystallized Intelligence (Gc) and possibly Short-term Memory 

(Gsm). 

Part II of Flanagan et al. [10] is basically a how-to guide for 

constructing a minimal but sound cross-battery test to measure 

CHC abilities. Since we will see the cross-battery approach again 

with the NTI “Armory”, we should consider Flanagan et al.’s core 

design ideas (pp.210-213) 

• Use good theory (e.g. CHC) so you have good factors. That way 

we are more likely to cut at the joints, getting scores for each 

separate cognitive faculty, which is especially important in 

clinical settings, such as diagnosing learning difficulties. 

• Use relatively pure indicators. Ideally, each task should measure 

a single factor, otherwise our indicator (the task score) contains 

reliable variance that is associated with another CHC construct, 

leading to confusion and misdiagnosis. 

• Conversely, Use at least two distinct, qualitatively different 

narrow abilities to measure a broad ability. Otherwise you’re not 

3

 No one interprets decathlon literally to mean 10 tasks. 

125
measuring Gc, but just VL or LD or LS, etc. (The Wechsler 

Verbal Comprehension Index is actually quite good in this 

regard.) 

CHC theory describes a relative complete taxonomy of cognitive

functions, but does not directly test abilities like attention, 

kinesthetic ability, causal understanding, tracking & timing, etc. 

Table 1: Our Assessment of CHC Abilities Measured by the 

BICA Decathlon 

Manual Control and Simple Motor Control tasks test abilities 

outside the scope of CHC theory. However, some of the manual 

control tasks involve integrating a series of visual actions (part of 

Gv) and remembering short sequences (Gsm). 

 The BICA materials suggest that task instructions are presented 

verbally, in which case they also test auditory processing (Ga) 

extensively. Nevertheless, if we are looking for more complete 

tests of cognitive ability in artificial agents, then CHC theory 

suggests we may want to supplement these decathlon entries with 

some that exercise other abilities: 

Gf – fluid intelligence 

Grw – reading/writing ability 

Gt – decision/reaction time 

Gs – processing speed 

Gq – quantitative knowledge 

 Of these, perhaps the hardest to measure is Gf. But we can make 

some progress with the others. 

We might also be less interested in innate aptitudes than in 

cognitive performance. After all, cognitive systems are supposed 

to learn, so we might assess their capabilities at a specific time. 

For such repeated testing, it would be helpful to have a large 

“armory” of tests which can be composed on the fly. That armory 

idea comes from O’Donnell et al [17 & 18] at NTI. 

4. THE NTI ARMORY 

In this section, we look at a cognitive performance evaluation 

“armory” developed and computerized by NTI, Inc. of Fairborn, 

OH; see O’Donnell et al. [17 & 18]. The original goal of this 

effort was to permit researchers to generate unique test batteries 

from the armory that would be tailored to the performance 

demands of specific jobs for people. NTI reviewed existing 

taxonomies including the CHC, and created a list of 18 broad 

“performance attributes” or cognitive functions such as Sustained 

Attention, Working Memory, Decision Making, Spatial 

Visualization, and Time/Velocity estimation. The creation of an 

armory of tests that have been described in terms of a single 

defined set of performance and cognitive skills is noteworthy for 

our Cognitive Decathlon purposes. The NTI report summarizes a 

vast literature, and took a big step towards applying that literature 

to cognitive metrics. 

Their idea was to rate each potential test/task against all of the 18 

cognitive functions, creating a characteristic signature vector. The 

NTI software then creates an “optimal” test battery on the fly to 

match the skills needed by a particular job. 

According to O’Donnell4

, “Since the armory was developed as a 

cognitive performance assessment tool, it has been used as a state 

measure, and has never been validated or compared to trait 

measures [such as CHC]. Some of the tests in the armory may 

have some history in the area of intelligence testing, but this was 

not our focus.” However, we can use CHC categories even to 

guide performance assessments. 

We envision a future Cognitive Decathlon web site where 

researchers could test the capabilities of their integrated cognitive 

agents by having their agents examined via administration of all 

or a subset of these and perhaps other tests. The advantage of this 

type of Decathlon is fairly straightforward. First, like CHC-based 

tests, these performance tests have a built-in comparison to human 

performance. Second, the tests are well understood within the 

 

4

 Personal communication. 

Task Level CHC* 

Vision Invariant Object Identification Gv

 Object ID: Size discrimination Gv

 Object ID with rotation Gv

 Visual Action/Event Recognition Gv, Glr

Visual Search Gv Search & 

Navigation 

Simple Navigation Gv, Gs

 Travelling Salesman Problem Gv, Gs, Glr

 Embodied Search Gv, Gs, Glr

 

Reinforcement Learning 

Gv, Gs, Glr, 

Gf, Gsm

Motor Mimicry --, Gsm, Gv Manual 

Control & 

Learning Simple (1-hand) Manipulation --, Gsm, Gv

 Two-hand manipulation --, Gsm, Gv

 Device Mimicry --, Gsm, Gv

 Intention Mimicry --, Gsm, Gv

Knowledge 

Learning Episodic Recognition Memory Glr, Gsm? 

 Semantic Memory/Categorization Glr, Gf, Gsm?

Object-Noun Mapping Gc, Glr Language 

& Concept 

Learning Property-Adjective Gc, Glr

 Relation-Preposition Gc, Glr

 Action-Verb Gc, Glr

 Relational Verb-Coordinated 

Action Gc, Glr

Simple Eye Movements --

Motor 

Control Aimed manual Movements --

* If presented verbally, all tasks also involve some auditory 

processing Ga, and language, Gc. 

126
psychological testing community. Third, the average “man on the 

street” can understand the intuition of administering the same test 

to natural and artificial intelligent systems. 

The NTI Armory is not sufficient for BICA’s goals, particularly 

because someone could use a collection of subroutines each of 

which was optimized and specialized for a particular test, rather 

than an integrated cognitive agent. But our goal is to refine the 

BICA Decathlon, not replace it. CHC theory has led us to look 

for diagnostic tests that fill the gaps, and decompose relatively 

cleanly. 

The specific tests in the NTI Armory are listed in Table 2. We 

provide a short description of some of these tests below. 

Some tests – Dichotic Listening, Stroop Visual, and Visual 

Vigilance – depend on fine details of human cognition that we do 

not expect to see duplicated in machine cognition. For example, 

the famous Stroop test presents a color word like “red” in another 

color (as we did here, for those viewing this in color). The 

participant must try to name the color of the word, but humans 

find that difficult, and are prone to mistakenly say the conflicting 

color name from the word itself. (There is no difficulty with noncolor words like “car”.) 

Table 2: The NTI Armory Tests 

 In fact, a CMU-led team [8] showed that a simple neural net 

would generate human-like Stroop results so long as you trained it 

with more word-naming than color-naming tasks, so that wordnaming was relatively automatic. That matched MacLeod and 

Dunbar’s [14] showing that color naming itself was relatively 

automatic when paired with the even less well-trained task of 

shape naming, and that sufficient training on shape naming 

reversed that effect. So tests like the Stroop task are very good 

candidates for systems that learn like humans do. 

Understanding the instructions may well be harder than taking the 

test itself. We do not want special-purpose agents that already 

know the task, so we must be able to describe the task to a 

general-purpose agent. The BICA proposal presumes a fair bit of 

verbal natural language processing (NLP). At minimum, agents 

would need to parse a formal language which can say, “You will 

get a task like this, and must remember x. Then you will get a 

distracter task where you have to do y, after which you will be 

asked to compare u and v to x.” 

Many of the NTI tasks put a lot of effort into directing human 

attention. As BICA imitation tasks like “do this” acknowledge, 

the ability to manage attention and indexical reference so the 

agent can have its attention directed is itself already a major 

achievement. The first round is likely to present tasks as the full 

set of percepts. 

Let us now consider a few of the NTI tests. As our goal is not 

necessarily to exactly duplicate human performance, we should be 

prepared to use “staircase” techniques (e.g. [22]) to quickly find 

the system’s limits, and then explore them. We recommend 

adding such features to almost all of the tests. 

5. SOME NTI TESTS 

5.1 Test 1: Continuous Memory 

The continuous memory test consists of a random series of visual 

presentations of numbers which the operator must encode in a 

sequential fashion. As each number in the series is presented for 

encoding, a probe number is presented simultaneously. The 

operator must compare this probe number to a previously 

presented item at a pre-specified number of positions back in the 

series. Once the operator has made the appropriate recall, he or 

she must decide if that item is the same as, or different from, the 

probe number. Thus, the task exercises working memory 

functions by requiring operators to accurately maintain, update, 

and access a store of information on a continuous basis. Task 

difficulty is manipulated by varying the length of the series which 

must be maintained in memory in order to respond to recall 

probes. Continuous Memory 

Dichotic Listening 

Digit Span 

Manikin (Low/High) 

Match to Sample 

Math Processing 

Motion Inference 

Novascan C (1 + 7) 

Precision Timing 

Peripheral InformationProcessing 

Rapid Decision Making 

Reaction Time - Choice 

Reaction Time - Simple 

Relative Motion (Join-Up) 

Sternberg - Letters 

Sternberg - Symbols 

Stroop - Visual 

Tower of Hanoi (Low 

/High) 

Tracking - Pursuit 

Tracking - Unstable 

Visual Vigilance 

Wisconsin Card Sorting 

Potential for Cog Decathlon: Obviously this is easy for a 

special-purpose program. However, it may still be a challenge for 

cognitive architectures like ACT-R which deliberately have a 

very limited working memory. For example, a recurrent neural 

net model will have a Markov horizon because computational 

constraints limit the chain depth. Also, any system operating “in 

the loop” with rich perceptions will be forced to limit attention 

and recall. We may have to bar some systems based on 

architecture, unless we can rely on a system gaming this test to 

fail another. Presenting the input “visually” (as images or feature 

vectors) is harder for “honest” systems, but still simple for 

special-purpose programs: just pipe the output of a trained digit 

classifier to a simple list processor, for example. 

5.2 Test 4 and 5: Manikin 

The Manikin Test as described here is a derivative of a task 

originally developed by [3] and popularized by the UTC-PAB 

[20]. The test is designed to index ability to mentally manipulate 

objects and determine orientation of a given stimulus. In this 

version, the test shows a vehicle such as an aircraft or a car. To 

one side is a male figure, and to the other side is a female figure. 

These figures and the object are lined up horizontally. Below the 

object and figures is a single query figure (male or female). The 

agent must determine whether the figure matching the query 

figure is to the right or the left of the vehicle, in the vehicle’s 

frame of reference . The figures may appear either upright or 

upside down and facing either toward or away from the subject. 

The 16 combinations of orientation, stimuli and side are pseudorandomly ordered. The number of trials selected for a given 

training or test session is under experimenter control. The NTI 

software uses stock images of the front or back of a sports car, 

and schematic man or woman figures (as you might see on 

restrooms, but in uniform). Unpracticed humans find most of the 

trials to be easy, but not when the vehicle is presented upside 

down and backwards. This test is considered to have two states in 

127
which somewhat different cognitive skills are measured. In the 

LOW TRAINING condition, the subject is familiar with the task, 

but has not reached a level of “automaticity.” In the HIGH 

TRAINING condition, the subject is so practiced that a different 

group of cognitive skills, such as procedural and working 

memory, are used to process the task. 

Potential for Cog Decathlon: This requires visual presentation 

and an understanding of handedness. It is likely a test that 

machines would find difficult to do as fast as humans, since it 

involves a lot of image rotation, an understanding of 

“front/back/side”, spatial awareness, and typical shapes of people 

and vehicles. It is still possible for a special-purpose program, but 

less so if the objects are chosen from a very large (and possibly 

unknown) set, and if we can apply obscurations to the image. 

Presuming a time limit, we can adapt this easily to test machines 

by reducing the time limit using a binary search. The metric for 

humans and machines could be the time-limit where they get 50% 

wrong. 

5.3 Test 8: Motion Inference (Time/Velocity 

Estimation) 

During the task, the subject sees a moving stimulus traversing a 

curved path. Approximately half way to a hash mark, the 

stimulus disappears. The subject’s task is to determine when the 

stimulus, moving at a constant speed, would have reached a hash 

mark located in a random position along the curved path. The 

hash mark range of positions is set in the test’s configuration 

program and can be anywhere between the beginning and end of 

the curve, but typically located in the last third of the path. The 

subject must infer how long the stimulus would take to reach the 

hash mark. The response required is a button press when the 

subject believes the stimulus would have reached the mark. The 

distracter is a simple “semantic” task. When the stimulus 

disappears, a series of four letters of the alphabet appear on the 

screen. The subject must immediately decide whether any of the 

letters are vowels. This decision is indicated with a response using 

a designated button on the response device (e.g., mouse). In 

effect, this interpolated task acts as a distracter to the subject in 

estimating the inferred motion. In this way, the subject is 

precluded from using methods such as counting, tapping, or 

singing to infer the motion. Once the response to the letters is 

made, the subject is required to estimate when the stimulus would 

have reached the stop point, and is to indicate this by pressing the 

designated button. This task really seems to require some practice. 

Potential for Cog Decathlon: In addition to an interesting 

tracking task in itself, the distraction task forces us to consider 

how we present the directions to the cognitive agent. This is a 

good test, because it requires division and direction of attention 

between different tasks demanding different capacities. The 

distraction task could easily be gamed (if x in vowels: ...), but 

once again, we seek other ways to prevent gaming. The visual 

tracking task should provide a challenge, and any agent capable 

of doing the visual tracking (given, say, a series of pixel planes) 

should be able to do visual inference of letters, which will make 

the task somewhat less trivial. 

5.4 Test 9: NovaScan C 

This test represents a special adaptation of the "multi-tasking" 

approach. Generally, in multi-tasking efforts the subject is free to 

adopt any strategy he or she wishes in order to achieve a final 

composite performance. This introduces some degree of difficulty 

in analyzing the task, particularly in diagnosing the nature of any 

decrements observed. NovaScan attempts to eliminate this 

ambiguity by using what has been called a "directed attention" 

rather than a "divided attention" paradigm. In the directed 

attention approach, the subject is still required to multiplex 

between two or more skill requirements. However, instead of 

being free to attend to each one whenever he/she wishes, the test 

directs the person to the test that must be attended to at any given 

time. This is done by having only one test appear on the screen at 

a time. In effect, the person has to keep one test's requirements in 

memory, while actively performing another test. In this way, the 

subject's strategy is highly constrained, and it is easier to 

determine where a cognitive decrement or improvement has 

occurred. Of course, it is still possible to introduce more than one 

task requirement at a time, as long as the demands of the tasks can 

be controlled. 

NovaScan is a generic paradigm. There are many tests that can be 

introduced into it, just as there are many tests that can be used in 

the traditional divided attention approach. The present application 

of NovaScan, (C) uses two of the individual tests described 

elsewhere in the armory (Manikin and Continuous Memory). In 

each, a task appears on the screen (e.g., Manikin) and the subject 

must perform it for some period of time. At irregular intervals, 

this task is replaced by another task (e.g., Continuous Memory), 

and the subject must process this for some period of time. When 

that task is again replaced with the first (Manikin) task, the 

subject must remember the demands of the second task 

(Continuous Memory) while again performing the first. This 

alternation continues for some defined period of time or number 

of presentations. In addition to these demands, the subject 

typically must monitor a dial in which the pointer is moving at a 

constant rate, but in an inconsistent manner (the Dial Task). The 

subject must detect when the dial has gone into a "danger" zone. 

To do this, the subject must establish a scan rate for the dial that 

optimizes the opportunity to detect a danger indication, while 

allowing time to optimally process the other tests. This paradigm 

therefore approximates complex real-world tasks where two or 

more basic cognitive or psychomotor requirements must be 

attended to, and an optimal multiplexing strategy must be adopted 

based on current experience. 

Potential for Cog Decathlon: The NovaScan paradigm offers a 

very flexible way to help prevent spoofing, since the agent must 

not only be able to do single tests, but switch between them. We 

should expect agents to have to learn the new combination, and 

then improve. Consider, for example, that learning to drive 

involves this kind of sequential directed attention, where subtasks 

are gradually automated. In fact, such considerations drove some 

of the early rule-generating systems. The instructions may still be 

the hardest part. 

5.5 Test 12: Rapid Decision Making 

The basic concept of this test is to present the subject with a 

display containing three "areas" that represent three levels of 

unspecified "danger". These areas are clearly marked with 

respect to the level of danger. At various times, symbols appear 

on the display indicating that a "vehicle" has entered into one of 

the areas. The vehicle appears as one of three types of symbol. 

One type clearly indicates that the vehicle poses minimal threat; 

128
another indicates that the vehicle is a clear threat, and third type 

indicates that it is uncertain whether the vehicle is friend or foe. 

The subject's task is to decide on the level of threat, based on the 

type of vehicle and the area of the display in which it is located, 

and to make a differential response based on that decision. This is 

to be done as rapidly as possible. The test is paced so that only a 

short period of time is available to make the decision before the 

next stimulus appears, and this interval may be adjusted by the 

experimenter. In essence, this test is a complex choice reaction 

time test where higher level cognitive processes must be used to 

determine what the stimulus means, and where there is a complex 

response selection. 

Potential for Cog Decathlon: This is obviously useful for a 

missile defense scenario. It naturally suggests a game where 

score is determined by a payoff matrix, where the values can be 

chosen at the start of the test. The main control variable is 

pacing. Other possibilities include number of locations and/or 

vehicle types. The uncertain vehicle is a nice touch, because 

optimal reward will require some utility calculations based on 

degree of certainty. The degree of uncertainty could be made to 

vary in a clear way, such as merging shape, or fading the image, 

or even just tagging it as uncertain and at what level. 

5.6 Test 24: Wisconsin Card Sorting 

 In the armory’s computerized version of this test, four groups of 

figures (called "key cards”) are shown to the subject on the 

screen. Each card shows different shapes, and a different number 

of shapes. Also, the shapes on each card are a different color. 

They are typically arranged as shown in Figure 1, and this pattern 

of colors, shapes, and number is the default option. 

Figure 1: Example shapes for the four "key" cards 

The participant is then presented a series of "test cards" 

containing various combinations of the shapes, colors, and 

number of objects shown in the key cards. The task is to decide 

which key card "matches" the presented test card. Since there are 

three different ways a test card can match a key card (by color, 

shape, or number) the subject must decide which sorting criterion 

to use. No rule is given to the subject for matching cards. 

However, feedback is given for each attempted match on whether 

it was “right” or “wrong”. This is based on a pre-established 

sorting criterion. Once the subject discovers the correct criterion 

and answers "correctly" six consecutive times, the criterion is 

switched to one of the other two. If the subject appears to be 

answering correctly for any number lower than six, and then 

makes an error, the count starts over (i.e., the subject must answer 

correctly six consecutive times). Normally, the types of shift in 

criterion are specified in the default condition. Among many 

dependent measures that may be collected, the number of 

matching categories completed and the number of “perseverative” 

errors (i.e., the number of matches attempted in which the same 

incorrect matching criterion was used) are perhaps most common. 

Perseverative errors indicate difficulty in changing approaches to 

problem solving, or inhibiting previously learned approaches. The 

task measures first the ability of the subject to conclude that there 

are 3 possible criteria by which to match the cards, and then 

assesses cognitive flexibility by requiring the subject to switch 

criteria to continue being successful at the task. The test is a good 

measure of adaptability and avoidance of perseveration. 

Potential for Cog Decathlon: This card sorting task is a good 

test of a cognitive agent’s ability to perform rule induction. It has 

the added twist that the rule has to be revised under some 

executive control when the rule is changed. An important control 

for comparison to human performance is the degree that the 

human has had prior experience with rule learning. This can be 

controlled somewhat with the prior knowledge that the cognitive 

agent has about the card representations. Like some of the other 

tests, e.g., the “join up” and “pursuit” tasks, if the agent has the 

appropriate learning mechanism this task should be easy and the 

advantage should be with the cognitive agent. Noise in the 

representation or other distracters could be added but then the 

difficulty goes up for the human subject perhaps beyond 

performance. 

6. GAPS IN THE NTI ARMORY 

The NTI Armory offers only partial coverage of all the potential 

dimensions of cognition. NTI’s expert panel rated each test across 

all 18 of their defined cognitive functions. At least four 

dimensions of cognition are not well represented: Problem 

Sensitivity, Math Functioning, Language/Semantics, and 

Declarative Memory. 

Problem sensitivity is the ability to recognize that a problem 

exists, not necessarily the ability to solve it. It is valued among 

emergency responders. Math functioning and language/semantics 

are self-explanatory. Declarative memory is memory of things 

from more than 20 minutes ago, hence a form of LTM but distinct 

from procedural LTM. So it would include both episodic (timebased) memory and other declarative (fact-based) memory. 

We have identified several potential supplementary tests. To 

cover fact-based declarative memory, we could include the 

California Verbal Learning Test (CVLT). Also, using Table 5.1 

from Flanagan et al. [10], the following items from common 

intelligence batteries are strong tests of LTM (Glr): 

Tests of Associative Memory 

• WJ-R Memory for Names 

• WJ-R Delayed Recall Memory of Names 

• WJ-R/III Visual-Auditory Learning 

• WJ-R/III Delayed Recall Visual-Auditory Learning 

• KAIT Rebus Learning 

• KAIT Delayed Recall Rebus Learning 

Tests of Ideational Fluency, Naming, or Declarative Memory 

• WJ-III Retrieval Fluency (Ideational Fluency) 

• WJ-III Rapid Picture Naming (Naming Facility) 

• Visual paired-comparison (Declarative Memory) 

Specific tests of language/semantics include the California Verbal 

Learning Test (CVLT) or any number of tests of crystallized 

intelligence from the WAIS and other intelligence batteries5

: 

• DAS Similarities 

 

5 List based on Flanagan et al. 2000a, Table 5.1.

129
• SB:IV Verbal relations 

• SB:IV Comprehension 

• SB:IV Absurdities 

• WJ-III Verbal Comprehension 

• WAIS Verbal Comprehension 

To remedy the shortcomings in the Math Functioning dimension, 

we could include either the Wechsler-Arithmetic which contains 

14 mental arithmetic brief story problems, the WJ-R/III 

Calculation and Applied Problems tests, or any number of similar 

tests of basic arithmetic. Story problems will require some 

language ability of course, while straight calculation tests could 

be trivial, if the agent can encode them directly into parseable 

code. We have been unable to identify a suitable test for problem 

sensitivity. An incident commander we spoke with suspects that 

this ability is usually assumed for emergency responders: training 

exercises will often require the responder to say, “Scene survey” 

and wait for the instructor to say “The scene is secure” or else 

fail, but no actual survey is performed.6

 

7. EPISODIC MEMORY 

Episodic memory is declarative long-term memory (Glr) 

specifically associated with times or events – episodes – in an 

agent’s history. It is a form of associative memory. Our ability to 

organize memories by events, such as yesterday’s meeting or our 

last summer vacation, depends on (or exemplifies) episodic 

memory. The NTI test armory is weak here, especially because 

tests of long-term memory require, on their interpretation, 20-

minute intervals. One of these tests would have to be paired with 

other tests that ran in the interval. However, the BICA tests are 

relatively strong. For example, one task requires the agent to 

remember which objects they have already encountered in which 

rooms. 

There are some dedicated episodic memory tests. One is the 

University of Southern California Repeatable Episodic Memory 

Test [19]. It consists of: 

...seven different lists, each co mposed of 15 semantically 

unrelated, high-frequency nouns. The words are presented in a 

different order on three study-test trials. After each study trial the 

subject recalls the words in any order. The test takes about 10 

min to administer and score. The recall protocol can be scored 

for (a) global mnemonic efficiency, ( b) primary and secondary 

memory, ( c) subjective organizati on, ( d) recall consistency and 

(e) recall as a function of serial position. 

It has been applied in several clinical papers (for example, to 

Alzheimer’s patients) to determine the pattern of memory 

deficiencies. Although it does not specifically require a 20-

minute delay, it could. It is designed to be repeatable, and could 

be made even more so by using WordNet to generate lists of the 

required type on demand. 

However, it requires a fair bit of semantic knowledge. Participants 

are expected to recall things by category, for example. 

Eventually, we want agents to be able to do this. In the meantime, 

however, we need a non-linguistic test of episodic memory. 

Several researchers in animal behavior (ethology) have been 

working on the problem. 

 

6

 Bob Koester, personal communication. 

Figure 2: Western Scrub-Jay caching or retrieving food. 

Scenery provides context for "episodic" memory. From N.S. 

Clayton, http://www.psychol.cam.ac.uk/cplcl/. Used with 

permission. 

Figure 2

Researchers at Cambridge have been investigating food-cache 

storing in corvids, especially scrub-jays [6 & 7]. The design, as 

shown in the photo ( ), involves a set of cache locations 

cued by features of the environment. The experimenters then 

compare the performance of caching birds, observing birds, and 

naïve birds on retrieval, attempting to control for various efficient 

search strategies. 

A similar experiment could be set up as a software task (like those 

in the NTI armory), using successive still images or video. A 

simpler version could use very “cartoon” locations and stimuli. 

The agent being tested can then be asked where agent Green 

placed the items, or agent Blue. This would allow us to test 

episodic memory for agents that do not yet meet all of the BICA 

presumptions. (Of course, with cognitive agents it need not be 

food caching!) 

8. CONCLUSION 

In this paper we have reviewed the history of the idea of a 

cognitive decathlon as a methodology for testing the capabilities 

of an intelligent agent. We argued that the CHC criteria 

summarized by Flanagan et al.’s [10] presentation of modern 

intelligence theory – the Cattel-Horn-Carrol model lead nicely to 

specific cognitive categories for a decathlon. We also looked at a 

specific set of tests, the “NTI Armory,” as candidates for a 

potential battery of tests. Admittedly, the NTI Armory offers only 

partial coverage of all the potential dimensions of cognition. We 

still need to complete the battery of tests for missing dimensions 

of cognition and describe how the tests would be administered to 

agent subjects. 

9. ACKNOWLEDGMENTS 

This paper is partially based upon work funded by DARPA and 

any opinions, findings, conclusions or recommendations 

expressed in this material are those of the authors and do not 

necessarily reflect the views of the U.S. Government. 

10. REFERENCES 

[1] Anderson & Lebiere 2003. The Newell Test for a theory of 

cognition. BBS 26:6, p.5. 

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[2] Bayer, S., Damianos, L., Hirschman, L. & Strong, G. A 

Summary of Previous Grand Challenge Proposals for 

Cognitive Systems. The MITRE Corporation. Prepared for 

DARPA IPTO, September 2004 Version 1.4 

http://www.mitre.org/work/tech_papers/tech_papers_05/05_

0947/index.html 

[3] Benson, A. J., Gedye, J.L. and Jones, G. M. Disorientation 

in flight due to a covert vestibular disorder, with associated 

generalised, muscular tension. Aerosp Med. 1963 

Jul;34:649–654. 

[4] Bringsjord, S. & Schimanski. B. 2003. “What is Artificial 

Intelligence? Psychometric AI as an Answer,” Proceedings 

of the 18th International Joint Conference on Artificial 

Intelligence (IJCAI-03) (San Francisco, CA: Morgan 

Kaufmann), pp. 887-893. 

[5] Bringsjord, S. & B. Schimanski 2004. “ ‘Pulling It All 

Together’ via Psychometric AI,” Achieving Human-Level 

Intelligence Through Integrated Systems and Research 

Technical Report FS- 04-01 (Menlo Park, CA: AAAI Press), 

pp. 9-16. 

[6] Clayton, N. S. and A. Dickinson. 1998. Episodic-like 

memory during cache recovery by scrub jays. Nature 295, 

272—278. 

[7] Clayton, N. S. and J. M. Dally and J. D. Gilbert and A. 

Dickinson. 2005. Food caching by Western scrub-jays 

(Aphelocoma Californica): a case of prospective cognition. 

J. Exp. Psychol: Anim. Behav. Proc. 31, 115—124. 

[8] Cohen, J.D., Servan-Schreiber, D. and McClelland, J. 1992. 

A parallel distributed processing approach to automaticity. 

American Journal of Psychology, 105(2), 239—269. 

[9] Cohen, P. R. 2005. If Not Turing’s Test, Then What? AI 

Magazine 26(4): Winter 2005, 61–67 

[10] Flanagan, D. P., McGrew, K. S. & Ortiz, S.O. 2000a. The 

Wechsler Intelligence Scales & Gf-Gc Theory: A 

Contemporary Approach to Interpretation. Allyn & Bacon, 

Boston. 

[11] Flanagan, D. P., Ortiz, S.O., & McGrew, K. S. 2000b. 

Contemporary issues in intellectual assessment. Powerpoint 

presentation. 

[12] Harrison, P. F. 2005. Is Autism a sensitivity to outliers? 

http://www.logarithmic.net/pfh/autism

[13] Keith, T., Fine, J., Taub, G., Reynolds, M. & Kranzler, J. 

2006. Higher-Order, Multi-Sample, Confirmatory Factor 

Analysis of the Wechsler Intelligence Scale for Children—

Fourth Edition: What Does it Measure? School Psychology 

Review, 35 (1), 108-127. (From a review posted on 

McGrew’s website, 

http://intelligencetesting.blogspot.com/2006/04/what-doeswisc-iv-measure-chc.html). 

[14] MacLeod, C. M. & Dunbar, K. 1988. Training and Strooplike interference: Evidence for a continuum of automaticity. 

Journal of Experimental Psychology: Learning, Memory, 

and Cognition, 14, 126—135. 

[15] Mueller, M. S., Jones, M., Minnery, B. S. and Hiland, J. M. 

H. 2007. The BICA Cognitive Decathlon A Test Suite for 

Biologically-Inspired Cognitive Agents. BRIMS 2007, 

Norfolk, VA. 

http://obereed.net/docs/MuellerBRIMS2007.pdf

[16] Newell, A. (1990). Unified Theories of Cognition. 

Cambridge, MA: Harvard University Press. 

[17] O’Donnell, R. D., Moise, S. and Schmidt, R. 2004. 

Comprehensive computerized cognitive assessment battery. 

Arlington, VA: Office of Naval Research; 2004. Contract 

No. N00014–01-C-0430. NTI, Inc. 

[18] O’Donnell, R. D., Moise, S. and Schmidt, R. Generating 

performance test batteries relevant to specific operational 

tasks. Aviation, Space, and Environmental Medicine 2005; 

76(7, Suppl.):C24–30. 

http://www.ingentaconnect.com/content/asma/asem/2005/00

000076/A00107s1/art00007 

[19] Parker, E. S., Eaton, E. M., Whipple, S.C., Heseltine and 

Bridge. 1995. J Clin Exp Neuropsychol. Dec;17(6):926-36. 

University of Southern California Repeatable Episodic 

Memory Test. 

[20] Perez, W. A., Masline, P. J., Ramsey, E. G. and Urban, K. 

E. Unified Tri-Services Cognitive Performance Assessment 

Battery: Review and Methodology, Technical Report Apr 

1984-Feb 1987. Systems Research Labs Inc., Dayton Ohio. 

[21] Sanghi, P. and. Dowe, D. L. 2003. A Computer Program 

Capable of Passing I.Q. Tests, in P P Slezak (ed), 

Proceedings of the Joint International Conference on 

Cognitive Science, 4th ICCS International Conference on 

Cognitive Science & 7th ASCS Australasian Society for 

Cognitive Science (ICCS/ASCS-2003), 13-17 July 2003, 

Sydney, NSW, Australia, pp 570-575. 

http://www.csse.monash.edu.au/~sanghi/iq.html

[22] Watson, A. B. & Pelli, D. G. (1983) QUEST: a Bayesian 

adaptive psychometric method. Percept Psychophys, 33 (2), 

113-20. 

http://www.psych.nyu.edu/pelli/pubs/watson1983quest.pdf 

[23] Vere S. 1992. Planning, Encyclopedia of AI, Shapiro (ed.), 

Second Ed. 

131
Using Metrics to Optimize a High Performance 

Intelligent Image Processing Code

Scott Spetka 

SUNY Institute of Technology 

and ITT Corp. 

Utica and Rome, NY, USA 

scott@cs.sunyit.edu

Susan Emeny 

ITT Corp. 

775 Daedalian Drive 

Rome, NY, USA 

Susan.Emeny@rl.af.mil 

George O. Ramseyer 

Richard Linderman 

Air Force Research Laboratory 

Rome, NY, USA 

George.Ramseyer@rl.af.mil

Abstract— Optimizing the execution of intelligent codes 

on high performance computer’s (HPC’s) has become more 

challenging as the numbers of processors increases. Single 

processors in many HPC’s have been replaced with dual 

processors, and more recently multiprocessors. This, 

combined with the inherent complexities of multi-core 

processors, has made the processing of intelligent codes even 

more complex on the latest HPC’s. The coming availability of 

thousands of processors in more affordable medium sized 

HPC’s offers the potential for improved performance for 

codes that can scale sufficiently to take advantage of hundreds 

of teraflops. Additionally, techniques for harnessing the 

performance potential of multi-code processors require the 

appropriate location of data in shared memories, or even 

shared level-2 caches, and can afford additional orders of 

magnitude performance increases. The key to designing code 

that uses the available teraflops wisely is an understanding of 

the application’s behavior. For intelligent systems, whose 

behavior may depend on heuristics evaluated at runtime, 

measurements and profiling runs provide the basis for system 

design decisions, regarding distribution of data and 

processing. This paper focuses on the metrics needed to 

optimize intelligent codes, and how a specific image 

processing code was instrumented to produce the required 

metrics.

Keywords: HPC, Latency, Performance, PCID, Optimization, FFT

I. INTRODUCTION

Because of recent developments in high performance 

computing, many codes that were optimized for older HPC 

systems need to be optimized again to take advantage of 

current HPC technologies. In addition, intelligent codes 

require techniques for dynamically adapting to changes in 

system behavior to optimize performance. This leads to 

variations in processing approaches, depending on the inputs 

to the executing code. In these cases, the selection of a 

processing technique can depend not only on the approach 

taken, but also on how well it would scale across available 

processing resources. It would also depend on the underlying 

system architecture and configuration. Distribution of 

processing on an HPC Linux cluster, built from SONY 

Playstation IIIs, would be different from a cluster of dual 

quad-core Xeon systems. 

At a lower level, improvements in networking and 

multi-core processors have introduced the possibility of 

remote DMA for networks [1] and shared level-2 cache, in 

addition to shared memory. Codes that were optimized for 

100Mb Ethernet or even gigabit Ethernet can benefit from 

rethinking algorithms for Infiniband, where network latency 

can be as little as 10 usec. Shared cacheing on dual-core and 

quad-core processors are being implemented to allow limited 

sharing of level-2 cache [2]. 

To study tradeoffs and optimization techniques, we started 

with a multiple frame blind deconvolution algorithm, called 

PCID (Physically Constrained Image Deconvolution) [3]. We 

profiled and measured the code to develop optimization 

techniques that could be used for improving its performance. 

We used a suite of test cases, representative of a broad range 

of inputs that we expect to find for real situations. In section 2, 

we introduce the test systems. In section 3, higher level 

measurements help to determine the percentage of peak 

performance that is currently being achieved by the code and 

the parts of the code that offer the best potential rewards for 

optimization. Section 4 focuses on lower level code behavior 

of networking and cache performance. Section 5 presents our 

conclusions. 

Permission to make digital or hard copies of all or part of this work for 

personal or classroom use is granted without fee provided that copies are 

not made or distributed for profit or commercial advantage and that 

copies bear this notice and the full citation on the first page. To copy 

otherwise, or republish, to post on servers or to redistribute to lists, 

requires prior specific permission and/or a fee. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA. 

Copyright 2008 ACM 978-1-60558-293-1...$5.00. 

II. TEST HARDWARE AND SOFTWARE

 This project is focused on two test HPC systems and the 

PCID software. The test systems both run the Linux operating 

system. One of the test systems is Jaws, a 5,120 processor 

132
Dell PowerEdge 1955. Each node contains two dual-core 

Xeon 3.0 GHz 64-bit Woodcrest CPUs, 8GB of RAM, and 

72GB of local disk space. The nodes are connected via Cisco 

Infiniband, running at 10Gbits/sec (peak). 

 The other HPC system has 12 head nodes, each with two 

quad-core Xeon 3.0 GHz 64-bit processors and 32GB of 

RAM. The head nodes are interconnected with Infiniband. 

Each head node has 24 SONY Playstation III backnodes 

connected through their gigabit Ethernet ports. Each of the 

288 Playstations has a Cell processor [4] with a PowerPC and 

6 Synergistic Processing Elements (SPEs). 

The PCID software is used for image deblurring. It uses a 

sequence of frames to compute a deblurring function that can 

be applied to input images to create a corrected image. The 

code is processor intensive, and offers choices for processing 

that allow users to select processing approaches to adapt the 

algorithm to their inputs. Optimizing PCID for out test 

environments requires determining appropriate test cases to 

exercise the PCID code, especially for cases that currently 

require longer executions. These cases may show the biggest 

improvement if our optimization succeeds. 

III. HIGH LEVEL MEASUREMENTS

 We measure the high level behavior of the system, running 

the PCID software, to determine the amount of time that is 

spent in key, processor intensive computation. The time is 

measured, both as a percentage of total execution time and as 

a measured elapsed time spent in each of the computationally 

complex functions. We expect that Fast Fourier Transforms 

(FFTs) will account for a high percentage of the processing 

time for an image processing algorithm that does a lot of 

matrix multiplication. 

 The gprof profiling tool [5] was used to generate call 

graphs and percentages of time spent executing each of the 

PCID functions. In addition, we used the Multi-Processing 

Environment (MPE) [6] to create graphical displays for 

communications between processors for the parallel execution 

of the PCID code. 

 We also instrumented the PCID code with time 

measurement software to measure the elapsed time for each of 

the computationally intensive parts of the software. In 

particular, we measured the time spent in each of the FFT 

functions and also broke the times down according to the 

calling function for the FFT. 

 Measuring the number of FFTs processed and the total 

processing time for FFTs allowed us to create a baseline 

performance metric for gigaflops/Sec. The number of floating 

point operations (flops) required to process FFTs in the code, 

based on the formula for the number of flops needed to 

perform a 1-D complex FFT of length n: 5n*log(n). 

 High level measurements helped to determine where there 

was the most potential for improvement in the code and to 

identify communication problems, for example, cases where 

processors were idle, while processes waited for 

communication from other processes. It also helped to 

identify metrics to evaluate our success in optimizing the code, 

by establishing initial baseline metrics. Figure 1. Jaws at MHPCC.HPC.MIL. 

IV. LOW LEVEL MEASUREMENTS

After identifying the functions that accounted for a large 

percentage of processing time, we proceeded to explore 

possible approaches to optimization at the lower level. Two 

basic approaches were used at this level. We implemented 

tests to verify that processor cores could share level-2 cache 

on quad-core processors. Some of the new processors keep 

track of cache hit rates and allow software to query the values. 

Also, performance measurements can reflect a relative lack of 

cache if performance degrades. 

 We also tried alternative libraries for FFT implementation, 

including Intel’s Integrated Performance Primitives (IPP) [7] 

and our own custom FFT implementation. The PCID code 

initially used the FFTW library [8]. Understanding the 

advantages and disadvantages of each FFT implementation 

would be difficult analytically. Developing metrics that 

suggest which code is best suited for each situation leads to 

improved overall optimization. 

 A combination of fine-tuning a particular FFT code and 

having alternative implementations to select for specific 

situations seems to be a successful approach to optimize this 

important class of HPC image processing codes. 

 

IV. CONCLUSION

 We are currently performing ongoing system 

measurements and optimizations of PCID. An advantage of 

using metrics for continual optimization of an HPC code is 

that, as new challenging uses of the system emerge, they can 

be addressed in the context of the previous optimizations. We 

do not have to wait for a complete analysis of the system, 

because we expect it to be changing with increased use. 

 Another advantage of using metrics for performance is that 

bugs in the system can be uncovered when unexpected results 

are produced. This is particularly useful when the code is 

133
under active development, as many intelligent systems are, 

since the system is always adapting to new knowledge. 

 Our approach works well, since it determines at an early 

stage in the optimization process, whether there is reason to 

expect a significant improvement in performance. It also 

helps find appropriate points to attack inefficiency for 

improved performance. New techniques will be developed 

and generalized for application to all HPC implementations, 

based on an improved understanding of the behavior of 

multi-core processors networked with Infiniband or the next 

generation of lower latency gigabit Ethernet. 

REFERENCES

[1] Understanding Infiniband – Cisco White Paper, 

 http://www.cisco.com/en/US/prod/collateral/ps6418/ps6419-

 /ps6421/prod_white_paper0900aecd8043ba1d.html. 

[2] Quad-Core Intel Xeon Processor 5400 Series 

 ftp://download.intel.com/products/processor/xeon/dc54kprodbrief.pdf

[3] Parallelization and Automation of a Blind Deconvolution Algorithm 

 http://ieeexplore.ieee.org/iel5/4134019/4134020/04134075.pdf 

[4] The Cell project at IBM Research - http://www.research.ibm.com/cell/ 

[5] GNU Profiler - http://sourceware.org/binutils/docs-2.16/gprof/ 

[6] Multi-Processing Environment (MPE) 

 http://www-unix.mcs.anl.gov/mpi/www/www4/MPE.html

[7] IPP http://www.intel.com/cd/software/products/asmo-na/eng/302910.htm

[8] FFTW – Fastest Fourier Transform in the West – www.fftw.org 

134
Measurement Techniques for Multiagent Systems

Robert N. Lass, Evan A. Sultanik, William C. Regli

Drexel University

Department of Computer Science

College of Engineering

3141 Chestnut Street

Philadelphia, PA 19104

{urlass, eas28, regli}@cs.drexel.edu

ABSTRACT

Multiagent Systems (MAS) are a software paradigm for building large scale intelligent distributed systems. Increasingly,

these systems are being deployed on handheld computing

devices, or on non-traditional networks such as mobile adhoc networks and satellite links. These systems present new

challenges for computer scientists in describing the performance of a system and analyzing competing systems. This

paper surveys existing metrics that can be used to describe

MASes and related components, and provides a framework

for analyzing MASes with a case study using DCOPolis, a

distributed constraint reasoning system.

1. INTRODUCTION

An agent is a situated computational process with one

or more of the following properties: autonomy, pro-activity

and interactivity. A multiagent system (MAS) is a system

with one or more agents. MASes are a software paradigm

for building large scale intelligent distributed systems. Increasingly, these systems are being deployed on handheld

computing devices, or on non-traditional networks such as

mobile ad-hoc networks and satellite links. These systems

present new challenges for computer scientists in describing the performance of a system and analyzing competing

systems.

Much of the research in this area is entirely theoretical,

in the sense that no examples of large-scale systems of this

type exist. As a result, most work utilizes simulators or metrics that have not been validated against real-world results.

Furthermore, there is a lack of standard terminology or even

an agreed upon set of functions that a MAS must provide.

Hopefully the recently published Agent Systems Reference

Model [7] will provide this in the same way that the OSI

reference model has for the field of computer networking.

This is not to say that the simulators or metrics have

no value. So many variables exist that comparing a fielded

system of this type against another fielded system is not

a straightforward task. In some cases the researchers may

Permission to make digital or hard copies of all or part of this work for

personal or classroom use is granted without fee provided that copies are

not made or distributed for profit or commercial advantage and that copies

bear this notice and the full citation on the first page. To copy otherwise, to

republish, to post on servers or to redistribute to lists, requires prior specific

permission and/or a fee.

PerMIS ’08 August 19–21, 2008, Gaithersburg, MD, USA

Copyright 2008 ACM 978-1-60558-293-1 ...$5.00.

not even have access to hardware or enough experience to

successfully run experiments with real systems [43].

Problems with current methods of evaluating decentralized systems are discussed at length in [23]. Specifically, the

authors claim that current practices have a tendency to be

inappropriately generalized, to use technically inappropriate but “standard” evaluation techniques, and to focus too

heavily on feasible systems. Generalization is caused by only

evaluating the performance of the system in a small portion

of the environmental and workload space. Standard evaluation techniques bias research towards systems that perform

well with regard to those techniques. The difficulty of establishing new methods may cause systems to be evaluated at

points that are not commensurate with their intended use.

As a result of these three points, research may become ossified: increasing the difficulty of making new discoveries.

Lastly, the authors discuss robustness: focusing on a few

evaluation points may not uncover behavior that may occur

in a more dynamic environment.

The main contributions of this paper are a procedure

for developing and testing frameworks and procedures for

MASes to avoid these problems, and to present results from

an example application of this procedure to a framework for

distributed constraint optimization. As advocated in [23],

the framework separates the implementation of the algorithms being studied from the platform (simulator, real 802.11

network, etc.) to allow code to be written once and then

tested in the simulator or run as part of a real system. The

latter also allows the simulation data, as well as algorithm

metrics to be verified.

2. MULTIAGENT SYSTEM MODEL

Models describe relationships between components of a

system to facilitate reasoning about the system. Many abstract models of MASes have been written. In this paper,

we use the model derived in the Agent Systems Reference

Model (ASRM), and classify metrics based on the layer of

this model to which they are applied. We believe that this

model is more relevant than others for applied researchers

because the various components of the model were informed

by reverse engineering of existing multiagent systems, rather

than theories about how multiagent systems ought to operate. In addition, the ASRM was not written by a single

research group, but a collection of people from industry, government and academia.

2.1 Abstract Model of a MAS

An abstract representation of a MAS is shown in Fig. 1,

135
and is taken from the Agent Systems Reference Model (ASRM) [7].

At the top of the diagram are agents, represented as triangles. Conceptually, an agent is a process with a sensor

interface that determines the state of the world. It gives

information about the world to a controller, performs some

computation, and may result in the effector taking some action to modify the world. A thermostat could be taken as

simple example: the sensor consists of a thermometer, the

controller decides whether or not to turn the air-conditioner

or heater on, and the effector is the air conditioner or heater

interface.

The agent is supported by an agent framework. An agent

framework is the software components that support agent

execution. In some agent systems, the agent framework may

be trivial, if the agents run natively on the platform (as opposed to in a virtual machine or some other local execution

environment). Most agent systems, however, are based on a

framework that supports key functionality agents commonly

use, such as services for migration, agent messaging, and

matchmaking. Examples of such systems are JADE [27],

Cougaar [14], and A-Globe [22].

Under the framework is the platform. The platform consists of all non-agent software present, such as the operating system, databases, networking software or window managers. As depicted in Figure 1, each platform may have

multiple frameworks on top.

The platform executes on a computing device, or a host.

This is the physical computing platform on which the software is executing. A host may have multiple platforms executing on it. These hosts are distributed in the physical

world, which is the bottom layer in the figure.

To summarize, measurement can take place at four layers in the model: agent, framework, platform, and environment/host. In addition, system measurements that cover

the whole system (i.e. all of the components functioning together) can be taken. Within each of these layers, there

are different levels and classifications of components to be

measured, such as:

• Framework: The OSI [52] layer 7 application protocol could be analyzed, the memory footprint, cpu

usage, and other framework related metrics.

• Platform: Except for in the trivial case where the

agents run directly on the platform, the OSI [52] layers

2–6 occur within the platform. Measurement could occur at any of these levels. This means the performance

of 802.11, Internet Protocol (IP), Transmission Control Protocol (TCP), Session Initiation Protocol (SIP),

and Secure Sockets Layer (SSL) may all be measured,

each of which is at a different OSI layer.

• Environment: This layer is primarily composed of

the OSI layer one.

3. METRICS SURVEY

3.1 Meta-Metrics

There are a number of types of metrics that can be applied

at each layer of the model. They are generally classified

based on their purpose, or based on the domain of the values

they may take on.

Figure 1: An abstract representation of a multiagent system. This diagram shows all of the different agents, frameworks, platforms (along with their

non-agent software), and hosts needed to deliver the

functionality of the system. Different colored circles represent different types of frameworks. The

framework layer links show the logical connections

that exist between hosts, the platform layer shows

the communications connections that exist between

hosts, and the environment layer shows the state

of the physical medium (in this case, radio signals)

used for communications between hosts.

136
3.1.1 Effectiveness vs Performance

Measures of Effectiveness (MoE) quantify the system’s

ability to complete its task in a given environment. In some

cases this could be a binary value (the system succeeds or it

fails) while in other cases it could be a range of values (the

system saved x% of the hostages).

Measures of Performance (MoP) are quantitative measures of some system characteristic, such as bandwidth required, power consumed, communications range or time to

perform some task. They do not describe the quality of the

solution, but the quality of obtaining the solution.

Often, these two types of measures will be combined to

say something about the performance required to achieve a

level of effectiveness with a system. For example, one might

produce a graph showing the trade off between time and

solution quality for a certain system.

3.1.2 Data Classification

The most widely adopted method of data classification divides data into one of four different categories [47]. Nominal

measurements are labels that are assigned to data. Ordinal

measurements are rankings; greater than and less than can

be applied to the measurements, but meaningful arithmetic

transformations are not possible. Interval measurements are

also numbers, but the difference between them has meaning.

Ratio measurements are the same as interval measurements,

except that there is a known zero point.

3.2 Agents and Frameworks

An agent is a situated computational process, and for our

purposes agents are the components that achieve the desired functionality of the system at the highest level. The

framework is a part of the system that provides functionality to the agents. Depending on the system, due to the way

in which agents and frameworks are differentiated, metrics

that are relevant for the agents in one system may be relevant to the framework in another system, and vice versa.

Therefore, such metrics are categorized together herein.

A method for comparing ontology matching algorithms

that is compatible with the accepted criteria of recall and

precision is proposed in [17]. The author states that this is

more accurate as it takes into account semantics, not just

syntax.

Quantifiable measures for autonomy are described in [5].

The autonomy metric is a number between 0 and 1, and is

always defined with respect to a goal and an agent. The

number is calculated by determining the percentage of decisions that are made by the agent to reach the goal. For

example, consider an agent a1 working to achieve goal g1. If

one out of every four decisions used to reach g1 were made

by a1, the autonomy metric with respect to a1 and g1 is 0.25.

If the agents vote on decisions, then the metric is the weight

that this agents vote has on the final decision. For example, if five agents each cast votes of equal weight for each

decision, each agent’s autonomy metric is 0.2.

For conflict resolution, metrics such as those used by the

distributed constraint reasoning community may be used.

Cycle-based runtime (CBR) [16], NCCC [36] and ENCCC [42]

are three popular metrics based on logical clocks that may

be extended to measure virtually any asynchronous decision

process.

3.3 Platform

3.3.1 Distributed Systems

Many MAS are distributed systems, and it follows that

techniques for analyzing distributed systems can be applied

to MAS analysis. Hollingsworth summarized metrics [25]

and techniques for evaluating the performance of distributed

systems [24]. Lynch gives an overview of many widely used

distributed algorithms, along with their analysis in [34]. The

reader is referred to these three publications.

3.3.2 Networking

Networking is major component of most realistic MASes,

and very diverse and active research in networking metrics is

ongoing. First is a brief overview of two types of networking

metrics, connectivity and capacity, followed by a discussion

of MANETs.

Connectivity.

Connectivity refers to the state of the communications

links between computers in a network. Often, this is represented as a graph with the nodes representing the computers

and the edges representing communications links. If a computer can communicate with another computer, there is a

communications link between them.

The volatility of these links depends on the type of network. On traditional wired networks, the communications

links between computers are relatively static. On a MANET,

the links between nodes change as the nodes move spatially.

The performance of the network at OSI layer three, specifically the routing protocol, is also critical. In [28], three different ad-hoc routing protocols are each tested under three

different scenarios. In these experiments, the scenarios differed in terms of the network load.

Capacity.

There are several ways of measuring cross-layer network

performance. First, by using a program such as netperf [29],

throughput can be measured for a given network topology

and configuration.

MANET.

Various metrics specifically for evaluating MANETs are

described by [15], mainly at the four lowest layers of the

OSI model. End-to-end throughput and delay, route acquisition time, percentage out-of-order delivery and efficiency.

The latter is a general term describing the overhead involved

in sending data. Three example efficiency ratios are given:

bits transmitted to bits delivered, control bits transmitted

to data bits delivered and control and data packets transmitted to data packets delivered. It also describes different

contexts under which a MANET may operate. These contexts include network size, connectivity, topological rate of

change, link capacity, fraction of unidirectional links, traffic

patterns, mobility and the fraction and frequency of sleeping nodes. When evaluating the performance of a MANET

system, it is important to note the context under which the

researcher performs the evaluation.

3.4 Environment / Host

These metrics describe some aspect of the environment in

which the system was tested are environmental measures.

In the case of a robot, this might be the physical world. In

the case of a software agent, this is the services, users, and

other agents with which it interacts.

137
In [1], the quantification of the complexity of a test environment is proposed. The intent is to allow one to measure

the task performance of an agent with respect to the tests’

complexities. A more specific example of the complexity of

a test environment is given in [38], which describes three

metrics for describing the “traverseability” of terrain by a

robot. Two are for roughness and one is for “crossability.”

Since humans can be part of the environment in which

agents operate, it may be useful to describe the level of

interaction agent(s) have with them. A classification system for autonomous systems is proposed in [26], based on

the complexity of the mission, independence from humans

and difficulty of the operational environment. Terms and

other metrics for autonomous systems are also defined in

this work.

3.5 System

System metrics are overall metrics that measure something about the system as a whole. When comparing different systems for a task, often the evaluator wants a brief

summary they can present to others on the overall performance or effectiveness of the system, making these metrics

some of the most relevant.

An approach to evaluating performance in surveillance

systems is presented in [20], along with domain specific metrics are also proposed.

There is much research in the literature on evaluating the

effectiveness of robots, which have many similarities with

MAS. A brief overview of metrics related to human-robot

interaction is provided by [46]. The robots’ performance

usually cannot be measured in terms of optimality, as they

have to deal with a messy environment, making it difficult

to objectively assess them. Often this means that the robots

are given a number of tasks that are taken to be representative and evaluated based on how well they are able to complete these tasks. For example, [4] deals with autonomous

robots in a disaster scenario. The authors propose metrics

that award points based on how well the robots are able to

map their environment and find disaster victims. In a hybrid

human-robot system, one method of analysis is to measure

the effect of the robot on the human user’s effectiveness at

a task [9]. Other works on evaluating human-robot interaction include [21], which presents a framework for evaluating

performance and testing procedures for human-robot teams,

and [39] which evaluates a number of metrics for how well

robots help humans complete tasks.

Another human-machine hybrid system is the integrated

automobile crash warning system, presented in [18]. Three

metrics describing effectiveness were given based on the warnings the system gave: percent true, percent false and percent missed. A measure of performance (see next section)

was also used describing how far before an area of danger a

driver will be able to stop.

A discussion of endurance testing for robots and a recommendation for all safety, security and rescue (SSR) robots to

undergo endurance testing is given in [31]. Using WEKA[50],

statistical analysis was performed on the failure data collected to determine the causes of fault.

The results of a long term experimental use of robots in a

joint effort between Swedish academic and military organizations was described in [33]. It included a qualitative analysis

of the users attitude towards the robots before, during and

after the study.

When the optimal or actual solution is known, one way

to evaluate effectiveness is to compare the optimal or actual

solution to the solution produced by the MAS. In [19], the

authors present a new approach to analysis of road recognition algorithms. In this approach, the feature extraction

results are compared to actual features from a National Institute of Standards and Technology (NIST) database. The

feature search trees were also used to describe the computational complexity of the search.

When it’s not clear what the optimal solution is, or when

there are many ways to describe the effectiveness of the system’s solution, several metrics may be needed. In [45], the

experimenters set up a slalom course, and wanted to measure the performance of a hybrid human-robot system at

navigating the course. There is no single metric that describes how well the system performed, so a number of performance measures were recorded such as time to navigate

the course, gates passed through, symbols seen, and the results of a human user’s survey. The latter covered efficiency,

effectiveness and user satisfaction.

Some of this work is more general. For example, in [30],

the authors proposes a general effectiveness metric P =

A − B, where A is the success metric, B is the failure metric and P is the combined performance metric. This type

of metric works with a wide variety of systems that have

some notion of success and failure. Similarly, in [11], the

authors proposes an information theoretic metric for evaluating the quality of the amount of information processed by

an intelligent system.

If a single performance metric is desired, a number of metrics can be combined. In [49], the authors propose a number

of performance metrics for the Mars Rover and a formula for

generating a composite performance score. The scores are

combined using a technique inspired by information theory,

described in [41].

A definition of performance, scalability and stability in

terms of multiagent systems, and an example of analyzing

a MAS for these factors is presented in [32]. In general,

performance is computational cost and throughput (computational complexity and message complexity), scalability is

the rate at which the overhead increases as the agent population increases, and stability is whether or not there is an

equilibrium point that the system will return to after perturbations. An example of analyzing these factors is given

for a MAS that solves a standard contract net [44] problem.

In many cases, a number of different metrics are needed

to get a sense of the performance of the system. An example of this is [13], which investigates benchmarks for UGVs

in terms of reconfiguration, communications and adaptation

and learning. Another is [8], in which four metrics (2 MOE,

2 MOP) are used to evaluate an algorithm for transforming

disparate data sets to a common coordinate system: convergence (MOP), speed (MOP), translation error (MOE) and

rotation error (MOE).

4. ANALYSIS FRAMEWORK FOR MULTIAGENT SYSTEMS

This section presents a framework for applying these metrics to a decision making task. There are three main components: selection, collection, and application. First the evaluator decides which metrics to use, which must be grounded

in some overall goal for the system. Next, the metrics are

138
collected by performing experiments. Finally, the metrics

are applied to the original goals to determine if the system

meets the goal or perhaps if one system performs better than

another.

4.1 Selection

There are an infinite number of metrics that could be applied to a system, and an infinite number of ways to apply

them. How does a researcher go about deciding which metrics need to be measured for his or her system?

The Goal, Question, Metric (GQM) [6] approach for evaluation was developed during a series of projects at the NASA

Software Engineering Lab. This technique is intended to

provide a focus to investigation and evaluation of systems.

In this approach the evaluator first chooses goals for different products, processes, and / or resources. There are four

parts to a goal: the purpose, the issue, the object and the

viewpoint. The example given in [6] is “Improve (purpose)

the timeliness of (issue) change request processing (object)

from the managers viewpoint (viewpoint).”

Next, the evaluator selects questions, usually with quantifiable answers, that must to be answered to understand if

the system meets the goal. Each goal may need multiple

questions.

Finally, the metric is a set of data associated with the

questions that can be subjective (depends on the point of

view, such as ease of use of a UI) or objective (independent

of the point of view, such as program size). This data is used

to answer the questions, which in turn informs the evaluator

about the goals.

As an example scenario to illustrate how the GQM approach works, consider evaluating two systems for solving

a Distributed Constraint Reasoning (DCR) problem [51] on

a MANET. First, we must decide on a goal, such as “Select (purpose) the system (object) providing the lowest average runtime in a bandwidth constrained environment (issue) from the point of view of the last agent to converge on

a solution (viewpoint).” There is still some fuzziness to the

statement, but the scope is narrower. For example, this goal

is not concerned with the networking cost of a system, the

amount of information an algorithm leaks to other agents,

or memory utilization. There are usually multiple goals in a

real evaluation, but for the rest of this example we will only

look at this single goal.

The next step is to select questions that allow to characterize the object with respect to the goal, such as “How long

does the system take to converge with test data A?” “How

long does the system take to converge with test data B?”

Alternatively, there may be metrics or tests that are commonly used in the domain in which the system operates.

For example, [31], describes a specific type of test that the

authors recommend performing on a certain class of robots.

4.2 Collection

From the questions chosen in the previous section we need

to select a set of metrics to collect that will allow us to

answer them. In the example questions we selected we were

only concerned with time to completion. So, we need to

collect runtime information for the system. This could be

a sophisticated solution, such as instrumenting the code to

record timing information, or it could be something more

informal such as having the user time it with a stopwatch.

Papers describing practices for conducting research, methods for analyzing data are classified here as “empirical methods.” Some of them are general, such as [3] which provides

some “rules of thumb” to keep in mind when comparing algorithms, and an example of the application of each of those

rules. One widely cited resource for empirical methods for

MASes is [12].

4.3 Application

In our example scenario, we asked the questions “How

long does the system take to converge with test data A?”

and “How long does the system take to converge with the

test data B?” to help us meet the goal ”Select the system

providing the lowest average runtime from the point of view

of the last agent to converge on a solution.” Al, all that is

left is to compare the runtime of each system to determine

which is the lowest. If the runtime using both sets of test

data is lower for one system, clearly that is the system to

select. If one system has a lower runtime for test data A

and another has a lower runtime for test data B, then we

have to either decide which data set is most similar to the

use the system will see once deployed, or we need to create

new goals and re-assess the system.

5. CASE STUDY: DCOPOLIS

A large class of multiagent coordination and distributed

resource allocation problems can be modeled as distributed

constraint reasoning (DCR) problems. DCR has generated a

lot of interest in the constraint programming community and

a number of algorithms have been developed to solve DCR

problems [37, 35, 40, 10]. A formal treatment of DCOP is

outside of the scope of this paper, and the reader is referred

to [51] for an introduction to the topic.

Informally, DCR is a method for agents to collaboratively

solve constraint reasoning problems distributedly with only

local information. The four main components of a DCR

problem are variables, domains, agents and constraints. Each

agent has a set of variables, to which it must assign values.

Each variable has an associated domain, which is the set of

all possible value assignments to the variable. Constraints

are a set of functions that specify the cost of any set of

partial variable assignments. Finally, each agent is assigned

one or more variables for which it is responsible for value assignment. DCOP algorithms work by exchanging messages

between agents, who give each other just enough information to allow each agent to make a globally optimal variable

assignment.

DCOPolis [48] is a framework for comparing and deploying

DCR software in heterogeneous environments. DCOPolis

has three key points:

1. The communications platform, DCR algorithm, and

problems instances are all modular and may be swapped

for a truly comprehensive analysis of algorithmic performance;

2. DCOPolis contributes to comparative analysis of DCR

algorithms by allowing different state-of-the-art algorithms to run in the same simulator under the same

conditions or to be deployed on “real” hardware in

“real” scenarios; and

3. DCOPolis introduces a new form of distributed algorithm simulation that shows promise of accurate prediction of real-world runtime.

139
DCOPolis has three primary abstract components: problems, algorithms, and platforms. The main function of DCOPolis is to provide an interface through which the three components can interact. By writing a new instance of any of

these components that properly adheres to DCOPolis’ API,

any algorithm should be able to solve any instance of any

problem while running on any platform—even without prior

knowledge of such. This makes implementation and testing

of new algorithms and platforms trivial.

In keeping with the example given in Section 4 (“Select

(purpose) the system (object) providing the lowest average runtime in a bandwidth constrained environment (issue) from the point of view of the last agent to converge

on a solution (viewpoint).”), let us apply the framework to

DCOPolis running two different algorithms.

• Agent: DCOPolis agents are instantiated with a local view of the problem and then assign values to their

variables, send messages to other agents, and change

the assigned values based on the messages they received from other agents. Here, we need to record the

time each agent takes to converge upon a solution.

• Framework: In this case, the framework is what the

ASRM refers to as a “NULL framework.” The functionality is contained within the agents, which interact directly with the platform through the Java Virtual

Machine. There is nothing to be measured here.

• Platform: Any of the metrics in Section 3.3.2 can

measure the performance of the network at the platform layer. Then an estimation of the system’s performance were the bandwidth to drop below our test

environment’s could be made. Also at this level, the

metric in [2] could also be used to determine which

bottlenecks could be optimized, if we were interested

in improving as well as comparing the systems.

• Environment: Our goal stated that we must be concerned with bandwidth constrained environment. The

main thing to measure here is available bandwidth.

6. CONCLUSION

MAS are complicated systems made up a number of interconnected components. Measuring these systems presents

new challenges, especially when these systems are deployed

in dynamic environments such as mobile ad-hoc networks.

This paper surveyed a number of metrics that can be used to

measure these types of systems, as well as a general framework for analyzing MASes and its application to an example

MAS, DCOPolis.

7. REFERENCES

[1] Michael L. Anderson. A flexible approach to

quantifying various dimensions of environmental

complexity. In 2004 Performance Metrics for

Intelligent Systems Workshop, 2004.

[2] Thomas E. Anderson and Edward D. Lazowska.

Quartz: a tool for tuning parallel program

performance. In Proceedings of the 1990 ACM

SIGMETRICS conference on measurement and

modeling of computer systems, pages 115 – 125, New

York, NY, USA, 1990. ACM Press.

[3] S. Balakirsky and T. R. Kramer. Comparing

algorithms: Rules of thumb and an example. In 2004

Performance Metrics for Intelligent Systems

Workshop, 2004.

[4] S. Balakirsky, C. Scrapper, S. Carpin, and M. Lewis.

Usarsim: Providing a framework for multi-robot

performance evaluation. In 2006 Performance Metrics

for Intelligent Systems Workshop, 2006.

[5] KS Barber and CE Martin. Agent autonomy:

Specification, measurement, and dynamic adjustment.

Proceedings of the Autonomy Control Software

Workshop at Autonomous Agents (Agents2019 99)  ̆ ,

pages 8–15, 1999.

[6] V. Basili, G. Caldiera, , and H.D. Rombach. The Goal

Question Metric Approach, pages 528–532. John Wiley

and Sons, Inc., 1994.

[7] Brandon Bloom, Christopher J. Dugan, Tedd Gimber,

Bernard Goren, Andrew Hight, Moshe Kam,

Joseph B. Kopena, Robert N. Lass, Israel Mayk,

Spiros Mancoridis, Pragnesh Jay Modi, William M.

Mongan, William C. Regli, Randy Reitmeyer, Jeff K.

Salvage, Evan A. Sultanik, and Todd Urness. Agent

Systems Reference Model. Drexel University,

Philadelphia, PA, 2006.

http://gicl.cs.drexel.edu/people/regli/reference modelv1a.pdf.

[8] Bruce Brendle. 3d data registrnation based on human

perception. In 2006 Performance Metrics for

Intelligent Systems Workshop, 2006.

[9] Jennifer L. Burke, Robin R. Murphy, Dawn R. Riddle,

and Thomas Fincannon. Task performance metrcis in

human-robot interaction: Taking a systems approach.

In 2004 Performance Metrics for Intelligent Systems

Workshop, 2004.

[10] Anton Chechetka and Katia Sycara. No-commitment

branch and bound search for distributed constraint

optimization. In AAMAS ’06: Proceedings of the fifth

international joint conference on Autonomous agents

and multiagent systems, pages 1427–1429, New York,

NY, USA, 2006. ACM Press.

[11] Rama Chellappa and Amit K. Roy Chowdhury. An

information theoretic evaluation criterion for 3d

reconstruction algorithms. In 2004 Performance

Metrics for Intelligent Systems Workshop, 2004.

[12] Paul R. Cohen. Empirical methods for artificial

intelligence. MIT Press Cambridge, MA, USA, 1995.

[13] Sesh Commuri, Yushan Li, Dean Hougen, and Rafael

Fierro. Evaluating intelligence in unmanned ground

vehicle teams. In 2004 Performance Metrics for

Intelligent Systems Workshop, 2004.

[14] BBN Corporation. Cognitive Agent Architecture

(Cougaar). http://www.cougaar.org/.

[15] S. Corson and J. Macker. Mobile Ad hoc Networking

(MANET): Routing Protocol Performance Issues and

Evaluation Considerations. RFC 2501, January 1999.

[16] John Davin and Pragnesh Jay Modi. Impact of

problem centralization in distributed constraint

optimization algorithms. In AAMAS ’05: Proceedings

of the fourth international joint conference on

Autonomous agents and multiagent systems, pages

1057–1063, New York, NY, USA, 2005. ACM Press.

[17] J ́erˆome Euzenat. emantic precision and recall for

140
ontology alignment evaluation. In IJCAI ’07:

Proceedings of the 21st International Joint Conference

on Artificial Intelligence, 2007.

[18] Jack J. Ference, Sandor Szabo, and Wassim G. Najm.

Performance evaluation of integrated vehicle-based

safety systems. In Performance Metrics for Intelligent

Systems Workshop, pages 85 – 89. NIST Special

Publication, 2006.

[19] M. Foedisch, C. Schlenoff, and R. Madhavan.

Performance analysis of symbolic road recognition for

on-road driving. In 2006 Performance Metrics for

Intelligent Systems Workshop, 2006.

[20] Michael Freed, Robert Harris, and Michael Shafto.

Measuring autonomous uav surveillence. In 2004

Performance Metrics for Intelligent Systems

Workshop, 2004.

[21] A. Freedy, J. McDonough, R. Jacobs, E. Freedy,

S. Thayer, and G. Weltman. A mixed initiative

human-robots team performance assessment system

for use in operational and training environments. In

2004 Performance Metrics for Intelligent Systems

Workshop, 2004.

[22] Agent Technology Group. A-globe.

http://agents.felk.cvut.cz/aglobe/.

[23] Andreas Haeberlen, Alan Mislove, Ansley Post, and

Peter Druschel. Fallacies in evaluating decentralized

systems.

[24] Jeffrey K. Hollingsworth, James Lumpp, and

Barton P. Miller. Techniques for performance

measurement of parellel programs. In Parallel

Computers: Theory and Practice. IEEE Press, 1995.

[25] Jeffrey K. Hollingsworth and Barton P. Miller.

Parallel program performance metrics: A comparison

and validation. In Proceedings of the 1992 ACM/IEEE

conference on Supercomputing, pages 4 – 13, Los

Alamitos, CA, USA, 1992. IEEE Computer Society

Press.

[26] Hui-Min Huang. The autonomy levels for unmanned

systems alfus framework. In Performance Metrics for

Intelligent Systems Workshop, pages 47 – 51. NIST

Special Publication, 2006.

[27] Telocom Italia. Java Agent DEvelopment Framework

(JADE). http://jade.tilab.com/.

[28] Per Johansson, Tony Larsson, Nicklas Hedman,

Bartosz Mielczarek, and Mikael Degermark.

Scenario-based performance analysis of routing

protocols for mobile ad-hoc networks. In MobiCom

’99: Proceedings of the 5th annual ACM/IEEE

international conference on Mobile computing and

networking, pages 195–206, New York, NY, USA,

1999. ACM Press.

[29] Rick Jones. Netperf.

http://www.netperf.org/netperf/NetperfPage.html.

[30] Balajee Kannan and Lynne E. Parker. Fault tolerance

based metrics for evaluating system performance in

multi-robot teams. In 2006 Performance Metrics for

Intelligent Systems Workshop, 2006.

[31] Jeffrey A. Kramer and Robin R. Murphy. Endurance

testing for safety, security and rescue robots. In

Performance Metrics for Intelligent Systems

Workshop, pages 247 – 254. NIST Special Publication,

2006.

[32] Lyndon Lee, Hyacinth Nwana, Divine Ndumu, and

Phillipe De Wilde. The Stability, Scalability and

Performance of Multi-agent Systems. BT Technology

Journal, 16(3):94–103, 1998.

[33] C. Lundberg, H.I. Christensen, and R. Reinhold.

Intellectual performance using dynamical expert

knowledge in seismic environments. In 2006

Performance Metrics for Intelligent Systems

Workshop, 2006.

[34] Nancy A. Lynch. Distributed Algorithms. Morgan

Kaufmann, 1996.

[35] Roger Mailler and Victor Lesser. Solving distributed

constraint optimization problems using cooperative

mediation. In AAMAS ’04: Proceedings of the Third

International Joint Conference on Autonomous Agents

and Multiagent Systems, pages 438–445, Washington,

DC, USA, 2004. IEEE Computer Society.

[36] A. Meisels, E. Kaplansky, I. Razgon, and R. Zivan.

Comparing performance of distributed constraints

processing algorithms, 2002.

[37] Pragnesh Jay Modi, Wei-Min Shen, Milind Tambe,

and Makoto Yokoo. An asynchronous complete

method for distributed constraint optimization. In

AAMAS ’03: Proceedings of the second international

joint conference on Autonomous agents and

multiagent systems, pages 161–168, New York, NY,

USA, 2003. ACM Press.

[38] V. Molino, R. Madhavan, E. Messina, T. Downs,

A. Jacoff, and S. Balakirsky. Treversability metrics for

urban search and rescue robots on rough terrain. In

2006 Performance Metrics for Intelligent Systems

Workshop, 2006.

[39] Dan R. Olsen. and Michael A. Goodrich. Metrics for

evaluating human-robot interactions. Proceedings of

PERMIS, 2003, 2003.

[40] Adrian Petcu and Boi Faltings. A distributed,

complete method for multi-agent constraint

optimization. In CP 2004 - Fifth International

Workshop on Distributed Constraint Reasoning

(DCR2004), Toronto, Canada, September 2004.

[41] Guillermo Rodriguez and Charles R. Weisbin. A New

Method to Evaluate Human-Robot System

Performance. Autonomous Robots, 14(2):165–178,

2003.

[42] Marius Silaghi, Robert N. Lass, Evan Sultanik,

William C. Regli, Toshihiro Matsui, and Makoto

Yokoo. Constant Cost of the Computation-Unit in

Efficiency Graphs. In The Tenth Annual Workshop on

Distributed Constraint Reasoning, May 2008.

[43] Emin Gun Sirer. Sextant deployment (accessed

10/31/2007).

http://www.cs.cornell.edu/People/egs/sextant/deployment.php.

[44] Reid G. Smith. The contract net protocol: High level

communication and control in a distributed problem

solver. In IEEE Transactions on Computers, volume

C-29 12, pages 1004 – 1113, december 1980.

[45] Brian Stanton, Brian Antonishek, and Jean Scholtz.

Development of an evaluation method for acceptable

usability. In Performance Metrics for Intelligent

Systems Workshop, pages 263 – 267. NIST Special

Publication, 2006.

[46] Aaron Steinfeld, Terrance Fong, David Kaber, Michael

141
Lewis, Jean Scholtz, Alan Schultz, and Michael

Goodrich. Common metrics for human-robot

interaction. ACM SIGCHI/SIGART Human-Robot

Interaction, pages 33–40, 2006.

[47] S. S. Stevens. On the theory of scales of measurement.

Science, 1946.

[48] Evan A. Sultanik, Robert N. Lass, and William C.

Regli. DCOPolis: A framework for simulating and

deploying distributed constraint optimization

algorithms. In The Ninth Annual Workshop on

Distributed Constraint Reasoning, September 2007.

[49] Edward Tunstel. Performance metrics for operational

mars rovers. In Performance Metrics for Intelligent

Systems Workshop, pages 69 – 76. NIST Special

Publication, 2006.

[50] Ian H. Witten and Eibe Frank. Data Mining:

Practical Machine Learning Tools and Techniques.

Morgan Kaufmann, 2005.

[51] M. Yokoo, E.H. Durfee, T. Ishida, and K. Kuwabara.

The distributed constraint satisfaction problem:

formalization and algorithms. IEEE Transactions on

Knowledge and Data Engineering, 10(5):673–685,

1998.

[52] Herbert Zimmerman. OSI reference model—the ISO

model of architecture for open system interconnection.

IEEE Transactions on Communications,

28(4):425–432, April 1980.

142
Performance of Super-Resolution Enhancement for 

LADAR Camera Data 

Shuowen Hu 

Army Research Laboratory 

2800 Powder Mill Rd 

Adelphi, MD 20783 

1-301-394-1678 

shuowen.hu@us.army.mil 

S. Susan Young 

Army Research Laboratory 

2800 Powder Mill Rd 

Adelphi, MD 20783 

1-301-394-0230 

ssyoung@arl.army.mil 

Tsai Hong 

NIST 

100 Bureau Dr 

Gaithersburg, MD 20899 

1-301-975-3444 

hongt@cme.nist.gov 

ABSTRACT

Laser detection and ranging (LADAR) camera systems are 

increasingly used in robotics applications for autonomous 

navigation and obstacle avoidance. Their compact size, high 

frame rate, wide field-of-view, and low cost are key advantages 

over traditional scanning LADAR devices. However, these 

benefits are achieved at the cost of spatial resolution. Therefore 

super-resolution image reconstruction technology can be applied 

to improve the resolution of LADAR camera data. Previous work 

by Rosenbush et al. applied the super-resolution algorithm of 

Vandewalle et al. to LADAR camera data, and observed 

quantitative improvement in image quality in terms of number of 

edges detected. This study uses the super-resolution algorithm of 

Young et al. to enhance the resolution of range data acquired from 

a commercial available LADAR camera. This work applies a 

preprocessing stage that increases the accuracy of sub-pixel shift 

estimation for improved registration of multiple LADAR camera 

frames and uses the triangle orientation discrimination 

methodology for a subjective evaluation. The objective is to 

measure the improvement in probabilities of target discrimination 

at various ranges achieved by super-resolution enhancement of 

LADAR camera data. 

Categories and Subject Descriptors

D.3.3 [Image Processing and Computer Vision]: Enhancement 

– Filtering, Registration. 

General Terms

Algorithms, Performance, Human Factors 

Keywords

Super-resolution, LADAR camera, image registration, triangle 

orientation discrimination methodology 

1. INTRODUCTION 

Laser detection and ranging (LADAR) is a crucial 

component for navigation in autonomous or semiautonomous robots. Current small robots generally employ 

a 2D scanning LADAR that scans along a single line and 

therefore cannot detect objects above or below the 

detection line [1, 2]. In indoor urban environments where 

the setting is highly cluttered with overhanging objects 

such as tabletops, the 2D scanning LADAR systems may 

not be sufficient for navigation and obstacle avoidance [1]. 

A new generation of small and compact 3D LADAR 

devices, named LADAR camera, offers a promising 

solution to small robot navigation in urban environments 

where modern warfare is often conducted. 

LADAR camera devices are compact and lightweight 

sensors that acquire a 3D range image of the surrounding 

environment. The SR-30001

 LADAR camera device 

Figure 1. SR3000Error! 

Bookmark not defined.

 

1

 Certain commercial equipment, instruments, or materials are 

identified in this paper in order to adequately specify the 

experimental procedure. Such identification does not imply 

recommendation or endorsement by NIST, nor does it imply that 

the materials or equipment identified are necessarily best for the 

purpose. 

LADAR Camera

This paper is authored by employees of the United States Government 

and is in the public domain. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA 

ACM ISBN 978-1-60558-293-1/08/08.

143
(Figure 1) used in this study weighs 162 g and measures 

(5.0 x 6.7 x 4.23) cm [3]. LADAR camera devices emit 

diffuse modulated near-infrared light and measure the 

subsequent phase shift between the original emitted light 

and the reflected light. The phase measurements are 

combined to calculate the range data based on the time-offlight principle [3]. The detector utilized by LADAR 

camera devices is a focal plane array (FPA), which is 

typically limited to a maximum size of (256 x 256) 

detectors. Consequently, these devices cannot achieve the 

resolution of scanning LADAR systems. This 

disadvantage of LADAR camera systems may be rectified 

by the application of super-resolution image reconstruction. 

Super-resolution algorithms utilize a series of lowresolution frames containing sub-pixel shifts to generate a 

higher resolution image. These algorithms are typically 

composed of two major stages: registration stage and 

reconstruction stage. During the registration stage, the 

shift with respect to a reference frame (usually the first 

frame of the series) is computed to sub-pixel (i.e. decimal 

pixel) accuracy. The second stage utilizes this sub-pixel 

information to interpolate the low-resolution frames onto a 

higher resolution grid. A necessary condition for 

successful super-resolution enhancement is the presence of 

differing shifts between the frames in the series. The 

differing shifts of each frame provide additional 

information from which to reconstruct the super-resolved 

imagery. Previous work by Rosenbush et al. [4] applied a 

super-resolution algorithm [5] to LADAR camera data, and 

observed improvement in image quality in terms of number 

of edges detected. In this work, the super-resolution 

algorithm of Young et al. [6] is applied to LADAR camera 

imagery. This algorithm separates the registration stage 

into a gross shift (i.e. integer pixel shift) estimation stage 

and a sub-pixel shift (i.e. decimal pixel shift) estimation 

stage for improved registration accuracy. Both sub-stages 

use the correlation method in the frequency domain to 

estimate shifts between the frame series and the reference 

image. The reconstruction stage of Young et al.’s 

algorithm applies the error-energy reduction method with 

constraints in both spatial and frequency domains to 

generate a high-resolution image [6]. Because LADAR 

camera imagery is inherently smoother than visible light 

imagery (LADAR camera data does not capture the texture 

or color of the scene), this work develops a preprocessing 

stage for improved image registration. Specifically, a 

wavelet edge filtering method [7] and a Canny edge 

detection method [4] are investigated and compared against 

the accuracy achieved with no preprocessing. The wavelet 

edge filtering method provided more accurate shift 

per-resolution enhancement of the 

LADAR camera data. 

ection algorithm to generate binary edge frame 

her frequency components as depicted in red in Figure 

estimation for LADAR camera data. 

To assess the improvement in super-resolution enhanced 

LADAR camera data, the authors conducted perception 

experiments to obtain a human subjective measurement of 

quality. The triangle orientation discrimination (TOD) 

methodology [8,9] was used to measure the improvement 

achieved with super-resolution. The TOD task is a fouralternative forced-choice perception experiment where the 

subject is asked to identify the orientation of a triangle 

(apex up, down, right, or left) [9]. Results show that the 

probability of target discrimination as well as the response 

time improves with su

2. METHODOLOGY 

2.1 Preprocessing Stage 

The purpose of the preprocessing stage is to emphasize 

LADAR camera image edges for improved frame 

registration. One investigated method was the use of multiscale edge-wavelet transforms [10] to calculate the 

horizontal and vertical partial derivatives of the input 

image at the second wavelet scale for each frame of the 

series. The two derivatives were then combined using sum 

of squares to produce a wavelet edge enhanced frame 

series. Another investigated method was the use of Canny 

edge det

series. 

To assess the benefit of preprocessing, the following 

procedure was followed. A synthetic frame series was 

generated with known sub-pixel shifts. First, an 

oversampled non-aliased scanning LADAR reference 

image (204 x 204) pixels was interpolated by an 

upsampling factor of eight (1632 x 1632) pixels using a 

Fourier windowing method [10]. Then, the simulated highresolution image was sub-sampled at different factors to 

produce several low-resolution frame series, each with a 

different degree of aliasing. Figure 2 shows the un-aliased 

spectrum of a discrete space signal (e.g. scanning LADAR 

image) produced by oversampling a continuous space 

signal at a sampling frequency greater than the Nyquist 

frequency. If the sampling frequency is below Nyquist 

(simulated by sub-sampling the oversampled image), the 

spectrum of the sampled signal is aliased with distorted 

hig

2. 

Synthetic frame series was generated by sub-sampling 

every m pixels in both dimensions of the simulated highresolution image, where m = 4, 8, 12, 16, 20, 28, 36, 48, 

56. Therefore the undersampling factors are m/8 (i.e., 0.5, 

1, 1.5, 2, 2.5, 3.5, 4.5, 6, 7), simulating different degrees of 

aliasing. For each undersampling factor, the sub-pixel 

shifts for each frame of the synthetic series were generated 

by varying the starting pixel position of sub-sampling 

according to a uniform random distribution (30 frames for 

each series). Then preprocessing using either the wavelet 

or Canny method was performed. Sub-pixel shift estimates 

from the preprocessed and no preprocessing series were 

compared to the known shifts. Let İi = (İxi , İyi) denote 

144
the registration error vector of the i

th frame where İxi and

İyi are the registration errors in the x and y directions. A 

mean absolute error (MAE) can be calculated for the 

frames of each synthetic series using the following 

equation: 

¦¦

i 1 nn i 1

where n 30 . The registration errors of the wavelet 

preprocessing method was compared to that of Canny and

no preprocessing metho

 

n

yixi

n

E i

11 22 H HH

ds to assess the accuracy at each 

undersampling factor. 

2.2 Triangle Orientation Discrimination 

Probabilities of target discrimination at different ranges can 

(TOD) Methodology 

The TOD methodology, developed by Netherlands TNO 

Physics and Electronics Laboratory (TNO-FEL), is a 

perception study that allows human subjects to provide a 

measure of image quality at various target ranges [9]. The 

test pattern is an equilateral triangle in one of four possible 

orientations (apex up, down, left, or right), and the 

measurement process is a four-alternative forced-choice 

psychological procedure that requires the observer to 

indicate the orientation. Variation of triangle contrast/size 

by changing target ranges results in a correct discrimination 

percentage between 25 % (pure guess) and 100 %. 

then be calculated to measure the quality of both the 

original and super-resolved data. 

The TOD method is suitable for electro-optical and optical 

imaging systems, and has been widely used in thermal and 

visual domain imagers. This methodology provides a 

simple task that has a close relationship to real target 

acquisition, and the results are free from observer bias 

[8,9]. The TOD methodology was adapted to LADAR 

camera data by using a target consisting of a square white 

foam board target (50 x 50) cm with an equilateral 

triangular hole (7.5 cm per side) cut into the board as 

shown in Figure 3. The triangular hole provides the 

necessary depth contrast against the board. 

Figure 3. TOD setup 

2.3 LADAR Camera 

The device utilized in this study is the SwissRanger SR3000Error! Bookmark not defined. LADAR camera. 

The camera emits diffuse 850 nm near-infrared light 

modulated at a default frequency of 20 MHz from a bank 

of 55 light emitting diodes. The non-ambiguity range 

achieved at this modulation frequency is 7.5 m. The SR3000Error! Bookmark not defined. has a pixel array of 

176 x 144 with a field-of-view of 47.5o

 x 39.6o, and can 

capture images at a maximum rate of 50 frames/s (variable 

with respect to the integration time setting). 

Figure 2. (Top) Un-aliased spectrum of signal sampled above 

Nyquist frequenc ttom) aliased at y, (mid) at Nyquist, and (bo

2.4 Data Collection 

Data collection for the experiment was conducted at a 

laboratory in the National Institute of Standards and 

Technology. The SR-3000Error! Bookmark not defined.

LADAR camera was placed 6.5 m from a beige wall as 

depicted in Figure 3. The target was positioned at (3, 3.5, 

4, 4.5, 5, 5.5, and 6) m from the camera. The investigated 

ranges were limited to between (3 and 6) m because 

inaccurate behavior of LADAR cameras was observed at 

very close and very far target distances [11]. At each 

range, the triangle was positioned at one of four possible 

orientations (apex up, down, left, right) with the center 

approximately 1 m high. For each orientation at each 

below Nyquist frequency. 

145
range, four trials were conducted. Each trial consisted of a 

sequence of 32 frames acquired by holding the camera. 

The natural motion of the hand while holding the camera 

provided the shifts required for the super-resolution 

algorithm. Motion is assumed to be limited to translations 

in the x (horizontal) and y (vertical) planes. Though slight 

rotation and translation in the z-plane (depth) might have 

occurred from holding the camera, these parameters were 

not considered in the current study. 

2.5 Data Processing 

For each series of 32 frames, the first 25 frames are utilized 

for super-resolution image reconstruction. The first frame 

was used as the reference frame from which pixel shifts 

were calculated for successive frames. The use of 25 

frames resulted in a resolution improvement factor of five 

in each direction for the super-resolved image. To ensure 

that the monitor modulation transfer function (MTF) was 

not a limiting factor in the experiment, the super-resolved 

images (250 x 250 pixels) were bilinearly interpolated by a 

factor of two to 500 x 500 pixels. The original imagery (50 

x 50 pixels) was bilinearly interpolated to 500 x 500 pixels 

for consistency between the baseline and super-resolved 

imagery. 

2.6 Perception Experiment 

The perception experiment was a four-alternative forcedchoice procedure (up, down, left, right). The imagery in 

this experiment was organized in the image cells and their 

naming convention is shown in Table 1. As shown in the 

row of original images in Table 1, the grayscale baseline 

range imagery was grouped into seven cells corresponding 

to the seven different target ranges. Each cell consisted of 

16 original low-resolution LADAR camera images (4 

orientations x 4 trials). Similarly, the grayscale superresolved range imagery was grouped into seven cells 

consisting of 16 images each as shown in the row of superresolved images in Table 1. The experiment therefore 

consisted of 14 cells with a total of 224 images. 

Range 

 m 

 A 

3.0 

B 

3.5 

C 

4.0 

D 

4.5 

E 

5.0 

F 

5.5 

G 

6.0 

Original 

Image 

A

A 

BA CA DA EA FA GA 

Superresolved 

image 

AB BB CB DB EB FB GB 

Table 1. Image cell format and naming convention

Nine subjects participated in the experiment in July 2008. 

The subjects were shown one image at a time with 

randomized presentation of cells and randomized 

presentation of images within each cell. The display was a 

19 inch flat panel (Dell 1908FPError! Bookmark not 

defined.) with a resolution of 1280 x 1024 pixels. 

3. RESULTS AND DISCUSSION 

3.1 Assessment of Registration Accuracy 

0.5 1 1.5 2 2.5 3.5 4.5 6 7

0

0.05

0.1

0.15

0.2

Undersampling Factor

Mean Absolute Error

Mean Absolute Error vs Undersampling Factor

Wavelet Preprocessing

Canny Preprocessing

No Preprocessing

Figure 4. Mean absolute registration error with 

standard deviation for each undersampling factor. 

Figure 4 shows the mean absolute error of registration at 

each undersampling factor for the generated synthetic 

experiments. The unit of error is fraction of a pixel. 

Wavelet preprocessing outperformed both the Canny 

method and no preprocessing method for undersampling 

factors of less than 6. Wavelet preprocessing was 

especially effective at low and moderate degrees of aliasing 

(undersampling factor of less than 3.5). If the imagery 

contained severe aliasing (undersampling factor greater 

than 6), then no preprocessing resulted in higher 

registration accuracy. The observed trend is expected. 

LADAR camera data is characteristically smooth due to the 

lack of texture information, so edge filtering with the 

wavelet method will improve registration. But if the data is 

severely undersampled that its mid to high frequency 

components are corrupted by aliasing, then wavelet edge 

filtering (which uses these severely corrupted frequency 

components) will result in poorer registration. The degree 

of aliasing in the imagery acquired with the SR3000Error! Bookmark not defined. is expected to be in 

the moderate range as super-resolved imagery using 

wavelet preprocessing yields fewer artifacts than imagery 

produced without preprocessing. 

146
3.2 Triangle Orientation Discrimination 

Perception Experiment 

Figure 5 shows grayscale and color images (color-coded to 

distance) of the TOD target oriented up at a distance of 5 m 

from the camera. The orientation of the equilateral 

triangular hole is difficult to discern in the original images 

at this distance as the triangular hole appears like a blurred 

circle. By contrast, the orientation is clear in the superresolution enhanced imagery. For imagery with target 

distances greater than 5 m, the orientation, as expected, was 

still more difficult to discern using the original LADAR 

camera imagery. But super-resolution at these greater 

distances proved to be effective. 

Figure 6 shows grayscale and color images of the TOD 

target oriented left at a distance of 4 m from the camera. 

As the target distance decreases, the orientation of the 

triangular hole becomes more visible in the original 

imagery, though the triangular hole still appears distorted. 

In the super-resolved image, the triangular hole does not 

appear distorted, and is shaped more like a triangle. 

Figure 7 shows the group-averaged chance-corrected 

probability of target discrimination at each target range. At 

all ranges, super-resolved imagery produced a higher 

probability of target discrimination with smaller intersubject variability. At a target distance of 3 m, the original 

imagery had a 77 % of the probability of target 

discrimination, while the super-resolved imagery reached 

100 %. The target discrimination performance is increased 

by 30 % using the super-resolution algorithm. As the target 

distance increased, subjects had more difficulty to 

discriminate the target orientation. At a target distance of 6 

m, the original imagery had a 20 % of the probability of 

target discrimination, while the super-resolved imagery 

reached 90 %. That is a 350 % improvement in target 

discrimination performance. In summary, the probability of 

target discrimination is increased by 30 % to 350 % for the 

target ranges from 3 m to 6 m using the super-resolution 

algorithm. 

 

. 

3 4 5 6

0

0.2

0.4

0.6

0.8

1

Ensemble Probability of Target Discrimination

Range (m)

Probability

Original Imagery

Super-resolved Imagery

 (a) original (b) super-resolved 

Figure 5. Grayscale (top) and color-coded (bottom) 

LADAR camera imagery for (a) original image and 

(b) super-resolved image of TOD target at 5 m. 

Figure 6. Grayscale (top) and color-coded (bottom) 

LADAR camera imagery for (a) original image and 

(b) super-resolved image of TOD target at 4 m. 

Figure 7. Chance-corrected probability of target 

discrimination at each target range. 

(a) original (b) super-res lved o

147
Not only were subjects able to achieve higher accuracy at 

all ranges with super-resolved imagery, but the response 

times were also faster with less variability for superresolved imagery at all ranges. Figure 8 shows the groupaveraged response times at each range with standard error 

bars representing inter-subject variability. At a range of 6 

m, subjects responded in an average time of 1.58 s using 

the super-resolved imagery, 23 % faster than the response 

time using original imagery. 

4. CONCLUSION 

Super-resolution image reconstruction is complemented by 

a wavelet preprocessing stage for improved image 

registration, yields significant benefits for LADAR camera 

imagery. In the triangle orientation discrimination 

experiment, subjects achieved higher accuracy at all 

investigated target ranges with faster response times and 

reduced inter-subject variability for super-resolved 

imagery. Complemented by super-resolution image 

reconstruction, the high frame rate, small size, and lightweight LADAR camera sensors will be ideal for 

autonomous or semi-autonomous robot navigation in urban 

indoor environments. In semi-autonomous robot 

navigation, super-resolution enhancement will provide 

human operators with increased target discrimination. In 

fully autonomous mode, super-resolved imagery will allow 

guidance software to improve obstacle avoidance. The 

incorporation of super-resolution into the US Army’s 

robotic applications will improve small robot performance, 

contributing to the soldier’s survivability and lethality. 

3 4 5 6

0

0.5

1

1.5

2

2.5

3

Ensemble Average Response Times

Range (m)

Average response time (s)

Original Imagery

Super-resolved Imagery

5. ACKNOWLEDGMENTS 

The authors would like to thank Dr. Joe Reynolds and Dr. 

Keith Krapels at US Army’s Night Vision and Electronic 

Sensors Directorate for their insights and helpful 

discussions. We thank Tommy Chang at NIST for helping 

the data in the NIST vision lab. 

6. REFERENCES 

[1] Ng, T. C. 2005. SIMTech technical reports, Vol. 6, No. 1, 

13-18, 2005. 

[2] Committee on Army Unmanned Ground Vehicle Technology 

2002. “Technology development for Army unmanned 

ground vehicles”, Sandia Report. 

Figure 8. Response times at each target range with 

standard error bars showing inter-subject variability. 

[3] MESA Imaging, 2006. SwissRanger SR-3000 Manual. 

http://www.mesa-imaging.ch/. 

[4] Rosenbush, G., Hong, T. H., Eastman, R. D. 2007. Superresolution enhancement of flash LADAR range data. In 

Proceedings of the SPIE, Vol. 6736, 67314. 

[5] Vandewalle P., Susstrunk S., Vetterli, M. 2005. A frequency 

domain approach to registration of aliased images with 

application to super-resolution. EURASIP Journal on 

Applied Signal Processing, 71459 

[6] Young, S. S., Driggers, R. G. 2006. Super-resolution image 

reconstruction from a sequence of aliased imagery. Applied 

Optics, Vol. 45, 5073-5085. 

[7] Devitt, N., Moyer, S., Young, S. S. 2006. Effect of image 

enhancement on the search and detection task in the urban 

terrain. In Proceedings of SPIE, Vol. 6207, 62070D 1-13. 

[8] Driggers, R. G., Krapels, K., Murrill, S., Young, S., Thielke, 

M., Schuler, J. 2005. Super-resolution performance for 

undersampled imagers. Optical Engineering, Vol. 44(1), 

14002. 

[9] Bijl, P., Valeton, J. M. 1998. Triangle orientation 

discrimination: the alternative to MRTD and MRC. Optical 

Engineering, Vol. 37(7), 1976-1983. 

[10] Young, S. S., Driggers, R. G., Jacobs, E. L. 2008. Signal 

Processing and Performance Analysis for Imaging Systems. 

Artech House, Norwood, MA. 

[11] Anderson, D., Herman H., Kelly A. 2005. Experimental 

characterization of commercial flash LADAR devices. In 

Proceedings of the International Conference of Sensing and 

Technology. 

148
Performance Evaluation of Laser Trackers

B. Muralikrishnan, D. Sawyer, C. Blackburn, S. Phillips, B. Borchardt, W. T. Estler 

Precision Engineering Division 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

ABSTRACT

The American Society for Mechanical Engineers (ASME) 

recently released the ASME B89.4.19 Standard [1] on 

performance evaluation of spherical coordinate instruments such 

as laser trackers. At the National Institute of Standards and 

Technology (NIST), we can perform the complete set of tests 

described in the Standard, and have done so for a variety of laser 

trackers. We outline the tests described in the Standard, discuss 

our capabilities at the large-scale coordinate metrology group, and 

present results from B89.4.19 tests conducted on a few trackers. 

We also outline an analysis approach that may be used to evaluate 

the sensitivity of any measurement, including the tests described 

in the B89.4.19 Standard, to different geometric misalignments in 

trackers. We discuss how this approach may be useful in 

determining optimal placement of reference lengths to be most 

sensitive to different geometric misalignments. 

Keywords 

ASME B89.4.19, large-scale metrology, laser tracker, 

performance evaluation, sensitivity analysis 

1. INTRODUCTION

Spherical coordinate measurement systems such as laser trackers, 

scanners and other devices are increasingly used in manufacturing 

shop floors for inspection, assembly, automation etc. These 

instruments are also sometimes used in the calibration of other 

lower-accuracy instruments such as industrial robots and even 

certain Cartesian coordinate measuring machines (CMMs). The 

spherical coordinate systems provide high accuracy at relatively 

low cost (in comparison to more conventional Cartesian CMMs ), 

and are portable and convenient to use. Because of the 

proliferation of such devices in recent years, there has been an 

increasing need for a uniform set of performance tests so that 

users and manufacturers share a common understanding of the 

capabilities of the instrument. 

In 2007, the American Society for Mechanical Engineers (ASME) 

published the ASME B89.4.19 Standard titled “Performance 

Evaluation of Laser-Based Spherical Coordinate Measurement 

Systems”. This Standard, for the first time, defined a common set 

of tests that can be performed by both the user and the 

manufacture to establish if an instrument meets the 

manufacturer’s performance specifications (MPE). This Standard, 

although limited to instruments that use a cooperative target such 

as retro-reflector, represents a significant step forward. It is the 

first and to date, the only performance evaluation Standard for 

spherical CMMs and establishes a framework for testing and 

evaluation of laser trackers and related devices. 

In this paper, we present an overview of the B89.4.19 Standard 

and highlight the different tests described in it. We discuss 

capabilities of the large-scale coordinate metrology group at NIST 

where a complete set of B89.4.19 tests may be performed. We 

show examples of laser trackers tested at NIST that meet the 

manufacture’s performance specifications and others that do not. 

Systematic errors due to geometrical and optical misalignments 

within a tracker are a major source of uncertainty in tracker 

measurements. An ideal performance evaluation test has high 

sensitivity to all misalignment parameters in a tracker’s error 

model. Given the error model, it is possible to numerically 

determine the sensitivity of each of the B89.4.19 tests to different 

misalignment parameters. We have performed such analysis and 

briefly discuss our method and results. 

2. THE ASME B89.4.19 STANDARD 

The ASME B89.4.19 Standard describes three types of tests to be 

performed on trackers to evaluate their performance. These are 

the ranging tests, the length measurement system tests and twoface system tests. 

 This paper is authored by employees of the United States Government and

 is in the public domain.

 PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA

 ACM ISBN 978-1-60558-293-1/08/08. Figure 1. The ASME B89.4.19 Standard. 

149
2.1 Ranging Tests 

Ranging tests assess the distance (or displacement) measurement 

capability of the instrument. The ranging system (an 

interferometer or an absolute distance measurement (ADM) 

system) establishes the unit of length and is therefore a critical 

component of the system. The tests as described in the Standard 

require the tracker to measure several calibrated lengths aligned 

along the line-of-sight of the tracker. The reference lengths 

employed may be calibrated artifacts, realized by free standing 

targets, or a laser-rail system. 

2.2 Length Measurement System Tests 

The length measurement system tests are similar to volumetric 

length tests on Cartesian CMMs. A calibrated reference length is 

placed at different positions and orientations in the measurement 

volume and is measured by the tracker. The error in the measured 

length is compared against the MPE to determine conformance to 

specification. There are several sources of mechanical and optical 

misalignments within the construction of a tracker that produce 

systematic errors in the measured angle and range readings and 

therefore in measured lengths. The length measurement system 

tests are designed to be sensitive to these misalignments. Again, 

the reference lengths employed may be calibrated artifacts, 

realized by free standing targets, or a laser-rail system. 

Figure 2. The NIST 60 m laser rail facility viewed 

from the tracker under test end; note the movable 

carriage with retroreflector. 

Laser tracker 

Reference

interferometer

Carriage with 

targets

2.3 Two-face System Tests Rail Some geometric misalignments are such that the errors in the 

measured angles of a fixed target change in sign when the same 

target is measured in the backsight of the instrument. Such 

frontsight-backsight measurements of a single target are called 

two-face tests. These tests are extremely useful because they 

capture a large number of geometric misalignments and they do 

not require a calibrated reference length. The Standard requires 

two-face tests to be performed at different positions within the 

work volume of the instrument. More details on the test positions 

may be found in [1,2]. 

 Figure 3. The LARCS laser rail.

3. LARGE-SCALE METROLOGY AT NIST 

The large-scale coordinate metrology group at NIST has the 

capability of performing the complete set of B89.4.19 tests. 

The ranging tests are performed in the 60 m long-length test 

facility where a laser-rail and carriage system is operational (see 

Figure 2). The carriage has two opposing retro-reflectors. One 

retro-reflector is used for the tracker under test while the other is 

used for the reference interferometer on the other end of the rail. 

The expanded uncertainty (k = 2) of reference length L is U(L) = 

5 Pm + 0.3 u 10-6L.

The length measurement and two-face system tests are performed 

in the large-scale laboratory. Currently, the reference length for 

the length measurement tests is realized using the laser-rail and 

carriage system (LARCS) [3] (see Figure 3). The LARCS 

(different from the 60 m laser-rail facility used for range 

calibration) employs a reference interferometer mounted on a rail 

(about 3 m long) that can be oriented in different ways 

(horizontal, vertical, inclined) to meet the B89.4.19 requirements. 

A carriage with two retro-reflectors rides on the rail. The tracker 

uses one retro-reflector while the reference interferometer utilizes 

the other. The expanded uncertainty (k = 2) of a nominal 

reference length L is U(L) = 3.4 Pm + 0.5 u 10-6 L for the LARCS 

system. We are now evaluating different artifacts that may be 

used as the reference length instead of the LARCS system [4]. 

4. TRACKER CALIBRATION EXAMPLES 

We have performed the B89.4.19 tests on different trackers at our 

facility at NIST. Some trackers that were tested met the 

manufacture’s specifications while others did not. We show 

results of ranging test performed on Tracker A in Figure 4. The 

data were recorded in the ADM mode of the tracker and 

substantially more points were recorded than required by the 

Standard. The errors in the measured lengths were within the 

manufacturer’s specifications and therefore acceptable. 

0 20 40 60 −0.1

−0.05

0

0.05

0.1

Distance (m)

Error (

μm)

Run #1

Run #2

Run #3

MPE

Figure 4. Ranging test results for Tracker A. 

150
Tests 5 through 8 are the two-face measurements at the near 

position (1 m) with the target at tracker height for four 

orientations of the tracker. Tests 9 through 12 are the two-face 

measurements at the near position (1 m) with the target at twice 

the tracker height for four orientations of the tracker (0q, 90q,

180q and 270q).

We present the results from the length measurement and two-face 

system tests for three trackers in Figures 5, 6, 7, 8, 9, and 10.

The length measurement system test charts (Figures 5, 7, and 9) 

may be interpreted as follows. The 35 length tests are in the order 

in which they appear in the Standard. Test 1 is the horizontal 

length measurement at the near position (1 m away, azimuthal 

angle of 0q). Tests 2 through 5 are the horizontal length 

measurements at four orientations of the tracker (0q, 90q, 180q

and 270q) at the 3 m distance. 

Tests 13 through 24 are a repetition of tests 1 through 12 but with 

the tracker 3 m away from the target. Tests 25 through 36 are a 

repetition of tests 1 through 12 but with the tracker 6 m away 

from the target. We discuss the tracker performance evaluation 

results next. Tests 6 through 9 are the horizontal length measurements at four 

orientations of the tracker at the 6 m distance. Tests 10 through 17 

are the vertical length measurements. Tests 18 through 25 are the 

right diagonal length measurements and tests 26 through 33 are 

the left diagonal length measurements. Tests 34 and 35 are the 

user-defined positions.

4.1 Tracker A 

Tracker A (see Figures 5 and 6) clearly meets the manufacture’s 

specification for length measurement and two-face system tests. 

The error in the measurement of a calibrated 2.3 m length placed 

6 m away from the tracker was less than 25 Pm, well under the 

manufacturer’s specification of 100 Pm. Small two-face errors, 

under 50 Pm, for this tracker indicate that most of its geometric 

errors have been properly compensated. 

The two-face charts (Figures 6, 8, and 10) may be interpreted as 

follows. The 36 two-face tests are in the order in which they 

appear in the Standard. Therefore, tests 1 through 4 are the twoface measurements at the near position (1 m) with the target on 

the floor for four orientations of the tracker (0q, 90q, 180q and 

270q).

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

−100

−50

0

50

100

Test # (In the order in which they appear in the Standard)

Error (μm)

090180270090180270090180270090180270090180270090180270090180270090180270

Hor MinHor 3mHor 6mVer 3mVer 6mRD 3mRD 6mLD 3mLD 6mUser Defined 1User Defined 2

(a)

Run 1

Run 2

Run 3

MPE

Figure 5. Length measurement system test results for Tracker A. 

1 2 3 4 5 6 7 8 9 10 11 12 1314 15 16 17 1819 20 21 22 2324 25 26 2728 29 30 31 3233 34 35 36

0

20

40

60

80

100

120

140

160

180

Test # (In the order in which they appear in the Standard)

Error (μm)

090180270090180270090180270090180270090180270090180270090180270090180270090180270

1m, Low1m, Med1m, High3m, Low3m, Med3m, High6m, Low6m, Med6m, High

(b) Run 1

Run 2

Run 3

MPE

Figure 6. Two-face system test results for Tracker A. 

151
4.2 Tracker B 

Figures 7 and 8 show the results of length measurement and twoface system tests for Tracker B. This tracker appears to have 

satisfactory length measurement performance, but demonstrates 

large two-face errors. 

Notice that the two-face error (Figure 8) demonstrates periodicity 

that is a function of the azimuth. In addition, the average two-face 

error (approximately 1.2 mm in Figure 8) does not change with 

distance of the target from the tracker. The average two-face error 

with increasing distance may arise from an offset in the beam 

from its ideal position (Tracker B does not have a beam steering 

mirror. Rather, the source is located directly in the head). Such an 

offset will result in decreasing error in the measured angle farther 

away from the tracker; consequently, the two-face error will be 

independent of range.

An explanation for the periodicity in the measured two-face data 

involves some subtlety. An eccentricity in the horizontal angle 

encoder will result in two-face errors showing periodicity that is a 

function of the azimuth. A least-squares fit of the data will 

therefore provide an estimate of the eccentricity. However, it 

turns out that when the two-face error, which is a convolved 

distance from horizontal and vertical angle error, is isolated into 

its constituent angle errors, the periodicity is in the vertical angle 

error. The vertical angle encoder has no functional relationship 

with the horizontal angle and therefore, the periodicity does not 

appear to be due to a geometric misalignment. The observed 

periodicity may be the result of stressing and relaxation of tension 

in cables within the tracker, or other such causes that are not 

considered in a geometric error model. 

Although Tracker B did have large two-face errors, the B89.4.19 

length measurement system test results (Figure 7) do not seem to 

be adversely affected by the large beam offsets. A careful 

consideration of the beam offset misalignment reveals that this 

term does not impact symmetrically placed lengths with respect to 

the tracker because the error at ends of the reference length cancel 

each other. Almost every B89.4.19 position is symmetrically 

placed with respect to the tracker. Asymmetrically positioned 

lengths will demonstrate large errors and may be used as the userdefined positions during the test. 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 −200

−150

−100

−50

0

50

100

150

200

Test # (In the order in which they appear in the Standard)

Error (μm)

090180270090180270090180270090180270090180270090180270090180270090180270

Hor MinHor 3mHor 6mVer 3mVer 6mRD 3mRD 6mLD 3mLD 6mUser Defined 1User Defined 2

(a)

Run 1

Run 2

Run 3

MPE

Test # 

Figure 7. Length measurement system test results for Tracker B. 

2000

Figure 8. Two-face system test results for Tracker B. 

1 2 3 4 5 6 7 8 9 10 11 12 1314 15 16 17 1819 20 21 22 2324 25 26 2728 29 30 31 32 33 34 35 36

0

500

1000

1500

Error (μm)

090180270090180270090180270090180270090180270090180270090180270090180270090180270

1m, Low1m, Med1m, High3m, Low3m, Med3m, High6m, Low6m, Med6m, High

(b)

Run 1

Run 2

Run 3

MPE

Test # (In the order in which they appear in the Standard) Test #

152
Several interesting points raised in this section are worth 

summarizing:

x Large length measurement or two-face system test errors 

typically suggest that geometric misalignments have not 

been properly compensated. 

x Two-face errors as reported in the B89.4.19 Standard are the 

convolved errors in both the horizontal and vertical angles, 

and scaled by the range. Raw horizontal and vertical angle 

errors from a two-face test contain more diagnostic 

information.

x The purpose of extracting the magnitude of physical 

misalignments from B89.4.19 tests is to estimate the error in 

other length measurements made within the work volume of 

the tracker. 

4.3 Tracker C 

Tracker C shows large errors in the length measurement system 

tests. The periodicity of the errors for Tracker C (Figure 9) may 

be the result of an eccentricity in the horizontal angle encoder, as 

well as a tilt in the beam as it emerges from its source. This 

tracker has the source located in the base and a beam steering 

mirror directs the beam to the target. Therefore, any tilt in the 

beam will also be a function of the azimuth. A least-squares bestfit may be performed to determine the magnitude of the 

eccentricity and tilt. 

The two-face error (Figure 10) shows increasing error farther 

away from the tracker. A tilt in the beam as it emerges from the 

source will produce a constant angle error that when amplified by 

the range results in larger two-face error farther away from the 

tracker. We do not have the manufacturer’s specification for twoface error for this tracker. The errors in Figure 10 are comparable 

to those of Tracker A and may therefore be acceptable, but 

nevertheless, there is evidence of improper compensation for 

geometric errors. 

In this section, we have suggested that the B89.4.19 test results 

may be employed in a diagnostic mode where physical 

misalignments are determined. A geometric error model is 

required for this purpose. Error models are also useful in 

performing sensitivity analysis where the sensitivity of any given 

test to any geometric misalignment is determined through 

numerical simulation. We describe sensitivity analysis next. 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

−300

−200

−100

0

100

200

300

Test # (In the order in which they appear in the Standard)

Error (μm)

090180270090180270090180270090180270090180270090180270090180270090180270

Hor MinHor 3mHor 6mVer 3mVer 6mRD 3mRD 6mLD 3mLD 6mUser Defined 1User Defined 2

(a)

Run 1

Run 2

Run 3

MPE

Test #

Figure 9. Length measurement system test results for Tracker C. 

4.4

1 2 3 4 5 6 7 8 9 10 11 12 1314 15 16 17 1819 20 21 22 2324 25 26 2728 29 30 31 3233 34 35 36

0

50

100

150

200

250

300

Test # (In the order in which they appear in the Standard)

Error (μm)

090180270090180270090180270090180270090180270090180270090180270090180270090180270

1m, Low1m, Med1m, High3m, Low3m, Med3m, High6m, Low6m, Med6m, High

(b) Run 1

Run 2

Run 3

MPE

Test #

Figure 10. Two-face system test results for Tracker C. 

153
5. SENSITIVITY ANALYSIS 

A spherical coordinate instrument such as a laser tracker is a 

mechanical assembly of different components and therefore 

subject to misalignments such as offsets (offset in the beam from 

ideal position, offset between the standing and transit axes etc),

tilt (tilt in the beam, tilt in the transit axis etc) and eccentricity 

(encoder eccentricity with respect to axis) during construction and 

assembly. It is general practice to correct for these misalignments 

by software compensation. A geometric error model [5] is 

required for this purpose that relates the corrected (true) range and 

angles to measured range and angles, and geometric 

misalignments within the tracker. 

The corrected range (Rc) and angles (horizontal angle: Hc,

vertical angle: Vc) of any coordinate in space are functions of 

several misalignment parameters within the construction of the 

tracker and also of the measured coordinate values at that location 

(Rm, Hm, Vm). The corrections 'Rm, 'Hm and 'Vm in Rm, Hm

and Vm respectively may be expressed as (linear models may be 

sufficient as a first approximation), 

),,(

),,(

),,(

1

1

1

VmVc Vm wx Rm Hm Vm

HmHmHc vx Rm Hm Vm

RmRmRc ux Rm Hm Vm

i

n

i

i

i

n

i

i

i

n

i

i

¦

¦

¦

 

 

 

 ' 

 ' 

 ' 

 

where x is any misalignment parameter (eccentricity in encoder, 

beam offset, transit axis offset from standing axis, beam tilt, etc),

and u, v and w are functions of measured range and angles. 

Because different commercially available laser trackers have 

different mechanical constructions, an error model applicable to 

one tracker may not necessarily be applicable to another. At 

NIST, we have modeled three broad classes of trackers: a) tracker 

with a beam steering mirror for which the Loser and Kyle [5] 

model is applicable, b) tracker with the laser source in the rotating 

head and c) scanner with source mounted on the transit axis with 

a rotating prism mirror that steers the beam to the target. 

As an example, an error model for a tracker with the source 

located in the head is given by 

).sin()sin( cos( ).

cos( ) cos( )

).sin()sin( cos( ).

cos( ) )sin()sin(. tan( )

)sin(.

7 9 9

73

21

6 9 9

6

1 4 5

2 8

 x Vm mx Vm mx Vm

xx Vm

Rm

x Vm

Rm

x VmVc

x Hm mx Hm mx Hm

x Hm

Vm

x

Vm

x

VmRm

x HmHc

RmRc x Vm x

z c d

n m

y a b

x t t

  

 

  

 

 



where x1t and x1m are beam offsets along the transit axis and its 

normal, x2 is the transit offset, x3 is the vertical index offset, x4t is 

the beam tilt, x5 is the transit tilt, x6x and x6y are the horizontal 

angle encoder eccentricities, x7x and x7y are the vertical angle 

encoder eccentricities, x8 is the bird-bath error, and x9a, x9b, x9c and 

x9d are the components of the mth order scale error in the encoder 

(1st order is not distinguishable from encoder eccentricity. Higher 

orders beyond 2nd order may be neglected). 

This error model may now be used to numerically estimate the 

sensitivity of any given test to geometric misalignments that are 

included in the model. As an example, consider the beam offset 

terms. We describe how the coefficients for the parameters in the 

error model were obtained, and then discuss the sensitivity of 

different B89.4.19 tests to this misalignment. 

x1t

x1m

A

O

T

M

P

N

Z

Vm

Y

X

Hm

Rm

Figure 11. Schematic of beam offset in a tracker where the 

beam originates from the head (there is no beam steering 

mirror). Axes OT, ON and OM are fixed to the tracker’s head 

and therefore rotate with the head about the Z axis.

5.1 Error Model Coefficients 

The beam originating from the source (at O) may be displaced 

from its ideal position by a constant offset (OA in Figure 11) to 

emerge from A, a misalignment parameter referred to as beam 

offset. The offset can be resolved into components along two 

orthogonal axes, M and T (x1m and x1t). In Figure 11, OT is the 

transit axis, P is the target, ON is the projection of the beam to the 

target on the XY plane, and OM is the normal to both the transit 

axis and beam to the target. XYZ is a fixed Cartesian coordinate 

system with origin at O. TNZ is Cartesian coordinate system, also 

with origin at O, but attached to the tracker head so that it can 

rotate about the Z axis. TPM is also a Cartesian system with origin 

at O and attached to the tracker so that it can rotate about the 

transit axis OT. The offset component along the transit (x1t)

produces an error in the measured horizontal angle. The 

correction for the beam offset is given by )sin(.

1

Rm Vm

x

Hm t ' .

The component along its normal (x1m) produces an error in the 

measured vertical angle, and its correction is given 

by Rm

x

Vm  1m ' .

154
5.2 Sensitivity to Two-face System Tests 7. CONCLUSIONS

The effect of beam offset on two-face tests described in the 

B89.4.19 Standard can be determined as follows. The corrections 

for the measured horizontal and vertical angles of a target placed 

distance Rm away from the front face of the tracker are given 

above. These corrections reverse in sign when the tracker is in the 

backsight mode. The apparent distance E in a two-face test is 

therefore given by for offset 

along the transit axis and for offset 

along OM. Both beam offset parameters are therefore sensitive to 

every two-face test described in the Standard by the same 

sensitivity factor of 2. 

t E Hm VmRm x ' 2)sin(..2 1

E RmVm ' 2.2 x1m

The recently released ASME B89.4.19 Standard provides a 

common set of performance evaluation tests that may be 

performed by both the manufacturer and the user to evaluate if the 

instrument meets the manufacture’s specifications. 

The Standard contains three types of tests. The ranging tests 

assess the instrument’s distance (or displacement) measuring 

capability. The length measurement and two-face system tests 

identify any systematic errors within the instrument’s 

construction, such as mechanical and optical misalignments. The 

length measurement system tests require a calibrated reference 

length (typically 2.3 m long) realized either as an artifact or 

using laser-rails, or between free standing targets calibrated by 

other means. The ranging tests require a reference interferometer 

and a laser-rail and carriage system where long lengths may be 

calibrated or some other means to independently measure long 

lengths reliably. The two-face tests require no reference lengths. 

They are simple and easy to perform, and capture a large number 

of geometric misalignments. 

5.3 Sensitivity to Length Measurement 

System Tests 

Systematic errors in measured range and angles lead to an error in 

the determination of the coordinates of each end of the reference 

length. This however does not necessarily imply an error in the 

calculated length between the two ends because the error vectors 

(vector between true coordinate and measured coordinate) at the 

two ends may simply result in translation and/or rotation of the 

length, but not a change in its magnitude. Sensitivity to length 

tests is achieved primarily if the error vectors at the two ends 

produce components along the length with non-zero sum. 

Components perpendicular to the length are generally not 

sensitive.

The B89.4.19 test results provide valuable diagnostic information 

as well. Using geometric error models of the tracker, it may be 

possible to estimate magnitudes of misalignments in the 

construction of the tracker. Such information may then be used in 

determining errors in other length measurements made within the 

work volume of the tracker. 

Geometric error models also serve a more general role. They may 

be used to determine the sensitivity of any given test to any 

geometric misalignment within the tracker. Such sensitivity 

analysis is useful in determining if a given set of performance 

evaluation tests effectively captures the misalignments, or if any 

modifications in the placement of reference lengths are necessary. 

Any symmetrically placed reference length (such as the 

horizontal, vertical or diagonal length tests in the Standard) is not 

sensitive to beam offset because it only serves to translate and 

rotate the length. The default position for the first user-defined 

test (asymmetrical vertical length test) is sensitive to beam offset 

along the M axis because the asymmetrical positioning of the 

reference length creates unequal error components at the two ends 

of the reference length which do not completely cancel each 

other.

8. REFERENCES

[1] ASME B89.4.19-2006 Standard – Performance Evaluation of 

Laser-Based Spherical Coordinate Measurement Systems, 

www.asme.org.

6. SUMMARY [2] W.T.Estler, D.S.Sawyer, B.Borchardt, and S.D.Phillips, 

Laser-scale metrology instrument performance evaluations at 

NIST, The Journal of the CMSC, Vol. 1, No. 2, pp 27-32, 

2006.

The complete set of B89.4.19 tests may be numerically simulated 

and the sensitivity of each test to every parameter in the error 

model can be determined. The results, tabulated as a twodimensional matrix with B89.4.19 tests in one axis and 

misalignment parameters in the other, is a “sensitivity matrix.” 

We have created such sensitivity matrices for the three classes of 

trackers for which we have developed error models. Such 

matrices are useful in assessing the capabilities and limitations of 

any set of performance evaluation tests. 

[3] D. Sawyer, B. Borchardt, S.D.Phillips, C. Fronczek, 

W.T.Estler, W. Woo, and R.W. Nickey, A laser tracker 

calibration system, Proceedings of the Measurement Science 

Conference, Anaheim, CA, 2002. 

[4] D. Sawyer, NIST progress in the development of a 

deployable high-accuracy artifact for laser tracker 

performance evaluation per ASME B89.4.19, Proceedings of 

the CMSC conference, Charlotte, NC, July 21-25, 2008. 

Analysis of such sensitivity matrices further leads to the 

identification of optimal length positions that are sensitive to 

specific geometric misalignments. For example, we mentioned 

that the beam offset misalignment parameter was not sensitive to 

horizontal, vertical, or diagonal length tests because of the 

symmetrical nature of the positioning of the reference length with 

respect to the tracker. Sensitivity analysis indicated that 

asymmetrical positioning is advantageous, and therefore may be 

considered as a user-defined test. 

[5] Raimund Loser and Stephen Kyle, Alignment and field 

check procedures for the Leica Laser Tracker LTD 500, 

Boeing Large Scale Optical Metrology Seminar, 1999. 

155
 Preliminary Analysis of Conveyor Dynamic Motion for 

Automation Applications

Jane Shi, Ph.D. 

GM R&D Center 

30500 Mound Road 

Warren, MI, USA 

Jane.Sh@gm.com

ABSTRACT

In order to eliminate the automation stop stations in automotive 

general assembly (GA) and enable robotic automation on 

continuous moving conveyors, it is essential that the conveyors’ 

dynamic motion behaviors at the assembly plant floor are 

characterized and quantified. A six degree of freedom (DOF) 

accelerometer with embedded data logging capability has been 

utilized to collect the conveyor dynamic motion data from several 

assembly plants. This paper summarizes conveyor dynamic 

motion data collected from several assembly plants, analyzes 

these dynamic motion data using simple statistical analysis to 

quantify the conveyor motion’s stability in the main direction of 

travel, and identify any frequency pattern of the conveyor 

dynamic motion data with the Fast Fourier Transformation (FFT) 

frequency analysis. 

Categories and Subject Descriptors

C.4 [Performance of Systems]: Performance attributes. 

C.3 [Special-Purpose and Application-Based Systems]: Process 

control systems; Real-time and embedded systems.

General Terms

Measurement, Verification. 

Keywords

Motion quantification, Statistical analysis, FFT 

1. INTRODUCTION

In automotive general assembly (GA), vehicle bodies are being 

carried on a continuous moving assembly line. The vehicle 

bodies are moving through hundreds of workstations where a 

variety of parts are being assembled together, typically by human 

operators as shown in Figure 1.

Current automation of assembly tasks are implemented in stop 

stations, i.e. the vehicle body stops and remains stationary for the 

entire time when the robotic assembly is being performed. A stop 

station in GA requires a long section of high speed conveyors 

before the stop station for job accumulation, then again a long 

section of high speed conveyors after the stop station for 

synchronizing with a slow moving conveyor and manual 

workstations. The GA automation stop stations are expensive: one 

stop station takes up an equivalent floor space of 7 manual 

workstations.

Figure 1 Automotive General Assembly 

Conveyors Transport Vehicle Bodies for 

Assembly Operations

One of the solutions to eliminate the automation stop stations in 

general assembly is to automate assembly operations on a moving 

line. Line tracking is the fundamental enabler for robotic 

automation on a continuous moving line. In order to develop 

adequate line tracking capabilities, the conveyor’s motion need to 

be characterized. This paper presents the method to collect the 

conveyor motion data, summarizes the collected data, and 

presents the motion frequency analysis results and basic statistical 

analysis results for both linear acceleration and computed linear 

speed. 

2. CONVEYOR MOTION DATA 

COLLECTION METHOD 

Permission to make digital or hard copies of all or part of this work for 

personal or classroom use is granted without fee provided that copies are 

not made or distributed for profit or commercial advantage and that 

copies bear this notice and the full citation on the first page. To copy 

otherwise, or republish, to post on servers or to redistribute to lists, 

requires prior specific permission and/or a fee. 

Line tracking of a moving vehicle body for assembly is mainly 

concerned with the vehicle body moving speed in the 3D space 

with respect to a fixed reference frame as shown in Figure 2. 

Given that OwXwYwZw is the fixed frame and OXYZ is the 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA. moving frame attached to the moving vehicle body, Xw is the 

Copyright 2008 ACM 978-1-60558-293-1...$5.00. 

156
main direction of conveyor motion. The goal of conveyor motion 

data collection is to record the frame OXYZ position or motion 

speed (Vx,Vy,Vz,Rx,Ry,Rz) or its acceleration with respect to the 

stationary frame for a coverage of an entire workstation.

Figure 2 Line Tracking Reference Frames 

An ideal method and its associated instrument to collect the 

vehicle body motion data should be simple to set up, easy to 

initiate for data recording, and non-intrusive to operators on the 

production line since the instrument has to be riding with the 

vehicle body on the conveyors for a number of repeated data 

sampling. In addition, minimum secondary processing of recorded 

raw data is desired. Many of high speed camera or laser tracking 

systems are complex to set up, require line of sight, and are 

intrusive to the natural production environment on the assembly 

plant floor. After investigating several available motion sensors, 

the six degree of freedom (DOF) accelerometer, EDR3D-6DOF 

[1], as shown in Figure 3, is chosen based on its capabilities of 

embedded simultaneous data logging of all 6 axes data: three 

linear accelerations and three angular velocities. EDR3D-6DOF 

allows about 30 minute data logging of linear acceleration and 

angular velocity at 500 Hz rate of 10 bit to fill up 4 megabytes of 

embedded flash memory. An external toggle switch simply turns 

on or off the data logging. In addition magnets provide convenient 

way of mounting the instrument to any steel surface. 

Table 1 below summarizes the measurement range and the 

resolution for all six axes. 

Table 1 Accelerometer Measurement Range and Resolution 

Parameter

Measurement 

Range

Resolution

X

Acceleration 2.23g 0.005g

1.93

in/sec^2

Y

Acceleration 2.28g 0.005g

1.93

in/sec^2

Linear

Accele

ration

Z

Acceleration 2.30g 0.005g

1.93

in/sec^2

X Rotation 78.5 deg/sec 0.0766 deg/sec 

Y Rotation 77.3 deg/sec 0.075488 deg/sec Angular

Velocity Z Rotation 79.6 deg/sec 0.077734 deg/sec 

When placed with X direction aligned with conveyor main travel 

direction, the EDR3D-6DOF is used to collect three linear 

accelerations and three angular velocities of conveyors from the 

assembly plants. 

3. RAW MOTION DATA COLLECTED 

Raw conveyor motion data have been collected from a total of 

five different types of conveyor at four different assembly plants 

from late June through early September of 2007. For each 

conveyor type, the accelerometer was placed on the conveyor to 

ride through a workstation or a section of multiple workstations. 

Conveyor motion data are repeatedly sampled five times so that 

the randomness of conveyor motion can be studied. During the 

active data recording period, any external disturbances to the 

natural conveyor movement, such as an operator stepping on the 

conveyor carriers or a heavy machine loading onto the vehicle 

body, were noted so that any exceptional signal in the raw data 

can be detected. In this paper, only representative samples of data 

are illustrated for two types of conveyors: a platform type of 

conveyor with stable and smooth motion, a chain type of 

conveyor with rough and jerky motion. 

Figure 4 shows three linear accelerations for a platform type of 

conveyor with stable and smooth motion. 

For a conveyor that exhibits rough and jerky motion, Figure 5 is 

an example graph of three linear accelerations. 

X

Y

Z

Xw o

Zw Yw

Ow

Figure 3 An Accelerometer with Embedded Data Logging 

Capabilities

Figure 4 Raw Linear Accelerations of a Stable Conveyor

157
Figure 5 Raw Linear Accelerations for a Jerky 

Conveyor 

Figure 8 Third Run of a Jerky Conveyor 

Please note that the scale of Figure 5 is significantly larger than 

the scale of Figure 4. 

The linear acceleration in X direction (main conveyor motion 

direction) exhibits significant jerky motion (blue) that is of short 

duration with big changes in X acceleration. Figure 6 through 9 

are four samples of the same workstation with jerky motion. 

Figure 9 Fourth Run of a Jerky Conveyor

Figure 7 Second Run of a Jerky Conveyor 

Figure 6 First Run of a Jerky Conveyor 

During the data collection period, the vehicle body stops at a 

random time for a time period and then starts again. Depends on 

the specific production activity, the stop and re-start occurs 

randomly. Figure 10 and 11 are two examples of captured stop 

and/or start of a conveyor. 

Figure 10 Normal Start of A Jerky Conveyor 

158
This section illustrates several representative data samples only. 

Given the multiple data sets for each of five types of conveyors, 

statistical analysis can identify the stability of each conveyor and 

allow the comparison of different types of conveyor. Signature 

motion of a conveyor can be identified so that the emulation of 

the representative motion can be rendered by other motion 

devices, such as a robot [2]. 

4. STATISTICAL ANALYSIS OF CONVEYOR

LINEAR ACCELERATIONS

Basic statistical analysis of three linear accelerations, the mean, 

the standard deviation, maximum and minimum value, has been 

performed and the results are summarized in Table 2. 

Table 2 Three Linear Acceleration Statistics 

As it is expected, the mean, as listed in column B,C,D, for three 

linear accelerations is zero. This means that there is no net 

acceleration for the linear motion even though the instant value of 

the acceleration can be quite large in either positive or negative 

direction as shown by the maximum and minimum values. 

The range of acceleration distribution is measured by one 

standard deviation, as listed in column E,F,G.. So the conveyor 

motion’s stability can be evaluated simply by the value of 

standard derivation. The smaller the standard deviation value, the 

more stable the conveyor motion. Although Conveyor 5 moves at 

lower average speed, it is most unstable conveyor with the widest 

range of speed and highest magnitude of jerk (change rate of 

acceleration).The next unstable conveyor is Conveyor 4. Stability 

of Conveyor 3 is similar to Conveyor 4. Conveyor 6 has better 

stability than previous two types of conveyor. Both Conveyor 1 

and 2 are significantly stable as shown by their standard 

derivation as well as maximum and minimum values. 

More sophisticated statistical analysis can be performed, possibly 

in future, to further analyze the dynamic motion data for detection 

of any relationships among the sample sets. 

5. FAST FOURIER TRANSFORMATION ANALYSIS

OF CONVEYOR LINEAR ACCELERATION

In order to detect any frequency patterns of the collected 

acceleration data, Fast Fourier Transformation (FFT) analysis has 

performed for all linear acceleration data. Sample graph of FFT 

analysis results are illustrated for a smooth conveyor, Figure 12 

and 13, and for a jerky conveyor by Figure 14 and Figure 15. The 

horizontal X axis is the frequency in Hz and the vertical Y axis is 

the power spectrum distribution at a particular frequency. The 

peaks are the frequency concentration of the acceleration. 

Figure 11 Normal Stop and Start of A Smooth Conveyor

Figure 12 FFT Results of First Run of a Smooth 

Conveyor 

Figure 13 FFT Results of Second Run of a Smooth 

Conveyor

159
Figure 14 FFT Results of First Run of a Jerky 

Conveyor 

Figure 15 FFT Results of Fifth Run of a Jerky 

Conveyor 

Table 3 is the summary of the frequencies for the first three 

highest peaks of FFT analysis results for a total of six conveyors. 

Table 3 FFT Frequency of Three Linear Accelerations 

When the highest dominant peak occurs at zero frequency, it 

means that zero acceleration is dominant as it is in Conveyor 1 

case, and the conveyor motion speed is constant. When multiple 

and equally strong peaks occur at different frequencies, it means 

that the conveyor acceleration varies at combined multiple 

frequencies as it is in Conveyor 5 case. Based on the FFT analysis 

results, it can be concluded that all jerky motion along the 

conveyor main travel direction is of random nature, i.e. they do 

not occur at a fixed frequency or fixed multiple frequencies with a 

regular pattern.

6. COMPUTED SPEED AND POSITION DATA

Given conveyors’ three linear acceleration data sampled at 

500Hz, conveyors linear speed can be computed with a numerical 

integration method. It has turned out that the computed speed and 

position can not reliably reflect the accurate stop and start 

scenarios. Any small linear trend or nonzero mean in acceleration 

data will cumulate over time and it will lead to significant error in 

computed speed and position. After several attempts and 

experiments, it is discovered that the following pre-processing 

and necessary filtering can yield good speed and position data. 

x First, the linear trend of the linear acceleration within every 

10 second period is removed

x Second, the acceleration data is filtered at 5 Hz since high 

frequency vibration is of no interest for speed computation. 

x Third, the mean is set to zero since it is assumed no net 

acceleration of the conveyor motion. 

x Finally, the speed and position are computed using the 

first order linear integration with 0.002 second 

interval.

Sample graphs of computed conveyor speed and the 3D position 

are illustrated for a smooth conveyor, Figure 16 and 17, and for a 

jerky conveyor by Figure 18 and Figure 19. The horizontal X axis 

is the time in seconds and the vertical Y axis is the speed 

(inches/sec) for the speed chart. 

Figure 17 Computed 3D Position of First Run of a 

Smooth Conveyor 

Figure 16 Computed Speed of First Run of a Smooth 

Conveyor

160
Basic statistical analysis of three linear speeds, the mean, the 

standard deviation, maximum and minimum value, has been 

performed and the results are summarized in Table 4. 

The range of speed distribution is measured by one standard 

deviation, as listed in column E,F,G.. So the conveyor motion’s 

stability can be similarly evaluated by the value of standard 

derivation. The smaller the standard deviation value, the more 

stable the conveyor motion. Although Conveyor 5 moves at lower 

average speed, it is most unstable conveyor with the widest range 

of speed and highest magnitude of acceleration (change rate of 

speed).The next unstable conveyor is Conveyor 4. Stability of 

Conveyor 3 is similar to Conveyor 4. Conveyor 6 has better 

stability than previous two types of conveyor. Both Conveyor 1 

and 2 are significantly stable as shown by their standard 

derivation as well as maximum and minimum values. The same 

conclusion of the conveyor motion stability has been determined 

using the acceleration standard deviation in Section 4. 

7. CONCLUSION AND SUMMARY

This paper presented a method of sampling conveyor motion data, 

illustrated raw linear acceleration data for two representative 

conveyors. Standard statistical analysis has been performed for 

both linear acceleration and computed linear speed to evaluate the 

conveyor motion stability. The Fast Fourier Transformation (FFT) 

has been performed on linear acceleration data to identify 

frequency pattern of the conveyer acceleration. The FFT analysis 

has shown that all jerky motion along the conveyor main travel 

direction is of random nature, i.e. they do not occur at a fixed 

frequency or multiple frequencies and do not have magnitude of 

regular pattern.

Based on the actual conveyor motion data collected from the 

assembly plants, the dynamic motion profile library has been built 

for each of conveyor type that is commonly used in the general 

assembly. These motion profiles can be used in laboratory 

experiments for developing new line tracking solutions and 

validating vendor supplied black box line tracking solutions that 

are targeted for plant floor deployment. 

8. ACKNOWLEDGMENTS

The author would like to acknowledge Bob Scheuerman, Rick F. 

Rourke Dave Groll Jim W. Wells Thomas McGraw, Charles W. 

Wampler, Neil McKay, and Roland Menassa. Their contributions 

of data collection, inputs, and consultations have made this 

project a success compfrom its initial concept to the final results. 

9. REFERENCES

[1] “EDR3D 6DOF Motionmaster User’s Manual”, IST, Inc. 2005 

[2] J. Shi, R. Rourke, D. Groll, P. Tavora,“Qunatification of 

Line Tracking Solutions for Automotive Applications”, 

PreMIS’08, 2008 

Table 4 Three Linear Speed Statistics 

Figure 19 Computed 3D Position of First Run of 

a Jerky Conveyor 

Figure 18 Computed Speed of First Run of a Jerky 

Conveyor 

161
3D Part Identification Based on Local Shape Descriptors 

Xiaolan Li1,2 Afzal Godil1 Asim Wagan1 

1

 National Institute of Standards and Technology, Gaithersburg, MD 20899, U.S.A. 

2

 Zhejiang Gongshang University, Hangzhou, Zhejiang 310018, China 

Contact: lixlan@nist.gov

 

ABSTRACT 

This paper explores 3D object recognition based on local shape 

descriptor. 3D object recognition is becoming an increasingly 

important task in modern applications such as computer vision, 

CAD/CAM, multimedia, molecular biology, robotics, and so on. 

Compared with general objects, CAD models contain more 

complicated structures and subtle local features. It is especially 

challenging to recognize the CAD model from the point clouds 

which only contain partial data of the model. 

We adopt the Bag of Words framework to do the partial-toglobal 3D CAD retrieval. In this paper the visual words dictionary is constructed based on the spin image local feature descriptor. The method is tested on the Purdue Engineering Benchmark. 

Furthermore, several experiments are performed to show how 

the size of query data and the dissimilarity measurement affect 

the retrieval results. 

Categories and Subject Descriptors 

I.2.10 [Vision and Scene Understanding]: Shape, Representations, data structures, and transforms. 

General Terms 

Algorithms, Performance, Reliability. 

Keywords 

CAD model retrieval, bag of words, spin image. 

1. INTRODUCTION 

Large number of 3D models are created everyday and stored in 

databases. In order for these 3D databases to be useful, we 

should be able to search on them. Therefore, identification, retrieval and classification of 3D objects are becoming an increasingly important task in modern applications such as computer 

vision, CAD/CAM, multimedia, molecular biology, robotics, 

and so on. 

With recent developments in 3D range scanners it is possible 

to capture 3D shapes in real time. However, because of the limitation of the point of view, the occlusion in the scene, and the 

real time requirement, only parts of the object can be captured 

during scanning. This proposes a challenging research problem: 

given an incomplete point cloud of an object, how to retrieve the 

corresponding complete model from a database. Solving this 

problem will also benefit several other applications, such as data 

registration [Mitra06], model fixing [Founkhouser04], and so 

on. 

Nevertheless, most of the 3D shape retrieval methods are 

based on global shape descriptors, which require the complete 

geometry of a 3D object, such as Light Field descriptors 

[Chen03], spherical harmonics descriptor [Kazhdan03], D2 

shape distribution [Osada02]. That these methods are not suitable for solving the problem provides an impetus to create methods for partial-to-global 3D shape identification and matching. 

Besides the benefits of partial-to-global retrieval, local descriptors can capture more local details than can the global ones. 

Compared with general objects, CAD models have more complicated structure with holes and other local features. Using 

global information, these subtle details can be neglected. From 

this aspect, local descriptors are better. 

In this paper, we present a complete framework for performing 3D partial shape identification on 3D CAD parts. Several 

experiments are performed to show how the size of query data 

and the dissimilarity measurement affect the retrieval results. 

The organization of the paper is as follows. Several related 

works are summarized in Section 2. Section 3 outlines the whole 

framework of our method, and introduces two crucial terms: 

bag-of-words and spin image. Then, the procedures of feature 

extraction and similarity computation are described in Section 4. 

In Section 5, we provide the 3D shape retrieval results on the 

Purdue Engineering Benchmark. 

2. RELATED WORK 

In order to perform 3D partial-to-global shape retrieval, the 

following methods have been proposed. [Podolak06] exploits 

the symmetry of the shape. [Mitra06] [Frome04] develop local 

shape signatures. Because of its simplicity and generality, the 

bag-of-words method, which is insensitive to deformation, articulation and partial missing data, has attracted lots of interest 

in 2D [Li05] and 3D [Shan06] [Liu06] [Ohbuchi08] fields. In 

[Li05], the method is applied to images by using a visual analogue of a word, formed by vector quantizing two regional descriptors: normalized 11*11 pixel gray values and SIFT descriptors. In [Shan06] and [Liu06], visual feature dictionary is constituted by clustering spin images in small regions. In order to 

procure partial-to-whole retrieval, Kullback-Leibler divergence 

is proposed as similarity measurement in [Liu06], while a probabilistic framework is introduced in [Shan06]. For the sake of 

collecting visual words, Ohbuchi et. al. [Ohbuchi08] apply SIFT 

algorithm to depth buffer images of the model captured from 

uniformly sampled locations on a view sphere. After vector 

quantization, Kullbak-Leibler divergence measures the similari-

(c) 2008 Association for Computing Machinery. ACM acknowledges that 

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royalty-free right to publish or reproduce this article, or to allow others to do 

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PerMIS'08, August 19-21, 2008, Gaithersburg, MD, USA 

ACM ISBN 978-1-60558-293-1/08/08.

162
ties of the models. But these methods focus on the retrieval of 

general objects. 

Compared with general objects, CAD models have a more 

complicated topology with holes and other local features. In 

[Ip07], partial CAD retrieval is achieved based on segmentation, 

which directly affects the retrieval results. This paper aims to 

develop a new method for 3D CAD parts identification in similar circumstance as in [Ip07]. That is, given an unknown partial 

3D point cloud of a part, we are trying to identify the part based 

on the known CAD model in a database. Moreover, our framework is closely related to that of [Liu06] and [Shan06], which 

does not require segmentation at all. 

3. OUR FRAMEWORK 

We first describe the whole framework of our method, and then 

introduce the concept of the spin image [Johnson99] and then 

give several examples. 

3.1 Our framework 

Our method is divided into two stages as shown in figure 1. The 

first stage is completed off-line, aims to construct a visual word 

dictionary based on a 3D database. First, local features are extracted from each model in the database. Second, a clustering or 

classification method is applied to the feature collection to construct the visual word dictionary. The second stage is on-line 

comparison. For the query data, we extract local features and 

search the dictionary for the nearest visual word. We then represent the query data with a feature vector, in which each element 

corresponds to one visual word in the dictionary, and the value 

denotes the frequency of the word appearing in the query data. 

Finally, a certain dissimilarity metric is chosen to compare the 

difference between the query data and the models in the database. A retrieval rank list is the output of the framework. 

Fig. 1. Our framework 

3.2 Spin image 

Fig. 2. Extracting low level features with spin images 

As shown in Figure 2, the spin image, which is invariant to the 

rotation and translation transform, characterizes the local appearance properties around its basis point p within the support 

range r. It is a two-dimensional histogram accumulating the 

number of points located at the coordinate (Į, ȕ), where Į and ȕ

are the lengths of the two orthogonal edges of the triangle 

formed by the oriented basis point p, whose orientation is defined by the normal n, and support point q. The final size of the 

spin images is defined by the width and the height of the spin 

plane. We choose it as the low level feature descriptor in this 

paper. Figure 3 demonstrates several spin images extracted 

from different positions from the bunny. 

Fig. 3. Demonstration of spin images. The support range r is 

defined as the radius of the model. The width and height of the 

spin image are all 256 

4. IMPLEMENTATION 

In this section we will elaborate the details of the method proposed in previous section. 

4.1 Low level feature extraction 

Because the 3D meshes may be composed of large and tiny 

triangles, instead of calculating spin images based on the mesh 

vertices [Johnson99], a two passes sampling procedure is performed here. Using Monte-Carlo strategy [Osada02], for each 

3D mesh, Nb oriented basis points p with normal n and Ns support points q are sampled uniformly on the surface in two passes 

163
respectively, where Nb=800, Ns=50000. Other parameters of 

spin image are defined as: 1) r =0.4R, where R is the radius of 

the mesh. 2) the width and height of spin images is set as 

w=h=10. 

Now a large number of spin images are collected from the 

3D shape database. Each mesh is represented with Nb spin images. 

4.2 Visual words dictionary construction 

With Nb*Nm spin images, where Nb is defined previously and Nm

is the number of 3D meshes we used for building the visual 

words dictionary, k-means algorithm is applied to agglomerate 

N clusters. Here N equals to 1500, which defines the size of the 

dictionary. Therefore, each spin image is assigned with the index of its nearest cluster. Actually, other clustering algorithms 

[Moosmann08] can be adopted to do the work. Further research 

needs to be done to analyze the effects of different clustering 

algorithms and the size of the dictionary. 

4.3 3D shape representation 

For a new shape data, no matter if it is a complete model or just 

a partial point cloud of an object; we represent it using the visual words in the dictionary. The representation can be derived 

via three steps as follows: 

1. Extract the low level features using spin images. 

2. Calculate the distances between the spin images and the 

visual words. The shortest distance indicates that we can 

use the corresponding visual word to record this spin image. 

3. Count the number of times each visual word appears on 

this shape. 

Therefore, each shape is represented by a vector fv=( x1, x2, ..., 

xN ). This is explained visually in figure 4. 

Fig.4. Shape representation 

4.4 Dissimilarity computation 

The requirements for dissimilarity measure for the partial-toglobal retrieval task are quite different than the global-to-global 

retrieval problem. As described in [Liu06], suppose there are 

query data composed of a head and a torso, it is highly probable 

that a human model is a candidate shape for this query. However, the human model is not a part of this query data. That 

means the distance between the query data and the model does 

not equal to the distance between the model and the query data. 

The dissimilarity metric should reflect this asymmetric property. 

To satisfy this requirement, an ordinary symmetric distance 

measurement, such as L1, L2, is not a suitable choice. KL divergence is one of the metrics which satisfies the asymmetric 

property. We will demonstrate the different retrieval results 

using L1 and KL distance metric in the next section. 

5. EXPERIMENTAL RESULTS 

The Purdue Engineering Benchmark (PEB) [Jaynti06], which 

contains 801 3D CAD models, is chosen as the 3D shape database. It is classified into 42 classes such as, “Discs”, “T-shaped 

parts” and “Bracket-like parts”. 

Figure 5 shows the Precision Recall curves [Shilane04] with 

KL divergence measurement when using different partial sizes 

of the object as query data. G-G means it is the PR curve for the 

global-to-global retrieval, P2-G means half of the original model 

is used as the query data, P3-G means one third of the original 

model is used as the query data, and so on. It verifies the intuitive feeling that less information will lead to worse retrieval 

results. However, even with reduced information reasonable 

performance is observed, suggesting robustness of the method. 

Fig. 5. The precision recall curves regarding with different size 

of the query data 

In order to show the effects of using different distance metric, 

we draw two PR curves corresponding to these two metrics (see 

figure 6). Only one sixth of the model is used as query data. 

Fig. 6. The precision recall curves regarding with different dissimilarly metrics 

Figure 7 provides two examples comparing the retrieval results of global-to-global retrieval and partial-to-global retrieval. 

The top figure shows the results when using a door as query 

shape. For Partial-to-Global retrieval, the left top part of the 

door is used as query data. In fact PEB contains only 7 door 

models; both G-G and P6-G retrieval rank all the 7 door models 

on the top of the retrieval list. The bottom figure shows results 

when using a gear as query shape. It shows that the P6-G re164
trieval is better than the G-G one, since P6-G find out more 

gears than G-G. Why does the partial-to-global retrieval perform 

better? It seems impossible. However, recalling the definition of 

the feature vector will provide some clues to the answer. The 

feature vector describes the frequency of the visual words appearing in the shape. When using the entire gear model to be the 

query data, the plane-kind of visual word overwhelm the other 

features. However, using partial of the object to be the query 

data, the gear teeth shape dominates the whole shape. So more 

gears are picked out, and listed on the top of the list. 

(a) First example to show the difference between Global-to-Global (G-G) and Partial-to-Global (P-G) retrieval. The left figures show the 

Global-to-G-G retrieval result using a complete model (the first image listed in the first line) as the query. The right figures show the P-G 

retrieval result using 1/6 part of the complete model (the second image listed in the first line) as the query. The top 20 models are listed 

orderly according to the similarity metric. 

(b) The second example to show the difference between G-G and P-G retrieval. The layout of the images is the same as that of (a). 

Fig. 7. Two examples of retrieval results

165
6. CONCLUSIONS 

In this paper, we propose to use the bag-of-words model for 3D 

CAD parts retrieval. The spin image is chosen as the local feature detector. We perform experiments to study the effectiveness 

of the method to solve the problem of partial-to-global 3D shape 

recognition. The results demonstrate the effectiveness of the 

method. 

ACKNOWLEDGEMENT 

We would like to thank the SIMA program and the IDUS 

program for supporting this work. 

REFERENCES 

[Chen03] D.Y. Chen, M. Ouyoung, X.P. Tian, Y.T. Shen. On 

visual similarity. based 3D model retrieval. Computer Graphics 

Forum (Eurographics ‘03), pp. 223-232. 

[Founkhouser04] T. Funkhouser, Kazhdan, P. Shilane, P. Min, 

W. Kiefer, A. Tal, S. Rusinkiewicz, and D. Dobkin, Modeling 

by example, SIGGRAPH 2004, pp. 652-663. 

[Frome04] A. Frome, D. Huber, R. Kolluri, T. Bulow, J. Malik, 

Recognizing objects in range data using regional point descriptors, ECCV 2004, pp. 

[Ip07] C.Y. Ip, S.K. Gupta, Retrieving matching CAD models 

by using partial 3D point clouds, Computer-Aided Design & 

Applications, Vol.4, No. 5, 2007, pp. 629-638. 

[Jaynti06] Jayanti, S. , Kalyanaraman, Y. , Iyer, N. , and Ramani, K. Developing An Engineering Shape Benchmark For 

CAD Models, Computer-Aided Design, Volume 38, Issue 9, 

Shape Similarity Detection and Search for CAD/CAE Applications, September 2006, Pages 939-953. 

[Johson99] A.E. Johnson, M. Hebert. Using spin images for 

efficient multiple model recognition in cluttered 3D scenes. 

IEEE Trans. On PAMI, 21(5), pp. 433-449, 1999. 

[Kazhdan03] Michael Kazhdan, Thomas Funkhouser, and Szymon Rusinkiewicz. Rotation Invariant Spherical Harmonic Representation of 3D Shape Descriptors. Symposium on Geometry 

Processing. June 2003. 

[Li05] L. Fei-Fei, P. Perona. A Bayesian Hierarchical model for 

learning natural scene categories. CVPR 2005, 524-531. 

[Liu06] Y. Liu, H. Zha, H. Qin, Shape topics : a compact representation and new algorithms for 3D partial shape retrieval, 

IEEE Conf. on Computer Vision and Pattern Recognition 

(CVPR’06), 2006, pp 

[Mitra06] N.J. Mitra, L. Guibas, J. Giesen, M. Pauly, Probabilistic Fingerprints for Shapes, Eurographics Symposium on Geometry Processing 2006. 

[Moosmann08] F. Moosmann, E. Nowak, F. Jurie. Randomized 

clustering forests for image classification. PAMI 2008, Vol.30, 

No. 9. 1632-1646.

[Ohbuchi08] R. Ohbuchi, K. Osada, T. Furuya, T. Banno, Salient local visual features for shape-base 3D model retrieval, 

IEEE Inter. Conf. on Shape Modeling and Applications 

(SMI’08),2008, pp. 93-102. 

[Osada02] Robert Osada, Thomas Funkhouser, Bernard Chazelle, and David Dobkin. Shape Distributions. ACM Transactions on Graphics, 21(4):807-832, October 2002. 

[Podolak06] J. Podolak, P. Shilane, A. Golovinskiy, S. Rusinkiewicz, T. Funkhouser, A planar-reflective symmetry transform for 3D shapes, SIGGRAPH 2006, pp. 

[Shilane04] P. Shilane, P. Min, M.Kazhdan, T. Funkhouser. The 

Princeton shape benchmark. Proc. of the Shape Modeling International 2004 (SMI'04), 04(00): 167-178, 2004. 

166
Calibration of a System of a Gray-Value Camera and an

MDSI Range Camera

Tobias Hanning

University of Passau

Innstr. 43

D-94034 Passau, Germany

tobias.hanning@uni-passau.de

Aless Lasaruk

University of Passau

Innstr. 43

D-94034 Passau, Germany

aless.lasaruk@uni-passau.de

ABSTRACT

We present a novel calibration approach for a system of a

range camera based on the Multiple Double Short-time Integration (MDSI) principle and a regular gray-value camera.

We use a white plate with a regular grid of black circles as a

calibration target. We expose the target to the camera system in different distances and angles. Our procedure returns

the intrinsic camera parameters of both cameras and their

relation to each other. We demonstrate the applicability

of our calibration procedure by discussing the calibration

results for a system of a 64 × 8-pixel MDSI range camera

developed within the European project MIDIAS and a common gray-value camera.

Keywords

Range camera, gray-value camera, calibration

1. INTRODUCTION

Camera calibration is a procedure of obtaining camera

model parameters by observing objects of known nature.

We call a calibration procedure for a system of cameras a

cross-calibration procedure, if the calibration parameters of

each of the cameras in the system are obtained iteratively

from the calibration parameters of the others and from the

mutual relation between the cameras in the system. In this

paper we present a cross-calibration procedure for a system

of a range camera based on the Multiple Double Short-Time

Integration (MDSI) approach and a regular gray-value camera.

A range camera is a grid of range pixels. Each range

pixel provides the distance between the observed object and

the pixel surface measured along a viewing ray. A feasible

way to realize a range camera based on the time-of-flight

principle has been presented by Mengel et al. [1, 2, 3]. Their

MDSI approach is even suitable for outdoor measurements

and thus for automotive applications without making the

laser illumination dangerous for the eye. According to the

MDSI approach each range pixel integrates the radiation

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emitted by a near infrared laser and reflected by the observed

objects during two time periods of different length. The

two time periods are given by repeated application of the

following procedure: Two intensity acquisitions, a short and

a long one, are made, starting consecutively at time t

l

i and

t

s

i respectively. For each of these intensity measurements a

separate laser pulse is emitted. Let φ(a, t) be the radiation

intensity measured in the point a of the active sensor area

A at time t and let ψ(a) denote the sensor sensitivity in

a. Then the (voltage) signals si and li corresponding to

the two integration measurements are given by the following

expressions:

si =

Z ts

i +Δs

ts

i

Z

A

φ(a, t)ψ(a)dadt,

li =

Z tl

i+Δl

tl

i

Z

A

φ(a, t)ψ(a)dadt.

Both acquisition periods start before the backscattered light

from the associated laser pulse reaches the sensor surface. It

is assumed that the inequality t

s

i + Δs < tli holds, although

the difference is very small. The short shutter period Δs is

chosen in such a way that si contains a fraction of the laser

radiation reflected from the scene. This fraction depends

on the round-trip run-time of the laser pulse. The second

shutter period Δl is significantly longer than Δs. Hence,

within the period Δl all laser pulse radiation reflected from

the solid angle of the scene is collected.

According to the MDSI principle single measurements in

(1) are repeated several times. This yields two sequences

s1,. . . , sn and l1,. . . , ln of intensity values corresponding

to the short and long integration periods respectively. By

integrating these intensities we obtain the values

s = Xn

i=1

si and l = Xn

i=1

li. (1)

We call the number n the number of analog integrations. According to [1] the distance to the observed object is linear in

the quotient s/l. In other words, for each range pixel and for

each integration index n there exist coefficients α

, β ∈ R,

such that for each pair of respective values s and l obtained

in Equation (1) for the distance to the corresponding observed scene d(s, l) is given by

d(s, l) = α

s/l + β. (2)

The number of analog integrations can be adjusted for

each range pixel distinctly at runtime. Hence, in each measurement cycle an MDSI range camera provides for each

167
pixel the values s and l and the corresponding number of

analog integrations n. For simplicity we assume that n is

constant for each measurement and equal for each range

pixel. Our approach can be generalized straightforwardly

to work with adaptive number of analog integrations. Since

the range pixels are located in a rectangular grid on the sensor surface, the matrix of the long and the short intensity

values respectively can be interpreted as a gray-value image

of the observed surface. We call these images the long and

the short intensity image respectively.

A calibration algorithm for an MDSI range camera is a

procedure, which obtains all necessary parameters to reconstruct the surface points incident to the viewing ray of

each range pixel. More precisely, a calibration procedure for

our MDSI range camera model according to [1] is an algorithm, which takes a series of intensity values s, l ∈ R obtained by observing objects of known nature for each range

pixel as input. The algorithm returns for each pixel and

for each integration index the surface reconstruction function w : R2 → R3. This function takes the intensities s

and l as input and returns the coordinates of the observed

surface point incident to the viewing ray with respect to

some suitable reference coordinate system. Hence, a calibrated MDSI range camera can be utilized as a coordinate

measuring machine. Notice that depending on the choice of

the reference coordinate system we obtain different surface

reconstruction functions. The two obvious reference coordinate systems are: the gray-value and the range camera

coordinate system. In this paper we give the surface reconstruction functions wg and wr for these two coordinate

systems.

In [4] we have shown that the Z-coordinates of reconstructed surface points can be obtained flexibly by observing a planar calibration pattern. In this approach the Zcoordinates are obtained in the coordinate system of the

gray-value camera, which observes the same scene, as the

range camera. The Z-coordinates are linear in the intensity

quotient as well: For each range pixel and for each integration index n there exist coefficients α, β ∈ R, such that

for each pair of the values s and l the Z-coordinate of the

observed surface point incident to the viewing ray is given

by

z(s, l) = αs/l + β. (3)

The price to pay for the simplicity and flexibility of the procedure in [4] was the requirement to keep the spatial relation

between the gray-value camera and the range camera fixed

after the calibration parameters have been computed. In

this article we use and significantly extend the techniques

presented in [4]. We present a simple and flexible range

camera calibration method, which utilizes a calibrated grayvalue camera. We apply the cross-calibration approach by

using data-fusion techniques to calibrate the whole system

first. From the calibrated system a gray-value camera independent range camera calibration can be easily obtained.

This independency from the distance reference device of our

calibration procedure is the major original contribution of

the present paper.

The outline of the paper is as follows: In Section 2 we

introduce our camera models. Section 3 describes the hardware setup and the data acquisition procedure from the

viewpoint of the user. In Section 4 we present the crosscalibration procedure for a general camera system combined

of an MDSI range camera and a regular gray-value camera. In Section 5 we apply the procedure to the range camera system combined of a 64 × 8-pixel range camera developed within the European project UseRCams and a common

gray-value camera. Section 6 summarizes our work.

2. CAMERA MODELS

We assume the gray-value camera to satisfy the pinhole

camera model with radial distortions. Therefore, the intrinsic parameters of the gray-value camera are represented

by the distortion function σg : R2 → R2 and the mapping

Ig : R2 → R2 with

Ig(x, y) = „

αg 0

0 βg

« 

x

y

!

+

„

xg

yg

«

. (4)

Each space point p ∈ R3 with respect to the coordinate

system of the gray-value camera is related to its image p ∈

R2 by

p = (Ig ◦ σg ◦ π)(p), (5)

where the projection π : R3 → R2 is defined by π(x, y, z) =

(x/z, y/z). The mapping Ig describes the transformation

from the projection to the image coordinate system. The

parameters αg and βg are equal to the focal length of the

corresponding pinhole camera divided by the pixel width

and height respectively. The parameters xg and yg define

the projection of the optical center on the image plane of

the gray-value camera in pixel coordinates. We use the distortion function

σg(x, y) = „

x + xPd

i=1 ki(x2 + y2)

i

y + y

Pd

i=1 ki(x2 + y2)

i

«

, (6)

where k1,. . . , kd are the distortion parameters and d = 2 or

d = 4. We call the parameters αg, βg, xg, yg, and k1,. . . , kd

the intrinsic parameters of the gray-value camera. Notice

that for the most gray-value cameras αg = βg is a good

approximation, since the pixels on common gray-value chips

are nearly squared. We call the mapping

Kg = Ig ◦ σg ◦ π : R3 \ {(x, y, z) ∈ R3 | z = 0} → R2 (7)

the camera mapping of the gray-value camera.

The range camera can be modeled as a finite pinhole camera. A finite pinhole camera is defined by the mapping

Kr(p) = π(PrR(p − t)) for a rotation matrix R ∈ R3×3, an

upper triangular matrix Pr ∈ R3×3 and a translation vector

t ∈ R3 (see [5] for details). The vector t together with R

forms the isometric transformation

T(p) = R(p − t) (8)

from the range camera coordinate system to the coordinate

system of the gray-value camera. Thus, for the range camera there exists a regular matrix A = PrR ∈ R3×3 and a

vector b ∈ R3, such that for each space point p ∈ R3 and its

corresponding range pixel coordinate p ∈ R2 there exists a

λ ∈ R with

λ

 

p

1

!

= Ap + b. (9)

Our calibration procedure returns the values A and b, from

which Pr, R, and t can easily be obtained: Since A is regular, we can determine Pr from A from an RQ-decomposition

168
A = PrR into an upper triangular matrix Pr with positive eigenvalues and an orthogonal matrix R. Such a decomposition can be obtained by a slightly modified QRdecomposition algorithm, which guarantees the positivity of

the diagonal entries of Pr (see e. g. [6]). Observing that

b = −PrRt = −At, we obtain the translation t = −A−1b.

We denote the matrix A−1 by M.

For a range pixel p and for our fixed number of number of

analog integrations consider the range function z : R2 → R

which, given the short and long intensities s and l, returns

the Z-coordinate of the observed object point incident to the

pixels viewing ray. According to Equation (3) there exist

α, β ∈ R with

z(s, l) = αs

l + β. (10)

Then from Equation (9) we obtain the following relation

between the space point p and its image point p

:

p = λA−1

 

p

1

!

− A−1

b = λM 

p

1

!

+ t. (11)

Let us have a closer look at the third component of p, which

is equal z(s, l). Denoting the third row of M by r we obtain

the following equation from which λ can be easily obtained:

z(s, l) = λr

 

p

1

!

− rb. (12)

Consequently, the surface reconstruction function wg with

respect to the coordinate system of the gray-value camera

for the pixel coordinates p and the chosen fixed number of

analog integrations is given by

wg(s, l) = z(s, l) + rb

r`p

1

 ́ A−1

 

p

1

!

− A−1

b. (13)

Using our abbreviations M = A−1 and t = −A−1b we obtain

wg(s, l) = αs

l + β + rb

r`p

1

 ́ M

 

p

1

!

+ t. (14)

Our range camera model has two types of parameters: The

parameters A and b do not depend on a particular range

pixel. On the other hand, the parameters α and β in (14)

are pixel dependent. These parameters must be estimated

for each range pixel separately. Notice that Equation (14)

can also be represented as wg(s, l) = us

l + v for u, v ∈ R3.

The values u and v then define the viewing ray associated

with the particular range pixel.

The remainder of this section deals with the problem of

obtaining the range camera parameters, which do not depend on the gray-value camera. Let for a certain range pixel

the distance reconstruction function d satisfy Equation (2).

From Equation (14) we obtain

d(s, l) = α s

l + β = ||wg(s, l) − t||, (15)

which yields

d(s, l) = αs

l + β + rb

r`p

1

 ́ ||M

 

p

1

!

||. (16)

Notice that M`p

1

 ́

is independent of s and l. Hence, we have

α = ||M`p

1

 ́

||α

r`p

1

 ́ and β = ||M`p

1

 ́

||(β + rb)

r`p

1

 ́ . (17)

Finally, we obtain the reconstruction function wr : R2 → R3

with respect to the coordinate system of the range camera

by

wr(s, l) = d(s, l) P −1 r

`p

1

 ́

||P −1 r

`p

1

 ́

||

. (18)

3. HARDWARE SETUP AND DATA ACQUISITION

The hardware setup consists of an off-the-shelf gray-value

camera and an MDSI range camera in rigid spatial relation.

For a successful calibration the field of view of the range

camera must be contained in the field of view of the grayvalue camera.

The calibration procedure consists of the following steps:

(i) Acquire calibration data by continuously exposing a

calibration pattern to the camera system.

(ii) Determine the intrinsic parameters of the gray-value

camera.

(iii) Determine the range camera parameters A and b

(iv) Determine for each range camera pixel (and optionally

for each integration index n) the Z-coordinate reconstruction parameters α and β in Equation (3).

(v) Optimize all parameters by nonlinear optimization using a suitable error function.

(vi) Optionally compute the range reconstruction function

for each range pixel using Equation (17) and (18).

It is possible to use one calibration target to perform all

the above steps. A suitable calibration target is for example

a white planar pattern with a regular grid of black circles

painted on it (see Figure 1). The size of the circles should

be chosen in a way that correspondent circles can be recognized as well in the gray-value images as in at least one

of the intensity images provided by the range camera. If

the resolution of the range camera is to low to recognize the

circles needed for precise plane reconstruction in step (iv)

one can choose a different calibration target (for example

with bigger circles) to determine the range camera parameters A and b in the step (iii). This is the only critical step,

where the target features must be reconstructed within the

intensity images of the range camera.

4. CROSS-CALIBRATION PROCEDURE

We now turn to the details of our cross-calibration procedure. The estimation of the intrinsic parameters of a grayvalue camera is a well studied problem (see e. g. [7, 8, 9])

Since our calibration pattern is suitable for a calibration of

the intrinsic parameters of the gray-value camera, we assume

the gray-value camera to be roughly calibrated. In fact, we

use the algorithm presented in [9] to perform this calibration. During our cross-calibration procedure the parameters

of the gray-value camera will be further improved.

We now turn to the step (iii) of our calibration procedure.

In step (i) we have obtained a sequence of synchronously

acquired gray-value and intensity images. Let j be the image

pair index within this sequence. Suppose, we have obtained

the centers of the black circles p1j ,...,pmj ∈ R2 in the grayvalue image and the corresponding centers of the same circles

169
p

1j ,...,pmj ∈ R2 in the short or long intensity image of the

range camera.

Given a calibrated gray-value camera Kg and the centers

of the circles c1,...,cm ∈ R3 with respect to the calibration

pattern, we obtain the positions of the centers observed by

the gray-value camera by determining

(Rj , tj ) = argmin

(R,t)∈SO3×R3

Xm

i=1

Kg(Rci + t) − pij2 (19)

(see e. g. [10]). We set cij := Rj ci + tj . Then cij is the

position of the center of the i-th circle observed in the j-th

image pair. With this we obtain for each circle the relation

λ

 

p

ij

1

!

= Acij + b, (20)

for λ ∈ R. Equation (20) is linear in A and b and, hence, admits a DLT algorithm for the estimation of these camera parameters. The equations for all i and for different positions

of the calibration pattern form an overdetermined system of

linear equations. We obtain a least-squares solution for A

and b by Housholder-Transformations [11]. For stability we

additionally apply the RANSAC algorithm to remove outliers. Notice that, in contrast to the calibration procedure

in [9] we do not need to impose additional constraints on A

and b, like for example orthogonality constraints.

The estimate of A and b obtained by the DLT-algorithm

turns to be very rough for back-projection purposes. More

precisely, let

wij = (cij )z + rb

r`p

ij

1

 ́

M

 

p

ij

1

!

+ t (21)

be obtained by replacing the z-coordinate z(s, l) in of the

reconstructed space point from Equation (13) by the Zcoordinate (cij )z of cij . Then the Euclidean distance ||Kg(wij )−

pij || between the projections of the reconstructed surface

points wij and their corresponding original image points pij

is high with respect to the gray-value image size. To determine the parameters A and b precisely we refine them by

minimizing the back-projection error

e(A, b) = X

j

i=1

Xm

i=1

(Kg(wij ) − pij )

2

. (22)

We solve the problem induced by the error function in Equation (22) by non-linear optimization using for the BFGS

algorithm [12]. Notice that we do not need any range information of the range camera in this step.

After estimates of A and b have been obtained, the range

parameters α and β from Equation (3) can be estimated for

each range pixel. We extend the procedure already given in

[4]. Suppose, for the range pixel p we have the intensity

values s and l while observing the plane with the equation

np = d, where n ∈ R3 with ||n|| = 1. Then, according to

Equation (14), we have

nw(s, l) = d. (23)

Substitution of w(s, l) from Equation (14) yields

αs

l + β = r

 

p

1

!

d − nt

nM`p

1

 ́ − rb. (24)

Equations (24) (for a fixed range pixel) for each pair of synchronously obtained images of the calibration plate form

a system of linear equations in the parameters α and β.

We obtain a least-squares solution for these parameters by

Housholder-Transformations [11]. Again, the RANSAC algorithm is additionally applied for stability (see Figure 4).

Notice the significant extention of the procedure described in

[4], where only plate positions orthogonal to the optical axis

of the gray-value camera were concerned. Indeed, Equation

(24) simplifies for n = (0, 0, 1) to

z(s, l) = αs

l + β = d. (25)

The final optimization step involves all collected data to

refine the parameters A and b and the parameters of the

gray-value camera. There are several error functions, which

can be considered in this step. According to our application,

we need besides optimal surface reconstruction properties

also optimal back-projection properties into the image of

the gray-value camera. Therefore a suitable error function

is

e(A, b, Kg) = X

j

i=1

Xm

i=1

(Kg(wg(sij , lij )) − pij )

2

. (26)

Here Kg is a short notation for all gray-value camera parameters. In particular Kg contains the distortion parameters

of σg. We solve the optimization problem induced by the

error function in Equation (26) by the BFGS algorithm [12].

The error function in Equation (26) involves also the optimization of the gray-value camera parameters Kg, which are

improved by this final optimization step. This completes the

cross-calibration procedure.

5. EXPERIMENTAL RESULTS

We have applied the calibration procedure described in

Section 3 and 4 to a system of a gray-value camera and a 64×

8-pixel MDSI range camera developed within the European

project UseRCams and a common gray-value camera.

We use a white plate with a regular grid of black circles painted on it as a calibration target (Figure 1). We

expose the board continuously to the camera system from

different directions and in different distances. For simplicity

we demonstrate the calibration procedure for a fixed equal

number of analog integrations for each range pixel.

The parameters A and b obtained in step (iii) are not

precise, if used for back-projection of reconstructed surface

points into the gray-value image. Figure 2 shows all pixels

detected within the gray-value image and the corresponding

back-projected pixels of the range camera after the final calibration step. Figure 3 shows the corresponding distribution

of the back-projection error given in Equation (22).

After the final calibration a different scene of the same calibration plate in the distance of approximately five meters

was evaluated to cross-validate our calibration result. For

the cross-validation we have used the data acquisition procedure described in step (i) of our calibration procedure in

Section 3. Figure 4 shows the obtained pixel characteristic

for one range pixel. For each calibrated range pixel and for

each plane with equation np = d, ||n|| = 1, reconstructed

by the gray-value camera we measure the absolute range

reconstruction error with respect to our calibration plate

nw(s, l) − d. (27)

170
Figure 1: Calibration plate

 160

 180

 200

 220

 240

 260

 280

 200 250 300 350 400 450 500

’proj.xy’

’real.xy’

Figure 2: Detected circles and the corresponding

back-projected centers of range pixels in the image

space of the gray-value camera

Figure 3: Distribution of the absolute backprojection error

-16

-15

-14

-13

-12

-11

-10

-9

-8

 7.6 7.7 7.8 7.9 8 8.1 8.2 8.3 8.4 8.5 8.6

’results/32x4x4.xy’ (6.437659)*x+(-65.066224)

Figure 4: Example pixel characteristic obtained

from noisy measurements with outliers using

RANSAC

171
This error is the Euclidean distance between the calibration

plate and the reconstructed surface point. To obtain com-

 0

 0.005

 0.01

 0.015

 0.02

 0.025

 0.03

 0.035

 0.04

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

Frequency

Absolute error (m)

Figure 5: Distribution of the range reconstruction

error

prehensive results for our experiment we have assumed the

range reconstruction error of all range pixels to be identically distributed. Under this assumption we can aggregate

sample data from all pixels together as being taken from a

single population. Figure 5 shows the distribution of the

absolute range reconstruction error for all calibrated pixels.

From the distribution in Figure 5 under the above assumptions we can conclude that errors with an absolute value of

at most 16.5cm occur in 75% of all cases and errors with an

absolute value of at most 29.5cm occur in 95% of all cases.

The error expectation of 0.000225217m confirms the accuracy of our calibration procedure and the correctness of our

model. In other words, the measured errors originate mostly

from the sensor noise.

6. CONCLUSIONS

We have introduced a flexible range camera model, which

is capable to provide range and surface data directly in the

reference coordinate system of the gray-value camera. We

have presented a cross-calibration procedure for a camera

system combined of an MDSI range camera and a regular

gray-value camera. Our procedure significantly extends calibration methods for MDSI cameras presented in the literature. Additionally, our calibration procedure provides also

regular, gray-value camera independent, parameters for the

range camera with respect to the coordinate system defined

by the optical system of the range camera. We have applied

the procedure to the range camera system combined of a

64 × 8-pixel range camera developed within the European

project UseRCams and a common gray-value camera. We

are able to show that our calibration procedure yields an unbiased distance- and surface reconstruction procedure. Furthermore, the calibration procedure can be applied mostly

autonomously without expert interaction.

7. REFERENCES

[1] Mengel, P., Doemens, G., Listl, L.: Fast range imaging

by CMOS sensor array through multiple double short

time integration (MDSI). In: International Conference

of Image Processing (ICIP). Volume I., Thessaloniki,

Greece, IEEE (2001) 169–172

[2] Mengel, P., Listl, L., Koenig, B., Toepfer, C.,

Pellkofer, M., Brockherde, W., Hosticka, B., Elkahili,

O., Schrey, O., Ulfig, W.: Three-dimensional cmos

image sensor for pedestrian protection and collision

mitigation. In: Advanced Microsystems for

Automotive Applications 2006, Berlin, Springer (2006)

23 – 39

[3] Mengel, P., Listl, L., Koenig, B., Pellkofer, M.,

Wagner, U., Wertheimer, R.: Time-of-flight camera

for pedestrian protection and collision mitigation. In:

6th European Congress and Exhibition on Intelligent

Transport Systems and Services. (2007) accepted.

[4] Hanning, T., Lasaruk, A., Wertheimer, R.: MDSI

range camera calibration. Advanced Microsystems for

Automotive Applications, Springer (2008)

[5] Hartley, R., Zisserman, A.: Epipolar Geometry and

the Fundamental Matrix. In: Multiple View Geometry

in Computer Vision. Cambridge University Press

(2000)

[6] Golub, G.H., van Loan, C.F.: Matrix Computations. 3

edn. John Hopkins University Press, Baltimore (1996)

[7] Tsai, R.: A versatile camera calibration technique for

high-accuracy 3d machine vision metrology using

off-the-shelf tv cameras and lenses. IEEE Journal of

Robotics and Automation 3 (1987) 323 – 344

[8] Weng, J., Cohen, P., Herniou, M.: Camera calibration

with distortion models and accuracy evaluation. IEEE

Transactions on Pattern Analysis and Machine

Intelligence 14 (1992) 965 – 980

[9] Zhang, Z.: A Flexible new technique for camera

calibration. Technical report, Microsoft Research

(1998) Technical Report MSR-TR-98-71.

[10] Hanning, T., Sch ̈one, R., Graf, S.: A closed form

solution for monocular re-projective 3d pose

estimation of regular planar patterns. In:

International Conference of Image Processing (ICIP),

Atlanta, Georgia (2006) 2197 – 2200

[11] Lawson, C.L., Hanson, R.J.: Solving Least Squares

Problems. Prentice-Hall, Englewood Cliffs, NJ (1974)

[12] Press, W.H., Flannery, B.P., Teukolsky, S.A.,

Vetterling, W.T.: Numerical Recipes in C. 2 edn.

Cambridge University Press (1992)

172
Dynamic 6DOF Metrology for Evaluating a Visual Servoing 

System

Tommy Chang, Tsai Hong, 

Michael Shneier 

Intelligent Systems Division, NIST 

Gaithersburg, MD 20899-8230

{hongt, tchang, 

shneier}@cme.nist.gov 

German Holguin, Johnny Park 

Robot Vision Laboratory 

Purdue University 

West Lafayette, IN 47907 

{gholguin,jpark}@purdue.edu

Roger D. Eastman 

Dept. of Computer Science 

Loyola College in Maryland 

Baltimore, Maryland 21210 

reastman@loyola.edu 

ABSTRACT 

In this paper we demonstrate the use of a dynamic, six-degree-offreedom (6DOF) laser tracker to empirically evaluate the 

performance of a real-time visual servoing implementation, with 

the objective of establishing a general method for evaluating realtime 6DOF dimensional measurements. The laser tracker provides 

highly accurate ground truth reference measurements of position 

and orientation of an object under motion, and can be used as an 

objective standard for calibration and evaluation of visual 

servoing and robot control algorithms. The real-time visual 

servoing implementation used in this study was developed at the 

Purdue Robot Vision Lab with a subsumptive, hierarchical, and 

distributed vision-based architecture. Data were taken 

simultaneously from the laser tracker and visual servoing 

implementation, enabling comparison of the data streams. 

Keywords

computer vision, laser tracker, dynamic 6DOF metrology, 

performance evaluation. 

1. INTRODUCTION 

Real-time three-dimensional vision has been rapidly advancing 

over the past twenty years, leading to a number of successful 

laboratory demonstrations, including real-time visual servoing 

[7,16,17]. However, the advances have frequently not yet made 

the transition to commercial products, due in part to a lack of 

objective methods for empirical performance evaluation. To 

ensure a new algorithm for optical flow, stereo, visual servoing, 

laser Simultaneous Localization And Mapping SLAM, or other 

dynamic visual 3D task is valid, it would be very helpful to have a 

reference standard sensor system (ground truth) along with 

appropriate metrics for the comparison of test systems with the 

reference system. Standards and test procedures for dimensional 

metrology are well-established and highly accurate for static 

measurements, with coordinate measuring machines and laser 

trackers giving position measurements to microns. However, the 

theory, technology, and test procedures are not well established 

for dynamic dimensional measurements in uncontrolled 

environments. 

In this paper we demonstrate the use of a dynamic, six-degree-offreedom (6DOF) laser tracker to empirically evaluate the 

performance of a real-time visual servoing implementation, with 

the objective of establishing a general method for evaluating realtime 6DOF dimensional measurements of an object or assembly 

component under moderately constrained motion. The proposed 

evaluation procedure collects data simultaneously from the laser 

tracker and the visual servoing system under test, so the two data 

streams can be compared. Laser trackers produce highly accurate 

position and orientation data at a high data rate and for the 

purposes of this study will be considered ground truth. 

The questions addressed in this work primarily focus on how to 

collect and compare the data streams. Issues here include 

synchronizing the data streams, so individual data points are taken 

at the same time; external calibration of the two sensors, so 

individual data points can be compared in the same coordinate 

system; and comparison metrics, so individual data points can be 

compared between the two sensors to determine how close the 

system under test comes to the ground truth. It would be useful to 

have comparison metrics that are robust to errors in 

synchronization and calibration, or even not dependent on 

calibration, to ensure accurate comparisons in the field. 

The real-time visual servoing implementation used in this study 

was developed at the Purdue Robot Vision Lab using a 

subsumptive, hierarchical, and distributed vision-based 

architecture for smart robotics [3,6,16,17]. This is a robust, 

advanced dynamic visual servoing implementation with a high 

level of fault tolerance to non-cooperative conditions such as 

severe occlusions and sudden illumination changes. The Purdue 

system combines a ceiling mounted camera with a trinocular 

system mounted on the robot end-effector, and uses position 

based visual servoing (PBVS). The work in this paper is aimed at 

the evaluation of sensors for PBVS, in which the servoing system 

senses the position and orientation of the part in 3D coordinates, 

as opposed to image based visual servoing (IBVS), in which the 

servoing system senses the position and orientation of the part in 

2D image coordinates. 

(c) 2008 Association for Computing Machinery. ACM acknowledges that 

this contribution was authored or co-authored by a contractor or affiliate of 

the U.S. Government. As such, the Government retains a nonexclusive, 

royalty-free right to publish or reproduce this article, or to allow others to 

do so, for Government purposes only. 

PerMIS’08, August 19-21, 2008, Gaithersburg, MD, USA 

ACM ISBN 978-1-60558-293-1/08/08.

2. PREVIOUS WORK 

The general need for empirical evaluation has been wellrecognized in the computer vision literature. Here we review 

articles on empirical evaluation of sensor-only 6DOF static and 

173
dynamic pose estimation, as well as articles on evaluation of 

visual servoing algorithms that may combine sensor evaluation 

with robot control issues. In reviewing the literature, there are a 

number of questions that can be asked: what is under evaluation 

(pose estimation only, pose calculated for visual seroving, or 

other tasks), how measurements are taken from the system under 

test, how ground truth or other reference measurements are taken, 

what metrics are computed from the measurements, and how the 

metrics are interpreted to give summary judgments on system 

performance. We also have looked at the conditions of each test 

to consider the objects, motions, occlusions and environment. 

For pose estimation, most evaluation papers consider static pose 

only [9,12] and not dynamic 6DOF sensor measurements of a part 

under motion. References [12,13] use Monte Carlo simulation for 

the evaluation of pose algorithm accuracy under noise and object 

orientations. In those articles, results are given for pose estimation 

for a complex industrial part and the error from unnamed ground 

truth is plotted as position or orientation error vs. the rotation of 

the object. The key result is to note the error as a function of part 

rotation varies considerably, spiking at ambiguous orientations of 

the object. Two papers that do consider dynamic pose are [10,15]. 

In [10] benchmarked video sequences are used for tests of a 

model-based algorithm with four parameter variations to analyze 

the relative contributions of subcomponents such as the edge 

detection operator or search technique. The results are given as 

deviations from the results of the one parameter set that 

successfully maintained track through the video sequences, but 

the nature and quality of this retrospective ground truth is not 

described in the article. In [15] three tracking approaches for 

6DOF pose estimation and grasping of hand-held objects are 

evaluated using ground truth from an unnamed infrared marker 

tracking system good to 1.5 meters in position but with no 

rotation accuracy or measurements per second cited. The three 

approaches run at 8 Hz to 25 Hz. The article gives results in 

graphs that compare ground truth position and orientation data to 

robot end-effector position and tracked position, but no 

quantitative or summary statistics are given for the graphed data. 

For visual servoing, many papers that present a new approach 

include an empirical evaluation, but since the paper emphasizes 

the development of the new approach, the evaluation section can 

be brief. An exception is [8] which uses sensitivity analysis and 

simulation to compute the contribution of image measurement 

errors to the calculated pose and control trajectory for PBVS and 

hybrid visual servoing. 

The metrics used to evaluate pose estimation and visual servoing 

systems vary. Typical is the mean and standard deviation of a 

measure of error in world coordinates, including individual 

differences for each coordinate, a norm for position and 

orientation separately, or rarely a combined norm for all 6 degrees 

of freedom. The orientation can be compared in roll-pitch-yaw or 

as quaternions. In experiments without ground truth in world 

coordinates, or for IBVS in which pose in world coordinates is not 

computed, errors are computed in the image domain. [5] uses the 

reprojection error in the image domain. In some visual servoing 

evaluations, the metric is the number of cases successfully 

completed during the experiments. 

In physical experiments in the evaluation of pose estimation or 

visual servoing, a mechanism must be used to generate motion, 

frequently a robot arm [2,4,15]. [15] uses an arm to move a 

camera towards a car battery through a known trajectory linear in 

both translation and angle, and repeats the motion 80 times to 

judge repeatability of the tracking algorithm. 

3. PURDUE LINE TRACKING SYSTEM 

Using robots to perform industrial assembly tasks is not new. In 

fact, robots have been used successfully in such applications over 

the past few decades. However, one common constraint still 

present in most of these applications is that the objects to be 

manipulated by the robot must be stationary in a known position, 

or moving along a well-known path with a very small amount of 

uncertainty. Consequently, industrial tasks such as painting, 

palletizing, welding, or decking have traditionally been set up in 

stationary locations in the assembly line where the involved parts 

have to come to a complete stop. 

In order to eliminate inflexible, expensive stationary stations in 

the assembly line, robots must be able to perform their tasks on 

moving targets. The Purdue Robot Vision Lab addresses this goal 

using a subsumptive, hierarchical, and distributed vision-based 

architecture for smart robotics [3]. The system consists of 

multiple real-time control modules running in parallel, where each 

module is controlled by a different tracking method, with unique 

capabilities with respect to accuracy, computational efficiency, 

sensitivity to varying conditions, etc. By taking the most reliable 

input from all the modules, the system is able to achieve a high 

level of fault tolerance and robustness to non-cooperative 

conditions such as severe occlusions and sudden illumination 

changes. 

In this architecture, each control module can be in a different 

hierarchy level. The more accurate the module is, the higher its 

hierarchy level. Modules from higher hierarchies can subsume 

functionality of modules in lower levels. Each module can run 

independently in a different computer over a network. Any 

number of modules is allowed in any given level of hierarchy, 

providing redundancy and fault tolerance. 

Each module is composed of two main parallel processes. The 

first process is the visual-tracking loop that estimates the 6DOF 

3D pose of the target object. This loop can be further broken 

down into three main parallel threads: data acquisition, data 

processing, and message exchange. The second process is the 

visual-servoing loop, which generates commands to the robot to 

move its end-effector to a desired position. This second loop is 

composed of two main threads: the message exchange and the 

control law calculation. 

Even though every control module is able to run at its own sample 

rate and accuracy level in our architecture, only one module will 

be able to pass its generated command to the robot controller. 

The arbitrator listens to all the control modules and decides which 

module input to use to control the robot, based on module 

availability, estimation reliability, and module hierarchy. 

Finally, the robot controller is implemented at the top of the robot 

controller interface. Therefore, the control modules in our system 

fall into the position-based look-and-move category [7]. This 

means that the robot controller is receiving commands directly in 

the Cartesian space, which makes the control plant much simpler 

compared to the image-based servoing category [3]. However, 

the position-based servoing requires camera calibration, robot 

calibration, and hand-eye calibration [6]. 

174
3.1 Peg and Hole Experiment 

In order to demonstrate the capabilities of this architecture, we set 

up a variation of the traditional peg-and-hole experiment (see 

Figure 1). In our experiment, we attached a hollow wooden 

cylinder to an engine cover part, and attached a peg to the endeffector of a 6DOF robot manipulator. The engine cover is loosely 

attached to a linear slide, so the main motion of the engine cover 

is provided by the motion of the linear slide. In addition, we also 

attached strings to the engine cover, which a human can 

manipulate to generate random motions of the engine cover 

during the experiment. The goal of this experiment is to 

command the robot to insert the peg into the cylinder on the 

engine cover while the engine cover is in motion, resembling the 

automation needed to perform tasks such as glass decking or 

wheel decking on-the-fly [16]. 

Our system consists of three control modules, a system arbitrator, 

and a robot controller interface. The three control modules are: 

coarse control, model-based fine control, and stereo-based fine 

control. 

Figure 1. Peg and Hole experiment 

3.2 Coarse Control 

The coarse control module resides at the lowest level in the 

system hierarchy, meaning that it will work only when the other 

two modules become unavailable or unreliable. Its main purpose 

is to provide an initialization point for the controllers with higher 

hierarchy. That is, the coarse control is intended to track the 

target and command the robot to an approximate location in front 

of it. This module only requires the level of accuracy that would 

place the end-effector in front of the target such that cameras for 

the other controllers can view the target. 

Coarse control visual-tracking uses a camera mounted on the 

ceiling with a view of the entire workspace. When the target 

object enters the workspace, the bar holding the target is detected 

and the 3D translational position of the bar in the coordinates of 

the robot is estimated. No rotation information is needed here. 

This estimated pose is passed to the visual-servoing loop that in 

this case would simply command the robot to move its endeffector near the target. 

3.3 Stereo-based Fine Control 

This is the control module that resides at the highest hierarchy 

level in the system, meaning that while tracking the target it 

subsumes the other two modules. It uses a stereo pair of cameras 

located on the robot's end-effector. 

The visual-tracking loop in this module uses a blob analysis 

algorithm to detect, in both cameras, three prominent coplanar 

features on the engine cover. Then, using the calibration 

information, the 3D coordinates of those features are 

reconstructed, and the 6DOF 3D pose of the target is estimated in 

the robot coordinate system [17]. Based on the estimated pose, 

the visual-servoing loop then performs the peg-and-hole motion 

using a Proportional-Integral-derivative (PID) control law. 

Since the 3D pose estimation relies on the visibility of three 

specific features on the engine cover, this module will only work 

if all three features are detected in both cameras. 

Using an efficient blob analysis algorithm makes this module run 

very fast. It takes an average of 8.2 ms to estimate the 3D pose of 

the target, which is more than sufficient to process stereo images 

at 30 frames per second. However, this approach requires some 

thresholds to extract the blobs, making this module sensitive to 

sudden illumination changes. 

3.4 Model-Based Fine Control 

The main purpose of this module is to provide redundancy to the 

stereo-based fine controller. It uses a monocular vision system 

and a known wire-frame model of the target [16]. 

The visual-tracking loop of this module first projects the model 

into the input scene with respect to the initial pose that is given by 

the coarse control module or the stereo-based control module. 

Then, it sequentially matches the straight lines of the wire-frame 

model to the detected edges in the scene for an updated 

calculation of the pose of the target. For robust pose estimation, it 

uses a backtracking scheme for correspondence search [16]. 

Since this module uses extracted edges in the image, as opposed 

to applying thresholding to extract blobs in the stereo-based 

control module, it is less sensitive to illumination changes. Also, 

since the number of model features used in this module is 

typically much larger than 3 (the bare minimum number of 

features required to estimate the pose of an object), it is naturally 

robust to partial occlusions. However, it is slower than the 

Stereo-Based controller. It takes an average of 48 ms to estimate 

the 3D pose of the target, where 80 % of the computation time is 

taken by the edge detection phase. 

4. EVALUATION EXPERIMENTS 

In the experiments, the visual tracking system was set up to 

perform the peg and hole task using an engine part cover as the 

target. The engine part was either stationary or moved by an 

overhead linear rail at a constant velocity. The part was suspended 

from the linear rail to allow the experimenters to move the part 

back and forth by an attached string. 

During each pass of the experiment, the position of the engine 

part was measured simultaneously by the Purdue visual tracking 

system and the NIST laser tracker. Data acquisition from each 

system was triggered by a common hardware signal, and the data 

time stamped and streamed to storage for off-line comparison. 

175
The key elements of the data collection system were the laser 

tracker, the simultaneous data collection, and the establishment of 

common coordinate systems through calibration. 

4.1 Laser Tracker 

Figure 2. SmartTRACK sensor below engine part 

The laser tracker system used consisted of two major components, 

a base unit and an active target, both made by Automated 

Precision Inc1

. (API). The active target is a SmartTRACK Sensor 

(STS) capable of determining its orientation in 3D space. 

Weighing 1.4 kg, the STS has an angular resolution specification 

of ±3 arc-sec (or ±0.000833... degrees). The complete 

manufacturer’s specification can be found in [18]. The base unit is 

the Tracker3TM Laser Tracking System (T3) which tracks the 3D 

position of the STS. The T3 system has ± 10 ppm absolute 

accuracy (e.g., ± 50 ȝm at 5 m). In addition, the base unit can be 

used with a passive target (a spherically mounted reflector (SMR) 

retro-reflective mirror) instead of the active target for single point 

measurements. 

Together, the T3 and STS provide an accurate but limited 6DOF 

pose estimation system. The STS and T3 devices can take 

measurements independently at their own rate or they can be 

connected to a common external trigger. 

4.2 Synchronization Issues 

Both the T3/STS system and the Purdue visual-tracking system 

allow an external signal to trigger their data acquisition. 

Although the STS/T3 system is capable of handling a trigger 

signal up to 150 Hz, the visual-tracking system requires a 30 Hz 

data stream. We use a single 30 Hz trigger signal shared by both 

systems. 

 

Y H X

1

 Certain commercial equipment, instruments, or materials are 

identified in this paper in order to adequately specify the 

experimental procedure. Such identification does not imply 

recommendation or endorsement by NIST, nor does it imply that 

the materials or equipment identified are necessarily best for the 

purpose. 

Although a shared trigger signal provides a solution to 

simultaneous measurements, the trigger itself needs to be reliable, 

repeatable, and controllable. We use a digital function generator 

that can be programmed to produce a clean squarewave signal. 

The digital function generator also allows us to start and stop the 

signal with a push of a button. The resulting signal is 

deterministic and free of the button-bouncing effect typically 

associated with inexpensive analog function generators. 

The data collection programs maintain their own sequence 

number, which is increased each time a trigger signal is received. 

In addition, the program time-stamps the sequence number with a 

microsecond timer from the computer clock. Both systems 

synchronize their computer clock with a NTP (Network Time 

Protocol) server every 10 s throughout the entire data collection. 

For data to be a matched pair, we require them to have the same 

sequence number. In addition, we check the difference between 

the corresponding timestamps and verify that the difference is 

small (i.e., the difference should never be greater than the period 

of the trigger signal shared by the two systems). 

4.3 External Calibration Issues 

To evaluate data collected during the experiments, we need to 

define metrics to compare the 6DOF pose data collected by the 

API T3/STS laser tracker and the Purdue line tracking system. 

There are eight coordinate systems involved, defined in Figure 2. 

We want to establish relationships between data collected in the 

coordinate system T of the laser tracker and one more coordinate 

systems of the Purdue system. We use the notation to 

denote the homogenous transformation from coordinate system Y 

to X, so H T W is a transformation from W coordinates to T 

coordinates. The 6DOF pose of the object O in the T3 coordinate 

system would be represented by . OH T

Figure 2. The coordinate systems of the Purdue Line Tracker 

and the STS/T3 Tracker System 

176
Figure 3. The world coordinate system 

External calibration provides an estimate of the homogeneous 

transformation matrix (H) between the world W, and the robot 

base B, where W is defined by the calibration pattern behind the 

target as shown in Figure 3. 

If we can successfully use the laser tracker coordinates T to 

establish the transformation HT r W H tween the world 

(W) and T3, we can relate the coordinate T to the robot base B 

coordinate as in Equation 1. 

W o T be

X 

Y 

Z 

Figure 4. The object coordinate system (Y=OB, Z=up) 

We don't have direct access to the origin of the engine cover O 

coordinates. Instead we use the Cartesian positions of three 

features (A,B,C), to reconstruct the coordinate frame for O with 

respect to coordinate T (see Figure 4). 

We use the T3 laser tracker with an SMR to measure A, B and C 

in T coordinates. We then compute the origin O as the midpoint 

between A and B, and use the position of C to complete the object 

reference frames. Hence we construct T or . 

Similarly, we constructT by measuring the origin of W. 

OH T H O

HW

T HS OHS

u HHH OTTSOS

Given from T3/STS system, we obtain from 

Equation 2. 

 Eq. 2 

Using Equation 1 and Equation 2, we establish transformations 

between the T3 base system T and the object system O in both the 

T3 and Purdue system, and compare those two transformations. 

The ground truth transformations provided by the T3/STS are on 

the left hand side, and the measurements provided by Purdue 

system and the hand-eye calibration are on the right hand side: 

u u u HHHHH OBBWOSSTTW Eq. 3 

HO This gives the relationship (laser) W W HO (visual)

H

 and the 

inverse between the two systems in a common coordinate system, 

where visual stands for the Purdue tracking system. 

Now we relate the two estimations of the inverse O W in the 

world coordinate system. In Equation 3, the calibration error in 

 , and W can’t be eliminated, so the absolute 

measurement approach was not used in this paper. 

T W H OHS B H

Oi H

Since the Purdue system is a tracking system, the differential pose 

with respect to time is computed every cycle. It is reasonable to 

compare the differential pose between ground truth and the 

Purdue system using the world coordinates. We define W (P)

GH )( Oi W

)()()( 1 1 Oi uWW Oi OiOi  PHPHPH

)()()( Oi WW Oi1 GHGH Oi  u 

)( OiOi 1 GH

)( 1 Oi PH

u HHH BWWTBT

as the pose of the engine part in the world coordinate at time i for 

the Purdue Tracking system as the pose of the engine 

part in world coordinate at time i for the ground truth system 

(laser tracker). 

We can then obtain the following relationships for each system 

between time i and time i+1: 

 

Oi 1 GH

As one can see from the above derivation, the differential 

measurement will not depend on coordinate system. This 

approach produces the same numerical result for 

and Oi in any coordinate system. 

5. EXPERIMENTAL RESULTS 

We present here preliminary results from a series of experiments 

conducted at Purdue in April, 2008. The protocol was to run three 

sets of experiments, one with the target stationary, one with the 

target moving with a simple linear velocity, and one with the 

target moving with a linear velocity but randomly displaced 

manually by the experimenters. The results are given below for 

the three sets. 

The experiment had two complications. One is that the calibration 

of the laser tracker and Purdue system proved difficult and we 

were not able to establish a full set of coordinate transformations 

between laser tracker and visual system data. We did establish 

enough to compare relative poses, which are reported. Also, the 

Eq. 1 

177
Purdue system is both a visual tracker and a robot control system. 

The data may at times confound the effects of both subsystems, as 

the robot introduces a physical motion. We only wished to 

evaluate the performance of the visual tracker. 

5.1 Stationary Tests 

The stationary tests allowed us to evaluate the basic performance 

of both systems and assure that the laser tracker was performing 

to specifications after shipping. The target was placed in four 

positions and data collected for 15 to 30 seconds for each. The 

results showed that both systems performed within specifications. 

Table 1 lists the standard deviations of the stationary data set 

measured by the STS/T3 system. The results are consistent with 

the specifications [7]. The laser tracker stayed in a fixed position 

so the target distance varied. 

Table 1. STS/T3 system: repeatability for stationary data 

Sample 

Size 

T3/STS mean 

distance (mm) 

2 std 

(mm) 

Position 1 466 3550.054 0.006 

Position 2 1157 3781.466 0.006 

Position 3 1050 3882.787 0.005 

Position 4 1018 4002.035 0.008 

Table 2 lists the standard deviations of the stationary data set 

measured by the Purdue system. The Purdue system moves the 

robot end-effector near the object, so the distance remains 

relatively constant. The results show a consistent value near 0.6 

mm at a range of approximately 2.6 m. 

Table 2. Purdue system: repeatability for stationary data 

Sample 

Size 

T3/STS mean 

distance (mm) 

2 std 

(mm) 

Position 1 466 2670.582 0.629 

Position 2 1157 2625.820 0.582 

Position 3 1050 2625.036 0.560 

Position 4 1018 2636.701 0.561 

For use as a reference system, a metrology technology should 

have an accuracy at least one order of magnitude greater than the 

system under test. In this case, the laser tracker is two orders of 

magnitude more accurate than the Purdue vision system. 

5.2 Linear Motion Tests 

In the linear motion tests, the target was moved about 1.5 meters 

left to right and tracked by both the laser tracker and the Purdue 

system. For each trial, the motion was repeated 30 times as the 

target moved, and then was quickly moved back to the start 

position. The backward sweep was ignored in the data analysis as 

the Purdue system only tracked during the forward motion. 

The differential motion as measured by both systems was used to 

determine the consistency between laser tracker and Purdue 

system. In effect, the comparison is being made on the measured 

speed of the target in each separate coordinate (X,Y,Z, roll, pitch, 

yaw). 

The data below are from pass 6 of the first trial, and are typical of 

the linear runs. The sample size is 453, with 33 ms between data 

points. In the graphs below the horizontal axis is frame number, 

and the vertical axis is the difference between the laser tracker 

motion change (delta) in each coordinate and the Purdue system 

delta. Since the laser tracker was accepted as ground truth, the 

difference is defined as the error in the Purdue system. 

In Figure 5 the errors can be seen to be consistent and relatively 

independent of position along the path, although that is yet to be 

evaluated statistically. The error does vary by coordinate – 

different coordinates proved to be more sensitive to the left-toright motion. In object coordinates the target is moving in the YZ plane, primarily in the Y direction, and the Z coordinate has 

slightly less error. Similarly, the roll angle is around the X axis, 

and proved an order of magnitude reduced in error over the other 

rotations. Table 3 quantifies the error values, while Figure 6 gives 

a histogram of the error values to show roughly symmetric, zero 

centered error distributions. For coordinate Y there appears to be 

a secondary peak in positive error. 

Figure 5. Pass 6 – Coordinate Errors in Delta vs. Frame 

Number 

Figure 6. Pass 6 – Coordinate Errors in Delta (histogram) 

178
Table 3. Pass 6 – Coordinate Error Statistics (n=453) 

 Mean Std Max Min 

X in mm 0.01614 0.45376 1.49003 -1.41190 

Y in mm -0.03513 0.33355 1.27399 -1.32852 

Z in mm 0.05206 0.21991 0.74652 -0.69851 

distance -0.04305 0.33273 1.21320 -1.50436 

Roll in deg 0.00168 0.04915 0.14368 -0.16532 

Pitch in deg 0.00088 0.40811 1.21672 -1.27938 

Yaw in deg 0.00184 0.21589 0.56194 -0.71260 

Total angle -0.04798 0.05195 0.03383 -0.28635 

5.3 Shaking Motion Tests 

In the shaking motion tests, the basic target motion and repetitions 

were identical to those in the moving target test, but the 

experimenters could pull a string to swing the target with an 

impulse motion. This was done through a series of different 

motions – first with no extra motion to match the linear case, then 

with the impulse motion varying by amplitude and frequency. 

The data below are from pass 3 of the first shaking motion trial. 

The sample size is 455, with 33 ms between data points. In the 

graphs below, the horizontal axis is frame number, and the 

vertical axis the difference between the laser tracker delta in each 

coordinate and the Purdue system delta. 

Figure 8. Pass 3 – Coordinate Errors in Delta vs. Frame 

Number 

The graphs show four impulse motions as the target was pulled 

back four times, relatively smoothly and consistently. The error 

first goes positive as the speed of the target slows down and the 

Purdue system undershoots the speed, and then negative as the 

Purdue system overshoots the speed. The graph scales have 

changed from the linear motion case, as the error range has 

approximately doubled. The Z axis remains the one with lowest 

error, while the roll angle error is greater compared to the linear 

motion tests as the impulse motion rotated the target around the 

X-axis. 

6. CONCLUSIONS 

In this paper we have demonstrated the use of a precision laser 

tracker to evaluate a state-of-the-art visual servoing perception 

system, with the objective of establishing general techniques for 

evaluating 6DOF sensors. The demonstration involved a 

synchronized data collection system that used a hardware trigger 

to collect at a 30 Hz rate, while the laser tracker has the ability to 

collect at up to 150 Hz. The laser tracker was verified accurate 

enough for the approximate 1 mm range of error that needed to be 

measured. 

Future work will involve a more detailed analysis of the data and 

the establishment of better calibration techniques and metrics to 

insure consistent comparisons between laser tracker and sensor 

data streams. 

Figure 9. Run 6 – Coordinate Errors in Delta (histogram) 

Table 4. Run 6 – Coordinate Error Statistics (n=453) 

 Mean Std Max Min 

X in mm 0.00219 1.13255 2.90429 -3.32659 

Y in mm -0.04633 1.26350 2.21070 -3.62808 

Z in mm -0.01445 0.58950 1.42051 -1.53047 

distance 0.90879 0.95975 3.77670 -1.84237 

Roll in deg 0.00362 0.30460 0.87745 -0.78979 

Pitch in deg -0.00329 0.50645 1.48264 -2.10615 

Yaw in deg 0.00103 0.23520 0.61750 -0.76112 

Total angle -0.42713 0.30752 0.15745 -1.51979 

7. ACKNOWEDGMENT 

We thank Elena Messina and Hui-Min Huang for the fruitful 

discussions. We thank Nick Scott, Alan Lytle, Chris Blackburn, 

Daniel Sawyer, Steve Phillips from NIST , Avi Kak from Purdue 

University, Jane Shi from General Motors , and Kam Lau, Alan 

Cui, Zaifeng Chen from API for their collaborations. 

179
8. REFERENCES 

[1] Chai, X., Shan, S., Qing, L. and Gao, W. 2006 Pose 

Estimation Based on Gaussian Error Models, International 

Conference on Biometrics, 2006: 136-143 

[2] Deguchi, K., 2000 A Direct Interpretation of Dynamic 

Images with Camera and Object Motions for Vision Guided 

Robot Control. International Journal of Computer Vision 

37(1): 7-20 (2000). 

[3] DeSouza, G. N. and Kak, A. C., 2004, A Subsumptive, 

Hierarchical, and Distributed Vision-Based Architecture for 

Smart Robotics, IEEE Transactions on Systems, Man, and 

Cybernetics -- Part B: Cybernetics, 34(5): 1988-2002. 

[4] Espiau, B., 1993 Effect of Camera Calibration Errors on 

Visual Servoing in Robotics. Experimental Robotics III, The 

3rd International Symposium, Kyoto, Japan, October, 1993: 

182-192. 

[5] Fiore, P. D, 2001 Efficient Linear Solution of Exterior 

Orientation, IEEE Trans. Pattern Analysis and Machine 

Intelligence, vol. 23(12): 140-148, 2001 

[6] Hirsh, R., DeSouza, G. N. and Kak, A. C., 2001 An Iterative 

Approach to the Hand-Eye and Base-World Calibration 

Problem, Proceedings of the IEEE International Conference 

on Robotics and Automation, Seoul, May 2001 

[7] Hutchinson, S.A., Hager, G.D., and Corke, P.I, 1996 A 

tutorial on visual servo control. IEEE Transactions on 

Robotics and Automation, 12(5):651--670, October 1996. 

[8] Kyrki, V., Kragic, D., and Christensen, H. I., 2006 

Measurement errors in visual servoing. Robotics and 

Autonomous Systems 54(10): 815-827 (2006) 

[9] Madsen, C.B, A comparative study of the robustness of two 

pose estimation techniques. In H.I. Christensen, W. Förstner, 

and C.B. Madsen, editors, Proceedings: ECVnet Workshop 

on Performance Characteristics of Vision Algorithms, held in 

conjunction with Fourth European Conference on Computer 

Vision, Cambridge, England, pp. 181 - 200, April 1996. 

[10] Preisig, P.. and Kragic, D., 2006 Robust Statistics for 3D 

Object Tracking. Proceedings of the Int. Conference on 

Robotics and Automation, Orlando, Florida, 2006. 

[11] Chai, X., Shan, S., Qing, L. and Gao, W. 2006 Pose 

Estimation based on Gaussian Error Models, Proceeding of 

International Conference on Biometrics (ICB2006), Lecture 

Notes on Computer Sciences (LNCS3832), D.Zhang, A.Jain 

(Eds.), pp136-143, Hong Kong. 

[12] Reid, G. J., Tang J., and Zhi, L., 2003 A complete symbolicnumeric linear method for camera pose determination, 

International Symposium on Symbolic and Algebraic 

Computation, Philadelphia, Pennsylvania 2003: 215-223. 

[13] Rivera-Ríos, A. H., Shih F. L, and Marefat, M. M. 2005 

Stereo Camera Pose Determination with Error Reduction and 

Tolerance Satisfaction for Dimensional Measurements, 

Proceedings of the Int. Conference on Robotics and 

Automation, Barcelona, Spain, 2005: 423-428. 

[14] Sepp, W., Fuchs, S. and Gerd Hirzinger. 2006 Hierarchical 

Featureless Tracking for Position-Based 6-DoF Visual 

Servoing, Proceedings of the IEEE/RSJ International 

Conference on Intelligent Robots and Systems (IROS) 2006, 

Beijing (China), 2006 

[15] Tonko, M. and Nagel, H. 2000 Model-Based StereoTracking of Non-Polyhedral Objects for Automatic 

Disassembly Experiments, International Journal of Computer 

Vision 37(1): 99-118 (2000). 

[16] Yoon, Y., DeSouza, G. N. and Kak, A. C., 2003 Real-time 

Tracking and Pose Estimation for Industrial Objects using 

Geometric Features, in Proceedings of the Int. Conference in 

Robotics and Automation, Taiwan, 2003 

[17] Yoon, Y., Park, J. and Kak, A.C. 2006 A Heterogeneous 

Distributed Visual Servoing System for Real-time Robotic 

Assembly Applications, in Proceedings of the Int. 

Conference on Robotics and Automation, Orlando, Florida, 

2006. 

[18] SMARTTRACK SENSOR, Automated Precision Inc., 

http://www.apisensor.com/PDF/SmartTrackeuDE.pdf, 2007. 

180
Integrating Reification and Ontologies for Mobile

Autonomous Robots

J. P. Gunderson

Gamma Two, Inc.

209 Kalamath Street, Unit 13

Denver, CO, USA

jgunders@gamma-two.com

L. F. Gunderson

Gamma Two, Inc.

209 Kalamath Street, Unit 13

Denver, CO, USA

lgunders@gamma-two.com

ABSTRACT

A significant problem that has plagued autonomous mobile

robots is the need to reason about a complex and dynamic

world in a timely fashion. Huge strides have been made in

artificial intelligence systems that deal with symbolic representations, and the hardware for robotics has seen significant

growth. However, autonomous robots have not seen equivalent improvement. In this paper we examine a technique

to couple deliberative reasoning systems with mobile robotic

platforms to enable the robot to reason about the world.

Mobile autonomous robots operate under extremely tight

constraints in power and computational loads, and must be

responsive to the dynamic environments in which they are

deployed. Since they do not have the luxury of operating

in a static, controlled environment, they must be capable

of quickly recognizing changes to the environment, assessing

the impacts of these changes, and implementing intelligent

responses to those changes. All of these requirements must

be met in a real-time environment, using limited computational resources. Since living organisms also operate under

these same constraints we present a design that is biologically principled. This design integrates both reactive and

deliberative components using a biologically principled component called a Reification Engine.

The Reification Engine acts as a bi-directional bridge

between the sensor domain and the symbolic domain. It provides the ability to map the changes detected by the sensors

into a symbolic representation, which is expanded by the onboard ontology to generate a semantic representation of the

salient aspects of problem. This, in turn, can be analyzed by

a deliberative system to generate a planned response to the

changes, which can be mapped by the Reification Engine

back into the sensor/effector space of the robot’s hardware.

Keywords

robotics, ontology, reification, artificial intelligence, autonomy, biologically inspired computing

Permission to make digital or hard copies of all or part of this work for

personal or classroom use is granted without fee provided that copies are

not made or distributed for profit or commercial advantage and that copies

bear this notice and the full citation on the first page. To copy otherwise, to

republish, to post on servers or to redistribute to lists, requires prior specific

permission and/or a fee.

PerMIS‘08 August 19 - 21 2008, Gaithersburg, MD, USA

Copyright 2008 ACM 978-1-60558-293-1 ...$5.00.

 	
 
 

 

 



Figure 1: The four major components of an autonomous robotic system. The Reasoning component provides the ability to determine how to

achieve goals. The Robot Chassis enables the system to execute the behaviors in the physical world.

The middle components - the Ontology and the

Reification Engine, translate between the symbolic

and the sensor-based domains.

1. INTRODUCTION

This research has been driven by a single question: “Where

is my Robot?” The last few decades have seen an explosion

in robotic systems in many domains, including factory and

laboratory automation[6, 11, 15, 22, 23], deep sea exploration[1, 12, 5], and exploration of deep space[20]. At the

same time we have seen the use of teleoperated systems in

search and rescue, bomb disposal, and surveillance aircraft;

all of which have saved lives. However, we have not seen an

equivalent explosion of autonomous systems.

An autonomous robot can be modeled as a system consisting of four major components. The first of these is the

physical manifestation of the robot - the sensors, effectors,

and electronics that make up the hardware. Since an intelligent, autonomous robot is being considered, the second

major component is the software that makes up the ‘brains’

of the autonomous robot. The reasoning component operates in a purely symbolic domain: it manipulates symbols

according to abstract rules. Between the reasoning and execution components lie two others - a mechanism to link

meaning to those abstract symbols (the ontology), and a

reification mechanism[9] that bridges the gap between these

symbols and the physical domain. The ontology and the

Reification Engine are the interface between the ‘brains’

and the ‘brawn’ - they translate between the domain of sensors and effectors into the domain of symbols and semantics.

These four components are shown in figure 1.

In this paper we will focus primarily on the interaction

between the ontology and the Reification Engine. Rather

than focusing on any specific robotic chassis, we will refer

to an abstract perception/action system. In the same way

we will refer to a generic deliberative system, rather than

181
any specific architecture for the generation of behaviors or

plans. We will focus on specific implementations of the ontology and the Reification Engine, since we are exploring

the integration between the mechanisms used to represent

knowledge in these two components.

2. REASONING

For most of its history, artificial intelligence has been focused on reasoning. Some of the earliest AI programs were

designed as problem solvers[13, 7], planners[18], or designed

to excel at games like checkers[19]. These programs manipulated symbols according to specific rules, and searched

through solution spaces to find plans that would achieve the

system’s goals. These systems frequently relied on ad hoc

representations of the symbols and their allowed manipulations.

Recently there has been more research into the use of ontologies as a standardized format for representing the meaning of symbols. The reasoning components of the ontology

use the relationships between the concepts as rules controlling the manipulation. In some systems, the ontology fills

the role of semantic memory in humans: a large diverse,

persistent storage of all available knowledge. Since only a

small portion of the entire knowledge base is needed for any

specific problem, a subset of the ontology is used to generate

the actual problem that the reasoning system processes (See

[10] Chapter 9 for more information). With mobile robots,

these ontologies must not only capture the abstract concepts

that are the focus of much of the research, they must also

capture the knowledge associated with the physical domain

in which the robot functions.

2.1 Personal Rough Ontologies

Current research into artificial intelligence has addressed

the need for an intelligent system to have a complex and detailed body of knowledge to function effectively in a complex,

dynamic, and uncertain world. Unfortunately, these ontologies are not well suited to deployment into autonomous

robots, since they tend to be computationally expensive.

However, an autonomous robot has a critical need for the

ability to reason effectively about the world into which it

is deployed, especially in unconstrained environments. We

demonstrate how the integration of a Reification Engine

with an ontology tailored for a robot’s needs can enable the

robot to function more effectively in a dynamic world.

We utilize a biologically principled form of an ontology,

designed for effective integration into an autonomous robot.

The key differences lie in the area of completeness and consistency. Most living systems do not have complex truth

maintenance systems analyzing every new fact or belief that

is added into their cognitive systems. In spite of this, they

far outperform most autonomous robotic applications. We

have extended (or crippled, depending on one’s viewpoint)

ontologies so that they can contain inconsistent data without causing logical operations to result in invalid states. This

is done by controlling the deductive reasoning to a limited

distance within the ontological graph. This has two significant benefits to autonomous robots. First,the computational complexity of navigating the ontological graph is dramatically reduced, since the expansion of edges eventually

tapers off to zero. Second, this mechanism acts as a focus

of attention which enables the extraction of a small, salient

subgraph to be used by the deliberative system for problem

solving - thus dramatically reducing the computational burden of the planning system. Because of this lack of truth

maintenance we call this a rough ontology. Since the system

will modify its ontology based on personal experience, we

call this a personal rough ontology (PRO).

The basic structure of an ontology is a directed multigraph:

Ontology ≡ (C, E) (1)

where: C is a collection of nodes; and

E is a collection of directed edges from

one node to another.

2.2 The nodes in the multi-graph

Referring back to Equation 1, we see that the multigraph

consists of a collection of nodes and a collection of directed

edges. Each node C corresponds to a symbolic representation of an entity. The base class for these nodes is a Cept,

hence the non-traditional use of C in equation 1. Each Cept

may have a collection of properties that describe it. These

properties are used in two ways. First, the ontological system can use these properties when applying rules, and second, the deliberative system uses these properties to develop

plans to achieve its goals. To facilitate these uses, the properties are represented as specific relationship arcs to other

Cepts.

Cept(C) ≡ (symbol, {P}, {R}) (2)

where: symbol is the symbolic representation of

the concept (its name);

{P} are the properties; and

{R} are the relationships to other Cepts.

The Cepts in our ontology represent the things about

which we have knowledge. These things correspond to the

subject and object of the relationships. The common element of these things is the symbol and the list of properties.

This base class is extended to represent specific types of

knowledge in the ontology.

The simplest variant of a Cept is a ConCept. This is what

is represented in a typical ontology. The ConCept extends

the basic Cept by adding the idea that a ConCept can represent either an abstract concept or something more concrete.

As an example, the ConCept of a chair represents a perceptible thing that might exist in the world; however the ConCept

of ‘laid-back’ is not something that is directly perceptible.

In the case of perceptible ConCepts, the Reification Engine has the responsibility of maintaining the mechanisms

that allow the recognition of objects in the real world, and

linking those perceived objects to the symbolic representations. This is done by adding a link from each perceptible

thing in the ontology to a data structure called a PerCept,

maintained by the Reification Engine, described in Section 3.

Much as the ConCepts correspond to nouns, the world is

also full of verbs - the actions and events that cause change.

Although knowledge about actions may seem to be fundamentally different than knowledge about things, they are

still symbolic representations about the world. In the chair

discussion above, it seemed natural that there would be a

relationship between a chair and the concept of sitting, just

as there seems to be a natural relationship between a bicycle and riding or a ladder and climbing. Note that the

182
conceptual symbol associated with sitting differs from the

mechanics of lowering ones body into a seated position -

that is a function of the perception/action system.

To represent the conceptual model of an action, we modify the base Cept class. This subclass is called an ActCept

in the ontology. The base class is extended by adding two

additional components - the conditions under which the action can be taken (e.g., to drive the car it is necessary to

have a car), and the possible outcomes of acting (you might

get where you want to go, or you might run out of gas). The

enabling conditions and outcomes can be directly mapped

onto the corresponding components of the action representation used by the deliberative system, and so the semantic

memory fulfills its design goal of being the repository of

knowledge for the reasoning system.

2.3 Relationships, the Edges of the Graph

Each edge in the multi-graph is a directed arc that leads

from the subject node to the object node. Directed arcs are

needed since not all relationships are symmetric, for example, if the type of the relationship is part of, it makes sense

to say that a leg is part of a chair; however the reverse is not

true. Each edge captures one specific type of relationship.

The representational schema for the arcs is:

Edge(E) ≡ (C, I, N, T, S, L) (3)

where: C is the class of

the relationship;

I is the unique identifier;

N is the destination node;

T is the transitivity;

S is the strength; and

L is the likelihood

that the relationship holds.

Each relationship E is an instance of a class of relationships. While the ontology is very generic, there seem to be

a number of relationship types that are common across ontologies for systems embedded in the physical world. These

include relationships like is a, has a, is part of, and is at.

To facilitate the encoding of capabilities we also add can do

which is the relationship between a ConCept and an ActCept

that it is capable of executing.

2.4 Transient versus Persistent Knowledge

Knowledge changes over time. While many ontologies are

designed to capture the relationships between permanent

concepts such as what it means to be a mammal or what

the definition of a prime number is; there is also a need

to represent more transient information. There is a vast

amount of relatively transient knowledge, far more than can

be maintained in working memory at any point in time.

So there must be a more permanent storage place. We

include this transient knowledge in the form of properties

attached to the ConCept, and use a specific relationship

instance of to link the individual ConCept to the framework of knowledge of more abstract concepts. In practice

we have two specialized relationships for handling instance

ConCepts: thing instance and location instance. These are

used to provide the linkage from the specific instances to two

corresponding nodes in the ontological frame work. These

are labeled as Place and Thing.

In addition, there are instance ConCepts that appear and

disappear from our knowledge base. We often encounter new

people in our day to day interactions. While some of them

may become friends or colleagues, many will be a single,

short-term encounter. While we are interacting with them,

we need to access the complex web of knowledge we have

of people, and this can be done by instantiating an ‘anonymous’ person ConCept. This provides access to generic background information that allows us to reason about this person, but we do not need (or want) to clutter our ontology

with references to every person we have ever encountered in

our lives.

The final type of symbolic knowledge is knowledge about

the current state of the world. In order for the planning

system to work it needs a relatively accurate model of the

state of the world. This is contained in the Current World

State (CWS). The CWS is the symbolic representation utilized by the deliberative system. A more spatially detailed

representation, called a Mental Model is used by the Reification Engine. When the robot encounters an object in

the real world, it attempts to classify the object, so that

a semantically tagged representation can be added to the

CWS. The CWS includes knowledge about the permanent

persistent features of the world, and it contains information

about the current state of previously encountered transient

objects. However, there is no pre-existing representation for

an object that is encountered for the first time.

As an example, consider a robot serving drinks at a cocktail party. It knows about the general layout of the room

- the walls, the big furniture, etc. This is permanent and

persistent data. It also knows about a few smaller chairs,

which are permanent, however, their current location may

change as the chairs get moved around. It does not have

instantiated representations for all the people who might

arrive. Rather, when the robot encounters a new object, it

will attempt to classify it. Using its sensor data, and the

PerCepts that correspond to the currently instantiated objects, if the object can be classified, both the CWS and the

Mental Model are updated with the new knowledge. If it

fails to classify the object, it then accesses the PerCepts

associated with more general concepts. For example, the

PerCept for a generic Person has a high probability of a

match, and the Reification Engine uses this to instantiate a new object in its CWS. This object is not permanent

- rather it is transient. It comes into existence, and, after

not being reinforced, it vanishes. In this way the size of the

ontology is not ever increasing with references to concepts,

objects, and entities that will never be accessed again.

3. REIFICATION ENGINE

The bi-directional mapping between the symbolic representations used by the ontology and the sensor based representation utilized by the perception/action system of an

autonomous robot is called reification (See Robots, Reasoning, and Reification[10] for more detail). This process is

derived from current research in cognitive science and neurophysiology. There has been research into the two areas of

Symbol Grounding (mapping symbolic representations onto

sensor based leaf terms) and Pattern Recognition (projecting from sensor based data onto symbolic representations).

One belief is that either of these approaches, if continued

sufficiently, will bridge the Sensor/Symbol gap. We believe

that there is no overlap between these two research areas,

and that a separate process - reification - is used by living

systems when they perform these mappings.

183


	







	







	 
	 


	



	

 

Figure 2: The structure of the Reification Engine

interactions with both the PRO and the Deliberative System. Due to the tight coupling of these systems, and the central role played by the Reification

Engine, the representations and services provided

by this system are highly specific to the underlying

sensors and actuators as well as the semantic representations needed by the deliberative system.

Reification provides these two services - mapping sensor data onto symbols and mapping symbols onto sensor

representations. The first of these pathways corresponds

closely to pattern recognition, and is treated as such in the

Reification Engine. The latter pathway is called preafference, after a term used by Walter Freeman[8]. Research

has shown that living systems significantly reduce the cognitive load associated with making sense out of the world by

loading their sensory cortices with approximations of what

they expect to perceive. If these approximations are close

enough, the higher cognitive functions are left out of the

loop, and the entity functions as a reactive system. However,

if there is enough of a discrepancy between the expected and

the actual, then the more expensive cognitive functions are

brought on-line to re-evaluate the situation, and generate

new solutions.

3.1 Reification Architecture

To bridge from the symbolic domain into the sensor domain and back again, the Reification Engine must have

one foot on each shore. The architecture of the Reification Engine is shown graphically in Figure 3. There are

three main components in the Reification Engine. The

core component is the library of PerCepts, which provide the

grounding in the sensor domain. Using these PerCepts, the

Reification Engine maintains a model of the world, this

  	

 




 


 


 	
 	 		

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Figure 3: Using the PerCept datasets, the Reification Engine maintains a Mental Model of the things

in the world, and their current state. This is used

to create a symbolic representation of the Current

World State, which is used, in turn, by the deliberative System. The Mental Model is used to both

simplify the recognition of sensor data (e.g. turning

it into symbolic information) and to generate preafference images of what the world would look like if

a predicted change were to occur.

Mental Model captures the sensor-derived knowledge about

what things are out there, where they are, and how they are

oriented. Finally, the Reification Engine manages a symbolic representation of the world. This CWS is provided to

the deliberative system, by way of the PRO. The library of

PerCepts capture the structural description of things in the

world that are perceivable.

In our model a PerCept is the data structure used to hold

the information associated with a perceived object. The

PerCept has two components: a sensor derived signature

that can be used to recognize the occurrence of the object,

and a symbolic component that links to the semantic representation in the ontology. In addition to these two data

components, the PerCept provides some basic functionality to the Reification Engine. Each PerCept is associated

with a single class of perceivable object. These PerCepts

have a symbolic tag (think of it as a name) and the sensory

definition of the object.

Imagine a chair. Many of us maintain a complex hierarchy

of chair types in our minds. There are kitchen chairs, office

chairs, recliners, chairs with wheels, chairs without backs,

chairs with padded seats, chairs that creak ominously when

we sit in them. There are specialized chairs: seats in automobiles, benches, couches, dentist’s chairs, and the ‘naughty

184
chair’ where children have to sit if they have misbehaved.

Yet, in spite of the array of possible chairs, we seem to have

a generalized concept of chair, at least enough to answer the

question “Is that a chair?” Much as in Plato’s notion of the

Ideal, or the concept of a ‘class’ in object-oriented programming, we have a complex structure of symbols that correspond to the different types of chairs. We can utilize those

symbols to reason about the types of chairs we encounter.

The PerCepts have one foot in this complex symbolic structure. Each PerCept requires a symbolic tag that links into

the semantic knowledge used by the deliberative system. If

the ontology has information that there exists Jim’s chair

which is a specific instance of a short wheeled chair; then

there must be a PerCept that is identified by the semantic

tag short wheeled chair, and there must be a thing in the

Mental Model which corresponds to the current state (perhaps position and orientation) of Jim’s chair.

The PerCepts also have one foot deep in the sensor world.

This sensor based representation is defined by the physical abilities of the body of the system. Each robot has its

own types and placement of sensors, so the things that it

perceives can and will have different sensor representations.

This is true in biological systems as well. We, as humans,

are very sight oriented[24], and so we attach visual representations to our semantics. We use vision as a primary

metaphor for understanding - do you see what I mean? Look

at it this way - at the beginning of the last paragraph, you

read the words “Imagine a chair.” For many of you, a visual

image formed in your mind. However, other species have

very different sensor modalities, and so their percepts will

vary considerably. Imagine a human, a dog, and a bat encountering the same insect. While the human would focus

on the appearance of the insect, the bat would more likely

form an acoustically based ‘image’ of the bug, and the dog

would generate a scent based model of great complexity.

We utilize a data-driven representation of the sensorium

that corresponds to the object represented by the PerCept.

This model is based on Brunswik’s lens model[4]. There are

two primary reasons for this approach, one is that it ensures

a direct correspondence between the mental model of the

thing and the perception of the thing. We create a dataset

which can be used as a template. This template can be

‘filled in’ with the specifics of the location and orientation,

and other details, to generate what the sensors would perceive. This contrasts with a more analytic representation of

an object and the necessary transforms that could be used to

generate the sensorium. There are several advantages to the

dataset approach. Since the identifying characteristics are

data, the Reification Engine can generate new PerCepts

by creating new data representations. If the analytic representation were used, the system would need to generate new

functions and add to its code. Of course, there is a significant

disadvantage to the dataset approach: the datasets can get

large, and are complex. The penalty we pay for the ability

to learn is that much of the mechanism of the Reification

Engine is dedicated to managing the PerCepts to provide

the functions of preafference and recognition.

3.2 Recognition

The Reification Engine uses the PerCepts to recognize

the state of the outside world. A simple brute force approach

would be to take the sensor data and attempt to match it

against every possible PerCept in the library. Of course

there might be a large number of PerCepts in the library,

each of which could be at any possible distance and a number of possible orientations. The computational complexity

of this task is daunting to say the least. We know that living

systems perform this process quickly and (in general) reliably. We also know that computer-based recognition is (in

general) neither.

We take advantage of the fact that sensing does not occur in a vacuum. Sensing and perception are one step in

a continuous cycle, which was preceded by an earlier perception stage. One of the core functions of reification is to

maintain a (more or less) continuous model of the PerCepts

that correspond to the state of the world[17]. The PerCepts

from the last perception, and the Mental Model built from

them, can be used as a guide to shorten the subsequent

perceptual process. This is based on the concepts of ‘thing

constancy’[21] and ‘object constancy’. In effect, the things

that we perceive do not (in general) magically appear or disappear. Thus, we evolve the previous model of the world,

based on our knowledge of what activities are occurring, and

predict the ensuing state of the world. With this predicted

model, we can confirm what we expect to see, at a far lower

computational cost than approaching the perceived world de

nova.

3.3 Preafference

The second function that the Reification Engine supports is the projection of the model onto the world. Preafference is the process of taking the Mental Model of the world,

and generating the view that the robot would see, if everything were like the model. This process produces a virtual

reality(VR) representation of the world as it is expected to

be. In effect, the Reification Engine acts as a rendering

engine for the mental model of the world. This rendered

image is used to speed up the process of confirming that the

world is pretty much what we expect. Fortunately, much of

the machinery needed to perform this function is shared by

the recognition task. It is only needed to use these functions in a different way to generate a preafference image,

rather than to recognize the objects in the world. Just as

a physical lens bends light regardless of the direction, our

cybernetic lens can be used to either project the sensor domain into the symbolic, or project the symbolic domain into

the sensorium.

To do this projection into the sensor domain, we take advantage of the fact that the Mental Model has a list of the

objects that are expected to be in the world, and their positions, orientations and properties. With this information,

and the machinery of the PerCepts, generating this rendered

image is relatively straight forward. In the case of a sonar

based perception system, this rendered image is a sonar image of what the sonars would return. The generation of this

image is done in three stages:

1. Select the objects that are in the field of view of the

robot;

2. Use the PerCepts, the pose of the object, and the pose

of the robot to generate individual images; and,

3. Fuse these individual images into a composite image.

The first of these steps is simply done to reduce the computational burden of the full process. Rather than attempting to build the sensor images of objects that might be in

185
another room, or even attempting to generate a complete

360◦ panoramic view, we only generate images for objects

that are likely to be in view. This is the same process that is

used in VR rendering systems in the form of bounding surfaces[16]. The Reification Engine uses the sensor parameters for the specific sensors, and slightly over estimates the

field of view of the robot. This angular interval is compared

with each of the individual objects. We take advantage of a

function of the PerCept that calculates the perceived angular extent of an object, based on its position and orientation,

and the position of the robot. A quick test to see if the two

intervals overlap is sufficient to determine if this object is in

the field of view.

The final step is for the Reification Engine to fuse these

individual views into a complete sensor image. If there is

only one object generating a sensor image, this task is trivial. The difficulties arise when there are multiple objects in

the field of view and there are occlusions (e.g., one object

generates a return that blocks the view of another object).

This is a common occurrence as the resolution of the sensor

increases. However, the techniques for resolving occlusions

have been well tested in visual rendering software. Utilizing the information encoded in the individual returns, and

the relative positions of the robot and each item, it is fairly

straight forward (if computationally intensive) to generate

a final rendered sensor image. This final preafference image

can be quickly compared against the actual sensor image to

see if there are major discrepancies.

3.4 Updating the Current World State

The final task of the Reification Engine is to take the

changes that have been made to the Mental Model, and

project them into the semantic space of the Current World

State. This process requires the translation from the sensor

driven, numerically based information in the Mental Model.

The key support structures for this translation are representations that link the semantic terms utilized by the deliberative system, with representations that are consistent with

the PerCepts. For example, The Mental Model maintains

precise locations of the objects that the robot knows about.

However, the deliberative system does not model the location of objects at this resolution. It keeps track of the fact

that the chair is over by the assembly bench, not that it is at

coordinates X=10,100, Y=500. So the Current World State

must maintain information at the level of detail needed by

the deliberative system, using the symbolic names of the

locations in the ontology.

As an example, imagine our robot traversing a room. At

the start of the motion, the robot has a Mental Model of the

room, its relative position to the walls, the distance to the

table, the location of the chair. When the robot moves forward, the Reification Engine updates the expected world

state, changing the position of the robot in the room. When

the sensory data arrives from the perception/action system,

the robot can ask the PerCept for the table “If I am in this

position, and looking this way, am I seeing you?” Since

the PerCept includes the necessary structural description,

it can quickly confirm (or deny) whether the sensory data

is consistent with the expectation. This can be continued

with the chair, the walls, the picture on the wall; and if the

world model is confirmed, it can be updated. This process

does not require querying every possible PerCept, or even

querying every expected PerCept for every possible position

and orientation. Rather, it quickly attempts to confirm the

expected world state.

3.4.1 Dealing with the Unexpected

Sure, but what if the world is not what the robot expects?

What if someone sneaked in and moved the chair, or simply stepped into the robot’s field of view? In this case the

presumptive confirmation of the world fails. Now the Reification Engine begins to expand the range over which the

search occurs. If there are people (or other moving entities) in the world model, they are added to the search “Is it

possible that this person stepped to the left?” “Is it possible that the chair moved?” “Am I really where I expect to

be?” If this level of relaxation of the model fails to produce

a consistent world model further relaxation may occur, less

likely objects are added to the search list (although it will

be a while before the robot considers the possibility that a

zebra has suddenly appeared in the living room). This is

consistent with the results of studies on humans in disasters. People who experience dramatic destruction (such as

coming out of a storm cellar after a tornado) report that for

several minutes they cannot place themselves in space, the

permanent features that they expected to see, the buildings,

the walls, the trees, have been altered to the point where

they cannot perceive a frame of reference. Nor is this limited to humans, pets can also experience disorientation due

to the disruption of their sensorium, notably the changes to

the landscape of scents that they use to define space[14].

3.5 Wrapping Up Reification

Reification appears to be a component necessary for autonomous systems to function effectively in a dynamic and

uncertain world. Reification is the mechanism that translates between the sensor domain - the world of images, echoes,

encoders, and force transducers - into the semantic domain

of chairs and trees, rooms and fragile packages. In this section we sum up the various pieces, and look at how they

work together to provide reification to the robot.

Reification can be viewed as a necessary middle-ware component for autonomous robots. It provides recognition services to map the sensorium into symbolic representations,

and provides the complementary service preafference to map

the expected state of the world into the anticipates sensor

representations.

The Reification Engine presented here both anchors the

deliberative symbols in the sensor domain, and attaches semantic tags to the patterns presented by those sensors. It

does this, not by extensively hard-coding the patterns, but

by associating the data derived patterns with the meanings

used by the ontology. The data derived patterns are encoded as PerCepts, utilizing the lens model pioneered by

Brunswik. This PerCept based approach has several benefits, as well as costs, in comparison to an analytic representation scheme. One of these benefits is that the data driven

approach is based on the actual properties of the objects as

viewed by the actual sensors, rather than an idealized model.

As a result, if a given sensor has an idiosyncrasy (perhaps

it is mounted at a slight angle), or if a specific object has

a unique property (e.g., it absorbs both IR and ultrasonic

pulses) that is reflected in the data derived pattern.

The second major benefit is that the patterns are simply

data. There are several basic algorithms that are grounded

in the physical relationships of the world: things like dis186
tance calculations, and the determination of relative angles. However, the representation of objects, sensors, and

the structural descriptions of the world are simply data.

This means that the cybernetic brain, and specifically the

Reification Engine, can modify these patterns as it experiences more of the world, and can modify the parameters

in response to the changes that the world will have on the

robot’s own structure. By using data structures for as much

as possible, the robot can both stay synchronous with the

dynamic world, and can update its mental representations

as it experiences new things.

4. INTEGRATION

The integration of the Reification Engine and the PRO

is driven by the need to effectively and efficiently share representations across a range of resolutions. The cycle can

be traced from almost any point, but we will start from a

change detected by the sensors in the perception/action System. Perhaps the sonars on the robot have been pinging a

doorway, and the range value in the opening is 4 meters. If

the door closes, the range drops to only 1.5m. The question

is how does the robot interpret this change in a way that

can be reasoned about?

The output from the sensor system is passed upwards

to the Reification Engine along the Recognition pathway.

Since the Reification Engine has a model of the CWS, it

can detect the change, determine that the the change affects the doorway, and query additional PerCepts to conclude that the change is likely to indicate that the door has

closed. The enables the Reification Engine to update the

symbolic representation of the CWS to include a closed door.

This symbolic information is passed to the PRO, which can

extract a new problem statement. This semantics of a closed

door (from the ontological relationships and properties) results in the extraction of possible actions that might affect

the door state, as well as actions that can circumvent the

closed door. These are packaged into a problem description which is passed to the deliberative system for solution

generation.

When the deliberative system produces a plan (purely

symbolic) it is passed down to the Reification Engine for

the generation of preafference maps, which are passed down

to the perception/action system for execution. Since each

action has the expected sensor-based representation of the

world required for its application, and the representation for

the expected outcome of the action, the perception/action

system can quickly detect any salient change to the environment that would require the invocation of the deliberative

system. In effect, we generate a purely reactive system on

the fly, and as long as things are going well, the computationally expensive operations are off-line.

Traditionally, mobile autonomous robots are built with

well developed perception/action systems and fairly light

weight deliberative systems. In fact much of the robotics research in the 1980’s and 1990’s focused on removing the deliberative systems entirely[2, 3]. This was based on the idea

that deliberation is computationally expensive, and representation of a world model is both expensive and hard to

maintain. Our research has shown that the correct application of representation in the PRO is far easier to maintain,

since the need for strict truth maintenance is reduced. In

addition, the use of a specialized reification mechanism can

actually reduce the computational overhead, while increasFigure 4: This chart compares the ability of the

robot to classify objects using simple recognition

versus a complete reification process. The full reification process first attempts to do a presumptive

classification, based on the last known position and

orientation of the object. If that fails, the recognition process is invoked. The quality of the classification is shown as the Jaccard Index between the

classification set and the actual state.

ing the functionality of the system.

In our tests the integration of the PRO and Reification

Engine into a deployed mobile robot was shown to reduce

the errors in classifying objects by 60%, and to reduce localization errors from 200mm to an average of 13mm (More

comprehesive test data can be found in [10], chapter 12).

In Figure 4 we show the relative improvement provided by

complete reification over simple pattern recognition alone.

These comparison tests were done using exactly the same

PerCepts, so there was no additional structural information available to the cybernetic brain. The only additional

information was that the brain had a Mental Model that

included the last position of the objects it knew about and

a PRO that linked the PerCept with the symbolic knowledge

of the object. Since it knew where the objects were the last

time it looked, it was able to generate a preafference image -

the way the world was expected to look. Using this expectation, the robot could quickly and accurately assess whether

the world was generally as it was expected to be. These results were generated with small perturbations of the actual

position of the objects away from their last known position. In spite of these perturbations, the preafference image

enabled the Reification Engine to increase its ability to

both model the world, and to maintain that model. This

clearly shows the benefits provided by reification in robotic

systems.

5. REFERENCES

[1] J. Ayers and J. Witting. Biomimetic approach to the

control of underwater walking machines. Philosophical

Transactions of the Royal Society A, 365:273–295,

2007.

[2] R. A. Brooks. Intelligence without reason. In

J. Myopoulos and R. Reiter, editors, Proceedings of

the 12th International Joint Conference on Artificial

Intelligence (IJCAI-91), pages 569–595, Sydney,

Australia, 1991. Morgan Kaufmann publishers Inc.:

San Mateo, CA, USA.

187
[3] R. A. Brooks. Intelligence without representation

(revised). In Mind Design II. The MIT Press,

Cambridge, MA, 2000.

[4] E. Brunswik. Representative design and probabilistic

theory in a functional psychology. Psychological

Review, 62:192–217, 1955.

[5] U. N. N. U. W. Center. Uuv, aus, and usv technology

and assessment. Broad Area Announcement 01-01,

2001. http://www.npt.nuwc.navy.mil/contract/

announce/baa/2001-01/#TOPIC13.

[6] J. F. Engelberger. Robotics in Practice: Management

and Applications of Industrial Robots. Kogan Page,

London, UK, 1980.

[7] G. W. Ernst and A. Newell. GPS: A Case Study in

Generality and Problem Solving. Academic Press,

London, UK, 1969.

[8] W. J. Freeman. The physiology of perception.

Scientific American, 242:78, February 1991.

[9] J. P. Gunderson and L. F. Gunderson. Reification:

What is it and why should i care? In Proceedings of

the 6th Workshop on Performance Metrics for

Intelligent Systems, page unknown, Gaithersburg, MD,

2006. National Institutes of Standards and Technology.

[10] L. F. Gunderson and J. P. Gunderson. Robots,

Reasoning, and Reification. Springer, in press.

[11] J. Hollingum. Unmanned vehicles go to war. Industrial

Robot, 25(6), 1998.

[12] D. B. Marco, A. J. Healey, and R. B. McGhee.

Autonomous underwater vehicles: hybrid control of

mission and motion. Autonomous Robots, 3(2–3), 1996.

[13] A. Newell and H. Simon. Gps, a program that

simulates human thought. In E. A. Feigenbaum and

J. Feldman, editors, Computers and Thought. R.

Oldenbourg KG., 1963.

[14] M. Pai. Latest tornadoes bring destruction; red cross

provides care, May 2008.

[15] L. E. Parker and J. V. Draper. Robotics applications

in maintenance and repair. In S. Nof, editor, Handbook

of Industrial Robotics, chapter 53. Wiley, New York,

1999.

[16] J. Pettre, P. de Heras, J. Maim, B. Yersin, J.-P.

Laumond, and D. Thalmann. Real-time navigating

crowds: Scalable simulation and rendering. Computer

Animation and Virtual World (CAVW) Journal -

CASA 2006 special issue, 2006.

[17] C. M. Portas, B. A. Strange, K. J. Friston, D. R. J.,

and C. D. Frith. How does the brain sustain a visual

percept. Proceedings of the Royal Society of London,

B, 267:845–850, 2000.

[18] E. D. Sacerdoti. Planning in a hierarchy of abstraction

spaces. Artificial Intelligence, 5:115–135, 1974.

[19] A. Samuel. Some studies in machine learning using the

game of checkers. IBM Journal, 3(3):210U–229, 1959.  ̋

[20] H. C. Schubert and J. P. How. Space construction: an

experimental testbed to develop enabling technologies.

In Proc. of the SPIE, volume 3206, 1997.

[21] A. K. Singh. Field Theory, chapter 14, pages 390–410.

Motilal Banarsidass Publishers, Delhi, India, 1991.

[22] T. Tsuda, D. Kato, A. Ishikawa, and S. Inoue.

Automatic tracking sensor camera system. In M. A.

Hunt, editor, Machine Vision Applications in

Industrial Inspection IX. SPIE–The International

Society for Optical Engineering, 2001.

[23] I. Walker, Hoover, A., and Y. Liu. Handling

unpredicted motion in industrial robot workcells using

sensor networks. Industrial Robot: An International

Journal, 33:56–59(4), 2006.

[24] F. Werblin and B. Roska. The movies in our eyes.

Scientific American, pages 72–79, April 2007.

188
 Quantification of Line Tracking Solutions for 

 Automotive Applications

 Jane Shi, Ph.D 

GM R&D Center

30500 Mound Road

Warren, MI, USA 

Jane.Shi@gm.com

Rick F. Rourke 

Dave Groll 

Peter W. Tavora 

GM Manufacturing Engineering

30300 Mound Road 

Warren, MI, USA 

Rick.f.Rourke@gm.com

Dave.Groll@gm.com

Peter.Tavora@gm.com

ABSTRACT

Unlike line tracking in automotive painting applications, line 

tracking for automotive general assembly applications requires 

position tracking in order to perform assembly operations to a 

required assembly tolerance. Line tracking quantification 

experiments have been conducted for a total of 16 test cases for 

two line tracking scenarios with three types of line tracking 

solutions: encoder based tracking, encoder plus static vision based 

tracking, and the analog sensor-based tracking for general 

assembly robotic automation. This paper presents the 

quantification results and identifies two key performance drivers 

fro line tracking for automotive assembly applications. 

Categories and Subject Descriptors

C.4 [Performance of Systems]: Performance attributes. 

C.3 [Special-Purpose and Application-Based Systems]: Process 

control systems; Real-time and embedded systems.

General Terms

Performance, Experimentation, Verification. 

Keywords

Position tracking performance. 

1. INTRODUCTION

In automotive general assembly (GA), vehicle bodies are being 

carried on a continuous moving assembly line through hundreds 

of workstations where a variety of parts are being assembled 

together as shown in Figure 1. 

In order to robotically assembly parts onto a continuous moving 

vehicle body, the performance of current available line tracking 

solutions for automotive general assembly applications should be 

well understood. For automotive general assembly applications, 

the vehicle body position at the point of assembly operations on a 

moving conveyor needs to be tracked by encoders or other 

sensors for the duration of the part assembly. This means that a 

specific position is to be tracked for a fixed time period with a 

required position tolerance. 

Figure 1 Automotive General Assembly 

Conveyors Transport Vehicle Bodies for 

Assembly Operations

In the past several months, a collaborative study has been 

conducted to thoroughly quantify the performance of three types 

of robotic line tracking solutions, encoder-based, encoder plus 

static vision, analog laser sensor-based. This paper describes the 

quantification methodology, illustrates the experimental setup, 

summarizes the quantification results, and identifies two key 

performance drivers fro line tracking for automotive assembly 

applications. Permission to make digital or hard copies of all or part of this work for 

personal or classroom use is granted without fee provided that copies are 

not made or distributed for profit or commercial advantage and that 

copies bear this notice and the full citation on the first page. To copy 

otherwise, or republish, to post on servers or to redistribute to lists, 

requires prior specific permission and/or a fee. 

2. QUANTIFYING LINE TRACKING 

SOLUTIONS

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA. 

Copyright 2008 ACM 978-1-60558-293-1...$5.00. 

189
Figure 3 Quantification Experimental Setup and Data 

Collection Method 

Zw

Upstream 

Boundary

Downstream 

Boundary

Part 

Detection 

Trigger 

Xw

Yw

X

Y

Z

The operating principal of the robotic line tracking is for a robot 

to use a sensor’s outputs to track a moving part as shown in 

Figure 2. 

Motion 

Direction

The Nominal 

Tracking Frame 

The World Frame 

Measured 

Position 

Figure 2 Robotic Line Tracking

A world frame is specified for the robot location. A nominal 

tracking frame is set to be rigidly attached to the moving part. 

Once part detection is triggered, a sensor, such as an encoder, 

measures the part position and robot uses the sensor’s reading to 

track the moving part. 

Several key technical issues need to be addressed when 

quantifying the performance of a line tracking solution: 

x How to measure the part position with respect to time? 

x How to measure the robot position with respect to time? 

x How to synchronize above two position measurements? 

x Which case of part movement should be evaluated? 

x How many of part movement cases should be evaluated? 

The relative position between the robot and the moving part is 

critical to the success of the line tracking application when robot 

is in a tracking mode. It is valid to combine the issue (1) and (2) 

to measure the relative position between the robot and the moving 

part. This means that only one relative position needs to be 

evaluated with respect to time. In the actual evaluation 

experiments described in the next section, the relative position is 

measured with Dynalog’s CompuGauge. At the same time, both 

part position and the robot position in the tracking mode are 

recorded and then relative position is computed with 

synchronized trigger. It has been determined that the computed 

robot position data is accurate enough for the evaluation purpose.

Application environment plays a critical role in deciding which 

and how many evaluation test cases for the part movement. 

Several key relationships we would like to determine: 

x Does the tracked position change for the same constant 

moving speed reached by different acceleration? 

x Does the tracked position change for different constant 

moving speeds? 

x How does the tracked position change for an unstable 

moving speed? 

A total of sixteen evaluation test cases are designed to cover three 

classes of motion profile including a variety of accelerations, an 

emergency stop case, and an unstable conveyor bounce motion as 

detailed in a later section. 

3. EXPERIMENTAL SETUP AND PERFORMANCE

DATA COLLECTION METHOD

In the experimental setup for the line tracking evaluation, the 

moving vehicle body is emulated by a robot on one dimensional 

rail as illustrated by Figure 3. 

Three main components of the experimental setup are as 

followings:

x Emulator: it is emulating a moving vehicle body on the 

assembly plant floor. A variety of motion profiles have been 

implemented by the Emulator as summarized in next section.

x Rail Follower: it is a robot transport unit (RTU) that utilizes 

one linear rail to follow the Emulator’s motion. 

x Pedestal Follower: it is a stationary six axes robot that 

utilizes its arm to follow the Emulator’s motion. 

Two types of tracking solutions have been evaluated: the rail 

tracking and the arm tracking: 

A. The rail tracking: the Rail Follower is tracking the Emulator 

with one linear rail motion. 

B. The arm tracking: the Pedestal Follower is tracking the 

Emulator with its 6DOF arm motion.

Both Emulator and Follower’s positional data are collected using 

a position recording software provided by the robot controller. 

The collected data are then calculated to derive the relative 

position between the Follower and the Emulator. The computed 

relative position was validated with Dynalog’s CompuGauge at 

the start of project. It has been determined that the computed 

relative position data is accurate to be within 5%. For all 

evaluation tests and their associated data graph, the recorded 

position data by the Follower and the Emulator are analyzed. 

190
4. QUANTIFICATION TEST CASES

Figure 4 Encoder Connects to the Robot Controller of the 

Rail or Pedestal Follower 

Three classes of vehicle motion profiles have been emulated by 

the Emulator for the quantification tests: 

x Stable motion with a variety of accelerations 

x E-Stop

x Actual measured conveyor bounce motion [1] 

A total of 16 test cases are designed and conducted for both the 

rail tracking and the arm tracking scenarios. For high volume 

assembly plants, three line rates are used as representative cases: 

40, 60, and 80 in Jobs Per Hour (JPH) which translates to 

conveyor speed in mm per second (mm/sec) The test cases are 

organized for three stable constant speeds (60mm/sec, 

120mm/sec, and 160mm/sec) with four different acceleration 

profile (rising edge of the speed chart) plus an emergency stop 

cases (acceleration with very high negative number). In addition, 

one special test case is included that is based on the actual 

measured conveyor bounce motion. 

Table 1 summarizes all test cases with a speed profile graph that 

illustrates the constant top speed and four accelerations and one 

emergency stop deceleration. 

Table 1 Evaluation Test Cases 

Line Rate 

(JPH)

Conveyor 

Constant

Speed 

(mm/sec) 

Acceleration

(mm/sec^2) 

Speed Profile 

(mm/sec vs. second)

150

320

650

745

40 JPH 

60 mm/sec 

-11190

150

320

650

745

60 JPH 

120

mm/sec 

-11190

150

320

650

745

80 JPH 

160

mm/sec 

-11190

40 JPH 

60 mm/sec

Bounce with 

various

magnitude

5. QUANTIFICATION RESULTS OF THE

ENCODER BASED LINE TRACKING SOLUTION

For the encoder based line tracking, the encoder is connected to 

the robot controller that drives the Follower as illustrated in 

Figure 4.

A set of gear boxes drive the encoder while the Emulator is 

moving per the specification of the speed profile in each test case. 

With a properly selected gear ratio, the resolution for the encoder 

is set to be at least 500 counts per mm. This represents minimum 

resolution of 0.002mm per count. The encoder digital counts are 

applied to the Follower in both rail and arm tracking cases every 

0.012 seconds. 

A digital I/O handshaking signal between the Emulator and the 

Follower simulates the part detection trigger to start the line 

tracking. In the data collection process, the trigger signal is 

emulated by a digital handshaking between the Emulator and 

Follower to start recording robot position data at the same time. 

Thus the relative position between the Emulator and the Follower 

can be computed during the data analysis. 

5.1 Rail Tracking Results 

All test cases are conducted for the encoder-based rail tracking 

and repeated at least three times to validate the repeatability. The 

position lag errors are plotted in Figure 5 through 7 for the 

constant conveyor motion cases. 

191
Figure 5 The Position Lag Error for the Encoder Based Rail 

Tracking: 60mm/sec Case

Figure 6 The Position Lag Error for the Encoder Based Rail 

Tracking: 120mm/sec Case

Figure 7 The Position Lag Error for the Encoder Based Rail 

Tracking: 160mm/sec Case

Figure 8 The Position Lag Error for the Encoder Based 

Rail Tracking: Emulated Conveyor Bounce Case 

For the constant motion cases, several observations can be made 

of encoder based rail tracking results: 

x Lag error is proportional, although not exactly linearly, to 

the stable top speed. 

x Higher acceleration does not increase the total lag error: it 

seems to have reduced the total lag error slightly (about 

1mm) for the rail tracking. 

x And all test cases are repeatable within 1mm.

For the emulated conveyor bounce motion case, the position lag 

error is plotted in Figure 8. 

Table 2 below summarizes the results of the encoder based rail 

tracking test cases. 

Table 2 Encoder (0.002mm Resolution) Based Rail Tracking 

Performance 

Line Rate 

(JPH)

Conveyor 

Constant

Speed 

(mm/sec) 

Acceleration

(mm/sec^2) 

Range of 

Position

Tracking

Error

(mm)

Repeatability 

(mm)

150

320

650

745

< 6.8mm < 0.5mm 40 JPH 

60 mm/sec -11190

(emergency 

stop)

Overshoot -

1.2mm < 0.5mm 

150

320

650

745

60 JPH < 12.5mm < 0.5mm 

120

mm/sec 

-11190

(emergency 

stop)

Overshoot -

2.1mm < 0.5mm 

150

320

650

745

80 JPH < 14.5mm < 0.5mm 

160

mm/sec -11190

(emergency 

stop)

Overshoot -

2.1mm < 0.5mm 

192
40 JPH 

60 mm/sec 

Bounce with 

various

magnitude

-3.8mm ~ 

16.0mm < 4.0mm 

Figure 10 The Position Lag Error for the Encoder Based 

Arm Tracking: 120mm/sec Case

Figure 11 The Position Lag Error for the Encoder Based 

Arm Tracking: 160mm/sec Case

Figure 9 The Position Lag Error for the Encoder Based 

Arm Tracking: 60mm/sec Case Figure 12 The Position Lag Error for the Encoder Based 

Arm Tracking: Emulated Conveyor Bounce Case

5.2 Arm Tracking Results 

All test cases are conducted for the encoder-based arm tracking 

and repeated at least three times to validate the repeatability. The 

position lag errors are plotted in Figure 9 through 11 for the 

constant conveyor motion cases. 

For the constant motion cases, similar observations can be made 

of encoder based arm tracking results: 

x Lag error is proportional, although not exactly linearly, to 

the stable speed. 

x Higher acceleration does not increase the total lag error: it 

seems to have reduced the lag error slightly (about 1mm) for 

the arm tracking. 

x And all test cases are repeatable within 2mm. 

For the emulated conveyor bounce motion case, the position lag 

error is plotted in Figure 12. The arm tracking error is within +16 

and -3 mm with a repeatability of about 5 mm. 

Table 3 below summarizes the results of the encoder based arm 

tracking test cases. 

Table 3 Encoder (0.002mm Resolution) Based Arm Tracking 

Performance 

Line Rate 

(JPH)

Conveyor 

Constant

Speed 

(mm/sec) 

Acceleration

(mm/sec^2) 

Range of 

Position

Tracking

Error

(mm)

Repeatabilit

y (mm) 

150

320

650

745

40 JPH < 6.0mm < 1.0mm 

60 mm/sec 

-11190

(emergency stop) 

Overshoot

-2.5mm < 1.0mm 

150

320

650

745

< 11.5mm 

60 JPH < 1.5mm 

120 mm/sec 

-11190

(emergency stop) 

Overshoot 

-4.0mm < 1.0mm 

193
150

320

650

745

80 JPH < 13.5mm < 2.0mm 

160 mm/sec 

-11190

(emergency stop) 

Overshoot

-4.5mm < 1.0mm 

40 JPH 

60 mm/sec 

Bounce with 

various

magnitude

-3.0mm ~ 

16.0mm < 5.0mm 

Figure 13 Setup of Vision System for Line Tracking 

Evaluation

Compared with the encoder based rail tracking, the arm tracking 

has

x similar position lag error,

x slightly worse repeatability, 

x and worse emergency stop performance. 

6. QUANTIFICATION RESULTS OF THE

ENCODER PLUS STATIC VISION LINE

TRACKING SOLUTION

When a static vision is used for the line tracking, the Follower 

uses the detected object location to correct its position relative to 

the object. This one time correction of robot’s position based on 

the vision results is “static” compared with the use of vision 

results at a fixed time period to track an object’s position [2]. The 

encoder counts are the sensor inputs that drive the Follower to 

track the Emulator. 

Table 4 lists the vision system setup used in the evaluation 

testing.

Table 4 Vision System Parameters 

Figure 13 illustrates the setup of the vision system used in the 

line tracking evaluation. 

The vision camera is attached to the Pedestal Follower and the 

vision grid object is attached to the Emulator so that there is no 

relative motion when the Follower is tracking the Emulator at the 

constant speed. 

The following procedures are implemented to quantify the static 

vision use in the encoder based line tracking: 

(1) Before the Emulator starts to move, the Arm Follower is 

centered with the vision calibration grid so that the vision 

can use it to “set reference”. This means that the vision snap 

and find operation will return a zero offset. 

(2) Enter a static 2D offset, (x1, y1, R1), to the Emulator robot 

so that the robot arm moves the specified offset before the 

Emulator starts moving. 

(3) After the Emulator reaches its constant speed, the camera 

mounted on the Pedestal Follower captures the image of the 

vision calibration grid. The second vision snap and find 

operation determines the vision offset (x2, y2, R2). 

(4) Apply the vision offset (x2,y2,R2) from step 3 to the 

Pedestal Follower so that the Pedestal Follower compensates 

the offset value. 

(5) Verify the applied vision offset: the camera mounted on the 

Follower captures the image of the vision calibration grid 

again. The third vision snap and find operation determines 

the offset (x3, y3, R3) that, in theory, should be zero if 

compensated correctly and perfectly. 

Table 5 summarizes the test cases and the performance for the 

static vision with the encoder based line tracking. 

Table 5 Static Vision (0.15mm Resolution) Arm Tracking 

Evaluation Results 

Offset Applied Offset Detected by Vision at 

Constant Speed 

Vision Offset 

after 

Compensating 

Detected Offset 

Constant Speed (mm/sec) 

X1 (mm) Y1 (mm) 

R1 (deg) 

X2 (mm) 

X2+X1 (mm) 

Y2 (mm) 

R2 (deg) 

X3 (mm) Y3 (mm) 

R3 (deg) 

0 0 0 -8.4 -8.4 -0.9 0 -1.3 0 0 

0 0 0 -8.4 -8.4 -0.8 0 -1.2 0 0 

0 0 0 -8.4 -8.4 -0.8 0 -1.2 0 0 

-5 0 0 -3.3 -8.3 -0.9 0 -0.5 0.1 0

5 0 0 -

13.3 -8.3 0 0 -1.9 0 0

-15 0 0 6.7 -8.3 -0.8 0 0.7 -

0.1 0

114

15 0 0 -

23.3 -8.3 -1.1 0 -3.1 -0.1 0

Camera

Lens

(mm)

Camera

Standoff

Distance 

(mm)

the Grid 

Object

Dimension

(mm x mm) 

Pixel 

Resolution

(mm/pixel)

Object

Resolution

(mm)

8 640 320 by 320 0.599 0.15

194
10 -15 3 -

18.6 -8.6 13.9 3.1 -2.2 2.2 0

10 -15 3.

1

-

18.6 -8.6 13.9 3.0 -2.2 2.2 0

-10 15 -2 1.9 -8.1 -

15.8 

-

2.0 -0.2 -

2.4 0

-10 15 -2 1.8 -8.2 -

15.8 

-

2.0 -0.1 -2.3 0

Figure 14 Position Correction is the Combination of Static 

Lag plus Initial Object Offset 

The first three columns (X1,Y1,R1) are the static offset of the grid 

object applied by the Emulator in step (2). The columns 

(X2,Y2,R2) are the object position detected by the vision system 

in step (3). The last three columns (X3,Y3,R3) are the object 

position detected by the vision systems in step (5) after the 

correction has been applied in step (4). 

The shaded column in Table 5, X2-X1, is the difference between 

the detected X offset and the applied X offset. The values in this 

column are the relative position lag detected by the vision when 

the Emulator is traveling at the steady state speed of 114mm/sec. 

This is this steady state position lag that is proportional to the 

constant speed of the Emulator. In this case (114mm/sec), it is 

averaged at 8.35mm with one standard derivation of 0.15mm.

Figure 14 below plots the position lag between the Emulator and 

the Pedestal Follower for the first seven rows in Table 5. 

Detailed analysis of the collected robot position data reveals that 

the corrected position is the combination of the static position lag 

(caused by the motion) and the initial object position offset. How 

accurately the robot can compensate the position is a different 

evaluation question that could be a separate investigation study. 

The rough indicator is the last three column (X3,Y3,R3) in Table 

5.

It is worthwhile to note that the vision grid is a perfect object for 

the vision system to recognize and locate. In actual applications, 

all factors should be considered carefully to achieve the best 

result. It is critical to understand that the selection of the camera 

focal length, the camera standoff distance to the object, and the 

conveyor constant speed all impact the final performance of the 

vision use in the line tracking applications. 

7. QUANTIFICATION RESULTS OF THE

ANALOG LASER BASED LINE TRACKING

SOLUTION

An analog ranging laser can be used in the place of an encoder 

where mounting an coder is not feasible in the line tracking 

applications. The analog laser ranging sensor, ILD1700-100 [3], 

uses the optical triangulation principal to measure the distance 

between the laser sensor and the smooth surface target as shown 

in Figure 15. The measurement range is between 70mm the Start 

of Measuring Range (SMR) and 170mm the End of Measuring 

Range (EMR). The midrange (MMR) is used for the line tracking 

application. This means that the analog laser signal drives the Rail 

or Pedestal Follower to maintain a constant distance with the 

Emulator. Customized software has been developed to use the 

analog laser sensor for the line tracking function. 

Figure 16 illustrates the setup for the analog laser based line 

tracking. While the Emulator is moving, the analog laser 

measures the distance between the Emulator and the Follower. 

This analog laser sensor based line tracking method is only 

concerned with one dimension: the conveyor main travel 

direction. It does not require the sensor to recognize any object 

geometry feature as in a traditional tracking method. Any flat 

reflecting surface can be used for the laser signal to return to its 

receiver. The goal is to keep the laser reading constant by driving 

the Follower to track the Emulator’s position. 

0 VDC SMR 

Measurement

Range 

5 VDC MMR 

10 VDC EMR 

Analog Output 

Figure 15 An Analog Ranging Laser Sensor ILD1700-100 

195
Figure 19 The Position Lag Error for Analog Sensor Based 

Rail Tracking: 120mm/sec Case

Figure 16 Analog Laser Based Line Tracking Solution Figure 18 The Position Lag Error for Analog Sensor Based 

Rail Tracking: 60mm/sec Case

Figure 20 The Position Lag Error for Analog Sensor Based 

Rail Tracking: 120mm/sec Case 

In order to use the analog laser sensor to track the Emulator, 

additional system components have to be set up. The analog 

signal is first digitized by an analog to digital (A/D) converter. 

Then the digital signal goes through a DeviceNet adaptor to 

interface with the DeviceNet module inside the robot controller as 

shown in Figure 17 below. 

For the constant motion cases, several observations can be made 

of encoder based rail tracking results: 

x Lag error is proportional, although not exactly linearly, to 

the stable top speed. 

x Higher acceleration does not increase the total lag error: it 

seems to have reduced the total lag error slightly (about 

1mm) for the rail tracking. 

x And all test cases are repeatable within 1mm.

For the emulated conveyor bounce motion case, the position lag 

error is plotted in Figure 8. 

A scan rate can be set for the device net interface module at 

12msec. This means that the digitized analog sensor can be read 

by the robot controller every 12msec. The line tracking software 

then utilizes the analog sensor inputs every scan period. There is 

an unknown system time delay between the sampled sensor 

reading and the use of such reading by the robot controller to 

track the Emulator. 

The analog laser sensor has measurement resolution of 

0.0006mm. Experiments have shown that the stable reading of the 

analog laser is around 0.0012mm when the analog sensor and the 

measured surface are both stationary. 

7.1 Rail Tracking Results 

All test cases are conducted for the analog sensor based rail 

tracking and repeated at least three times for validating the 

repeatability. The position lag errors are plotted in Figure 18 

through 20 for the constant conveyor motion cases. 

Figure 17 Analog Laser Ranging Sensor Connection to a 

Robot Controller 

Analog Laser Sensor 

NCDT1700-100 

Allen-Bradley Analog 

Input Module 

Allen-Bradley AND I/O 

Communication Adapter 

For the constant motion cases, several observations can be made 

of analog sensor based rail tracking results: 

x Lag error is proportional to the top stable speed. 

x Higher acceleration causes significant overshoot before the 

Rail Follower can stabilize its speed to match the Emulator 

speed as illustrated in Figure 21. 

Robot Controller 

Device Net

Interface 

Module

196
Figure 21 The Rail Follower Overshoots Before 

Stabilizes in High Acceleration Case 

For the emulated conveyor bounce motion case, the position lag 

error is plotted in Figure 22. 

Figure 22 The Position Lag Error for the Analog Sensor 

Based Rail Tracking: Emulated Conveyor Bounce Case 

Compared with the encoder based rail tracking result shown in 

Figure 8, The analog laser based rail tracking exhibits significant 

overshoot and oscillation.. Further examination of the Rail 

Follower speed identifies the root cause of the large position lag 

error as shown by Figure 23. With the analog sensor’s inputs, the 

Rail Follower can not closely follow the Emulator speed. 

Figure 23 The Emulator Speed vs. The Rail Follower Speed 

with the Analog Laser 

Table 6 below summarizes the results of the analog laser rail 

tracking test cases. 

Table 6 Analog Laser (0.0012mm Resolution) Based Rail 

Tracking Performance 

Line Rate 

(JPH)

Conveyor 

Constant

Speed 

(mm/sec) 

Acceleration

(mm/sec^2) 

Range of 

Position

Tracking

Error

(mm)

Repeatabilit

y (mm) 

150

320

650

745

40 JPH < 7.0mm < 2.5mm 

60 mm/sec 

-11190

(emergency stop) 

Overshoot

-5.5mm < 1.0mm 

150

320

650

745

< 14.0mm < 2.0mm 

60 JPH 

120

mm/sec 

-11190

(emergency stop) 

Overshoot

-8.0mm <1.0mm 

150

320

650

745

< 18.5mm < 4.0mm 

80 JPH 

160

mm/sec -11190

(emergency stop) 

Overshoot

-12.0mm < 2. 0mm 

40 JPH 

60 mm/sec 

Bounce with 

various

magnitude

-3.0mm ~ 

21.0mm < 5.0mm 

Compared with the encoder based rail tracking of Table 2, the rail 

tracking with the analog laser has

x larger position lag error for constant motion speeds,

x worse repeatability, 

x significantly worse emergency stop performance, 

x and significantly larger position lag error for the dynamic 

motion speed.

7.2 Arm Tracking Results 

All test cases are conducted for the analog laser based arm 

tracking and repeated at least three times to validate the 

repeatability. The position lag errors are plotted in Figure 24 

through 26 for the constant conveyor motion cases. 

197
Figure 24 The Position Lag Error for the Analog Sensor 

Based Arm Tracking: 60mm/sec Case

Figure 25 The Position Lag Error for the Analog Sensor 

Based Arm Tracking: 120mm/sec Case

Figure 26 The Position Lag Error for the Analog Sensor 

Based Arm Tracking: 160mm/sec Case

Figure 27 The Emulated Speed vs. The Arm Follower 

Speed with the Analog Laser Sensor

Figure 28 The Position Lag Error for the Analog Laser 

Arm Tracking: Emulated Conveyor Bounce Case

Figure 29 The Emulator Speed vs. The Arm Follower 

Speed with the Analog Sensor

For the constant motion cases, similar observations can be made 

of encoder based arm tracking results: 

x Lag error is proportional to the top stable speed. 

x Higher acceleration causes significant overshoot before the 

Arm Follower can stabilize its speed to match the Emulator 

speed as illustrated in Figure 27. 

For the emulated conveyor bounce motion case, the position lag 

error is plotted in Figure 28. 

Compared with the encoder based arm tracking results shown in 

Figure 12, the analog laser based arm tracking exhibits significant 

overshoot and oscillation.. Further examination of the Arm 

Follower speed identifies the root cause of the large position lag 

error as shown by Figure 29 below. With the analog sensor’s 

inputs, the Arm Follower can not closely follow the Emulator 

speed. 

198
Table 7 below summarizes the results of the analog laser sensor 

based arm tracking test cases. 

Table 7 Analog Laser (0.0012mm Resolution) Based Arm 

Tracking Performance 

Line Rate 

(JPH)

Conveyor 

Constant

Speed 

(mm/sec) 

Acceleration

(mm/sec^2) 

Range of 

Position

Tracking

Error

(mm)

Repeatability 

(mm)

150

320

650

745

< 6.5mm < 1.0mm 40 JPH 

60 mm/sec -11190

(emergency 

stop)

Overshoot

-5.0mm < 1.0mm 

150

320

650

745

60 JPH < 12.0mm < 2.0mm 

120

mm/sec 

-11190

(emergency 

stop)

Overshoot

-7.5mm < 1.0mm 

150

320

650

745

80 JPH < 17.0mm < 2.0mm 

160

mm/sec -11190

(emergency 

stop)

Overshoot

-10.0mm < 1.0mm 

40 JPH 

60 mm/sec 

Bounce with 

various

magnitude

-2.0mm ~ 

19.0mm < 6.0mm 

Compared with the encoder based arm tracking of Table 3, the 

arm tracking with the analog laser has 

x larger position lag error for constant motion speeds,

x worse repeatability, 

x significantly worse emergency stop performance, 

x and significantly larger position lag error for the dynamic 

motion speed. 

8. CONCLUSIONS

Unlike the line tracking for automotive paint applications where 

the speed match between the robot and the vehicle body plays 

critical role for the paint quality, the line tracking for automotive 

general assembly applications requires position tracking of the 

system to perform assembly operations within a required 

assembly tolerance for a period of time. By comparing and 

contrasting experimental results, key performance drivers for the 

robotic line tracking can be concluded. Among three line tracking 

solutions, the encoder-based tracking method offers the tightest 

and most responsive robotic tracking performance. The encoder 

plus static vision based tracking method can be used for 

compensating the steady-state tracking position lag and the initial 

object offsets. The analog sensor-based tracking method is the 

least responsive due to its delayed signal propagation in the entire 

system. 

Two key drivers have been identified for impacting the line 

position tracking performance: 

x Sensor resolution: it limits how tight the robot system can 

track the conveyor line motion. 

x Actual time delay of applying the sensor data: it limits how 

dynamically responsive the robot system can respond to the 

change in the conveyor line motion. 

By understanding current capabilities of line tracking solutions, 

appropriate robotic automation systems can be developed and 

designed for a variety of GA applications. Key fundamental 

system drivers can be specified for robots to track the moving 

conveyor accurately enough for the specific assembly tolerance 

plus the environment uncertainty with adequate dynamic response 

at the appropriate location for the general assembly automation. 

9. ACKNOWLEDGMENTS

The authors would like to acknowledge Bob Scheuerman, Marty 

Linn, Marjorie Winston, Thomas McGraw, Ke Zhang-Miske, 

Brooks A. Curtis, Ronald Reardon, Loring Dohm, Michael Poma, 

Neil McKay, Charles W. Wampler, and Roland Menassa. Their 

inputs, support, contribution, and knowledge have shaped this 

project from its initial concept to the final results. 

10. REFERENCES

[1] J. Shi, “Preliminary Analysis of Conveyor Dynamic Motion 

for Automation Applications”, PreMIS’08, 2008 

[2] G. DeSouza, “A Subsumptive, Hierarchical, and Distributed 

Vision-based Architecture for Smart Robotics”, Ph.D. 

Dissertation, School of Electrical and Computer Engineering, 

Purdue University, May 2002 

[3] Analog Laser Ranging Sensor ILD1700 www.microepsilon.com

199
Mobile Robotic Surveying Performance for 

Planetary Surface Site Characterization 

Edward Tunstel 

Space Department 

Johns Hopkins University 

 Applied Physics Laboratory 

Laurel, MD 20723 USA 

Edward.Tunstel@jhuapl.edu 

ABSTRACT

Robotic systems will perform mobile surveys for scientific and 

engineering purposes as part of future missions on lunar and 

planetary surfaces. With site characterization as a task objective 

various system configurations and surveying techniques are 

possible. This paper describes several examples of mobile 

surveying approaches using local and remote sensing 

configurations. A geometric measure of area coverage 

performance is applied to each and relative performance in 

surveying a common area is characterized by expected 

performance trends. Performance metrics that solely express 

geometric aspects of the task are limited in utility as decision aids 

to mission operators. As such, the importance of enriching such 

metrics by incorporating additional attributes germane to 

surveying on planetary surfaces is highlighted. 

Keywords

robotic surveying, planetary surface exploration, in-situ remote 

sensing, area coverage performance, site characterization 

1. INTRODUCTION 

Task-oriented algorithms that support systematic mobile surveys 

using science instruments are needed for planetary surface 

characterization on science missions. They are also needed for insitu resource mapping on robotic missions that serve as precursors 

to human exploration missions. Typical objectives of site surveys 

include sensor coverage of designated areas. Area coverage 

problems for mobile robotic survey systems commonly employ 

sensing devices requiring close proximity to or contact with the 

measured phenomenon. Examples of such “local sensing” 

devices include ground penetrating radar, metal detectors for 

humanitarian de-mining, fluorescence imagers for organic 

molecule detection, a variety of spectrometer types, etc. Mobile 

robotic vehicles, or rovers, that carry survey systems comprised of 

local sensing devices must physically cover most, if not all, of the 

terrain in the designated survey area. 

Remote sensor-based area coverage contrasts with these more 

common area coverage problems for mobile robotic surveys. 

Remote sensing instruments (e.g., based on radar or optical 

devices such as lasers) can acquire measurements at significant 

distances away from the measured phenomenon. Measurements 

along a line-of-sight to detect airborne phenomena such as surface 

gas emissions, for example, account for coverage of terrain below 

that line-of-sight. This permits a two-dimensional search over 

terrain using discrete linear measurements from a distance (similar 

to scanning laser rangefinders). 

Remote sensor-based methods are not applicable to all surveying 

tasks. For surveys in which they are not a better solution, they are 

often excellent complements to local sensor-based methods. That 

is, remote sensor-based surveys can serve as an efficient means to 

cover wide areas with the purpose of localizing smaller areas at 

which local sensor-based surveys of higher resolution are 

appropriate. 

Mobility algorithms for surveying provide a means to 

systematically acquire measurements covering an area to be 

surveyed by transporting sensors and instruments to multiple 

locations and vantage points. Algorithms employing parallel-line 

transects or parallel swaths are commonly used to address robotic 

area coverage problems by single robots [1, 2] and multiple robots 

[3] when using local sensing devices. Full and partial coverage 

planners have also been proposed for rovers that survey terrain 

using local sensing devices [4]. Remote sensor-based survey 

approaches for rovers have recently been proposed for single- and 

two-rover systems performing measurements through the nearsurface atmosphere [5, 6]. 

This paper examines examples of both mobile survey types and 

applies a geometric measure of their area coverage performance. 

It further suggests additional attributes germane to surveying tasks 

for planetary surface exploration. The additional attributes are 

intended to enrich the effectiveness and relevance of basic 

geometric measures or support formulation of new metrics for 

planetary surface domains. 

2. LOCAL SENSOR-BASED SURVEYING 

Due to required proximity to measured phenomena and relatively 

small footprints of sensitivity, local sensing devices typically 

necessitate dense coverage of a designated survey region by the 

host mobile platform. As such, local sensor-based mobile surveys 

seek to acquire measurements that cumulatively cover all or most 

of the survey region. Associated survey sensors or instruments 

are typically mounted on a rover body or deployed on a roverPermission to make digital or hard copies of all or part of this work for 

personal or classroom use is granted without fee provided that copies are 

not made or distributed for profit or commercial advantage and that 

copies bear this notice and the full citation on the first page. To copy 

otherwise, or republish, to post on servers or to redistribute to lists, 

requires prior specific permission and/or a fee. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA. 

Copyright 2008 ACM 978-1-60558-293-1...$5.00. 

200
attached boom or manipulator arm. Rover mobility serves to 

transport the footprint of the survey instrument(s) over terrain 

along trajectories that fill the survey region. Fig. 1 depicts this 

scenario. 

Figure 1. Local sensor-based surveying along n parallel 

transects of length m. 

Among alternative survey trajectories for the mobile platform, 

parallel transects, spirals, and random walks have been proposed. 

Parallel transects are most commonly applied for coverage tasks 

although a spiral coverage approach was proposed for mobile 

mining of regolith on the lunar surface as part of a so-called spiral 

mining system [7]. Recent field tests, focused on planetary 

surface site characterization, used a rover operating ground 

penetrating radar (GPR) along parallel transects covering a 700 m 

x 700 m survey region [8]. This instrument was used to map the 

subsurface structure at the site. A total traverse distance of 20.5 

km was sufficient to cover the survey region using densely spaced 

parallel transects (with no overlap of the GPR sensor footprint on 

adjacent transects) [8]. 

Basic geometric measures are often used to measure area 

coverage performance of such local sensor-based survey 

algorithms. Examples include measures of distance traveled and 

percent of total area covered [2]. Variants of the latter have been 

proposed based on distribution of measurement samples within 

the cells of a tessellated grid representation of the survey region 

[4]. Here, we apply a basic geometric measure comprising a 

combination of such attributes. It is referred to as the quality of 

performance, QoP, defined as a ratio of area covered to distance 

traveled [9]. Applying this metric to the recent field test result 

mentioned above would yield a QoP of 24 based on the survey 

region area and total traverse distance. In general, the QoP for a 

local sensor-based survey along parallel transects (Fig. 1) is 

computed as 

 

Qp = m(n1)p

[mn +(n1)p]

 (1) 

where m is the transect length, n is the number of transects 

traversed, and p is the separation distance between adjacent 

transects and is assumed here to be comparable to the survey 

sensor footprint. The numerator and denominator of Eq. (1) 

respectively represent the area surveyed and total distance 

traversed during the survey. 

In the next section we discuss mobile surveying using in-situ 

remote sensing and apply the same metric to area coverage 

performance of several types of remote sensor-based survey 

trajectories. 

3. REMOTE SENSOR-BASED SURVEYING 

Mobile remote sensor-based surveys can be performed by 

measurement systems whose components are separated by a 

distance across terrain. Such systems are comprised of an 

active/passive instrument component on one end and a 

passive/active component on the other end. One end could be 

stationary while the other is mobile (fixed-mobile) or both ends 

could be mobile (mobile-mobile). Both are considered here 

beginning with a fixed-mobile configuration, which is suitable for 

single-site surveys (unless the fixed component is also 

transportable to other sites). 

3.1 Single-Site Remote Sensing Surveys 

Consider a fixed-mobile configuration comprised of an active 

rover-mounted instrument, a passive receiver or retroreflector at a 

fixed location a distance away, a rover pan-tilt unit to point the 

instrument at the passive component for measurements, and the 

rover itself to move the instrument spatially over terrain. The 

passive component would remain stationary at a position central 

to a designated survey region. This configuration is similar to 

those of Total Station systems commonly used by civil engineers 

for land surveys and comprised of a theodolite on one end and 

stationary 360° retroreflector on the other. Like a civil engineer, a 

rover using such a survey system can acquire measurements from 

any radial direction when the fixed component is within line-ofsight and measurement range. 

For mobile surveys, measurements are coordinated with rover 

mobility to survey terrain via a series of measurements across a 

distance d, which varies with rover position relative to the fixed 

component (Fig. 2). Such mobile robotic systems are under 

development for planetary surface surveying to achieve optical 

measurements at maximum distances of hundreds of meters [10]. 

The long-range measurement capability coupled with rover 

mobility enables wide-area surveys. 

Figure 2. Example of a distributed fixed-mobile measurement 

configuration. 

Concentric circular or spiral trajectories are compatible with 

distributed fixed-mobile configurations for remote sensor-based 

surveying. A designated survey region with a fixed instrument 

component at its center can be covered by traversing concentric 

circular trajectories as follows. The location of the fixed 

component is known and considered to be the origin of an inertial 

coordinate system in which the survey region and task is defined. 

Rover pose during surveys is estimated relative to this coordinate 

system. Beginning at a designated radial distance from the fixed 

component, the rover moves in arc-increments stopping 

periodically on the trajectory to acquire measurements. We refer 

to these measurement locations as m-nodes. Measurements along 

a line-of-sight between the rover-mounted active instrument and 

the fixed component account for 2-D coverage of terrain below 

the line-of-sight. Such measurement techniques are used on Earth 

201
with laser-based spectrometers to probe for and detect gas 

emissions during environmental site surveys [11], and they are 

being developed for the same on Mars [10]. An accumulation of 

such linear measurements from discrete radial locations and 

distances achieves survey region coverage. 

The following four parameters are used to configure a concentric 

circular trajectory covering a given survey region (Fig. 3): 

innermost circle radius, 1; radial distance, c, between 

circumferences of consecutive circles; arc length, s, between 

consecutive m-nodes on a circle; and positive integer, n, 

designating the nth or outermost circle including the survey region. 

The algorithm assumes that the rover is already within the survey 

region and that the fixed component is within line-of-sight from 

the rover [5]. If it is not, then no measurement is made. The 

survey completes when the nth circular trajectory is followed. 

Figure 3. Concentric circular remote sensing survey and 

parameters. 

A fixed-mobile configuration performs a spiral survey in a similar 

manner, differing only in that the rover drives in arcs along a 

trajectory of continuously increasing radius and needs no specific 

maneuvers to transition between successive spiral branches at 

larger radii [5]. Fig. 4 illustrates the spiral survey trajectory, 

which is parametrically similar to a circular survey. 

Figure 4. Overhead view of spiral remote sensing survey and 

parameters. 

Both surveys are configured in a flexible manner to achieve 

desired degrees of measurement and area coverage resolution 

using the four parameters (, , s, n). The surveys are primarily 

constrained by rover kinematic limitations, instrument maximum 

range, and terrain topography in the survey region whether 

executed radially inward or outward. 

3.2 Single-Site Remote Survey Performance 

Related research on distributed surveying [9] introduced the 

quality of performance metric defined earlier. We also apply this 

metric here as a basis for comparing expected performance of the 

concentric circular and spiral trajectories for distributed 

surveying. 

The area of a survey region covered by either a concentric circular 

or linear spiral trajectory is equal to or roughly the same as A = 

n

2

, where n is the radius of the outermost circle or spiral 

branch. Areas within the survey region that are occupied by the 

stationary instrument component (at the origin of the survey 

coordinate system) and non-traversable obstacles are neglected. 

The total traverse distance Dc required for a concentric circular 

survey is the sum of distances traveled on each circumference and 

the radial separation distances, c, between them: 

 

Dc = 2i

i=1

n















	





+(n1) c (2) 

yielding the following QoP, 

 

Qc = n

2

2i

i=1

n















	





+(n1) c

. (3) 

For each linear spiral branch traversed (every = 2 radians), the 

spiral radius  increases by s (Fig. 4), i.e.,  = (s/2). It can be 

shown [12] that the total traverse distance Ds required for a linear 

spiral trajectory is then expressed as 

 

Ds = s

4

 n

2

 (4) 

where n is the maximum spiral angle reached. The resulting QoP 

is then 

 

Qs = 42

n

2

s n

2 . (5) 

Based on the QoP metric the two fixed-mobile configurations for 

remote sensor-based surveying can be compared. With roughly 

the same survey region area, their QoPs are distinguished by 

distance traveled. If the spiral begins and ends as shown in Fig. 4, 

then n = 2n, and Ds = sn2

. For closest equivalence between 

the two trajectories, let the first circle radius be equal to the initial 

spiral radius, 1, and let 1 = c = s. Under these conditions, 2 = 

1 + c = 2c, 3 = 3c, 4 = 4c, and so on. The summation term 

in Eq. (2) then becomes a function of an arithmetic series and 

simplifies as follows. 

m-nodes 

202
 

i

i=1

n

 =c + 2c + 2c +... + nc (6) 

 

= c(1+ 2 + 3+... + n)

= c 1

2[ ] n(n +1) 

Using this result in Eq. (2), we have 

 

Dc = 2 c 1

2[ ] n(n +1) +(n1) c (7) 

 

= c n2 +( +1)n1 [ ] . 

Therefore, Dc > Ds independent of an equivalent separation 

distance. A rover executing a concentric circular survey of n

circles would need to traverse over (4n–1)c meters more to cover 

the same area as it could with a spiral trajectory of n branches. As 

an example, to traverse a survey trajectory of n = 3 concentric 

circles separated by c = 10 m, a rover would drive a linear 

distance of 397 m; to survey a roughly equivalent area using a 

spiral trajectory of n = 3 branches separated by s = 10 m it would 

drive a linear distance of 283 m, or 29% less in this case. 

3.3 Multiple-Site Remote Sensing Surveys 

An example of a mobile-mobile, or tandem, survey system 

configuration is illustrated in Fig. 5. Both rovers could carry the 

active and passive components of the distributed survey 

instrument (e.g., for redundancy), or each rover could carry the 

companion component to the other’s payload. Such survey 

configurations are suitable for multiple-site surveys due to the 

mobility of both platforms. The same dual mobility enables this 

tandem configuration to perform a number of approaches to 

remote sensor-based mobile surveying including, as special cases, 

the approaches described above for single-site surveys. 

Figure 5. Tandem distributed remote sensing configuration. 

3.4 Multi-Site Remote Survey Performance 

A tandem-robot system was proposed in [6, 9] in which one robot 

carried an active instrument and the other carried the instrument’s 

passive receiver. The robots would cooperatively perform remote 

sensor-based surveys using either parallel-swath or circular 

patterns where the width of a swath is the separation distance 

between the robots. The QoP metric was applied to compare 

several variants of these survey patterns including those illustrated 

below in Fig. 6. These survey approaches are referred to here as 

tandem-parallel and tandem-circular, and the QoPs for each are: 

 

Qtp = mntp

[2mn + 2(n1)tp]

 (8) 

 

Qtc = (n tc / 2)2

 tc

2 n2 + 2n4 ( )

 (9) 

where m is the length of a surveyed parallel swath (see Fig. 6), tp

and tc are the robot separation/measurement distances during a 

survey, and n (in both equations) is the total number of swaths 

surveyed [9]. The denominators of Eqs. (8) and (9) express the 

total distances, Dtp and Dtc, traversed by both robots for the 

respective tandem survey types. 

Figure 6. Tandem parallel and circular remote sensing survey 

trajectories. 

4. CHARACTERISTIC PERFORMANCE 

OF MOBILE SURVEYS 

The use of a common performance metric to comparatively rank a 

set of options provides a valuable basis or choosing the best 

option for a given task. However, direct one-to-one comparisons 

of the mobile surveying approaches discussed above are not 

straightforward given their respective differences in survey 

system configuration and survey trajectories. In fact, they can be 

prescribed for considerably different types of survey tasks in 

practice. Nonetheless, somewhat common grounds for 

comparison would provide a general sense for the relative 

performance of each approach. As a useful compromise a 

characteristic comparison is made here, still using a common 

metric, but based on assumptions that serve to equalize 

differences across the set of options. We use the QoP as the 

common metric here but any of a variety of metrics could be used 

instead. 

203
Consider a mobile survey of a designated region with common 

area, A, and performed by each of the local and remote sensorbased methods discussed above. Recall that the metric for each 

survey type is the total area covered divided by the total distance 

traversed, D, during the survey (QoP = A/D). Since A is 

considered to be a common survey region size, differences in the 

QoP are a function of differences in D only. Further assume that 

each survey is designed for a comparable area coverage 

resolution; this would call for equal values of the parameters p, 

c, s, tp, and tc. For the respective QoPs given by Eqs. (1), (3), 

(5), (8), and (9), the distance traveled is a function of the area 

coverage resolution. For simplicity, we assume a value of unity 

as the common value for the respective resolution parameters. 

With this assumption the expression of distance traversed for each 

QoP becomes a function of parameter n only, with the exception 

of Qp and Qtp, i.e., the local parallel and tandem-parallel survey 

metrics in Eqs. (1) and (8). If we assume a square survey region, 

then the length of a transect for a local parallel survey becomes m

= (n-1)p = (n-1), since p is set to unity. Similarly, the length of a 

swath for a remote tandem-parallel survey becomes m = ntp = n, 

since tp is set to unity. With all traverse distances as functions of 

the n-parameter for each survey type the following characteristic 

expressions, D(n), can be created 

 

Dp(n) = n2 1 (10) 

 

Dc(n) = n2 +( +1)n1 (11) 

 

Ds(n) = n2 (12) 

 

Dtp(n) = 2n2 + 2(n1) (13) 

 

Dtc(n) = 1

2 n2 + n2. (14) 

Note that Eqs. (10)-(14) are only characteristic of the respective 

distances traversed due to the different meanings for n for each 

survey type, i.e., the number of parallel transects, concentric 

circles, spiral branches, and parallel swaths. For this discussion 

we will generally refer to n as the number of survey passes. Fig. 7 

shows the characteristic trends of traverse distances required by 

each mobile survey configuration to cover the same area with 

comparable coverage resolution. 

The characteristic trends are shown for up to 100 survey passes. 

As the number of survey passes increases the characteristic 

distances for the circular and spiral remote sensor-based surveys 

increase at the fastest and roughly the same rate. Circular remotesensing surveys require the longest characteristic traverse 

distances. The inset graph in Fig. 7, which shows the same trends 

for up to an order of magnitude less survey passes (up to 10), 

reveals a more pronounced difference between expected distances 

required for circular and spiral surveys. The QoPs for these 

fixed-mobile surveys would be expected to decrease most rapidly 

with large numbers of survey passes, while higher QoPs would be 

expected for spiral surveys with low numbers of passes. For the 

tandem configurations, parallel circular surveys would be 

expected to perform better than parallel swath surveys, which 

would require characteristically longer traverse distances. The 

QoPs for tandem approaches would be expected to be higher than 

those of fixed-mobile approaches for the same survey region and 

coverage resolution. This reflects the advantage of using more 

than one rover for distributed remote sensing survey tasks [6]. 

The popular parallel transect survey approach for single rovers 

with local sensing devices has the slowest trend of increasing 

distance as the number of survey passes increases. Thus, its QoP 

would be expected to be high and least impacted by n, relative to 

the other approaches, for surveying the same area at a comparable 

coverage resolution. 

Figure 7. Characteristic traverse distances for mobile survey 

configurations. 

5. ENRICHING METRICS FOR SURVEYS 

ON PLANETARY SURFACES 

Thus far we have considered evaluation of coverage performance 

for surveys based on simple geometric measures of area and 

distance. Other important measures should be considered to 

enrich performance evaluation in the domain of planetary robotic 

systems and otherwise resource-constrained field robot systems. 

In fact, the selection of a candidate survey trajectory type for a 

given survey region can be based on metrics that provide some 

measure of relative resource usage during trajectory following 

(e.g., time, power, survey data storage). Selection of a survey 

type can also be based on any known physical constraints about 

the survey region such as terrain topography or the size and 

distribution of phenomena to be measured. 

Past work provides guidance in this direction. For example, 

maximization of incident solar energy on rover solar arrays has 

been considered as a determinant for selection among several 

survey trajectory types [13]. Another study applied an energy 

efficiency metric, defined as a ratio of area covered to energy 

consumed, to evaluate parallel line, circular spiral, and square 

spiral trajectories [12]. Other attributes can be adopted that are 

germane to surveying for planetary surface exploration but 

proposed in the context of mobility/navigation or task 

performance. These include terrain traversability measures such 

as obstacle abundance [14, 15] and number or effort of rovers and 

humans operators involved [16]. While identifying domain 

specific attributes that would enrich the relevance of existing 

geometric measures is helpful, the manner in which they would be 

incorporated into a metric formulation is also worth considering. 

Computationally complicated metric formulations can sometimes 

make the use of a metric as a decision aid difficult or can obscure 

the interpretation of the metric. In the domain of planetary site 

characterization a host of system, mission, and/or environmental 

constraints will affect the performance of mobile surveying tasks. 

204
Performance metrics based solely geometric aspects of the task do 

not capture other important performance impacts of the task, and 

therefore are particularly limited as decision aids. Mission 

operators will be better equipped to select appropriate survey 

methods when using metrics that account for a broader range of 

performance impacts that include system resources, terrain 

information or task constraints in addition to geometric measures 

like the QoP. 

As one example of how a resource attribute can change and 

influence the effectiveness of a basic metric consider the 

following. In [12], energy consumed by robot wheel motors was 

considered based on an empirically derived model of DC motors. 

Differences in energy efficiency were attributed in part to the 

required amount of turns necessary to follow the search pattern. 

Depending on how a rover mobility system executes a traverse, 

many turns-in-place may be executed throughout a survey. Such 

maneuvers are not captured by a metric like the QoP and unless 

energy consumption is considered, the overall performance of a 

survey could be obscured. The study considered energy 

consumed during accelerations in addition to during turns, which 

led to a conclusion that circular spiral surveys were most efficient 

for larger survey areas while parallel line scans were most 

efficient for small survey areas [12]. This conclusion is based on 

the fact that the robot continuously moves without stopping and 

turning when executing spiral trajectories, thus consuming less 

energy over longer distances required for spiral surveys. Finally, 

consider that while distance traversed and energy consumed are 

correlated in most cases, if terrain traversability is ignored then a 

mobile surveying metric will not capture the distance or energy 

impacts of surveying a rough and rocky terrain cluttered with 

obstacles. Due to such considerations, we advocate for 

enrichment of metrics for mobile surveying tasks to improve their 

utility as decision aids for actual mission operations. 

6. SUMMARY AND CONCLUSIONS 

Science and engineering surveys will need to be conducted by 

mobile robotic systems to characterize sites on planetary surface 

missions. Various system configurations and surveying 

techniques are possible and a basis for selecting and evaluating 

the options is needed. Performance metrics provide some basis 

for decisions in this regard and a simple geometric measure is 

applied to five mobile survey approaches that have been proposed 

for robotic site characterization. The relative performance trends 

of the survey approaches were characterized based on a geometric 

assessment of their expected performance in surveying a common 

area at a comparable area coverage resolution. It is asserted that 

metrics solely expressing geometric aspects of survey task 

performance are particularly limited for selecting or evaluating 

survey options for planetary surface missions. The importance of 

capturing additional important attributes such as system resources, 

terrain information, or mission-related task constraints in 

performance metrics is discussed. Such enrichment is advocated 

to improve the utility of performance metrics as decision aids to 

mission operators. 

7. REFERENCES 

[1] Garcia, E. and Gonzalez de Santos, P. 2004. Mobile-robot 

navigation with complete coverage of unstructured 

environments. Robotics and Autonomous Syst. 46, 195-204. 

[2] Wong, S.C., Middleton, L, MacDonald, B.A. 2002. 

Performance metrics for robot coverage tasks. In Proc. of the 

Australasian Conf. on Robotics and Automation (Auckland, 

New Zealand, Nov. 2002). 7-12. 

[3] Mei, Y., Lu, Y.-H., Hu, Y.C. and Lee, C.S.G. 2006. 

Deployment of mobile robots with energy and timing 

constraints. IEEE Trans. on Robotics, 22, 3, 507-522. 

[4] Fong, T., Bualat, M., Edwards, L., Fluckiger, L., et al 2006. 

Human-robot site survey and sampling for space exploration. 

In Proc. of the AIAA Space Conf. (San Jose, CA, 2006). 

[5] Tunstel, E., Anderson, G., Wilson, E. 2007. Autonomous 

mobile surveying for science rovers using in situ distributed 

remote sensing. In Proc. of the IEEE Intl. Conf. on Systems, 

Man, and Cybernetics (Montreal, Oct. 2007). 2348-2353. 

[6] Anderson, G.T., Hashemi, R.R., Wilson, E., Clark, M. 2000. 

Application of cooperative robots to search for water on 

Mars using distributed spectroscopy. In Proc. of the Intl. 

Symp. on Robotics and Applications, WAC (Maui, HI). 

[7] Schmitt, H.H., Kulcinski, G.L., Sviatoslavsky I.N. and 

Carrier III, W.D. 1992. Spiral mining for lunar volatiles. In 

Proc. of the 3rd Intl. Conf. on Engineering, Construction, and 

Operations in Space III (Denver, CO) 1162-1170. 

[8] Fong, T., Allen, M., Bouyssounouse, X., Bualat, M.G., et al 

2008. Robotic site survey at Haughton Crater. In Proc. of the 

9th Intl. Symp. on Artificial Intelligence, Robotics and 

Automation in Space (Los Angeles, CA, February 2008). 

[9] Hashemi, R.R., Jin, L., Anderson, G.T., Wilson, E. and 

Clark, M. 2001. A comparison of search patterns for 

cooperative robots operating in remote environments. In 

Proc. of the International Symp. on Information Technology: 

Computing and Coding (Las Vegas, NV) 668-672. 

[10] Wilson, E.W., Tunstel, E.W. and Anderson, G.T. 2007. 

BioGAS spectrometer for biogenic gas detection and location 

on the surface of Mars. In Proc. of the AIAA Infotech@ 

Aerospace Conf. and Exhibit (Rohnert Park, CA, May 2007). 

[11] Hashmonay, R.A. and Yost, M.G. 1999. Innovative approach 

for estimating fugitive gaseous fluxes using computed 

tomography and remote optical sensing techniques. Journal 

of Air Waste Management Assoc. 49, 8, 966-972. 

[12] Mei, Y., Lu, Y.-H., Hu, Y.C. and Lee, C.S.G. 2004. Energyefficient motion planning for mobile robots. In Proc. of the 

IEEE Intl. Conf. on Robotics and Automation (New Orleans, 

LA) 4344–4349. 

[13] Shillcutt, K.J. 2000 Solar Based Navigation for Robotic 

Explorers. Doctoral Thesis. Robotics Institute, Carnegie 

Mellon University (Pittsburgh, PA) CMU-RI-TR-00-25. 

[14] Tunstel, E. 2007. Operational performance metrics for Mars 

Exploration Rovers. Journal of Field Robotics: Quant. Perf. 

Eval. of Robotic and Intelligent Systems, 24, 8-9, 651-670. 

[15] Sukhatme, G.S. and Bekey, G.A. 1996. Multicriteria 

evaluation of a planetary rover. In Proc. of the IEEE Intl. 

Conf. on Robotics and Automation (Minneapolis, MN). 

[16] Elfes, A., Dolan, J., Podnar, G., Mau, S. and Bergerman, M. 

2006. Safe and efficient robotic space exploration with telesupervised autonomous robots. In Proc. of the AAAI Spring 

Symposium (Stanford, CA, March 2006) 104-113.

205
Evaluating Situation Awareness of Autonomous Systems

Jan D. Gehrke

Center for Computing Technologies (TZI)

Universität Bremen

Am Fallturm 1, 28359 Bremen, Germany

jgehrke@tzi.de

ABSTRACT

Autonomous systems proved to be very successful in specialized problem domains. But their perception, reasoning,

planning and behavior capabilities are generally designed to

fit special purposes. For instance, a robotic agent perceives

its environment in a way that was defined in advance by

a human designer. The agent does not exhibit a certain

perception behavior because it actually thinks it would be

reasonable to do so. But with an increasing level of autonomy as well as a larger temporal and spatial scope of

agent operation higher-level situation analysis and assessment become essential. This paper examines criteria for

evaluating situation-awareness of autonomous systems and

proposes methods to satisfy them. An example application

scenario is presented that provides initial results for evaluating situation-aware systems.

1. INTRODUCTION

Autonomous systems are being developed for numerous

application areas. These systems proved to be very successful in specialized problem domains, e. g., road driving, area

exploration, or robot soccer. Nevertheless, in many cases,

the perception, reasoning, planning and behavior capabilities of autonomous systems are designed to fit a special

purpose. For instance, a robotic agent perceives its environment in a way that was defined in advance by a human designer. Therefore, the agent does not show a certain

perception behavior because it actually thinks it would be

reasonable to do so. It is a reflex rather than a deliberate

action. For a lot of applications this might be sufficient.

But with an increasing level of autonomy as well as a larger

temporal and spatial scope of agent operation higher-level

situation analysis and assessment become essential. We will

focus on knowledge-based autonomous systems that require

up-to-date knowledge to decide on their next course of action. Knowledge-based systems are particularly challenging

if they require knowledge of distant locations and/or prediction of future events. These systems cannot rely on their own

Permission to make digital or hard copies of all or part of this work for

personal or classroom use is granted without fee provided that copies are

not made or distributed for profit or commercial advantage and that copies

bear this notice and the full citation on the first page. To copy otherwise, to

republish, to post on servers or to redistribute to lists, requires prior specific

permission and/or a fee.

PerMIS ’08, August 19–21, 2008, Gaithersburg, MD, USA

Copyright 2008 ACM 978-1-60558-293-1 ...$5.00.

sensory capabilities only. They need to infer future states

and communicate with other agents to share information.

Situation assessment depends on the current goals of the

autonomous system and knowledge about the state of the

world. The relevance of a specific piece of information or

some kind of information for situation assessment is determined by the current plan and other potential plans under

consideration. Information relevance leads to the pragmatic

dimension of knowledge-based systems, i. e., information on

how to use information. Usually, this is implicitly specified

by the decision system. For instance, the decision system

may use behavior rules whose rule body implies the information needed to evaluate the rule head. Problems arise if the

decision-relevant information is not available to the agent.

Depending on the applied knowledge representation and reasoning mechanism, missing information is simply considered

undefined, default-valued, or false. The latter applies for

predicates when using negation as failure [7] as in logic programming. This seems inadequate for autonomous systems

in partially observable environments. Even the Open World

Assumption turns out to be insufficient for situation assessment. While it prevents to assume wrong states of the unknown world and to base inferences on them, it does not

directly enable to reason about what is unknown. As a consequence, the system would not be able to assess a situation

correctly, e. g., to detect a harmful risk, because it has a lack

of information which it is not aware of.

Hence, autonomous systems doing situation assessment

have to be enabled to detect unknown information, thereby

becoming known unknowns. This detection process must

be governed and prioritized by information relevance. If

the agent’s sensory capabilities cannot provide information

needed, other agents or information sources have to be inquired. As an alternative, the agent has to accept its lack of

information and address it, e. g., by more cautious behavior.

Only autonomous systems possessing such higher level

reasoning capabilities are able to have true situation awareness [10]. It even becomes more complicated if agents have

to reason about future events. Such agents would need

prediction abilities including knowledge on how the world

evolves in order to qualify the probability that some information does not change in a given time interval. In spacious environments with mobile robots, additional spatial

reasoning about information dynamics is required. This paper outlines a classification of criteria for situation awareness

of autonomous systems and suggests knowledge representation and reasoning methods to address them.

The remainder of this paper is structured as follows. Sec206
tion 2 discusses issues of situation awareness in established

autonomous system architectures. Section 3 defines and examines awareness criteria and possible techniques to implement them. A corresponding example scenario for a preliminary study is presented in section 4). The paper concludes

with a discussion of this survey (Sect. 5) and a summary

(Sect. 6).

2. AUTONOMOUS AGENTS AND

SITUATION AWARENESS

Intelligent agents are a fundamental concept in Artificial

Intelligence for autonomous decision-making. For most applications domains of agents up-to-date and precise knowledge on the state of the world is crucial for system performance. But surprisingly a lot of usual architectures do

not explicitly consider the acquisition of information needed.

This limitation might lead to suboptimal, wrong, or even disastrous decisions. Thus situation awareness for autonomous

systems intends to evaluate and establish the basis for decision making depending on the agent’s current tasks and

goals.

Williams et al. [22] have a similar goal. They evaluate

the so-called groundedness of representations in autonomous

systems (mainly those applied in RoboCup competitions).

The approach defines a measure for the capability of creating and maintaining correct associations between representations and their (physical) real-world counterparts in

the system’s knowledge base. Proposed qualities of groundedness include, e. g., relevance, accuracy/precision, uncertainty management, and self-awareness w. r. t. the state of

the robot body, location, and sensors. The corresponding

system evaluation is rather qualitative and performed offline

by humans. Thus, the approach provides useful criteria for

system evaluation but does not enable the system to reason

about itself in order to improve its groundedness.

The simple reflex agent, as the most basic kind of agent,

is the worst example for groundedness or situation awareness. Such agents are governed by condition/action rules

and always do the same thing given the same perception. In

contrast to the model-based reflex agent it has no internal

state influencing its decisions [20]. Both reflex agents cannot be considered situation-aware. The simple reflex agent

only takes into account instantaneous knowledge; the modelbased variant has no notion of information relevance because

it has no explicit goals. Anyway, there may be simple but

useful tasks that are successfully handled by reflex agents.

The most important term in AI is the rational agent.

Wooldridge defines an agent to be “rational if it chooses to

perform actions that are in its own best interests, given the

beliefs it has about the world” [23, p. 1]. But this definition

could also consider an agent rational if it chooses an action

without knowing the state of the world. Thus, the situationaware agent extends and substantiates the classical rational

agent definition. The belief about the world is no longer

taken for granted but actively controlled by knowledge acquisition as an additional reasoning process.

The belief-desire-intention (BDI) model has become a prevalent approach in academia for deliberative software agent

architectures (cf. [23, 15]). It is based on a theory of human

practical reasoning developed by Bratman [6]. Human practical reasoning, according to BDI, consists of deliberation,

i. e., deciding what state should be achieved, and meansends reasoning, i. e., deciding how to achieve it. In the BDI

model, an agent is represented by its subjective knowledge

about the world (beliefs) and persistent goals that should

be achieved (desires). Desires and current beliefs result in

achievable goals and possible actions towards them. Finally,

in a process of deliberation, the agent commits to a goal

and a corresponding plan (intention). The fundamental BDI

model does not consider the assessment of beliefs in terms of

completeness, correctness/uncertainty, or being up-to-date

with respect to the goals to be achieved. Additionally, the

model does not take into account different levels of decision

making with respect to real-time requirements or temporal

scope of action and decision making.

The Real-time Control System (RCS) developed at National Institute of Standards and Technology (NIST) models

an intelligent system as a hierarchy of goal-directed sensoryinteractive control processes [2] representing organizational

levels as well as temporal scopes of decision making. The

process hierarchy in RCS enables the decomposition of subtasks to different agents as well as different planning intervals within a single agent. Each level contains computational elements for sensory processing, world modeling, value

judgment, and behavior generation [1]. Situation awareness

could be assigned to the higher-level RCS world modeling

components with a tight connection to behavior generation

and sensory processing. That is, RCS could be augmented

in world modeling by goal-oriented pro-active knowledge acquisition that is governed by behavior generation demands

and may provide a focus of attention in sensory processing.

3. CRITERIA FOR SITUATION

AWARENESS

Situation awareness is a field of research that commonly

examines information requirements of humans for special

jobs such as facility monitoring or flying aircraft [10]. Endsley [9, p. 97] describes situation awareness as “the perception of the elements in the environment within a volume of

time and space, the comprehension of their meaning and the

projection of their status in the near future”. This leads to

Endsley’s three levels of situation awareness:

• Level 1 – Perception: Basic perception of important

information.

• Level 2 – Comprehension: Correct interpretation

and integration of perceptions as well as relevance assessment.

• Level 3 – Projection: The ability to predict future situations based on current perceptions and background knowledge.

Although the definition and the three levels of awareness

are intended for human situation awareness they can be

adopted for autonomous systems, too. Nevertheless, there

are a lot of technical requirements that are partially taken

for granted regarding humans but much more challenging for

technical systems. Thus, this section proposes the following

criteria for situation awareness of autonomous systems and

possible methods to fulfill them:

1. Reasoning about ignorance: The agent’s knowledge base can be queried for unknown or uncertain

information.

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2. Model of perception abilities: The agent is aware

of its sensors and the kind of information they may

generate.

3. Model of information relevance: Based on the current set of goals or a general utility function as well as

applied decision rules, the agent can identify information needed and qualify its importance for its performance measure.

4. Model of information dynamics: Knowledge on

information dynamics that provides stability information for prediction of future states of the world.

5. Spatio-temporal reasoning: The model of information dynamics is applied for temporal reasoning on

change over time and spatial reasoning on neighborhood and hierarchies of regions

6. Social ability: If agents need information beyond

their sensory capabilities they have to cooperate with

other agents for external information acquisition.

3.1 Reasoning about Ignorance

To enable an autonomous system to measure awareness in

a given situation the system needs to know what it does not

know (known unknowns). That is, it has to detect a possible

lack of knowledge in its knowledge base. This is particularly

important and challenging in environments that are highly

dynamic and only partially observable. Unfortunately, many

logic-based systems use negation as failure in reasoning, i. e.,

propositions or predicates are assumed to be false if there

is no fact or prove stating the opposite. This closed world

assumption (CWA) is opposed to the open world assumption

(OWA) which does not make any assumptions about missing

knowledge. Instead, logical inference only relies on given

facts.

Open world reasoning is particularly applied in ontologies

and description logics [3] for concept subsumption in ontology TBoxes, i. e., the schema level of a knowledge base.

Situation awareness is rather focused on the instance or assertional level (ABox) of a knowledge base. While the open

world assumption also applies for ABox reasoning, it does

not provide inferences that would directly provide information on unknown facts. In contrast, a query for the truth of

facts that are neither known nor deducible will just return

false.

As a consequence, CWA and OWA reasoning systems will

create a biased view of the state of the world that is very

likely to be wrong. If decisions rely on that wrong beliefs

system performance is jeopardized. But a strictly logical

approach to reason about agent ignorance will raise several

difficulties for the logical foundations of representation and

reasoning as well as computational efficiency. A structural

approach that keeps track of knowledge base changes and instantly replies to queries on ignorance is probably preferable.

Anyway, a three-valued logic with OWA reasoning would be

required, too.

In general, a strictly logic-based knowledge representation

in dynamic environments is debatable. These approaches do

not sufficiently handle the uncertainty that is an inevitable

consequence in such domains. Though logics are still very

useful and powerful for representing background knowledge

of an autonomous system, dynamic environmental properties should rather be represented by probabilistic approaches

with aleatory variables. In particular, Bayesian inference

provides powerful means to reason about uncertainty. A

corresponding approach for value measurement of missing

information is presented in Sect. 3.3.

3.2 Model of Perception Abilities

While it is important to be aware of ignorance, agents

might deliberately or of necessity choose to decide instantly

although having incomplete or uncertain knowledge. This

might be due to limited resources or perception abilities, i. e.,

sensors. An autonomous system that desires a certain kind

of information may not be able to acquire this information

from its own sensors or data sources. In such cases, it is

obviously not reasonable to wait for that information before

the decision for which it is considered helpful.

But deliberate ignorance requires background knowledge

on what information can be obtained or not. This knowledge

can be provided by a sensor model that describes sensors by

the type of information they may deliver as well as precision,

accuracy, spatial range, and response time. A related ability,

the projection of future events, is discussed in Sect. 3.4.

For situation-aware agents we created an OWL-DL [4] ontology of possible sensors and their properties. This ontology

does not describe concrete sensor, e. g., some special LIDAR

product. Instead, it represents

• types of sensor devices (simple and complex),

• the (usually physical) quantities that are measured,

• the unit of measurement (e. g. SI units),

• the method of measurement (mechanical, electrical,

optical, chemical etc.), and

• the sensor quality in terms of measurement errors, precision/accuracy, range, response time etc.

Examples of modeled sensors are those for electrical quantities (i. e. ohmmeter, galvanometer, voltmeter, etc.), electromagnetic radiation sensors for a given spectrum (i. e. infrared, visible light, etc.), acoustic sensors, thermal sensors

and range sensors etc. The basic sensors were called detectors. But sensors as well as measured quantities can also

be more complex. For instance, a weather “sensor” provides

more than just one quantity and may aggregate raw measurements to some qualitative information.

The general advantage for agents using this ontology is

that they can logically infer whether they have a sensor

(or other information source) that will provide a desired

information on some quantity or other environmental feature. Additionally, an ontology-grounded value description

will allow for better interpretation of sensor data. The ontology also enables agents to communication about desired

information abstracting from the specific sensors used (cf.

Sect. 3.6).

3.3 Model of Information Relevance

In large and dynamic environments there will be a lot

of information that is inaccessible or unknown to the autonomous system. Other information is available but there

are no sufficient resources for processing. Obviously this

also holds for humans but they perform very good in a lot

of tasks anyway. This is because the major part of the state

of the world is simply irrelevant. Humans have the basic

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cognitive capability to focus on the relevant stimuli and ignore the others. For low-level tasks this human capability

is not based on a deliberation of relevance but basic cognitive functions, e. g., within superior colliculus for visual,

auditory and somatosensory stimuli. Only relevant stimuli

arrive at short-term memory [16].

When trying to imitate this human capability in a cognitive approach to autonomous systems it is practically impossible to design a generic approach for all purposes. Low-level

attention control will require low-level implementation because of real-time constraints. But there are also other kinds

of information that allow for higher-level assessment of information relevance for determining a focus of attention. Such

information is related to decisions with temporal scopes beyond the servo level with 0.05 seconds plans (cf. [2]).

Based on the current set of goals or a general utility function as well as applied decision rules, the agent could identify

information needed and qualify its importance for its performance measure. For goal-oriented systems with rule-based

decisions, information (as logical predicate) is relevant if it is

contained in the body of some rule whose head is going to be

evaluated. While this could be identified in a quite straightforward way on syntax level, such a system would require to

determine predicates with unknown truth value. This again,

has to apply some reasoning on ignorance (Sect. 3.1).

Utility-based systems with probabilistic knowledge representation need to assess information relevance differently.

Here we consider a decision-theoretic agent that tries to

maximize its utility based on expected utility of each action

A with possible outcomes O1 to On of different probabilities

given a set of evidences E. In simple cases there is a single

decision (not a sequence) and a corresponding action with

a discrete distribution of results. Then, the expected utility

of action A is defined by:

EU(A|E) = n

i=1

P(Oi(A)|Do(A), E) · U(Oi(A))

Here the best action α = maxA EU(A|E) depends on the

given evidence E. Thus α will potentially change given additional evidence Ej :

αEj = max A EU(A|E,Ej )

Intuitively, the relevance (or value) VEj of a new evidence

Ej is then defined as the difference in expected utility of

the chosen action after and before knowing Ej . But because

the agent needs to evaluate the value before acquiring the

information it will need to average over possible assignments

ejk of Ej , i. e.,

VEj =



k

P(Ej = ejk|E) · EU(αejk |E,Ej = ejk)



− EU(α|E)

This approach is proposed in information value theory by

Howard [13]. If the acquisition of information Ej is costly

it is only worthwhile if its price is less than its value (presupposing utility is measured in same quantity as price).

Note that the information value formula presupposes perfect information. Uncertain information can be included by

modeling a probabilistic relation from the uncertain variable

to the actual variable.

In order to apply this relevance measurement to assess

and potentially increase situation awareness an agent will

Figure 1: Simple decision network example for a

route selection problem (adapted from [20, p. 598])

need to proceed in a systematic way. That is, there is

no sense in evaluating relevance of all possible information

(i. e., aleatory variables). The agent needs some background

knowledge on utility-influencing factors.

This knowledge can be provided as a simple list or, more

elaborately, as a decision network (or decision diagram) [14].

A decision network combines Bayesian inference with actions

and utilities as additional types of nodes besides the usual

chance nodes. The factors directly influencing agent utility

are represented as parent chance nodes. Possible outcomes

of actions are modeled as child chance nodes of each action

respectively. There may be additional chance nodes that

influence other chance nodes as in Bayesian networks. An

example is given in Figure 1.

This decision problem representation enables a systematic ordering of information evaluation and acquisition by

traversing the network from the utility node(s) along the

path with highest influence on utility. For this purpose, it is

necessary to distinguish sensor nodes as special chance nodes

since only evidence from sensor nodes is actually available.

Unfortunately, the design of decision networks features

the same difficulties as in Bayesian networks: one needs to

assign prior probabilities as well as conditional probabilities

based on sufficient experience. Because this is not given in

general, the agent should be able to update the Bayesian influence model based on ongoing experience. Updates should

primarily concern the assignment of probabilities. Creating

new Bayesian links between chance nodes is likely to fail due

to insufficient statistical evidence in complex and dynamic

environments causing possible post-hoc or cum-hoc fallacies.

3.4 Model of Information Dynamics

Whereas decision-theoretic information-gathering agents

can be implemented based on decision networks there are

special requirements in dynamic environments with decisions of long temporal and spatial scope. As an example,

we will use a simple route planning task with a truck that

aims at finding the fastest route between two locations in

a road network. A decision network for that problem could

include chance nodes for influencing factors such as construction work, weather, traffic, time of day, and others (cf.

Fig. 1).

The special challenge is that these factors describe future

states of the world as well as properties of distant locations.

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Consequently, the relevant information is not available from

own sensors (distant information) or even theoretically unavailable (future states). Anyway, background knowledge on

information dynamics can help infer or estimate such information. If the agent knows that some environment property

(e. g., weather) holds in an area of certain extension (e. g. a

particular stretch of a freeway) it is easily able to infer from

a property of one location to the same property at another

location within that area (cf. Sect. 3.5). It gets much more

complicated when the agent has to infer this property in an

neighboring area. There will be no general probabilistic relation here. It may depend on the property, location, time,

and possibly several other factors.

On the other hand, an environment property that is stated

to hold for a larger area should allow to deduce this property

for sub-areas based on known region partonomies. Again,

this inference will provide uncertain information. The statement for a large area will usually only average all locations

therein. Thus, single locations might be very different.

Similar considerations also hold for the temporal dimension. A situation-aware system needs prediction abilities

to estimate probabilities of variable assignments at future

states or it has to acquire reliable predictions from other

sources. Obviously, this becomes less achievable when the

predicted state is far in the future. On the other hand, there

are variables that will not change or only change slowly or

rarely.

Re-iterating the above examples, weather or traffic feature some expected stability and transition probability from

one state to another, respectively. Such dynamics are often

modeled with Hidden Markov Models (HMMs), Kalman filters, or, more general, dynamic Bayesian networks (DBN).

That is, one defines an influence or sensor model and a time

transition model for the property. Classical DBNs presuppose a fixed discretization of time from one state to another.

But in general a reasonable time discretization for a Markov

transition model will depend on an average stability of the

modeled property. Additionally, information stability may

again depend on other factors and change from state to the

following.

While DBNs try to infer from sensor evidence and a variable assignment at one state to that of a following (or previous) state, situation-aware agents might not need such

kind of prediction for rather distant decisions (i. e. several

hours). In some cases these predictions, if possible, will

tend to be very uncertain anyway. The most na ̈ıve autonomous system will just assume that everything that holds

presently will stay that way all along. A situation-aware system should at least consider that the world is dynamic and

have some idea about these dynamics. It might be sufficient

to know the expected stability (or half-life-period) of each

property/variable in order to evaluate the probability that

the current value will persist until the desired time in the

future. If such persistence is evaluated to be unlikely (i. e.

below a predefined threshold) the system is forced to rely on

prior probabilities.

In general we advocate the inclusion of dynamic Bayesian

networks in decision networks, i. e., dynamic decision networks.

3.5 Spatio-temporal Reasoning

If the situation-aware autonomous system evaluates relevance of missing information it will also need to qualify time

Figure 2: Spatio-temporal region defined by vehicle motion on a road stretch with uncertain driving

time.

Figure 3: Spatio-temporal region with uncertain departure time.

and space when/where the desired property value holds.

In the truck agent routing example the weather or traffic

at some distant freeway stretch will influence the expected

driving time. When trying to acquire the information from

some external source or sensor for that region, the agent

also has to consider the expected time when it plans to arrive there. Unfortunately, the arrival gets more and more

uncertain with increasing distance of that location.

Figure 2 depicts the situation for a road stretch at the beginning of a truck tour. While the departure time is known

arrival time is uncertain. The uncertainty of arrival time or

driving time can be provided by a decision network (or regular Bayesian network). But the agent needs to determine

the expected spatio-temporal region it will move in to qualify the information for that freeway in space in time. We

will call this a region of relevance for that agent.

We propose to choose a threshold as a quantile in probability distribution of arrival time to specify a confidence

interval of arrival time. The upper bound of that interval

will determine the upper temporal bound of the region of

relevance for that freeway stretch. All spatio-temporal information overlapping that region is considered potentially

relevant w. r. t. value of information (Sect. 3.3).

These regions of relevance will expand in temporal directions for distant locations because uncertainty of departure

time increases with uncertainty of arrival time for previous

regions. A region of relevance for distant locations is shown

in Figure 3.

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For qualitative topological inference on this regions the

agent can apply usual spatial calculi such as Region Connection Calculus (RCC) [19]. This is of particular interest

when agents want to share information and need to determine whether there is potential for cooperation. The regions

of relevance are then complemented by regions of expertise,

i. e., regions other agents can provide information for.

3.6 Social Ability

Social ability is one of the minimal criteria for intelligent

agents defined by Wooldridge and Jennings [24]. In this

context, social ability refers to communication with other

agents. For situation-awareness communication is needed

when there is relevant information that is neither available

from own sensors nor inferable by reasoning. For instance,

information on distant locations needs to be acquired from

external sources.

In practice, the mere ability of communication will not

suffice. A situation-aware system must determine that some

information cannot be acquired from own sensors (Sect. 3.2)

but is available from other sources instead. This includes the

discovery of such sources, a common communication language with agreed content semantics, and price negotiations

if information is subject to charges.

4. APPLICATION SCENARIO

One particular application domain in our research has

been autonomous logistics [21]. That means, there are agents

as autonomous decision makers that represent one or more

logistic objects (e. g. truck, container, or pallet) and control

logistic processes locally. This usually requires cooperation

with other logistic agents as well as continuous acquisition

of information for decision-making. This information is provided by local sensors (e. g., humidity sensors for monitoring

of perishable goods) as well as external data sources (e. g.

for weather and traffic reports).

When developing an autonomous logistics system, we evaluate agent behavior by stochastic simulation before deployment. That is, the developed agents as well as test mocks

representing external agents and other entities run in a simulated logistics environment before they are released to a

real-world environment. For this purpose we implemented

the multiagent-based simulation system PlaSMA (Platform

for Simulations with Multiple Agents). PlaSMA is based

on the FIPA-compatible multiagent development environment JADE [5]. Multiagent-based simulation (MABS) applies object-based modeling [18, 8] as well as discrete time,

distributed simulation techniques [11]. In MABS, the agents

are parallel logical simulation processes that, in general, represent objects of the simulation model at the same time.

Thus, MABS is a natural way to test agent behavior and

interaction.

We applied this simulation platform for studies of agent

situation awareness in vehicle route planning (similar to the

example in section 3). Uncertainty in vehicle route planning is an everyday problem in transportation over longer

distances. The shortest route is not always the fastest.

Even when considering maximum allowed or average expected speed on single roads the planned routes may prove

to be suboptimal. While suboptimal solutions are a natural

property in dynamic, open environments with partial observability, usual route planning does not make use of much

up-to-date or background information that would be obtainable and correlates with travel time.

We conducted simulation studies [12] that help find the

utility or relevance of environmental information on travel

time and its application in route planning cost functions.

Furthermore, the experiments should provide evidence for

the time in the future when incoming information is useful

and the robustness when working with uncertain or wrong

information.

Inductive machine learning was applied to pre-processed

traffic information in order to learn traffic models for specific roads depending on weather, time of day, and day of

week [12]. The data was based on German and Austrian

traffic censuses. The learned traffic model includes prediction rules like

[Speed=60]

<= [Day=Mo] [Time=morning]

[Weather=moderate..good]

That is, average possible speed on the corresponding road

is expected to be 60 kmph on Monday mornings if weather

conditions are from moderate to good. Such predictions

were integrated in a truck agent’s utility function for best

routes in a transportation process. As part of the agents

knowledge acquisition component, the planning system initiates the gathering of weather information within a certain

distance towards its destination. This information from external weather services together with time and date information is used to consult the rule base for a travel time prediction. The time and date in these rule base queries again

depends on prediction of travel time to reach the location of

interest (cf. discussion in Sect. 3.5).

In several stochastic simulations these predictions turned

out to be valuable. Situation-aware vehicle agents were up to

6.3 % faster on average than regular, non-predictive agents.

Additionally, the standard deviation of travel time was reduced by 28 %. With significance level α = 0.05 the simulated results to not differ more than 0.0016 % from the

actual values. Thus, dedicated means to increase situationawareness are actually shown to be of advantage in the presented logistics scenario.

5. DISCUSSION

The survey on situation awareness in this paper identifies criteria for knowledge representation and reasoning of

autonomous systems in dynamic environments. In particular, the paper focuses on domains with decisions that may

have a larger spatio-temporal scope. We do not claim that

the means proposed for implementing these criteria are imperative. Furthermore, a reference implementation of the

described approach is work in progress. The presented application example still relies on some pre-designed information acquisition behaviors instead of fully goal-oriented and

deliberate acquisition. An extended conceptual architecture

that includes explicit information acquisition for situation

assessment was proposed in [17].

The general question arises whether situation awareness

turns out to be necessary or even futile for particular autonomous systems. Furthermore, most systems will probably only fulfill a subset of all criteria. Some criteria are

probably not imperative for some degree of situation awareness. Endsley [10] also distinguishes three levels for human

situation awareness that could match a particular subset

211
of the criteria proposed here. Relevance assessment is certainly mandatory for level 2 (comprehension). Representing

and reasoning with information dynamics pertains to level 3

(projection). But social ability (i. e. information exchange)

is beyond the scope of Endsley’s approach. This criteria

could establish a fourth level of awareness. On the other

hand, a system could be able to share information but not

be capable of projection. So it does not fit in as an extension

of level 3.

But assuming an agent that is matching all criteria: Is

such an agent capable of actually measuring (i. e. quantifying) its situation awareness? We think that information

value theory has the answer. The difference between the

expected utility with current sensory evidence and the expected utility given complete sensory evidence (considering

perception abilities) could provide a corresponding measure.

But future research has to be done for a complete theory of

situation awareness and its assessment.

6. CONCLUSION

This paper provides a survey on situation awareness for

autonomous systems by analyzing features and limitations

of existing architectures and proposing a set of criteria to

be satisfied by situation-aware agents. The proposed criteria build upon the definition of human situation awareness

by Endsley [9, 10] but take into account the special requirements and needed capabilities of technical systems. The

proposed criteria are reasoning about ignorance, an agent

perception model, information relevance assessment, a model

of information dynamics and associated spatio-temporal reasoning capabilities, and social ability for acquiring information beyond own sensors.

The presented logistics routing scenario shows that seemingly barely relevant information on environmental properties can significantly increase performance of autonomous

agents. Future work will address a theoretical foundation of

situation awareness and its measurement based on dynamic

decision networks and information value theory.

7. ACKNOWLEDGMENTS

This research is funded by the German Research Foundation (DFG) within the Collaborative Research Center 637

“Autonomous Cooperating Logistic Processes: A Paradigm

Shift and its Limitations” (SFB 637) at the University of

Bremen, Germany.

8. REFERENCES

[1] J. Albus. A reference model architecture for intelligent

unmanned ground vehicles. In Proceedings of the SPIE

16th Annual International Symposium on Aerospace /

Defense Sensing, Simulation and Controls, pages

303–310, Apr. 1–5 2002.

[2] J. Albus, T. Barbera, and C. Schlenoff. RCS: An

intelligent agent architecture. In R. M. Jones, editor,

Intelligent Agent Architectures: Combining the

Strengths of Software Engineering and Cognitive

Systems, number WS-04-07 in AAAI Workshop

Reports. AAAI Press, 2004.

[3] F. Baader, D. Calvanese, D. L. McGuinness, D. Nardi,

and P. F. Patel-Schneider, editors. The Description

Logic Handbook. Theory, Implementation and

Applications. Cambridge University Press, 2nd edition,

2007.

[4] S. Bechhofer, F. van Harmelen, J. Hendler,

I. Horrocks, D. L. McGuinness, P. F. Patel-Schneider,

L. A. Stein, and F. W. Olin. OWL web ontology

language reference. Available from

http://www.w3.org/TR/owl-ref/, Feb. 10 2004.

[5] F. Bellifemine, A. Poggi, and G. Rimassa. Developing

multi-agent systems with a FIPA-compliant agent

framework. Software-Practice and Experience,

31(2):103–128, Feb. 2001.

[6] M. E. Bratman. Intention, Plans, and Practical

Reason. Harvard University Press, Cambridge, MA,

USA, 1987.

[7] K. L. Clark. Negation as failure. In H. Gallaire and

J. Minker, editors, Logic and Data Bases, pages

293–322, New York, 1978. Plenum Press.

[8] P. Davidsson. Multi agent based simulation: Beyond

social simulation. In Multi-Agent Based Simulation,

Second International Workshop (MABS 2000),

number 1979 in LNCS, pages 97–107, Boston, MA,

USA, July 8–9 2000. Springer-Verlag.

[9] M. R. Endsley. Design and evaluation of situation

awareness enhancement. In Proceedings of the Human

Factors Society 32nd Annual Meeting, volume 1, pages

97–101, Santa Mocica, CA, USA, 1988. Human

Factors Society.

[10] M. R. Endsley. Theoretical underpinnings of situation

awareness. A critical review. In M. R. Endsley and

D. J. Garland, editors, Situation Awareness Analysis

and Measurement, pages 3–32. Lawrence Erlbaum

Associates, Mahwah, NJ, USA, 2000.

[11] R. Fujimoto. Parallel and Distributed Simulation

Systems. John Wiley & Sons, New York, NY, 2000.

[12] J. D. Gehrke and J. Wojtusiak. Traffic Prediction for

Agent Route Planning. In International Conference on

Computational Science (ICCS 2008), number 5103 in

LNCS, pages 692–701, Krak ́ow, Poland, June 23–25

2008. Springer-Verlag.

[13] R. A. Howard. Information value theory. IEEE

Transactions on Systems Science and Cybernetics,

SSC-2(1):22–26, Aug. 1966.

[14] R. A. Howard and J. E. Matheson. Influence

diagrams. Decision Analysis, 2(3):127–143, Sept. 2005.

[15] S. Kirn, O. Herzog, P. Lockemann, and O. Spaniol,

editors. Multiagent Engineering: Theory and

Applications in Enterprises. Springer-Verlag, 2006.

[16] E. I. Knudsen. Fundamental components of attention.

Annual Review of Neuroscience, 30:57–78, July 2007.

[17] M. Lorenz, J. D. Gehrke, J. Hammer, H. Langer, and

I. J. Timm. Knowledge management to support

situation-aware risk management in autonomous,

self-managing agents. In Self-Organization and

Autonomic Informatics (I), volume 135 of Frontiers in

Artificial Intelligence and Applications, pages 114–128,

Amsterdam, 2005. IOS Press.

[18] H. V. D. Parunak, R. Savit, and R. L. Riolo.

Agent-Based Modeling vs. Equation-Based Modeling:

A Case Study and Users’ Guide. In MABS 1998,

pages 10–25, Paris, France, 1998. Springer-Verlag.

[19] D. A. Randell, Z. Cui, and A. G. Cohn. A spatial logic

212
based on regions and connection. In B. Nebel, C. Rich,

and W. Swartout, editors, Proceedings of the 3rd

International Conference on Principles of Knowledge

Representation and Reasoning, pages 165–176. Morgan

Kaufmann, 1992.

[20] S. J. Russell and P. Norvig. Artificial Intelligence: A

Modern Approach. Prentice Hall, Upper Saddle River,

NJ, USA, 2nd edition, 2003.

[21] B. Scholz-Reiter, K. Windt, and M. Freitag.

Autonomous logistic processes - New demands and

first approaches. In Proceedings of the 37th

CIRP-International Seminar on Manufacturing

Systems, pages 357–362, Budapest, May 19–21 2004.

[22] M.-A. Williams, P. G ̈ardenfors, A. Karol, J. McCarthy,

and C. Stantom. A framework for evaluating

groundedness of representations in systems: From

brains in vats to mobile robots. In IJCAI-05 Workshop

on Agents in Real-Time and Dynamic Environments,

pages 17–24, Edinburg, UK, July 30 2005.

[23] M. Wooldridge. Reasoning about Rational Agents. The

MIT Press, 2000.

[24] M. Wooldridge and N. R. Jennings. Intelligent agents:

Theory and practice. The Knowledge Engineering

Review, 10(2):115–152, 1995.

213
NIST/IEEE Virtual Manufacturing Automation 

Competition: From Earliest Beginnings to Future 

Directions 

Stephen Balakirsky 

National Institute of Standards and 

Technology 

100 Bureau Drive 

Gaithersburg, MD 20878 

stephen@nist.gov 

Raj Madhavan 

National Institute of Standards and 

Technology 

Gaithersburg, MD 20878 

Oak Ridge National Laboratory 

Oak Ridge, TN 37831 

raj.madhavan@nist.gov 

Chris Scrapper 

National Institute of Standards and 

Technology 

100 Bureau Drive 

Gaithersburg, MD 20878 

chris.scrapper@nist.gov 

ABSTRACT

This paper provides an overview of the National Institute of 

Standards and Technology (NIST)/IEEE Virtual Manufacturing 

and Automation Competition (VMAC). Detailed information will 

be provided on the competition’s objectives, history, and 

operation. In addition, the supporting software infrastructure will 

be discussed. 

Categories and Subject Descriptors

I.2.9 [Robotics]: Autonomous vehicles; 

commercial robots and applications; kinematics 

and dynamics,; workcell organization and 

planning.

General Terms

Performance, Experimentation, Verification, 

Management. 

Keywords

Competition, simulation, manufacturing, 

USARSim. 

1. INTRODUCTION 

Automated Guided Vehicles (AGVs) represent an integral 

component of today’s manufacturing processes. Major 

corporations use them on factory floors for jobs as diverse as 

intra-factory transport of goods between conveyors and assembly 

sections, parts and frame movements, and truck trailer 

loading/unloading. The National Institute of Standards and 

Technology (NIST) is currently running a program to develop test 

method standards for the next generation of AGVs. These test 

methods specifically target small- and medium-sized 

manufactures and the problems that they face in applying 

automation to legacy manufacturing facilities. 

In order to assess future automation needs, focus on solutions, and 

ease entry of new features into AGV product lines, NIST is 

striving to form a coalition that brings together the three 

communities of industrial end-users, researchers, and 

manufacturers of AGV equipment. This coalition will then focus 

on moving from real-world problems, to research activities, to 

system features. As the first thrust of this effort, NIST performed 

outreach to several small- and medium-sized manufactures. Phone 

interviews and site visits were conducted, and a common 

automation need emerged. This need is for both unit loaders and 

forklifts to operate in unstructured cramped environments to 

deliver parts and materials for use in the manufacturing process. 

Automating these systems to operate in unstructured 

environments presents an exciting area of current research in 

robotics and automation. Unfortunately, the traditional entry 

barrier into this research area is quite high. Researchers need an 

extensive physical environment, robotic hardware, and knowledge 

in research areas ranging from mobility and mapping to behavior 

generation. An accepted approach to lowering this entry barrier is 

through the use of simulation systems and open source software. 

The use of simulation significantly reduces the amount of 

infrastructure required, the number of AGV systems needed, and 

the risk to both humans and robots. In addition, hardware-in-theloop (HIL) or real/virtual testing allows for the exploration of 

scenarios that would be unsafe to pursue with actual robotic 

equipment. 

NIST turned to the IEEE to build researcher involvement in this 

new coalition by submitting a successful proposal to the 

Washington section of the Robotics and Automation Society of 

IEEE to create a new Virtual Manufacturing and Automation 

Competition (VMAC). 

2. VMAC PRELIMINARIES 

By soliciting proposals from IEEE members and local student 

branches and robotic clubs in the Greater Washington area 

(Maryland, Virginia, and the District of Columbia), the organizers 

were able to bring together eight teams from regional universities 

consisting of faculty mentors, undergraduate students, and 

graduate students. The original VMAC participants are shown in 

Figure 1. The educational institutions that participated in this 

effort were: two teams from Hood College (Frederick, MD), one 

team from George Mason University (Fairfax, VA), and two 

This paper is authored by employees of the United States Government 

and is in the public domain. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA 

ACM ISBN 978-1-60558-293-1/08/08.

214
teams from University of Maryland Eastern Shore (Princess Anne, 

MD). Two teams from George Washington University 

(Washington, DC) and one team from Morgan State University 

(Baltimore, MD) dropped out of the competition due to lack of 

interest and other timing conflicts. 

It has been NIST’s experience that competitions are an effective 

means of stimulating interest and participation among students. 

Competitions tend to get the students excited about the 

technologies and encourage larger participation in the research 

community. As mentioned earlier, one of the main motivations for 

the VMAC was to lower the entry barrier for teams to participate 

in the competition. As such, it was decided that the teams would 

be provided with all of the hardware and software necessary to 

compete. This included the Unified System for Automation and 

Robot Simulation (USARSim) [2] system, the Mobility Open 

Architecture Simulation and Tools (MOAST) robotic control 

framework [1], and the hardware to run the controller (a Linux 

PC). In addition to the hardware and software, two 

workshop/tutorials were held and a user’s support group was 

established. The first workshop was a 2-day event that took place 

in October 2007 at NIST in Gaithersburg, MD. During this 

workshop, participants were acquainted with the software base 

(USARSim and MOAST) and participated in the design of the 

competition events. A follow-up workshop was held at Hood 

College in February 2008 to track progress and provide hands-on 

assistance with any outstanding issues. 

Figure 1 : Members of the teams from the inaugural VMAC 

workshop. 

2.1 USARSim 

The USARSim project was originally created in 2002 by Carnegie 

Mellon University (CMU) and the University of Pittsburgh to 

study human-robot interaction in the area of Urban Search and 

Rescue (USAR); hence the original acronym USARSim [8, 13]. 

The first release of USARSim was built by creating modifications 

to Epic’s Unreal Engine 2 game engine1

. It supported models for 

 

e. 

1

 Certain commercial software and tools are identified in this 

paper in order to explain our research. Such identification does 

not imply recommendation or endorsement by the authors, nor 

a few differential drive robotic platforms, a restricted set of 

sensors, and a small set of USAR specific test arenas. In addition, 

the robotic platforms could only be controlled through the use of 

the RETSINA [11] multi-agent system softwar

In 2005, USARSim was selected as part of the base infrastructure 

for the RoboCup Rescue Virtual Robot Competition. The virtual 

robot competition is an annual international event that highlights 

research in diverse areas such as multi-agent cooperation, 

communications networks, advanced mobility, mapping, and 

victim search strategies. In addition to the competition, USARSim 

management was taken over by NIST and an international 

development community was established on the open source 

sourceforge.net website. While much of the original structure of 

the code was maintained, the code was reorganized and interfaces 

were standardized around SI units. The first official release 

(Version 1.0) was produced in October 2005. 

A large-scale development effort accompanied the transition to 

sourceforge and the involvement of the Robocup community. 

Version 3.31, released in July 2008 offers 15 different sensors, 

from odometry to an omnidirectional camera. 23 different robotic 

platforms are now available; these include wheeled robots, cars, 

tracked vehicles and flying robots. In addition, many of the 

sensors and robots have undergone rigorous validation in order to 

prove their similarities and difference from the real devices [6, 9, 

12]. With a growing community of users, urban search and rescue 

applications were no longer the only target area of interest for 

USARSim. In 2007, NIST provided additional modifications to 

USARSim to make it compatible with the manufacturing domain. 

These additions included a robotic forklift and unit loader AGV as 

shown in Figure 2. In order to introduce dynamics into the factory 

simulation, a “factory controller” was also introduced. This 

controller allows for the external control of conveyors, box 

chutes, and sensors that are able to interact with the vehicles under 

test. Due to the broader range of use that USARSim now enjoys, 

its acronym was maintained while its name was changed to 

Unified System for Automation and Robotics Simulation. 

Figure 2: Forklift and unit loader AGVs created for 

USARSim. 

 

does it imply that the software tools identified are necessarily 

the best available for the purpose. 

215
2.2 MOAST 

The MOAST framework builds upon several decades of robotic 

architecture and control system work that has been performed by 

NIST. The framework is designed to be a sample implementation 

of the 4D/RCS reference model architecture [4,5]. The RCS 

reference model architecture is a hierarchical, distributed, realtime control system architecture that decomposes a robotic system 

into manageable pieces while providing clear interfaces and roles 

for a variety of functional elements. 

Figure 3 depicts the general structure of each echelon (level) of 

the 4D/RCS hierarchy. Each echelon in 4D/RCS contains a 

systematic regularity and is composed of control nodes that follow 

a sense-model-act paradigm. These control nodes are sensory 

processing (SP), world modeling (WM), value judgment (VJ), and 

behavior generation (BG). Sensory processing is responsible for 

populating the world model with relevant facts. These facts are 

based on both raw sensor data and the results of previous SP (in 

the form of partial results or predictions of future results). WM 

must store this information, information about the system self, and 

general world knowledge and rules. Furthermore, it must provide 

a means of interpreting and accessing this data. BG computes 

possible courses of action to take based on the knowledge in the 

WM, the system’s goals, and the results of plan simulations. VJ 

aids in the BG process by providing a cost/benefit ratio for 

possible actions and world states. 

Figure 3: Generic 4D/RCS control node. 

All of the echelons in 4D/RCS follow the sense-model-act 

paradigm with the principal difference between echelons being in 

the knowledge requirements and the fidelity of the planning space. 

This regularity in the structure enables flexibility in the system 

architecture that allows scaling of the system to any arbitrary size 

or level of complexity [7]. 

In 2005, MOAST was officially released on sourceforge as a 

public domain robotic control system. Since that time, it has 

attracted an international developer community and now contains 

control modules for robotic vehicles, manipulators, and end 

effectors. Figure 4 depicts the currently implemented echelons of 

the control system and their responsibilities. The central idea 

behind the VMAC competition is that research groups would be 

able to select their area of expertise and modify a small subset of 

control modules in order to improve the overall system 

performance. After the competition, each research group is 

required to contribute their modified modules back to the 

community. Thus, all teams benefit from each other’s strengths. 

Figure 4: Control module responsibilities in the MOAST 

implementation of 4D/RCS. 

2.3 Competition Design 

This competition design was based on the successful RoboCup 

Rescue Virtual Robots Competitions [3]. Since all code used in 

these competitions is open source, participants are able to learn 

from their competitors and concentrate their research in their 

particular areas of expertise. It was envisioned that researchers 

from multi-agent cooperation, mapping, communications 

networks, and sensory processing backgrounds would all be 

interested in participating. 

The initial competition design was formulated by using the 

SCORE framework [10]. This framework specifies that an overall 

system scenario be defined, and then basic elemental skills that 

allow for the successful completion of the scenario be extracted. 

Systems are then evaluated on both their ability in the elemental 

tasks as well as the overall scenario. 

From the outset, the competition was to be based on real-world 

scenarios. Based on NIST’s industry outreach effort, the scenario 

chosen was a factory setting that had significant clutter, maze-like 

passageways of various widths, and dynamic obstacles. The 

objective was to have several Ackerman-steered AGVs pick-up 

packages at a central loading station, and deliver these packages 

to one of several unloading stations. The package destinations 

were encoded in a Radio Frequency IDentification (RFID) Tag on 

each package. 

Utilizing the SCORE framework, this scenario was decomposed 

into elemental tasks that included traffic management, route 

planning, accurate path following, and docking with 

loading/unloading stations. While the baseline code provided to 

the teams was capable of performing the objectives, it was far 

from optimal. 

As time progressed, it became apparent that performing a 

complete SCORE evaluation of all of the elemental tasks and the 

overall scenario was an overly ambitious set of tasks for the first 

year of the competition. A decision was made to break the 

competition into several discrete best-in-class elemental tasks that 

would contribute to the scenario, and to leave the end-to-end 

objective and remaining elemental tasks for next year. The tasks 

of accurate route following and docking with loading/unloading 

stations were chosen as the VMAC tasks for the 2007-2008 

competition year. 

216
For the competition, the teams examined the BG modules at the 

prim and AM echelons in order to improve upon the existing 

baseline operation of the control system. 

3. VMAC COMPETITION 

The regional competition was held on April 18th 2008 at NIST. 

The competition was broken down into two tasks: path following 

and docking. For both tasks, the teams were required to accept a 

standard command message as input. They were free to use as 

much of the provided infrastructure as they desired (e.g. 

groundtruth). 

For path following, the input consisted of a set of constant 

curvature arcs that were to be followed. In order to allow 

observers to examine the system’s real-time performance, the 

target trajectory’s arcs were shown in the simulated world. These 

arcs were represented as a red centerline with a blue error radius 

as shown in Figure 5. The vehicle could then be observed while 

driving in the simulation. In addition to the simulated view, as 

shown in Figure 6, the passageway boundaries and vehicle 

centerline trajectory were plotted in real-time and statistics were 

automatically generated. As the path progressed, the arc 

complexity was increased and the error radius was reduced. Hood 

College produced the best-in-class algorithm for path following 

followed by George Mason University in a close second. The 

scoring criteria included the distance traveled before the first 

crossing over the error radius and the average path and speed 

deviation. The team’s score, as shown in Figure 7, was displayed 

in real-time during the competition. 

Figure 5: Example of the path following task. The red line is 

the centerline that is to be followed. The blue line represents 

the allowable error radius for the center of the vehicle. 

Docking ability was measured by placing the AGV in a room with 

a docking station. The input for the docking behavior consists of 

the upper right and lower left corners of both the room and 

docking table, as well as the desired location of the vehicle’s 

center point when docked. As shown in Figure 8, the AGV was 

required to successfully dock without a collision, where docking 

amounts to parallel parking a rear steered Ackerman vehicle. 

Upon successful docking, the AGV was placed in a smaller room 

and the procedure was repeated. The size of the room ranged in 

size from 10m x 10m to 4m x 4m. Once again, Hood College 

received top honors in this competition. They were able to 

successfully dock in every room in which they were placed. 

Figure 6: Plot of robot centerline trajectory and error 

boundaries. Note that allowable path deviation decreases as 

with distance traveled. 

Path data file VMAC_CompDay1/pathPts.dat

Tean's data file VMAC_CompDay1/team_logs/team1_v4.dat

Commanded Speed 0.4

Path Length 116.795183

Vehicle Path Deviation Normalizing Factor 1.167

Number of Deviation Outside Error Bound 7

Total Time of Deviation Outside Error Bound 6.1981

Completed Entire Path TRUE

Total Time of Run 401.0019

Distance Traveled During Run 153.004972

Distance Traveled Along Path During Run 116.102756

Mean of Speed During Run 0.381603

Standard Deviation of Speed During Run 0.123377

Mean of Deviation During Run 0.266681

Standard Deviation of Deviation During Run 0.284552

Total Time of Run 216.8005

Distance Traveled During Run 81.185515

Distance Traveled Along Path During Run 64.84049

Mean of Speed During Run 0.374628

Standard Deviation of Speed During Run 0.1308

Mean of Deviation During Run 0.304629

Standard Deviation of Deviation During Run 0.327008

0.7 Percentage Completed 55.51640773 38.86149

0.1 Deviation of Speed from Commanded Speed -39.043 -3.9043

0.1 Deviation of Vehicle from Commanded Path -54.12485004 -5.412485

1 Completion Bonus 10 10

total 39.5447

Performance Evaluation of Path Following Until First Deviation

Summary of Results

File Information

Path Information

Performance Evaluation of Deviations Over Entire Run

Performance Evaluation of Path Following Over Entire Run

Figure 7: Sample of statistics gathered for each run of the 

path following elemental evaluation. 

3.1 Follow-on with a Real Platform 

One of the main criticisms of simulation is that algorithms that 

work in virtual reality do not translate well to the real-world. The 

VMAC competition tried to address this concern by allowing the 

winning team’s code to run on the NIST surrogate AGV. This 

transition was made possible due to USARSim and MOAST

providing validated models of real-world sensors and robotic 

platforms. In addition, the MOAST implementation provides for 

standardized interfaces that are followed by both our real platform 

and the simulation. 

217
Figure 8: Example of the docking task. The vehicle was 

required to dock with a loading station without experiencing 

any collisions. Upon success, the vehicle was moved to a space 

with less maneuver room and the test was repeated. 

Figure 9: The winning code from Hood College was placed 

without change on NIST’s surrogate AGV. The vehicle was 

able to successfully navigate and dock with a loading area. 

Significant differences exist between the NIST surrogate vehicle 

and the simulated AGV. For example, the simulated AGV is a 

rear-steered Ackerman vehicle while the NIST surrogate is skid 

steered. However, the modularity of the 4D/RCS architecture 

makes many system specific details irrelevant to higher echelons 

in the architecture. A constant curvature arc sent from the AM 

echelon to the PRIM echelon must be accurately followed. AM is 

unaware of how PRIM will follow that arc. It is up to PRIM to 

account for the individual vehicle differences. 

Figure 9 shows the NIST AGV driving through a performance test 

metric that allows for vehicle side clearance and free space for 

turns to be precisely controlled. The Hood College code was run 

without alteration on the NIST vehicle and docking procedures 

were successfully performed. 

3.2 ICRA Participation 

The successful National VMAC has been used as a model for a 

virtual manufacturing competition that is now an annual event at 

the robot challenge which is part of the IEEE International 

Conference on Robotics and Automation (ICRA). The first step to 

making this a reality occurred recently when with funding from 

IEEE, the organizers and the winning team from Hood College 

were able to demonstrate their code to all attendees for the first 

two days of the ICRA conference that was held in Pasadena, 

California from May 19-23, 2008. 

4. FUTURE 

The organizers are continuing this highly successful joint 

RAS/NIST effort with already approved follow-on funding from 

RAS. The teams from this year’s competition are demonstrating 

and presenting their research as team-description papers during a 

special session at the annual Performance Metrics for Intelligent 

Systems (PerMIS’08) Workshop held at NIST. The seeds from 

last year’s funds are already bearing fruit. Several of the 

Universities are planning courses based on the material and 

expertise that they have gained as a direct result of their 

participation in this competition. In addition, a public forum and 

website (www.vmac.hood.edu) has been created where 

participants are able to post and answer questions and initiate 

discussions with other members. The continued funding will 

facilitate expanding the user base and building a self-sustaining 

community that is able to pool resources and create improvements 

to the simulation system. Additional corporate interest is also 

being generated with a major manufacturer being interested in 

expanding the competition to include the autonomous handling of 

pallets by a forklift in the factories buffer zone area (the area 

where shipments are first received and unloaded). 

In terms of the actual competition, a national competition is being 

planned for the 2008-2009 year and the organizers have submitted 

a proposal requesting that the VMAC be included as an event in 

the robot challenge at ICRA’09 to be held in Kobe, Japan. As a 

lead-in for next year’s national competition, all of the Hood code 

has now been checked-in to the CVS repository of MOAST. 

5. ACKNOWLEDGMENTS 

The authors would like to thank NIST and the Robotics and 

Automation Society (RAS) of IEEE for their continued support of 

this effort. This work was made possible through a grant received 

under the RAS new initiatives competition. 

6. REFERENCES 

[1] MOAST Homepage. http://moast.sourceforge.net . 2007. 

 [2] USARSim Homepage. http://usarsim.sourceforge.net . 

2007. 

 [3] RoboCup Rescue Virtual Robots Competition. 

http://www.robocuprescue.org/wiki/index.php?title=Virtu

alrobots . 2008. 

 [4] Albus, J., "Outline for a Theory of Intelligence," IEEE 

Transactions on Systems Man and Cybernetics, Vol. 21, 

1991, pp. 473-509. 

 [5] Albus, J., Bostleman, R., Madhavan, R., Scott, H., 

Barbera, A., Szabo, S., Hong, T., Chang, T., Shackleford, 

W. P., Shneier, M., Balakirsky, S., Schlenoff, C., Huang, 

H., and Proctor, F., "Intelligent Control of Mobility 

218
Systems," Computational Intelligence in Automotive 

Applications, Vol. 132/2008, Studies in Computational 

Intelligence, Springer Berlin, Heidelberg, 2008, pp. 237-

274. 

 [6] Balaguer, B. and Carpin, S., "Where am I? A Simulated 

GPS Sensor for Outdoor Robotic Applications,"

Proceedings of the First International Conference on 

Simulation, Modeling, and Programming of Mobile 

Robots, 2008. 

 [7] Balakirsky, S. and Scrapper, C., "Planning for On-Road 

Driving through Incrementally Created Graphs,"

Proceedings of the 7th International IEEE Conference on 

Intelligent Transportation Systems, 2004. 

 [8] Lewis, M., Sycara, K., and Nourbakhsh, I., "Developing a 

Testbed for Studying Human-Robot Interaction in Urban 

Search and Rescue," Proceedings of the 10th International 

Conference on Human Computer Interaction (HCII'03), 

2003. 

 [9] Pepper, C., Balakirsky, S., and Scrapper, C., "Robot 

Simulation Physics Validation," Proceedings of the 

Performance Metrics for Intelligent Systems (PerMIS) 

Workshop, 2007. 

 [10] Schlenoff, C., Steves, M., Weiss, B., Shneier, M., and 

Virts, A., "Applying SCORE to Field-based Performance 

Evaluations of Soldier Worn Sensor Technologies," 

Journal of Field Robotics, Vol. 24, No. 8-9, 2006, pp. 671-

698. 

 [11] Sycara, K. and Pannu, A. S., "The RETSINA multiagent 

system (video session): towards integrating planning, 

execution and information gathering," Proceedings of the 

Second International Conference on Autonomous Agents, 

ACM, New York, NY, 1998. 

 [12] Taylor, B., Balakirsky, S., Messina, E., and Quinn, R., 

"Design and Validation of a Whegs Robot in USARSim,"

Proceedings of the Performance Metrics for Intelligent 

Systems (PerMIS) Workshop, 2007. 

 [13] Wang, J., Lewis, M., and Gennari, J., "A Game Engine 

Based Simulation of the NIST Urban Search & Rescue 

Arenas," Proceedings of the 2003 Winter Simulation 

Conference, 2003. 

219
Analysis of a Novel Docking Technique for Autonomous

Robots

Henson, G., Maynard, M., Liu, X., Dimitoglou, G.

Department of Computer Science

Hood College

Frederick, MD 21701, USA

{gah1, mmaynard, xliu, dimitoglou} @hood.edu

ABSTRACT

Autonomous robot docking requires accurate path following and ultimately, accurate alignment with the target location, typically a docking station. In this paper we develop

a novel, partially heuristic, technique that allows accurate

docking for Ackerman-steered vehicles. The technique is validated via simulation. Multiple experiments were performed

to better understand and analyze the heuristic element of the

technique. The results underscore the impact of the vehicle’s

steering characteristics in docking precision and may prove

valuable in attempting to remove the heuristic element.

Categories and Subject Descriptors

I.2.9 [Robotics]: Autonomous vehicles; I.6 [Simulation

and modeling]: Applications

General Terms

Robotics, Simulation

Keywords

Mobile robot motion-planning, simulation

1. INTRODUCTION

Autonomous mobile robots are designed to perform certain tasks. Typically to perform these tasks, robots have

to plan their path, avoid objects and navigate in the operational environment. Often task completion requires approaching a target location where some additional final operation is required, such as moving an actuator. In manufacturing environments docking to a target location (e.g. a

palette shelf or a conveyor belt) is a common final operation.

The docking process itself can be complex, requiring maneuvering and precision which can be affected by the size and

shape of the workspace and the physical dimensions and maneuverability of the robotic platform.

Permission to make digital or hard copies of all or part of this work for

personal or classroom use is granted without fee provided that copies are

not made or distributed for profit or commercial advantage and that copies

bear this notice and the full citation on the first page. To copy otherwise, to

republish, to post on servers or to redistribute to lists, requires prior specific

permission and/or a fee.

PerMIS’08 August 19-21, 2008, Gaithersburg, MD, USA.

Copyright 2008 ACM 978-1-60558-293-1 ...$5.00.

In this paper we examine docking of an autonomous robotic

platform by knowing only two locations in the workspace:

the point of origin and the target location. We propose an

algorithm that allows docking using only numerical calculations considering, besides the robot’s physical geometry, the

origin and target location. We presume the robot has no

proximity detection capability or any other relevant sensor

payload and the workspace is obstacle-free.

The following section provides a description of the environment and robotic platform assumptions and constraints for

the docking problem. In Section 3, the proposed technique

is presented. Section 4 describes the simulation experiments

conducted to confirm the validity of the proposed algorithm

and to collect some performance metrics with respect to

docking accuracy.

2. OPERATIONAL ENVIRONMENT

We assume the operational environment to be a rectangular workspace (W). In the workspace there is a docking location (D) and an arbitrary starting location (L1) for the robot

(A). The robot, an Ackerman-steered, Automatic Guided

Vehicle (AGV) is fitted with a roller deck.

The docking location also has a roller deck which should enable the AGV to unload cargo if it is properly docked. An

area in front of the dock is also the target location (LD)

the robot must reach by maneuvering in the obstacle-free

workspace (Figure 1). Since there are no obstacles in the

workspace, there are many more paths [3] in the configuration space (C-space) that can be expressed as a continuous

map:

τ : S ∈ [0, 1] → τ (s) ∈ C (1)

where τ (0) = Li is the initial configuration and τ (0) = LD

is the target configuration of the path. However, Equation

1 does not take into account the additional requirement of

arriving at the dock in the correct orientation (pose).

For task completion, the robot needs to arrive at the target

location LD and also to park in such a way that the roller

decks of both the vehicle and the dock are aligned. This

excludes any docking approach that does not conclude with

the left wide side of the vehicle aligned to the dock’s roller

deck.

In the environment, the following is known:

1. the coordinates of the four corners defining the workspace

and the room boundary

2. the coordinates of the corners defining the dock

3. the initial (L1) and target (LD) robot locations

220
Dock Robot

Initial Location Target Location

L1 L D

Workspace

Figure 1: A generalized view of the workspace with

the robot in its initial position.

4. the initial orientation (pose) of the robot and its physical dimensions.

The point we will use as the location of the robot in the

world during the simulation is between the front wheels.

The side to side location is calculated by centering the loading site on the UnitLoader to the center of the docking station.

3. APPROACH

The problem of docking the robot is the same as parallel

parking a vehicle next to a fixed location.

We begin by calculating the required maneuvers in reverse

order. This simplifies the problem as we obtain both the

final position and the required orientation. We can then calculate the points that form a traversable path to the robot’s

position.

The key point in this path is the point that the robot travels

to immediately before arriving at the docked position. We

call this this the penultimate point (p) and it is chosen to

provide a simple traversable path to the docking position as

well as being easily reachable from the robot’s current location.

The final docking position the robot needs to obtain is

k

1.608m

1.096m VEHICLE CHARACTERSTICS

Width: 1.096m

Length: 1.608m

Height: 0.8m

Speed: 5m/sec

Max Steer Angle: 79.9 deg 

m

Figure 2: Robot physical dimensions.

calculated using the physical dimensions of the robot and

the location of the docking station. Because the navigation coordinates are calculated using a point (k) in the front

mid-line of the robot, another point (m) is calculated to determine the point of alignment between the center of the

dock and the center of the vehicle’s roller deck (Figure 2).

The docking target location is half of the robot’s width from

the docking side of the docking station. Once this docking

point is calculated, a penultimate point can also be calculated.

The penultimate point also needed to be located in such a

place as to allow the robot to easily reach the docking location.

To take advantage of the vehicle’s rear steered Ackerman

design, we chose to approach the docking position using the

robot’s reverse direction. This put the steering wheels in the

front and allowed a smoother motion to pivot to the docking

location.

To accomplish this, the penultimate point can be on either

side (left or right) of the docking location to allow the robot

to reverse into the correct position. The optimal LD point

is determined according to the physical dimensions of the

docking station and the physical geometry of the vehicle.

Algorithm 1 illustrates in pseudocode the required steps in

order to calculate the x and y coordinates for both the penultimate (p) and goal point (LD). The terms half robot length

and half robot width are measurements that are used to

properly align the vehicle and its roller deck to the dock

and its roller deck.

Once these calculations are made, function FollowPath

performs the steering and direction maneuvers for the vehicle to begin moving first towards the calculated penultimate

point and then to the goal point.

While the p is a single reachable point in the workspace, we

consider it to have a much larger footprint indicated by a

tolerance, which is an arbitrary radius around the center of

p.

The goal point, however, does not have such tolerance as any

deviation may indicate a misalignment with dock, rendering

the unloading of any package impossible.

Algorithm 1 Calculate and Find the penultimate point p

p.x ← dock.center.x + robot length;

p.y ← dock.center.y + half robot length;

LD.x ← dock.center.x + rollerdeck nav point offset;

LD.y ← dock.center.y + half robot width;

repeat

FollowPath towards p

distance = current.location − p

until distance < pt

repeat

FollowPath towards LD

distance = current.location − LD

until distance < pt

4. SIMULATION

4.1 Experimentation

The developed docking algorithm was exercised, tested

and verified using a simulation infrastructure comprised of

USARSim [5, 7], a Gamebots [2] variant of the Unreal Engine [6] and the Mobility Open Architecture Simulation and

Tools (MOAST)[4] framework [1].

4.1.1 Design

The simulation environment provides a number of configurable parameters for the vehicle that can be adjusted to

modify the navigation performance.

For the experiments a Unit Loader AGV was used and all

parameters were kept at their default settings. As we were

more concerned with docking accuracy rather than the path

following speed or reducing task completion, none of these

parameters were altered. Velocity, in particular, remained

constant at 5m/sec.

221
The critical element to the success of a docking attempt is

the determination of the penultimate point.

The single success factor in this experiment is the accurate

docking of the vehicle to the dock. As the penultimate point

(p) is arbitrarily determined with respect to the dock, we

examined the possibility of moving p to examine if different

locations would yield more accurate results. Through experimentation, we determined the optimal (fully aligned) goal

point (LD) to be at xy-location (-0.26, -2.36).

Assuming a constant vertical distance from the initial location (L1) to the p, multiple points were examined on the

horizontal axes by increasing and decreasing the distance to

the dock.

The intention of the experimentation was to measure the

performance of the vehicle with respect to its accuracy in

arriving at the optimal location by changing the proximity

of p.

The expectation was that a more distant p may result in

more accurate docking. This expectation was based on how

coarse Ackerman-steered vehicles are when maneuvering, therefore more distance from the dock should have resulted in a

more ”comfortable” steering environment.

4.1.2 Execution & Analysis

In Table 1, the coordinates of seven executions illustrate

the different p positions and their corresponding LD locations. In the simulated workspace, the optimal docked LD

is (-0.57, -2.39).

The results indicate a considerable spread of values in the

horizontal distance from the optimal LD x-location of -0.57

with deviations as large as 0.62m (ID 2).

Table 1: x,y coordinates of various p points and their

corresponding final docking locations

ID Penultimate (p) Location Final Location (LD)

1 (-1.57, -2.39) (-0.03, -2.40)

2 (-1.37, -2.39) (0.05, -2.39)

3 (-1.17, -2.39) (0.04, -2.39)

4 (-0.97, -2.39) (-0.26, -2.36)

5 (-0.77, -2.39) (-0.15, -2.17)

6 (-0.67, -2.39) (-0.18, -2.04)

7 (-0.57, -2.39) (-0.29, -1.96)

These effects are most prominent in Figure 3. Superimposed on an xy-axis, seven penultimate points (P1 − P7)

are examined on the horizontal axis.

Penultimate point P1 enables the vehicle to reach and dock

as LD4 which is the optimal target location LD. Subsequent

executions with p closer to the dock (e.g. P5 − P7) result

in far LD’s. Similarly, executions with p further away from

the dock (e.g. P1 − P3) also end up in points distant from

the dock LD’s.

As expected, LD4 is aligned with the center of the dock

(Dcenter) but not adjacent to it. Because LD4 is calculated

to be in the middle of the vehicle, a distance is required to

ensure that at least half of the vehicle’s width and some additional space is allotted to ensure proper proximity but not

collision with the dock.

5. CONCLUSION AND FUTURE WORK

Autonomous robot docking is an interesting problem with

many practical applications.

-2 -1

-1

-2

-3

P

1 P

2 P

3 P4 P5 P6 P7

LD4 LD7

LD6

LD5

LD3

LD2

LD1

x

y

Figure 3: Graphical depiction of multiple simulation

executions with varying penultimate points.

However, specific vehicle characteristics that may affect steerability may render the application of the technique more

challenging and far less accurate than expected. Using an

Ackerman-steered vehicle provided such a challenge.

To address the problem, a simple technique was developed

that enables Ackerman-steered vehicles to accurately dock.

The technique is based on the assumption that certain environment and workspace information is known. The key element of the techniques is heuristically determining a penultimate point (p) off the final docking destination that enables

the vehicle to maneuver and essentially parallel park next to

the docking station. The technique was verified using a simulation environment and the proposed algorithm performed

as expected in the synthetic workspaces. As the determination of p is based on heuristics, numerous different p points

on the horizontal axes were examined to assess their viability. The results were somewhat unexpected as docking

accuracy varied for both closer and more distant p points.

Further examination is required to better understand the

reasons for the variation in accuracy, particularly for distant points, as well as more work for the further analysis of

the collected data.

Beyond the simulated experimentation, the proposed docking technique was also tested using a physical platform, an

actual AGV. Albeit the vehicle was skid-steered, therefore

it had a greater degree of maneuverability, the results ware

congruent with the expected behavior and the simulations

presented in this paper: the vehicle docked perfectly next to

the dock.

We anticipate that a deeper examination of the observed

vehicle behavior will enable the development of intelligent,

adaptive and non-heuristic-based methods for the calculation of one or more penultimate points.

6. ACKNOWLEDGMENTS

The authors are grateful to S. Balakirsky (NIST), R. Madhavan (NIST/ORNL) and C. Scrapper (NIST) for their guidance with the Virtual Manufacturing & Automation Competition (VMAC). The authors also appreciate the continuous and generous support provided by Dean Bands and the

Hood College Graduate School.

7. REFERENCES

[1] S. Balakirsky and E. Messina. MOAST and USARSim -

222
a combined framework for the development and testing

of autonomous systems. In Proceedings of the 2006

SPIE Defense and Security Symposium, 2006.

[2] G. A. Kaminka and M. M. Veloso et al. Gamebots: a

flexible test bed for multiagent team research.

Commun. ACM, 45(1):43–45, 2002.

[3] J-C. Latombe. Robot Motion Planning. Springer, 1990.

[4] MOAST project. http://moast.sourceforge.net, accessed

June 1 2008.

[5] S. Carpin M. Lewis S. Balakirsky, C. Scrapper.

USARSim: providing a framework for multi-robot

performance evaluation. In PerMIS 2006, 2006.

[6] Unreal Engine (UNR). http://www.epicgames.com,

accessed June 1 2008.

[7] USARSim. http://sourceforge.net/projects/usarsim,

accessed June 1 2008.

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229
Algorithms and Performance Analysis for Path Navigation 

of Ackerman-Steered Autonomous Robots

G. Henson, M. Maynard, G. Dimitoglou, X. Liu

Department of Computer Science

Hood College

Frederick, MD 21701

{gah1, mmaynard, dimitoglou, liu}@hood.edu



	




		

 	

 		


 




	  	
	  
  		

    	



      	

  	    		  	



	
		

	

      

	

  

  	




  	
      	    
  	

		  
    	
  
  
  




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235
Wireless Communications in Tunnels for Urban Search 

and Rescue Robots 

Kate A. Remley, Galen Koepke, 

Dennis G. Camell,

Chriss Grosvenor 

NIST Electromagnetics Division 

325 Broadway 

Boulder, CO, USA 80305 

+1 303 497-3652 

remley@boulder.nist.gov

Lt. George Hough 

New York City Fire Department 

New York City, NY USA 

gch9@columbia.edu

Robert T. Johnk 

Institute for Telecommunications 

Sciences

325 Broadway 

Boulder, CO, USA 80305 

bjohnk@its.bldrdoc.gov

ABSTRACT

We report on propagation tests carried out in a subterranean 

tunnel to support improved wireless communications for urban 

search and rescue robots. We describe single-frequency and 

ultrawideband channel-characterization tests that we conducted, 

as well as tests of telem etry and control of a robot. We utilize 

propagation models of both single-frequency path loss and 

channel capacity to predict robot performance. These models can 

also be used for optimizing wireless communications in tunnels of 

various sizes, materials, and surface roughness. 

Categories and Subject Descriptors

Defining and measuring aspects of an intelligent system. 

Evaluating components within intelligent systems 

General Terms

Measurement, Perform ance, Reliability , Experimentation, 

Standardization, Verification. 

Keywords

Multipath; radiowave propagation; RMS delay spread; robot; 

urban search and rescue; wireless communication; wireless 

system 

INTRODUCTION

Researchers from the Electrom agnetics Division of the National 

Institute of Standards and Technology (NIST) and the Fire 

Department of New York (FDNY) conducted tests of radiowave 

transmission and detection in tunnels at the Black Diamond Mines 

Regional Park near Antioch, California on March 19-21, 2007. 

Our goal was to investigate propagation channel characteristics 

that affect the reliability of wireless telem etry and control of 

Urban Search and Rescue (US&R) robots in tunnels and other 

weak-signal environments. We describe measurement methods 

that we used to study parameters relevant to robot performance. 

We also use the m easured data to verify models of radiowave 

propagation in tunnels. These models can be used to predict robot 

performance in tunnels having characteristics different from the 

ones we measured, such as subways and utility tunnels. This work 

supports the development of technically sound standards for 

US&R robots [1-3]. 

We used both time- and frequency -domain techniques to study 

issues such as channel multipath and loss that may impede 

successful wireless communications in tunnels. We tested both 

video and control of a robot inside a mine tunnel. We also 

implemented propagation models of path loss and channel 

capacity and compared our measured results to these m odels. We 

summarize below the data we collected and interpret the key 

findings from the study, which is described in its entirety in [4]. 

Recently, the wireless field has seen a renewed interest in 

studies of signal propagation in both mine and subway tunnels, 

following a good deal of study on mine communications in the 

1970s. A seminal work on mine tunnel propagation by Emslie et 

al. [5], studied radiowave propagation in small underground coal 

tunnels (4.3 m wide x 2.1 m high) for frequencies ranging from 

200 MHz to 4 GHz. Emslie developed a model for propagation in 

tunnels that is used today . Recently, Rak and Pechak [6] applied 

Emslie’s work to sm all cave galleries for speleological 

applications, confirming Emslie’s findings that once a few 

wavelengths separate the transmitter and receiver, the tunnel acts 

as a waveguide that strongly attenuates signals below the 

waveguide’s cutoff frequency. Because the walls of the tunnel are 

not perfectly conducting, signals operating above the cut-off 

frequency also experience significant loss. In a recent paper, 

Dudley, Lienard, Mahmoud, and Degauque [7] performed a 

detailed assessment of operating frequency in a variety of tunnels. 

They found that as frequency increases, the lossy waveguide 

effect decreases. 

Our measurements, covering a much wider frequency range 

than [7], and implementation of the model of [6] also confirm the 

lossy waveguide effect in the tunnels we studied. This effect can 

have a significant impact on choice of frequency for critical 

applications such as US&R operations, where typically 

infrastructure such as a repeater network is not available and lives 

may be at stake. 

Another factor in tunnel com munications is m ultipath caused 

by reflections off the walls, floor, and ceiling of the tunnel. This 

was clearly seen in the work of Dudley , et al. [7] . Multipath can 

have a pronounced effect on successful transmission of wideband 

data. Multipath interference m ay affect certain frequencies in a 

wideband signal while sim ultaneously having little im pact on 

other frequencies. This frequency selectivity can make decoding 

signals difficult for the demodulator in a receiver. 

We studied the severity of multipath in the tunnel environment 

by m easuring the RMS delay spread, as well as the success or 

failure of wideband data transfer by use of a commercially 

available robot. We compare our m easured results to a model of 

channel capacity based on Shannon’s theory of channel capacity 

(c) 2008 Association for Computing Machinery. ACM acknowledges that this contribution was authored or co-authored by a contractor

or affliate of the U.S. Government. As such, the Government retains a nonexclusive, royalty-free right to publish or reproduce this article,

or to allow others to do so, for Government purposes only.

PerMIS’08,August19-21,2008,Gaithersburg,MD,USA.

ACM ISBN 978-1-60558-293-1/08/08. 236
[6]. This theorem provides a basis for predicting the success of 

wireless communication in multipath environments. 

We first describe the m easurements we carried out and 

interpret the results. We then discuss the models we implemented 

and how they can be used to optimize radio communications for 

US&R applications. 

1. TEST ENVIRONMENT 

The Black Diam ond Mines are part of an old silica m ine 

complex that was used early in the 1900s to extract pure silica 

sand for glass production. As such, the walls of the mine shafts 

are rough and consist of sandy material. 

Two tunnels were studied, the Hazel-Atlas North (here called 

the “Hazel-Atlas” tunnel) and Hazel-Atlas South (here called the 

“Greathouse” tunnel). The tunnels are located beneath a mountain 

and are joined together deep inside, as shown in Figure 1(a). The 

dimensions of the Hazel-Atlas tunnel varied from approximately 

1.9 m (6’, 3”) x 1.9 m to as much as 2.6 m (8’, 5”) x 2.4 m (8’, 

0”). The dimensions of the Greathouse tunnel were somewhat 

bigger, up to approximately 3 m square in places. The HazelAtlas tunnel contained railroad tracks spaced 61 cm (24”) apart. 

Both tunnels consisted of a straight section followed by a 90 

degree turn around a corner, as shown in Figure 1(a). Below we 

report on results for the Hazel-Atlas mine tunnel, shown in more 

detail in Fig. 1(b). The complete set of data on both tunnels can be 

found in [4]. 

Figure 2 shows photographs of the tunnel, including: 2(a) the 

portal (entrance) of the Hazel-Atlas m ine; 2(b) approaching the 

right-angle turn shown in Figure 1(b); and 2(c) past the turn. The 

photos show the rough, uneven walls in the tunnels, some with 

wooden shoring, and the railroad tracks. 

2. MEASUREMENTS

2.1 Narrowband Received Power 

We m easured the power received outside the tunnel from a 

transmitter placed at various locations inside the tunnel. We 

collected single-frequency (unmodulated, carrier only ) receivedpower data at frequencies near public-safety bands 

(approximately 50 MHz, 150 MHz, 225 MHz, 450 MHz). 

Gathering inform ation at these frequencies helps to provide a 

choice of optimal frequency for the US&R com munity for this 

environment, both for robot communications and for other ty pes 

of radio communication. These data provide insight into the lossy 

waveguide effect mentioned in the Introduction. 

The handheld transmitters we used were radios similar to 

those of first responders, except they were placed in ruggedized 

cases and were modified to transmit continuously . Each radio 

transmitted a signal of approximately 1 W through an 

omnidirectional “rubber duck” antenna mounted on the case. 

During the tests, the radio antennas were approximately 0.75 m 

from the floor, a height similar to that of the robot we studied. 

We carried the radio transm itters from the entrance to 

locations deep within the tunnels while continuously recording 

the received signal. From the Hazel-Atlas tunnel portal, we 

moved the transmitter approximately 100 m down a straight 

tunnel, then turned a corner and proceeded another 100 m , as 

shown in Fig. 1(b). 

The receiving equipm ent was located just outside the portal. 

Omnidirectional discone receiving antennas were m ounted on 

tripods, as shown in Fig. 2(a). We used a narrowband 

communications receiver to convert the received signal to audio 

frequencies, where it was digitized by a computer sound card and 

recorded on a com puter. This instrument, when combined with 

NIST-developed post-processing techniques [1, 8] , provides a 

high-dynamic-range measurement sy stem that is affordable for 

most public-safety organizations. Part of the intent of this project 

Greathouse

Portal

Hazel-Atlas

Portal

(b) 

Figure 1: (a) Overview of the Hazel-Atlas mine tunnel 

complex. The network of mines is located deep within a 

mountain. The dark-shaded areas are accessible. (b) Close-up 

view of the Hazel-Atlas tunnel. The dashed line shows the path 

along which we took measurements, including the right-angle 

turn at 100 m. The triangles indicate the distance in meters, the 

ovals correspond to locations shown in Fig. 3, and the 

receiving equipment is labeled RX.

100

120

200

160

140

180

RX

#1/#5

#3

#2/#4

(a) 

237
was to dem onstrate a user-friendly sy stem that could be utilized 

by US&R organizations to assess their own unique propagation 

environments. 

(a) 

Figure 3 shows representative m easured received-power data 

at frequencies of 50 MHz, 162 MHz, and 448 MHz acquired 

while the transmitters were carried by foot through the tunnel. 

The signals were sampled at approximately 48 kHz and the power 

averaged over one-second intervals. The left and right halves of 

the graph show measurements made walking into and out of the 

tunnel, respectively , and thus m irror each other. The vertical 

dashed lines on the graph correspond to the entrance (#1, #5), turn 

(#2, #4), and turn-around point (#3) in the measurement path, as 

shown in Fig. 1(b). 

The cut-off frequency for this ty pe of tunnel is difficult to 

define since the walls behave as lossy dielectrics rather than 

conductors. These conditions are discussed in [9] , where the 

attenuation constant is found to vary as the inverse of frequency 

squared [Section 2.7, pp. 80-83] . Hence, we would expect higher 

attenuation at the lower frequencies but no sharp cut-off. Further 

complications in this tunnel ar e the axial conductors (cables, 

water pipes, rails) that may support a TEM-like mode of 

propagation, the irregular cross-section, and the side chambers 

and tunnels. 

For the Hazel-Atlas mine tunnel, we see in Fig. 3(a), strong 

attenuation of the 50 MHz signal and in Fig. 3(b), the received 

power of the 162 MHz signal also decreases rapidly as the 

transmitter moves into the tunnel. This rapid attenuation is due to 

the lossy waveguide effect described in references [4-7] . The 

signal for the 448 MHz carrier frequency (Fig. 3(c)) exhibits less 

attenuation and this is where the models of [5] may apply. Signals 

may travel even further at higher frequencies, as discussed in [5-

7]. This frequency dependence may play a significant role in 

deciding which frequencies to utilize in US&R robot deploy ment 

applications, as will be discussed in Section 3. 

2.2 Excess Path Loss and RMS Delay Spread 

We also conducted measuremen ts at several stationary 

positions covering a very wide frequency band. These “excesspath-loss” m easurements provide the received signal power 

relative to a direct-path signal over a frequency band. When 

transformed to the time domain, the wide frequency band yields a 

short-time-duration pulse. This pulse can be used to study the 

number and duration of multipath reflections in an environment. 

Our synthetic-pulse, ultrawideband sy stem is based on a 

vector network analy zer (VNA). Our measurements covered 

frequencies from 25 MHz to 18 GHz. The post-processing and 

calibration routines associated with it were developed at NIST 

[10]. In the synthetic-pulse system, the VNA acts as both 

transmitter and receiver. The transmitting section of the VNA 

sweeps over a wide range of frequencies a single frequency at a 

time. The transmitted signal is amplified and fed to a transm itting 

antenna. For this study, we used omnidirectional discone antennas 

for frequencies between 25 MHz and 1.6 GHz, and directional 

horn-type transm itting and receiving antennas for frequencies 

between 1 GHz and 18 GHz. 

(b) 

(c) 

Figure 2: (a) Portal into the Hazel-Atlas mine tunnel. (b) 90 m 

inside showing the bend depicted in Fig. 1(b) and the rough, 

sandy wall material. (c) Wood shoring approximately 150 m into 

the tunnel. The robot we tested can be seen on the cart between 

the railroad tracks. 

238
The received signal was picked up over the air in the tunnel 

by the receiving antenna and was relay ed back to the VNA via a 

fiber-optic cable. The fiber-optic cable phase-locks the received 

signal to the transmitted signal, enabling post processing 

reconstruction of the time-domain waveform associated with the 

received signal. The broad range of frequencies and time-domain 

representation provide insight into the reflective m ultipath nature 

of the tunnel that cannot be captured by use of single-frequency 

measurements. The receive antenna m ust rem ain fixed during 

each m easurement, so these tests are carried out at discrete 

locations, unlike the single-frequency tests. 

We m easured excess path loss every 20 m starting 

approximately 10 m into the tunnel. The VNA was located at the 

Hazel-Atlas portal. The transm itting antenna was located at the 

portal as well. The graphs show data starting from 0 Hz, however 

the valid (calibrated) measurement range is stated for each graph. 

50 100 150 200 250 300 350 -140

-120

-100

-80

-60

-40

-20

0

#2#3#4#5

time [sec]

P

avg [dBm]

#1 #2 #3 #4 #5

50 MHz

Figures 4 and 5 show measured excess path loss over a wide 

frequency band measured 50 m and 120 m, respectively , in the 

Hazel-Atlas tunnel. Note that at 120 m, we have passed the rightangle turn in the tunnel. The t op curve in each graph represents 

the received power level, referenced to the calculated free-space 

path loss at that location. The bottom curve represents the noise 

floor of the measurement system. 

(a) Figure 4 shows that even in a line-of-sight condition 

approximately 50 m from the tunnel entrance, the spectrum of the 

received signal display s significant frequency dependence. At 

frequencies between 25 MHz and 1.6 GHz (Fig. 4(a)), the lossy 

waveguide effect is shown by the rapidly decreasing signal on the 

left-hand side of the graph. We see that a carrier frequency higher 

than approximately 700 MHz would suffer less loss compared to 

lower frequencies in this particular tunnel. Figure 4(b) shows 

frequencies from 1 GHz to 18 GHz. In this case, we see frequency 

dependence in received power caused by strong reflections, as 

shown by the deep nulls and peaks in the top curve of Fig. 4(b). 

Once the receiving antenna turns the corner, see Fig. 5, the 

signal takes on a more random variation with frequency since 

transmission consists of reflected signals only . For frequencies 

from 25 MHz to 1.6 GHz (Fig. 5(a)), the received signal power is 

near the noise floor of the receiver since the two curves almost 

overlay. For the higher frequencies (Fig. 5(b)), we see that the 

average received signal level is relatively constant with 

frequency, but the peaks and nulls are still significant. 

Finally, we present the RMS delay spread for the Hazel-Atlas 

mine tunnel in Table 1 for frequencies from 25 MHz to 1.6 GHz 

and 1 GHz to 18 GHz. We see that the shortest delay spreads are 

found by use of the directional antennas. The complete set of 

UWB excess-path-loss data is given in [4]. 

2.3 Tests of Robot Communications 

We carried out tests on a commercially available robot. Control 

and video were as-built for the com mercial product. We used the 

omnidirectional antennas that came with the system for all tests in 

order to assess the default capabilities of this robot. 

The robot we used is controlled with a 2.4 GHz spreadspectrum, frequency-hopping protocol, which was configured to 

transmit in the unlicensed 2.4 GHz industrial, scientific, and 

medical (ISM) band. The control channel utilizes a modulation 

bandwidth of approximately 20 MHz. The output power of the 

bidirectional control link is nominally 500 mW. 

The robot transmits video by use of one of ten channels 

between 1.7 GHz and 1.835 GHz. The robot we tested transm itted 

at 1.78 GHz by use of an analog modulation format that was nonbursted and non-frequency-agile. The video channel utilized 

approximately 6 MHz of modulation bandwidth. The output 

power was nominally 2 watts. 

50 100 150 200 250 300 -140

-120

-100

-80

-60

-40

-20

0

time [sec]

P

avg [dBm]

#2#3#4#5

#1 #2 #3 #4 #5

162 MHz

(b) 

(c) 

0

Figure 3: Received-power data in the Hazel-Atlas Mine for 

three carrier frequencies: (a) 50 MHz, (b) 162 MHz, (c) 

448 MHz. In each case the #2 and #4 vertical dashed lines 

correspond to the turn at 100 m: once on the way into the 

tunnel and once on the way out. The #3 dashed line represents 

the end point at 200 m, shown in Fig. 1(b). 

50 100 150 200 250 -140

-120

-100

-80

-60

-40

-20

time [sec]

P

avg [dBm]

#2#3#4#5

#1 #2 #3 #4 #5

448 MHz

239
The robot controller was located at the entrance to the tunnel, 

shown in Fig. 6. We positioned the robot inside the tunnel after 

the first bend in a non-line-of-site condition. The robot was 

moved through the tunnel on a cart, as shown in Fig. 2(c), so that 

we could check the control link even after video was lost. Every 

10 m, the video quality and control link were checked. Video was 

rated qualitatively by the robot operator, and control was checked 

by the ability of the operator to m ove the robot arm , and verified 

by a researcher in the tunnel. No attempt was made to provide 

more granularity in these tests. That is, we assum ed that m oving 

the arm up was equivalent to moving it down or rotating it. 

Table 2 shows the results of our tests. We were able to 

communicate with the robot in a non-line-of-sight condition deep 

within the tunnel. This is consistent with the results of Fig. 5(b), 

which indicates that signals in the low gigahertz range should 

propagate farther than those at lower frequencies. 

Table 2 also shows that control of the robot was possible 

much deeper into the tunnel than we were able to receive video, 

even though the output power of the video channel is higher (2 

watts for video vs. 0.5 watt for control). However, a much higher 

data rate is necessary to maintain high-quality video transmission, 

as opposed to the relatively small amount of data needed to 

control the robot. Transm itting this large am ount of data requires 

a m ore stringent success rate than for the control channel; 

therefore, failure of the video before the control is not 

unexpected. The delay experienced in controlling the robot when 

it was deep in the m ine indicates packet loss and resend for error 

correction under weak-signal conditions. 

-140

-120

-100

-80

-60

-40

-20

0

20

0 200 400 600 800 1000 1200 1400 1600

Frequency (MHz)

Excess Path Loss (dB)

d=50

noise 10

0 3000 6000 9000 12000 15000 18000

Frequency (MHz)

-140

-120

-100

-80

-60

-40

-20

0

20

Excess Path Loss (dB)

D=50 m

noise 

BD mine Hazel Atlas

(b) 

Figure 4: Excess path loss measurements over a wide frequency 

band carried out 50 m from the portal of the Hazel-Atlas mine. 

(a) 25 MHz to 1.5 GHz. (b) 1 GHz to 18 GHz. 

(a) 

(a) 

-140

-120

-100

-80

-60

-40

-20

0

20

0 200 400 600 800 1000 1200 1400 1600

Frequency (MHz)

Excess Path Loss (dB)

d=120

noise 10

(b) 

Figure 5: Excess path loss measurements carried out 120 m from 

the portal of the Hazel-Atlas m ine. (a) 25 MHz to 1.6 GHz. (b) 

1 GHz to 18 GHz. 

(a) 

0 3000 6000 9000 12000 15000 18000

Frequency (MHz)

-140

-120

-100

-80

-60

-40

-20

0

20

Excess Path Loss (dB)

D=120 m

noise @100

Distance 

(m) 

RMS 

Delay Spread 

Low Freqs. 

(ns) 

RMS 

Delay Spread

High Freqs. 

(ns) 

0 31.0 14.4 

10 25.3 17.6 

20 18.5 7.6 

30 15.9 15.0 

40 17.0 11.5 

50 15.5 13.1 

60 19.7 20.6 

70 17.2 11.1 

80 15.2 10.0 

90 15.2 8.4 

100 15.7 9.6 

110 x 7.5 

Table 1: RMS Delay Spread for the Hazel-Atlas mine tunnel. 

Center column: Frequencies from 25 MHz to 1.6 GHz measured 

with omnidirectional antennas. Right column: Frequencies from 

1 GHz to 18 GHz measured with directional antennas. The grayshaded areas represent a non-line-of-sight propagation condition. 

240
3. MODELED RESULTS 

3.1 Single-Frequency Path Gain Models 

To study the extent of waveguiding in these tunnels, we 

implemented an analy tical m odel that sim ulates signal 

propagation in tunnel environm ents having various phy sical 

parameters [5, 6, 11] . Briefly , the model assumes a dominant 

EH11 mode in a lossy rectangular waveguide with the attenuation 

D in dB/m expressed for vertical polarization as 

D D TUNNEL  D ROUGHNESS D TILT , 

 (1) 

where 

 ̧

 ̧

1

·

 ̈

 ̈

©

§

   1 1

1 343.4 3 3

2

TUNNEL

R

R

a R b H

H

H D O

, (2a) 

 ̧

1

·  ̈

©

§  44

22

ROUGHNESS

11 343.4

ba

D h OS

, (2b) 

O

TS D

22

TILT 343.4

, (2c) 

and O is the wavelength, a is the width of the tunnel, b is the 

height of the tunnel, and h is the roughness, all in meters. Other 

parameters include HR, the dielectric constant of the rock walls, 

and T, the angle of the tunnel-floor tilt in degrees. 

We set the parameters of the model to approximate the HazelAtlas tunnel, given below in Tabl e 3. This model works well only 

for frequencies will above the cut-off frequency , that is, for 

wavelengths significantly less than the dimensions of the tunnel 

[5, 6] . Hence, in Fig. 7 we show results for 448 MHz only. At 

distances around 80 m, the signal was able to propagate through 

an air vent as well as through the tunnel, so the overall received 

signal level increases. The good ag reement between the measured 

and modeled data led us to conclude that waveguiding play s a 

significant role in radio propagation in these tunnels. 

The model also lets us explore which frequencies may be 

optimal for robot or other wireless communications in the tunnel. 

Figure 8 compares a number of commonly used emergency 

20 40 60 80 100

-120

-100

-80

-60

-40

-20

0

Distance (m)

Path Gain (dB)

448 MHz model

448 MHz measured

Figure 7: Comparison of measured and modeled data for the 

Hazel-Atlas tunnel. The carrier frequency is 448 MHz. The 

modeled data simulate waveguide propagation for a waveguide 

whose physical parameters approximate those of the tunnels. 

Parameter Value 

Width 

Height 

Wall roughness 

Hr

tilt

2 m 

2 m 

0.3 

6 

1°

Table 3: Parameters used in tunnel model. 

Distance in 

tunnel (m) 

Table 2: Results of wireless communication link tests carried out 

inside Hazel-Atlas tunnel at Black Diamond Mines Regional 

Park. 

Figure 6: Robot operator positioned at the entrance to the HazelAtlas mine tunnel. The robot was operated in a non-line-of-sight 

condition more than 100 m inside the tunnel. 

Video quality 

(1.7 GHz) 

Control of arm 

(2.4 GHz) 

100 good yes 

110 good yes 

120 poor (intermittent) yes 

130 poor (intermittent) yes 

140 very poor yes 

150 none yes 

160 none delay experienced 

170 none intermittent control 

180 none delay experienced 

190 none delay experienced 

200 none delay experienced 

205 none none 

241
responder frequencies as a function of distance within the tunnel. 

As discussed in [5, 6] , the frequency -dependent behavior of the 

tunnel leads to a “sweet spot” in frequency. Below the sweet spot, 

signals do not propagate well, due to the effect of waveguidebelow-cutoff attenuation and wall loss. Above the sweet spot, 

free-space path loss (which increases with frequency ) and DTILT

dominate and signals do not propagate well. Again, models such 

as these may enable a choice of appropriate frequency for US&R 

robot communications in tunnel environments. Note that these 

results are valid only for a tunnel with these dimensions, wall 

materials, and surface roughness. The curves would need to be 

recalculated for other types of tunnels. 

We also used the m odel to investigate the video performance 

of the robot, described in S ection 3.c. The frequency-hopping 

control channel would need to be modeled by use of other 

methods, since it consists of several narrowband channels 

frequency hopping within a wide modulation bandwidth. In Fig. 

9, we plot the estimated path gain at a carrier frequency of 

1.78 GHz for the tunnel environment with a right-angle turn 

100 m from the receiver. We used the parameters in Table 3 for 

the model. A path gain of í40 dBW was used as an 

approximation for the turn in the tunnel at 100 m, based on work 

done by Lee and Bertoni in [12] . We plot the flat earth path gain 

for comparison. 

Figure 9 also shows the theoretically com puted excess link 

margin (ELM). The ELM is the difference between the received 

signal strength and the minimum receiver sensitivity. The receiver 

sensitivity is determined by the therm al noise of the receiver and 

the receiver’s front-end amplifier noise (5 dB, as a rule of thumb). 

The thermal noise is given by N = kTB, where k is the Boltzmann 

constant, T is the temperature in Kelvin, and B is the bandwidth of 

the receiver. In order for a wireless link to be m aintained, the 

ELM must be greater than zero dB. 

The ELM plotted in Fig. 9 agrees well with the measured 

results from Table 2, which show that the video completely drops 

out between approximately 140 m and 150 m. Given the 

fluctuation in signal strength due to multipath fading in this tunnel 

environment, once the link margin drops below 10 dB at 

approximately 120 m, the video quality degrades and the picture 

becomes intermittent. 

0 50 100 150 200 -150

-100

-50

0

Distance (m)

Path Gain (dB)

Tunnel

Flat Earth

ELM=0dB

500 1000 1500 2000 2500 3000 3500 4000

-200

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

Frequency (MHz)

Path Gain (dB)

10m

20m

30m

40m

50m

60m

70m

80m

90m

100m

Increasing 

distance 

into tunnel

Frequencies 

with lowest 

loss in tunnel

Figure 9: Path gain curves for tunnel with a right-angle turn 

at 100 m (solid) and flat earth (dashed) environments. The 

curve labeled “ELM = 0” indicates where the excess link 

margin calculation predicts loss of signal. As shown, this 

occurs approximately 150 m into the tunnel. 

3.2 Channel Capacity Model 

In general, received RF power and bandwidth effectively 

place an upper bound on the capacity of a com munications link. 

The Shannon channel capacity theorem [13] can be used to 

predict the approximate maximum data rate for tunnel 

communications, even though the Shannon theorem is based on 

the assumption of a Gaussian noise (low multipath) environment. 

For a given m odulation bandwidth, the received signal power 

relative to the noise power determines the theoretical upper limit 

on the data rate (channel capacity ). The Shannon capacity 

theorem is given by 

Figure 8: Path gain versus frequency for various distances 

in a tunnel having physical characteristics similar to those of 

the Hazel-Atlas tunnel. Frequencies around approximately 

400 MHz to 1 GHz propagate better than either lower or 

higher carrier frequencies.

 log2   /1 NSBC , (3) 

where C is the channel capacity in bits/second, B is the channel 

bandwidth in hertz, S is the received signal power in watts, and N

is the measured noise power in watts. The capacity represented by 

this equation is the upper lim it, and in reality the capacity would 

be difficult to attain with real hardware. 

For an analog transmission, Shannon’s limit gives us a way to 

estimate the channel capacity . The National Television S ystem 

Committee (NTSC) analog video channel that our robot used has 

a video bandwidth of 4.2 MHz and a transmission rate of 

approximately 30 frames per second, where each frame consists 

of 525 scanning lines, giving a line rate of 15.734 kHz [14]. We 

can place an upper bound on the am ount of data that could be 

transmitted in each line by considering a ty pical implementation 

of NTSC, where each line is digiti zed into 768 pixels. This gives 

a digital scanning rate of approximately 12 MHz. The 

specification of 768 pixels per line is used in studio environments. 

We expect the potential channel capacity to be lower in the 

analog transmission case. 

Figure 10 shows simulations of the Shannon limit for our 

robot’s 4.2 MHz video bandwidth, 1.78 GHz video channel. Table 

4 shows the distance into the tunnel where 12 Mb/sec 

transmission rate occurs assuming our maximum possible channel 

242
capacity to be various fractions of the Shannon limit. Based on 

this information, we would expect to encounter video problems 

somewhere between 120 m and 130 m into the tunnel, which 

Table 2 shows is indeed where we started to experience signal 

degradation. Thus, we are able to form a rough estimate of the 

distance into the tunnel where we expect the video to fail based 

on a simple implementation of the Shannon theorem. 

4. CONCLUSION

We have presented measured data collected in a subterranean 

tunnel environment. Results show ed waveguide-below-cutoff and 

wall attenuation effects. We saw frequency -dependent peaks and 

nulls in the channel due to strong m ultipath reflections and 

attenuation in the tunnel. In non-line-of-sight conditions, we saw 

classic Rayleigh-distributed noise-like signals. 

We implemented models that m ay be used to predict 

radiowave propagation and modulated-signal performance within 

tunnels for robots or other wire less devices. Using the models, it 

was possible to ascertain the optimal carrier frequency range for a 

robot within this tunnel environment. The intent of this work is to 

improve radio communications for urban search and rescue robots 

when they transmit wideband, digitally modulated signals. We 

hope that these data will prove us eful in standards development, 

as well as improved technology and sy stem design for the 

emergency-responder community. 

5. ACKNOWLEDGEMENT

The authors thank Alex Bordetsky of the Naval Postgraduate 

School for facilitating the m easurements during recent 

interagency m arine interdiction operation sy stem tests. We also 

thank Bill Dunlop, Steve MacLaren, and Dave Benzel of 

Lawrence Livermore National Laboratory for logistical and 

technical support. We are indebted to Frederick M. Remley for 

details on the NTSC video standard. 

0 50 100 150 200

0

50

100

150

200

Distance (m)

Capacity (Mb/sec)

100% of Shannon Capacity

90% of Shannon Capacity

80% of Shannon Capacity

70% of Shannon Capacity

Figure 10: Channel capacity predicted by the Shannon 

theorem for a carrier frequency of 1.78 GHz and a video 

modulation bandwidth of 4.2 MHz. At 120 m, where we 

experienced intermittent video, 80 % of the Shannon limit is 

15.4 Mb/sec and 70 % of the Shannon limit is 13.5 Mb/sec. 

6. REFERENCES

[1] Elena Messina, “ Performance Standards for Urban Search and 

Rescue Robots,” ASTM Standardization News, August 2006, 

http://www.astm.org/cgibin/SoftCart.exe/SNEWS/AUGUST_2006/messina_aug06.html . 

[2] National Institute of Standards and Technology, “Statement of 

Requirements for Urban Search and Rescue Robot Performance 

Standards-Preliminary Report” 

http://www.isd.mel.nist.gov/US&R_Robot_Standards/Requirements

%20Report%20(prelim).pdf 

[3] K. A. Rem ley, G. Koepke, E. Messina, A. Jacoff, G. Hough, 

“Standards development for wireless com munications for urban 

search and rescue robots,” Proc. Int. Symp. Advanced Radio 

Technol., pp. 66-70, Boulder, CO, Feb. 2007. 

[4] K.A. Remley, G. Koepke, C.L. Holloway, C. Grosvenor, D. Camell, 

J. Ladbury, D. Novotny, W.F. Young, G. Hough, M.D. McKinley, Y. 

Becquet, J. Korsnes, “Measurements to support broadband 

modulated-signal radio transmissions for the public-safety sector,” 

Natl. Inst. Stand. Technol. Note 1546, Apr. 2008.

[5] A.G. Emslie, R.L. Lagace, and P.F. Strong, “Theory of the 

propagation of UHF radio waves in coal mine tunnels,” IEEE Trans. 

Antennas and Prop., vol. 23, no. 2, Mar. 1975, pp. 192-205. 

[6] M. Rak and P. Pechac, “UHF propagation in caves and subterranean 

galleries,” IEEE Trans. Antennas and Prop., vol. 55, no. 4, April 

2007, pp. 1134-1138. 

[7] D. G. Dudley, M. Lienard, S.F. Mahmoud and P. Degauque, 

“Wireless propagation in tunnels,” IEEE Antennas Prop. Mag., vol. 

49, no. 2, April 2007, pp. 11-26. 

[8] M. Rütschlin, K. A. Remley, R. T. Johnk, D. F. Williams, G. 

Koepke, C. Holloway, A. MacFarlane, and M. Worrell, 

“Measurement of weak signals using a communications receiver 

system,” Proc. Intl. Symp. Advanced Radio Technol., Boulder, CO, 

March 2005, pp. 199-204. 

Fraction of Shannon capacity 

(%) 

Distance into tunnel 

(m) 

100 133 

90 129 

80 122 

70 114 

Table 4: Distance into tunnel for a channel capacity of 

approximately 12 Mb/sec. 

[9] P. Delogne, “Leaky Feeders and Subsurface Radio Communications, 

IEE press, 1982. 

[10] B. Davis, C. Grosvenor, R.T. Johnk, D. Novotny, J. Baker-Jarvis, M. 

Janezic, “Complex permittivity of planar building materials 

measured with an ultra-wideband free-field antenna measurement 

system,” NIST Journal of Research, Vol. 112, No. 1, Jan.-Feb., 2007, 

pp. 67-73. 

[11] G. Hough, “Wireless robotic communications in urban 

environments: issues for the fire service,” Thesis, Naval 

Postgraduate School, March 2008. 

http://theses.nps.navy.mil/08Mar_Hough.pdf

[12] J. Lee and H. Bertoni, “Coupling at cross, T, and L junctions in 

tunnels and urban street canyons,” IEEE Trans. Antennas Prop., vol. 

51, no. 5 , May 2003, pp. 926-935. 

[13] C.E. Shannon, “Communication in the presence of noise,” Proc. IRE, 

vo. 37, no. 1, Jan. 1949, pp. 10-21. 

[14] C.A. Poynton, “A Technical Introduction to Digital Video,” Wiley, 

1996, pp 26-27. 

243
A Performance Assessment of Calibrated Camera

Networks for Construction Site Monitoring

Itai Katz, Nicholas Scott, Kamel Saidi

National Institute of Standards and Technology

100 Bureau Drive Stop 8611

Gaithersburg, MD, 20899-8611, USA

{itai.katz, nicholas.scott, kamel.saidi}@nist.gov

ABSTRACT

Monitoring the status of construction activity is a key factor in maximizing efficiency and reducing cost on capital

construction sites. In contrast to human inspection, an automated technology would provide more frequent updates.

However, real-time construction site monitoring remains an

elusive goal because of many factors including the environment’s large size and dynamic behavior. Calibrated camera

networks have recently been developed to enable smart environments, where the location of people and objects in the

scene are updated in real-time. Despite a growing interest

in this technology, a detailed performance analysis has not

been conducted. In this paper, empirical results on the calibration and static 3D localization error are presented for

a calibrated camera network prototype using four cameras.

Using a total station to provide ground truth, the cameras

are calibrated and points in the workspace are reconstructed

in 3D by combining observations from each image plane. Results show that performance is well suited for localizing objects typically found on a construction site (although scaling

errors have not yet been characterized).

Keywords

construction automation, calibrated camera network, performance evaluation

1. INTRODUCTION

1.1 The Problem

Situation awareness on a construction site is a key element in maintaining a safe and productive project. In industries such as manufacturing, where the work environment

is highly controlled and predictable, situation awareness is

relatively easy to achieve. However, the dynamic and cluttered nature of a construction site makes a similar degree

of control virtually impossible. Nevertheless, in order for

project managers and others to make informed and timely

This paper is authored by employees of the United States Government and

is in the public domain.

PerMIS’08 August 19-21, 2008, Gaithersburg, MD, USA

Copyright 2008 ACM 978-1-60558-293-1/08/08.

decisions, they must have accurate information of the current status of all project activities. Decisions made based

on old or inaccurate information could have wide-reaching

ramifications on the schedule, budget and safety of a project,

particularly on large capital projects.

Critical information needed for proper decision-making includes:

• Locations of workers and equipment

• Locations of bulk materials and manufactured construction components

• Level of completion for construction activities

• Locations of potential safety hazards

1.2 Camera Networks as a Solution

In this paper, we propose a solution to the situation awareness problem on construction sites using calibrated camera

networks. Rather than simply providing raw video feeds,

calibrated camera networks provide a method to abstract

the data into a form that is more readily usable. While

these systems are well known in the academic community [3],

their use in the construction industry is novel. This paper

extends previous results in [4] on localization error for longbaseline methods using an alternative calibration technique.

The data set is 50 % larger and better characterizes the work

volume.

1.3 Outline

Below we introduce the calibrated camera network (CCN)

concept and describe a potential role in the construction

domain. Section 2 provides an overview of CCNs and illustrates how they could potentially be applied to the construction domain. Section 3 demonstrates the setup and testing

of a camera network and reports on experimentally-derived

errors for 3D localization. Conclusions are provided in Section 4.

2. CALIBRATED CAMERA NETWORKS IN

CONSTRUCTION

2.1 System Description

A CCN is a collection of three or more vision sensors

whose positions and orientations in 3D space have been determined. In contrast to a collection of isolated cameras,

CCNs have two key differences:

244
1. Each camera in the network is a ”smart” node that

combines an image sensor, on-board computing, and

the capability to network with other nodes (typically

wirelessly). This allows each node to independently

carry out low-level image processing tasks (e.g., background subtraction) or more sophisticated vision algorithms (e.g., pedestrian detection). By communicating

only the output of these algorithms, rather than the

raw video streams, bandwidth is conserved.

2. Each camera is calibrated with respect to a common

coordinate system (i.e., the pose and internal parameters – intrinsic and extrinsic – of the cameras are

known). This step is performed before the nominal

operating mode and allows the 2D image planes to be

combined in order to recover 3D structures.

An example of a CCN is shown in Figure 1. In principle,

a CCN can be used to detect and track objects in 3D, and

to perform geometric reconstruction.

Figure 1: Photo of a calibrated camera network with

four cameras. The checkerboard pattern in the center is a calibration target.

2.2 Benefits Over Existing Sensors

There are various manufacturers of video cameras designed

specifically for remote monitoring of construction sites. Although these systems could be of benefit for large sites where

continuous, in-person monitoring is impractical, the effort

required by the human operator increases with the number

of video feeds to be monitored. As the number of feeds

increases, visual clutter for the human operator also increases and the ability to discriminate interesting or anomalous events can actually decrease [4].

A CCN has additional advantages over other 3D tracking

sensors such as laser trackers, ultra wideband locators, laserbased localization systems, and high-frame rate 3D imaging

systems. The advantages include:

• Robustness to noise: Individual localization errors can

be averaged together. Localization error can be reduced by incorporating additional nodes into the network.

• Occlusion handling: CCNs are inherently redundant.

By placing cameras around the perimeter of the workspace,

occluded objects can still be tracked as long as they remain visible in two or more cameras.

• Arbitrarily-sized workspace: Adding coverage in a CCN

can be achieved by incorporating additional nodes into

the network.

• Token-less operation: Tracking an object or a person does not require placing a token such as a RadioFrequency Identification (RFID) tag, optical receiver,

or other cooperative target on the object being tracked.

• Passive operation: As long as multiple cameras in a

CCN can ”see” an object within a workspace, no supplementary illumination source is necessary to track

that object.

• Decentralized communication: Since the nodes in a

CCN can form an ad-hoc mesh network in order to

share and transmit data, as long as a node can see at

least one other node within the network, the CCN can

function in noisy environments where a central device

acting as the bridge between multiple wireless sensors

can experience range and interference problems.

2.3 Site Deployment

Prior to installation at a construction site, a suitable camera configuration must be determined that will provide the

desired tracking performance. The number and layout of

cameras will depend on many factors including the workspace

volume, camera field of view and resolution, and the desired spatial and temporal resolution. An exploration of

the tradeoff between camera resolution and the number of

cameras is discussed in [2]. For a given point in space, two

cameras are sufficient to recover the 3D position, however,

additional cameras will tend to improve the system performance by reducing the uncertainty.

Once a configuration has been chosen and the camera network has been installed on-site, the system must be calibrated. Calibration requires characterization of both intrinsic and extrinsic parameters for each camera. Intrinsic calibration determines a set of internal parameters (focal length,

image center, pixel size, and lens distortion) that define how

points in 3D are projected onto the 2D image plane of the

camera. Extrinsic calibration determines the relative position and orientation of each camera. Both calibrations are

commonly performed by taking images of calibration targets

and then exploiting the known target dimensions to determine the unknown parameters [5].

2.4 Applications

The real-time 3D localization capabilities of CCNs can assist with a number of problems relevant to the construction

industry. The following are some examples of CCN construction applications:

• Personnel, equipment and material tracking

• Automated project status monitoring

• Productivity assessment

• Automated safety and security alerts

245
3. EXPERIMENT

The majority of CCN literature focuses on short-baseline

(< 5 m) configurations. Despite growing interest, a detailed

performance analysis of long-baseline (> 5 m) calibrated

camera networks has not been conducted.

3.1 Procedure

Four cameras were mounted indoors on tripods roughly 4

m high and were arranged in a rectangle with dimensions of

approximately 12 m x 6 m. Each camera had a resolution

of 1024 pixels x 768 pixels, and the height, angle, and field

of view were adjusted to provide an overlapping workspace

volume of roughly 4 m x 4 m x 2.4 m. To provide ground

truth points for determining camera poses, the positions of

36 points distributed throughout the work volume were observed with a total station. Twelve coplanar points were

taken at three different heights (roughly 0 m, 1 m, and 2

m). A black 3.81 cm retroreflector was used both as a cooperative target for measurement with a total station as well

as a visible target in the camera images. The retroreflector was placed either directly on the ground or on a tripod

set to the desired height. The model of total station used

provides 0.2 mm spatial uncertainty, an order of magnitude

better performance than estimated for the camera network.

For each observation, the 3D position of the retroreflector

was found with the total station, while the corresponding 2D

pixel coordinates in each image were manually identified. An

example of an image from one of the cameras is shown in

Figure 2. Note the retroreflector mounted on the tripod in

the center of the image.

Figure 2: A typical view from one camera. The

tripod in the center holds a retroreflector.

Intrinsic and extrinsic calibration, including lens distortion parameters, were obtained using the well-known Direct

Linear Transformation (DLT) algorithm. First described in

1971 [1], the DLT method has become the gold-standard algorithm for camera calibration. For convenience, we briefly

describe its derivation below. A thorough explanation is beyond the scope of this paper, however the interested reader

is directed to [3] for a complete derivation.

The projective model for a pinhole camera maps 3D world

coordinates to 2D pixel coordinates by way of a projection

matrix. The basic equation is given by

λ

2

4 x

y

1

3

5 = P

2

6

6

4

X

Y

Z

1

3

7

7

5

(1)

where [x y 1]T is the homogenous pixel coordinate vector,

[X Y Z 1]T is the homogenous world coordinate vector, P is

the 3 x 4 projective matrix which encompasses both intrinsic and extrinsic parameters, and λ is an arbitrary scaling

factor. Given a pixel coordinate vector [xi yi]

T and world

coordinate vector [Xi Yi Zi]

T , the objective is to solve for P.

Through straightforward manipulation, (1) can be rewritten

in linear form as

2

6

6

6

6

6

4

X1 Y1 Z1 1 0 0 0 0

0 0 0 0 X1 Y1 Z1 1

.

.

. .

.

. .

.

. .

.

. .

.

. .

.

. .

.

. .

.

.

XN YN ZN 1 0 0 0 0

0 0 0 0 XN YN ZN 1

−x1X1 −x1Y1 −x1Z1

−y1X1 −y1Y1 −y1Z1

.

.

. .

.

. .

.

.

−xN XN −xN YN −xN ZN

−yN XN −yN YN −yN ZN

3

7

7

7

7

7

5

2

6

6

6

4

P1

P2

.

.

.

P11

3

7

7

7

5 =

2

6

6

6

6

6

4

x1

y1

.

.

.

xN

yN

3

7

7

7

7

7

5

(2)

where the elements of P can be solved for using the method

of least mean squares. When lens distortion parameters are

taken into consideration, (2) takes on a non-linear form. In

this case, an initial estimate for P can be obtained linearly,

and a non-linear, iterative solver can be used to jointly refine the estimate for P and the distortion parameters. This

process is depicted in Figure 3.

Direct Linear 

Transform

Non-linear 

Minimization

Manual Point 

Selection

images

camera

total station









Xi

Yi

Zi

1













xi

yi

1





P

Figure 3: Process for calibrating a CCN

The approach to reconstructing 3D points from multiple camera images follows directly from (1), where P and

[xi yi]

T are known, and [Xi Yi Zi]T are the unknown values

to be solved for. Geometrically, this is equivalent to projecting a line from the focal point of each camera through the

pixel viewing the retroreflector. The reconstructed point is

that which minimizes the perpendicular distances to these

projected lines.

To test performance, a subset of the 36 observed points

was reserved for calibration and the remaining points were

246
used to measure error. The number of points in the calibration subset varied from 10 to 35 and were chosen at random.

This process was repeated 1000 times. Each of these calibration subsets was used to calibrate three camera networks

consisting of 2, 3, and 4 cameras, respectively. The error

metric used is the average Euclidean distance between the

reconstructed point and the ground truth point as observed

by the total station. The results are discussed in Section 3.2.

3.2 Results

Several trends are evident from the analysis presented in

Figure 4. Reconstruction error tends to decrease as the number of calibration points increases. Reconstruction error also

decreases with additional cameras. With four cameras and

35 calibration points, the CCN can resolve points to within

7 cm of ground truth, on average. This level of performance

is inadequate for precision control applications, but is wellsuited for tracking movements of relatively large objects such

as personnel and heavy equipment.

10 15 20 25 30 35 0

0.02

0.04

0.06

0.08

0.1

0.12

# Calibration points

Reconstruction error (m)

CCN point reconstruction error

4 cameras

3 cameras

2 cameras

Figure 4: The localization error of the calibrated

camera network decreases as the number of calibration points is increased.

4. CONCLUSION

Situation awareness is a critical factor in maintaining a

safe, efficient construction site. As the quantity of information increases, intelligent sensors will become increasingly

important. Calibrated camera networks are well suited to

this role by providing 3D imaging capabilities that are complementary to existing technologies. In this paper, we described the characteristics and design considerations of camera networks, and empirically showed that errors within 7

cm are achievable.

As an in-depth experimental verification of calibrated camera networks has largely been unexplored, the experiment

described in this paper can be considered a pilot study. Future experiments will characterize the effect of calibration

schemes, workspace volume, and lighting variations on camera network error.

5. ACKNOWLEDGMENTS

The authors would like to thank Nicolas Philippon for

his invaluable support of the data collection that made this

work possible.

6. REFERENCES

[1] Y. I. Abdel-Aziz and H. M. Karara. Direct linear

transformation from comparator coordinates into

object space coordinates in close-range

photogrammetry. In Proceedings of the Symposium on

Close-Range Photogrammetry, Falls Church, Virginia,

1971. American Society of Photogrammetry.

[2] P. Carr, P. J. Thomas, and R. Hornsey. Performance

benefits and limitations of a camera network. In

Proceedings of SPIE Digital Wireless Communications

VII and Space Communication Technologies, volume

5819, pages 328–339, March 2005.

[3] R. I. Hartley and A. Zisserman. Multiple View

Geometry in Computer Vision. Cambridge University

Press, ISBN: 0521623049, 2000.

[4] R. Rosenholtz, Y. Li, and L. Nakano. Measuring visual

clutter. Journal of Vision, 7(2):1–22, 2007.

[5] Z. Zhang. A flexible new technique for camera

calibration. IEEE Transactions on Pattern Analysis

and Machine Intelligence, 2000.

247
A Queuing-Theoretic Framework for Modeling and

Analysis of Mobility in WSNs

Harsh Bhatia

Dhirubhai Ambani Institute of

of ICT

Near Indroda Circle,

Gandhinagar

Gujarat - 382007, India

harsh_bhatia@daiict.ac.in

R.B. Lenin

Department of Computer

Science

University of Arkansas

at Little Rock

Little Rock, AR 72204, U.S.A.

rblenin@ualr.edu

Aarti Munjal

Department of Mathematical

and Computer Science

Colorado School of Mines

1500 Illinois St, Golden, CO

80401, U.S.A.

amunjal@mines.edu

S. Ramaswamy

Department of Computer

Science

University of Arkansas

at Little Rock

Little Rock, AR 72204, U.S.A.

sxramaswamy@ualr.edu

Sanjay Srivastava

Dhirubhai Ambani Institute of

of ICT

Near Indroda Circle,

Gandhinagar

Gujarat - 382007, India

sanjay_srivastava@daiict.ac.in

ABSTRACT

In this paper, we present a complete framework for modeling

and analysis of Mobility in Wireless Sensor Networks using

OQNs with GI/G/1 nodes and single-class customers. We

formalize and present three variations - gated queues, intermittent links and intermittent servers. We suitably modify

and use the Queuing Network Analyzer (QNA) to study performance measures including: throughput, average waiting

time (end-to-end delay), and packet loss probability. The

results are verified by simulation in OMNeT++.

General Terms

Performance, Theory

Keywords

Unreliable servers, squared coefficient of variation, Poisson

process, Rayleigh and exponential distributions

1. INTRODUCTION

Open queuing networks (OQNs) have been widely used

as efficient tools to analyze the performance measures in

computer and communication systems ([2], [6], [8], [9]). For

many classes of OQNs, elegant and efficient solution methods exist. Well known closed product-form solutions are

available for simplified networks such as Jackson and BCMP

networks under a number of restrictions ([14],[5]). These

networks, however, do not always apply in practice.

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personal or classroom use is granted without fee provided that copies are

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permission and/or a fee.

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In wireless sensor networks with mobile nodes – we refer

them as Mobile Wireless Sensor Networks (MWSNs) – the

link between any two nodes will be either available or unavailable due to node mobility. Node unavailability is caused

by poor node signal strengths due to low battery, weather

conditions or both, or when the node is out of radio-range.

In [11], the authors have developed a random walk based

mobility model for a MWSN and have derived the probability distributions of link availability between any two nodes.

In [4], the authors had used a queuing network for delay

analysis of wireless ad hoc networks in which static nodes

are distributed uniformly and independently over a torus of

unit area. In this network, the transition probabilities for

forwarding packets from one node to another node are considered as functions of communication area of nodes of ad

hoc networks.

The mobility of nodes in a MWSN can be captured in

terms of gated queues, intermittent links or intermittent

servers of the queuing networks under investigation with immobile nodes. Hence, in this paper we analyze three types

of OQNs with GI/G/1 immobile nodes and single-class customers - one with gated nodes, second with intermittent

links and third with intermittent servers. We use appropriate distributions for the time durations for gate open/close,

link up/down, and server up/down. We also suitably modify the Queuing Network Analyzer (QNA), a method proposed by Kuhn [10], and later expanded by Whitt [16] to

approximate performance measures of large OQNs with general inter-arrival and general service distributions; to study

the performance measures of networks under investigation

with general distributions for the time duration of gate open

and close, link up and down, and server up and down. The

performance measures include throughput, average waiting

time (end-to-end delay), customer loss probability and path

availability.

The paper is structured as follows. Section II introduces a

general OQN and its performance measures. In section III,

the QNA method is discussed. In sections IV, V and VI, we

modify the QNA method for OQNs with gated nodes, with

248
interrupted links and with interrupted servers, respectively.

In section VII, we briefly outline the validation of our results

and present out conclusions.

2. GENERAL OQN

A queuing network is a natural extension of a collection of

interactive queuing systems, referred to as nodes. Consider

an OQN with M single-server and infinite buffer nodes. Let

μi denote the mean service rate and λ0i denote the mean

external arrival rate at node i. Let pij , i, j = 1, 2,...,M,

denote the transition probability by which customers finishing service at node i will join node j. The matrix P =

(pij ) is the sub-stochastic matrix such that with probability 1 − PM

j=1 pij customers finishing service at node i will

leave the network. The average arrival rate λj and the departure rate λj0 of customers at node j are given as follows

for j = 1, 2,...,M,

λj = λ0j +XM

i=1

pijλi; λj0 =

 

1 −XM

i=1

pji!

λj . (1)

For an acyclic network (where customers are not allowed

to revisit the nodes) with Poisson external arrivals and exponential service times, the total arrivals at node i follow a

Poisson process with rate λi given by (1). For cyclic networks, due to dependency amongst the arrival streams, the

total arrivals at node i do not follow Poisson process though

the external arrivals and service times are Poisson and exponential, respectively, in all nodes. The Jackson and BCMP

networks are examples of cyclic networks [14]. For these

networks, the steady-state joint probability distribution of

number of customers in all the nodes of the network admits

product-form solution and hence leading to closed-form solutions for performance measures like average wait times for

customers in the network.

For networks with GI/G/1 nodes, finding closed-form solutions for performance measures is more subtle. To overcome this difficulty, the QNA method is used to find approximate solutions for the performance measures of OQN with

GI/G/1 nodes. We discuss this method in more detail in

section 3.

For the queuing networks under investigation in sections

4, 5 and 6, one can analyze the performance measures like

throughput, customer loss probability, and average waiting

time. These measures are defined as follows.

The throughput T of the network is given by

T = XM

j=1

λj0, (2)

where λj0 is given by (1).

The customer loss probability PL is given by

PL = γ − T

γ , with γ = XM

j=1

λ0j . (3)

where γ is the total inflow to the network. The average

waiting time Ws of a customer in the network (end-to-end

delay) is given by

Ws = XM

j=1

Wsj , with Wsj = Wqj +

1

μj

, (4)

where Wsj , Wqj and μj are the average waiting time, average queuing time and average service rate at node j, j =

1, 2,...,M. In this paper, we find analytical formulas for

Ws of the proposed queuing-theoretic framework.

3. QNA METHOD

The QNA is an approximation technique and a software

package developed at Bell Laboratories to calculate approximate congestion measures of a network of queues [16]. It is

a powerful tool to analyze general queuing networks. The

most important feature of the QNA is that the external arrival processes need not be Poisson, and the service-time

distributions need not be exponential. The QNA can provide a fast approximate solution for large networks.

The QNA has been used extensively in many theoretical

and practical applications and the results have been compared with simulation results and/or the results of other

techniques ([15], [7], [13]). The low relative error percentage

makes QNA one of the most important tools for analyzing

general networks.

The input to QNA comprises of the number of nodes M,

mean arrival rate λ0i and squared coefficient of variation

(SCV) c2

0i for external arrivals at node i, i = 1, 2,...,M,

mean service rate μi and SCV c2

si for service time at node

i, i = 1, 2,...,M, and the transition (routing) probabilities

pij , i, j = 1, 2,...,M.

The total arrival rate at node i is given by (1). The traffic

intensities or utilization of node i is given by ρi = λi/μi. The

arrival rate from node i to node j is given by λij = pijλi.

The proportion of arrivals to node j from node i is given by

qij = λij/λj , i = 0, 1,...,M. The SCV of the total arrivals

at node j is calculated as follows [16]:

c

2

aj = aj +XM

i=1

bij c

2

ai, (5)

where aj and bij are derived after considering merging and

splitting of traffic streams and are given as follows:

aj = 1+ wj{(q0j c2

0j − 1)

+Xm

i=1

qij ˆ

(1 − pij )+(pijρ2

i xi)

 ̃

} (6)

and bij = wjpij qij (1 − ρ2

i ), xi = max1≤i≤M(c2si, 0.2), wj = ˆ

1 + 4(1 − ρi)

2(vj − 1) ̃−1

, and vj = ˆPm

i=0 qij  ̃−1

. The

SCV c2

aj can also be calculated as follows [16, eqn. (41)]:

c

2

aj = 1 − wj + wj

XM

i=1

pij c

2

ij , (7)

where c2

ij is the SCV of the traffic flow from node i to node

j and is given by

c

2

ij = qij [1 + (1 − ρ2i )(c

2

ai − 1)

+ρ2

i (c

2

si − 1)] + 1 − qij . (8)

The expressions in (6) and (8) are obtained by setting m =

1 (number of servers in each node) and vij = 0 in equations

(25) and (41) of [16], respectively. The approximate formula

for the average waiting time of a customer at node j is then

given by [16]

Wqj = λj (c2

aj + c2sj )gj

2(1 − ρj ) , (9)

249
where gj is a function of ρj , c2

aj and c2

sj , such that gj = 1 for

c2

aj ≥ 1. On substituting (9) in (4) we get the end-to-end

delay Ws.

4. OQN WITH GATED NODES

We consider an OQN as discussed in section 2 with the

following modifications: each node has a gate which goes

on and off with rates α and β with variances von and voff ,

respectively. When the gate is on, the customers are allowed

to enter the queue, otherwise they are lost including the

external arrivals as shown in Figure 1.

μ

μ

μ

1

3

2

λ

λ

λ

1

2

3

λ

3

λ

2

λ1 λ 1 λ

2

λ2

λ

3

λ

λ1

,

,

,

,

3

,

,

,

,

,

p11

p12

p13

p21

p22

p23

p33

p31

p32

λ

01 λ03

λ02

λ

30

λ20

α

β

α

β

α

β

λ10

Figure 1: 3-node OQN with gated nodes

Let λ

j denote the mean arrival rate of the interrupted arrival process, due the presence of on-off gate, at node j. The

total arrival rate λj at node j due to external and internal

traffic flows at node j is given by λj = λ0j + PM

i=1 pjiλ

i.

Theorem 1. The mean arrival rate λ

j = ponλj and SCV

c

2

aj of the interrupted arrival process at node j, due to presence of the on-off gate, is given by

c

2

aj = c

2

aj + kλj , (10)

where pon is the probability that the gate of node j is on and

is given by

pon = β

α + β , and (11)

k = α(vonα2 + voff β2)

(α + β)2 . (12)

Proof: In [3], the author has analyzed switched general

process (SGP), denoted by A, wherein the arrivals to the

queuing system switches between two general renewal processes A1 and A2 with rates λ1 and λ2 according to a general

renewal switching (on-off) periods V1 and V2 with rate α and

β, respectively. The author has derived the effective mean

arrival rate λ and SCV C(A) of A as

λ = λ1E[V1] + λ2E[V2]

E[V1] + E[V2] ,

C(A) = λ1C(A1)E[V1]

λ(E[V1] + E[V2]) +

λ2C(A2)E[V2]

λ(E[V1] + E[V2])

+ (λ1 − λ2)2 ˆ

E[V1]

2V ar[V2] + E[V2]2V ar[V1]

 ̃

λ(E[V1] + E[V2])3 ,

where E[Vi] and V ar[Vi] are the mean and variance of

Vi, i = 1, 2, respectively.

Since in our network, arrivals are not allowed to enter a

node when its gate is closed, we have λ2 =0= C(A2).

Setting λ1 = λ, E[V1]=1/α, E[V2]=1/β, V ar[V1] = von

and V ar[V2] = voff , we get

λ = β

α + β λ, (13)

C(A) = C(A1) + λα(vonα2 + voff β2)

(α + β)2 . (14)

Since λj is the total arrival rate at node j of the queuing

network with gated nodes, the mean arrival rate λ

j and SCV

c

2

aj of the effective arrival process at this node j are obtained

by replacing λ by λ

j , λ by λj , C(A) by c

2

aj and C(A1) by

c2

aj in (13) and (14). Hence the theorem. Q.E.D

The utilization at node j is given by ρj = λ

j/μj and the

arrival rate from node i to node j is given by λ

ij = λipij .

The proportion of arrivals from node i to node j is given

by qij = λ

ij/λj , i ≥ 0. Customers from node j leave the

network with rate

λj0 =

 

1 −XM

i=1

pji!

λ

j , j = 1, 2,...,M. (15)

Substituting (15) in (2) and in (3), the throughput T and

customer loss probability PL(N) can be calculated, respectively.

The c2

aj in (10) is computed as follows: For j = 1, 2,...,M,

c

2

aj = aj +XM

i=1

bij c

2

ai + k

XM

i=1

bijλi, (16)

where k is given by (12). By replacing λj by λ

j and c2aj by

c

2

aj , we can use the QNA method (modified) presented in

section 3 to compute the Wqj , j = 1, 2,...,M of this gated

OQN.

5. OQN WITH INTERMITTENT LINKS

We consider an OQN as discussed in section 2 with the

following modifications: the link connecting between any

two nodes goes on and off with rates α and β with variances

von and voff , respectively. When the link is on between

nodes i and j, the customers departing node i are allowed

to enter the queue of node j with probability pij as shown in

Figure 2. In the model discussed in previous section, when

the gate of a node is off, then the node is disconnected from

the entire network since no other node can send customers to

this node. This is, however, an unrealistic assumption model

as for as its application to MWSNs are concerned because in

MWSNs, a link between two nodes may be down, but these

nodes may still be connected to other nodes in the network.

250
μ

μ

μ

1

3

2

λ

λ

λ

1

2

3

λ

3

λ

2

λ1 λ 1 λ

2

λ2

λ

3

λ

λ1

,

,

,

,

3

,

,

,

,

,

p11

p12

p

13

p21

p22

p23

p33

p31

p32

λ

01 λ03

λ02

λ30

λ20

λ10

β

α

α

β

β

α

α

β

α β

β

α

β

α

α

β

β

α

Figure 2: 3-node OQN with intermittent links

Theorem 2. The mean arrival rate λj and SCV c

2

aj of

the interrupted arrival process, due to presence of the on-off

links, at node j of the network is given by

λj = λ0j + ponXM

i=1

λij , (17)

c

2

aj = 1 − wj (1 −XM

i=1

pij c2

ij − k

XM

i=1

pijλij ), (18)

where pon is the probability that the link between two nodes

is on and is given by (11) and wj is the same as the one

given in (6) and k is given by (12).

Proof: Due to the presence of on-off links between nodes

i and j, the mean arrival rate λ

ij between these nodes is

obtained by simply replacing λ by λij and λ by λ

ij in (14).

That is,

λ

ij = ponλij . (19)

Similarly, the SCV c2

ij of the traffic flow between node i and

node j is obtained by replacing C(A) by c

2

ij , C(A1) by c2ij

and λ by λij in (14). That is,

c

2

ij = c

2

ij + kλij , (20)

where k is given by (12).

P

The total arrival rate at node j is given by λj = λ0j + M

i=1 λ

ij . On substituting for λij from (19) in this equation,

we get (17).

The SCV c2

aj of the total traffic flow to node j is obtained

by replacing c2

ij by c

2

ij in (7). That is,

c

2

aj = 1 − wj + wj

XM

i=1

pij c

2

ij , (21)

On substituting (20) in (21) yields (18). Hence the theorem. Q.E.D.

Using (17), (2) and (3), we can compute the T and PL.

Using (18) and (9) we can compute Wqj at node j for j =

1, 2,...,M.

6. OQN WITH INTERMITTENT SERVERS

We consider an OQN as discussed in section 2 with the

following modifications: the server in each node goes on and

off with rates α and β, respectively. When the server of

node j is on, the customers are served at the rate μj and

the server is off, the customers will wait in the queue until

the server becomes on. A 3-node network with intermittent

servers is shown in Figure 3.

β α

μ

1

λ01

λ

02

λ30

λ03

λ20

λ λ1 10

λ

2

λ3

β α

μ3

β α

μ

2

λ

3 p31

λ1

p

13

λ 1 p

12

2 p21 λ

λ

2 p22

3 p32 λ

λ

2 p

23

λ

3 p33

λ1 p

11

0

0

0

Figure 3: 3-node OQN with intermittent servers

Theorem 3. For the network under investigation, the mean

service rate μ

j = ponμj and the SCV of the effective service

time distribution is given by

c

2

sj = c

2

sj + kμj , (22)

where pon is the probability the server at node j goes on

and is given by (11) and the constant k is given by k =

αp2

on

(1+c2

off )

β2 with c2

off being the SCV of the server off distribution.

Proof: This model falls under the category of the unreliable server models. In [1, section 10.2.2], the authors have

given the first two moments of the effective service time distribution for an unreliable server with general service and

general up and down time distributions as follows1:

E[G] = E[B](1 + ηE[D]) (23)

E[G2] = E[B2](1 + ηE[D])2 + E[B]ηE[D2], (24)

where G is the random variable denoting the effective service

time of an interrupted server whose down time is given by

the random variable D. E[B] and E[B2] are the first and

second moments of the processing time of this unreliable

server when it is up and η is its expected up time. Though

the second moment result is proved with the assumption that

the arrivals follow Poisson process, it can be proved that it

holds even for general arrival process when the arrivals are

renewal processes. Dividing (24) by square of (23) yields

c

2

s = c2s +

η(1 + c2

off )

E[B]E[D]2(1 + ηE[D])2 , (25)

1Reproduced here for ease of reading and completeness.

251
where c

2

s , c2s and c2

off are the SCVs of the effective service time, processing time and server off time distributions,

respectively.

For node j of the queuing network under investigation we

have E[B]=1/μj , E[D]=1/β, E[G]=1/μ

j , η = α, c2

s =

c

2

sj , c2

s = c2

sj . Hence the theorem is proved on substituting

these in (23) and (25). Hence the theorem. Q.E.D.

Since there are no changes in the arrival process and its

moments, the inflow of customers is equal to the outflow as

we do not lose any customers and hence PL = 0. We can

get other performance measures by simply replacing μ by

μ

, c2

sj by c

2

sj in the standard QNA.

7. NUMERICAL RESULTS

To verify the analytical results, we simulated these three

types of queuing network models. The stopping criterion for

the simulation guaranteed a maximum relative error of 5%.

The relative error in the simulation was computed from the

associated confidence interval, which was obtained through

the usual normal distribution approximation.

We used OMNeT++ [12], a discrete-event simulation package to perform all the simulations. In the simulation, the following inputs were given depending on the type of networks.

For all the three types of networks: External arrival distributions and the corresponding rates λ0j , j = 1, 2,...,M. Service time distributions and the corresponding rates μj , j =

1, 2,...,M. For the gated nodes network: On-off distributions of M gates and the corresponding rates α and β. For

the intermittent links network: On-off distributions of links

and the corresponding rates α and β. For the intermittent

server network: On-off distributions of servers and the corresponding rates α and β.

Ws Node j 1/μj λ0j QNA Simulation Error

1 0.0400 2.0 0.0711 0.0682 4.0925

2 0.0400 2.0 0.1422 0.1365 4.0127

3 0.0400 2.0 0.1196 0.1137 4.9038

4 0.0400 2.0 0.2915 0.2965 1.7307

5 0.0400 2.0 0.1030 0.0979 4.9087

6 0.0400 2.0 0.2248 0.2219 1.2865

7 0.0400 2.0 0.0756 0.0723 4.3541

8 0.0400 2.0 0.1025 0.0996 2.8141

9 0.0400 2.0 0.0722 0.0690 4.3974

10 0.0400 2.0 0.0648 0.0622 3.9498

Table 1: Network with 10 gated nodes

We did not use any other information like SCV and distribution of internal arrivals. In each simulation we computed the following statistics: mean and standard deviation

of inter-arrival times, Wsj for each node, the customer loss

probability and Ws of the network.

In Tables 1 - 3, we have compared both analytical and

simulation results for queuing networks with specific distributions for on-off durations of gates, links and servers and

service time of servers. In all the examples, the external

arrivals to the networks are assumed to follow Poisson processes.

In Table 1, we considered a network with 10 gated nodes,

deterministic service, and Rayleigh on and off times with

rates α = 0.7181, β = 0.0319. In Table 2, we considered

a network with 10 nodes connected by intermittent links,

exponential service, and exponential on and off times with

rates α = 10/9, β = 25. In Table 3, we considered a network with 10 intermittent server nodes, deterministic service, Rayleigh on and off times with rates α = 0.7181, β =

0.0319.

Ws Node j 1/μj λ0j QNA Simulation Error

1 0.0400 2.0 0.0724 0.0719 0.7026

2 0.0400 2.0 0.1029 0.1026 0.3236

3 0.0400 2.0 0.0962 0.0950 1.2475

4 0.0400 2.0 0.1222 1.1207 1.2520

5 0.0400 2.0 0.0902 0.0885 1.8765

6 0.0400 2.0 0.1173 0.1159 1.2080

7 0.0400 2.0 0.0750 0.0746 0.4724

8 0.0400 2.0 0.0896 0.0881 1.6272

9 0.0400 2.0 0.0781 0.0762 2.3851

10 0.0400 2.0 0.0679 0.0675 0.5775

Table 2: 10-node Network with intermittent links

The simulation values match with the analytical values

given by QNA with very less relative error. In most of the

cases, the relative error (last columns in all tables) is approximately 1%.

Ws Node j 1/μj λ0j QNA Simulation Error

1 0.0511 2.0 0.0504 0.0485 5.0933

2 0.1415 2.0 0.1423 0.1544 9.0869

3 0.1036 2.0 0.1043 0.1047 1.0618

4 0.0653 2.0 0.6283 0.0626 4.1172

5 0.0832 2.0 0.0833 0.0812 2.3861

6 0.4423 2.0 0.4494 0.4051 8.4119

7 0.0546 2.0 0.0544 0.0524 4.0811

8 0.0823 2.0 0.0825 0.0808 1.7634

9 0.0516 2.0 0.0514 0.0491 4.8271

10 0.0450 2.0 0.0449 0.0432 3.8929

Table 3: Network with intermittent server nodes

8. CONCLUSION

The research work presented in this paper provides a queuingtheoretic framework to model and analyze MWSNs by means

of a mechanism that leverages the power of QNA. While

QNA is an approximation technique, the results show that

it results in very less error; and its use is highlighted by its

applicability to model and analyze the vagaries of complex

real-world networks. The paper is an attempt to analytically address this emerging need in this area; and hence

we have made some realistic assumptions. Our current research is directed towards relaxing some of these assumptions, finding various other parameters - such as incorporating finite buffers, varying battery levels of a node and

prevailing weather conditions; and identifying appropriate

statistical distributions for such parameters.

Acknowledgment

This work is based in part, upon research supported by

the National Science Foundation (grant nos. CNS-0619069,

EPS-0701890 and OISE 0650939), National Board of Higher

Mathematics, India (grant no. 48/5/2004/R&D-II/2120),

NASA EPSCoR Arkansas Space Grant Consortium (grant

252
no. UALR 16804), and Acxiom Corporation (contract no.

281539). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the funding

agencies.

9. REFERENCES

[1] I. Adan and J. Resing. Course note on queueing

theory. http://www.win.tue.nl/ iadan/que/, 2003.

[2] D. Bertsekas and R. Gallager. Data Networks. Pearson

education, 2006.

[3] V. N. Bhat. Renewal approximations of the switched

Poisson processes and their applications to queueing

systems. Journal of the Operational Research Society,

45(3):345–353, 1994.

[4] N. Bisnik and A. Abouzeid. Queueing network models

for delay analysis of multihop wireless ad hoc

networks. In Proceeding of the 2006 international

conference on Communications and mobile computing,

pages 773–778, Vancouver, British Columbia, Canada,

2006. IWCMC’06.

[5] E. Gelenbe and G. Pujolle. Introduction to Queueing

Networks. John Wiley and Sons, 1987.

[6] G. Giambene. Queueing Theory and

Telecommunications – Networks and Applications.

Springer, 2005.

[7] B. R. Haverkort. Approximate analysis of networks of

P H/P H/1/K queues with customer loss: Test results.

Annals of Operations Research, 9:271–291, 1998.

[8] B. R. Haverkort. Performance of Computer

Communication Systems – A Model-Based Approach.

Wiley, 1999.

[9] F. J. Hayes and T. V. Ganesh Babu. Modeling and

analysis of telecommunications networks.

Wiley-Interscience, Hoboken, New Jersey, 2004.

[10] P. Kuhn. Approximate analysis of general queueing

networks by decomposition. IEEE Transactions on

Communications, 27(1):113–126, 1979.

[11] A. B. McDonald and T. Znati. A mobility-based

framework for adaptive clustering in wireless ad hoc

networks. IEEE Journal on Selected Areas in

Communications, 17(8):1466–1487, 1999.

[12] OMNeT++. http://www.omnetpp.org/index.php,

2007.

[13] G. Schneider, M. Schuba, and B. R. Haverkort.

QNA-MC: A performance evaluation tool for

communication networks with multicast data streams.

In R. P. et al., editor, Tools’98, 1469, pages 63–74,

Spain, 1998. Universitat de les Illes Balears, Lecture

Notes in Computer Science, Springer-Verlag.

[14] J. Walrand. An Introduction to Stochastic Modeling.

Academic Press, 3rd edition, 1998.

[15] W. Whitt. Performance of the queueing network

analyzer. The Bell System Technical Journal,

62(9):2818–2843, 1983.

[16] W. Whitt. The queueing network analyzer. The Bell

System Technical Journal, 62(9):2779–2815, November

1983.

253
Towards Information Networks to Support Composable 

Manufacturing 

Mahesh Mani 

Design and Process Group 

Manufacturing System Integration Division 

National Institute of Standards and Technology 

100 Bureau Drive, Gaithersburg, MD USA 

(301) 975 -5219 

mahesh@nist.gov 

Junho Shin 

Enterprise Systems Group 

Manufacturing System Integration Division 

 National Institute of Standards and Technology 

100 Bureau Drive, Gaithersburg, MD USA 

(301) 975 -3654 

junho.shin@nist.gov 

Albert. T. Jones 

Enterprise Systems Group 

Manufacturing System Integration Division 

National Institute of Standards and Technology 

100 Bureau Drive, Gaithersburg, MD USA 

(301) 975 - 3554 

albert.jones@nist.gov 

Ram D. Sriram 

Design and Process Group 

Manufacturing System Integration Division 

National Institute of Standards and Technology 

100 Bureau Drive, Gaithersburg, MD USA 

(301) 975 -3507 

sriram@nist.gov 

ABSTRACT

Rigid, supply-chain organizational structures are giving way to 

highly dynamic collaborative partnerships. These partnerships 

will develop rapidly by composing global manufacturing 

resources in response to open market opportunities and they will 

disband just as rapidly when those opportunities disappear. 

Cooperation, coordination, and distributed decision-making will 

be critical to the success of these dynamically composable 

systems. That success, in turn, will depend on the creation of a 

manufacturing information network that automates as much as 

possible, the identification, formalization, encoding, and sharing 

of appropriate manufacturing- and business-related knowledge. 

In this paper we present some of the issues and requirements 

associated with the creation of such networks. 

Categories and Subject Descriptors

C.2.1 [Computer-Communication Networks]: Network 

Architecture and Design- Distributed networks. 

General Terms

Algorithms, Management, Performance, Design, Standardization, 

Languages 

Keywords

Manufacturing information networks, interoperability, common 

vocabulary, standards, composable manufacturing 

1. INTRODUCTION 

For most of the 20th century, competitive advantage was defined 

by the production and labor capabilities of individual original 

equipment manufacturers (OEMs). In the mid 90s, OEMs sought 

to reduce production and labor costs by outsourcing those 

capabilities globally. Thus, the rigid supply chain structures of the 

past are slowly giving way to virtual supply networks of 

collaborative partnerships. These partnerships will develop 

rapidly by composing global resources in response to market 

opportunities and they will disband just as rapidly when those 

opportunities disappear. These resources now include designers, 

engineers, planners, transporters, suppliers, fabricators, 

assemblers, buyers, vendors, and service providers, among others. 

The only way to improve competitive advantage in such a 

networked system is to improve the orchestration of all of these 

resources so that they behave as if they were a single virtual 

factory. 

A major concern in these networked systems is the availability of 

the right product, process, and business information when and 

where it is needed. We believe that this requires a separate 

integration infrastructure, which we call the manufacturing 

This paper is authored by employees of the United States Government 

and is in the public domain. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA 

ACM ISBN 978-1-60558-293-1/08/08.

254
information network (MIN). A MIN will enable the discovery, 

coordination, and automated exchange of information regardless 

of where it resides in the system. The reason that discovery, coordination, and automated exchange is so important is that the 

system orchestrator must have (1) intimate, real-time knowledge 

of the capabilities and capacities of all potential partners (2) 

accurate predictions of customer demands and product 

requirements, (3) the ability to match supplier capabilities to those 

requirements, and (4) the skills to manage the entire, global set of 

production and delivery schedules. 

In this paper we present our vision for a MIN, which is based on 

the concepts of the internet of services (IOS) and service-oriented 

architecture (SOA). The rest of the paper is organized as follows: 

Section 2 first presents the modeling of composable 

manufacturing systems followed by section 3 briefly discussing 

information exchange in composable manufacturing systems. 

Section 2 and 3 aim to present the diverse information exchange 

in MIN. Section 4 briefly presents the commonly used standards, 

reference models and business processes. Sections 5 and 6 present 

our proposed MIN approach and related research issues 

respectively. Finally Section 7 presents our conclusions. 

2. MODELING COMPOSABLE 

MANUFACTURING SYSTEMS 

Bringing complex products to customers requires close 

collaborations among a number of functions including design, 

engineering, manufacturing, and logistics. As noted above, these 

functions are performed by resources that are geographically 

distributed around the world. As described in [1,2] these resources 

are modeled frequently as autonomous, interacting software 

agents with each agent executing one function. Agents are 

implemented as intelligent web-based applications that wrap 

functional applications and manage electronic information 

exchange. The communications protocols used by these software 

agents have been developed by FIPA (Foundation of Intelligent 

and Physical Agents)1

, an IEEE Computer Society standards 

organization that promotes agent-based technology and the 

interoperability of its standards with other technologies. These 

simple protocols govern the information data flow through the 

participating agents, thus ensuring seamless data and information 

transfer. Their potential benefit is that the agents can exchange 

the same information as their real-world counterparts. The 

principal drawback is that they are not powerful enough to allow 

the agents to understand most of that information. Therefore, 

interoperability remains a major impediment for software agents, 

just like it does for their real-world counterparts. 

3. INFORMATION EXCHANGE IN 

COMPOSABLE MANUFACTUING 

SYSTEMS 

Information exchange is critical for collaborations and 

management at every phase of the product lifecycle. In current 

supply chains, these exchanges take place typically through 

numerous message-based transactions between the various 

partners. The granularity and complexity of the information 

exchanged depends on the type of transaction and the partners 

 

1

 http://www.fipa.org/specifications/index.html 

involved. The type of transaction is based on an agreed upon 

understanding of the business process being executed (see section 

4). This understanding is possible because (1) the partners are 

known in advance, that is the organizational structure is 

somewhat rigid and (2) the negotiation is dictated by the OEM, 

who sits at the top of a command/control hierarchy. 

Several recent reports on the "Future of Manufacturing" predict 

two major changes in these supply chains [3,4]. First, OEMs' 

former command-and-control business model will evolve into 

more of a collaborative and negotiated partnership model. 

Second, the supply base will no longer be static and known in 

advance; rather, it will change regularly. In this new environment 

where systems are composed dynamically, the existing 

transaction-based approach will not be adequate for all 

information exchanges. Before describing the MIN approach, we 

briefly review some commonly used information standards and 

reference models governing message transactions and business 

processes. 

4. COMMONLY USED STANDARDS, 

REFERENCE MODELS AND BUSINESS 

PROCESSES 

A number of supply-chain Common Business Processes (CBP), 

information standards, messaging standards, and reference models 

have been defined. Business process specification is a declaration 

of the partners, roles, collaborations, choreography and business 

document exchanges that make up a business process. Some are 

industry specific and some are not. CBPs are industry neutral and 

re-usable business processes. Various components of a common 

business process specification can be re-used to create new 

business processes (See Figure 1]. Re-use will typically occur at 

the business process, business collaboration, business transaction, 

and business document model components. 

Business Transaction

Business Collaboration

Roles

Partner Types

Choreography Transition Guard

Business Collaboration

Reuse

Business Transaction

Reuse

Process Composition

/ Decomposition

Business Process

Reuse Cata ol g of Com

mon

Business Process

Figure 1. Catalog of Common Business Processes2

ANSI X12 (also known as ANSI ASC X12) is the official 

designation of the U.S. national standards body for the 

development and maintenance of Electronic Data Interchange 

(EDI) standards. X12 has an underlying syntax, which is an ANSI 

standard. Within that syntax, there are directories of data 

elements, composite data elements, segments, and messages. 

There are conventions for placing messages in an "envelope" 

 

2

 http://www.ebxml.org/specs/bpPROC.doc

255
which identifies the sender and receiver and other attributes of a 

transmission3

. 

EDIFACT (Electronic Data Interchange for Administration, 

Commerce, and Transport) is the international Electronic Data 

Interchange developed under the United Nations. EDIFACT has 

an underlying syntax, which is an ISO standard. Within that 

syntax, there are directories of data elements, composite data 

elements, segments, and messages4

. It also provides interactive 

exchange protocols and standard messages. 

EIDX represents the Electronics Industry Data Exchange Group. 

As part of the Computing Technology Industry Association 

(CompTIA), EIDX is committed to advancing industry growth 

through the development of standards, best practices, 

accreditations, professional education and development, tools and 

business solutions5

. EIDX provides implementation guidelines 

for EDI and XML-based vocabulary standards. 

RosettaNet is an independent, self-funded, non-profit consortium 

dedicated to the development and deployment of standard 

electronic business interfaces. These standards form a common eBusiness language, aligning processes between supply chain 

partners on a global basis. RosettaNet’s Partner Interface 

Processes (PIP) standards allows trading partners of all sizes to 

connect electronically to process transactions and move 

information within their extended supply chains6

. 

The Open Applications Group Integration Specification (OAGIS) 

is an effort to provide a canonical business language for 

information integration. It uses XML as the common alphabet for 

defining business messages, and for identifying business 

processes (scenarios) that allow businesses and business 

applications to communicate. OAGIS provides the definition of 

business messages in the form of Business Object Documents 

(BODs) standards and example business scenarios that provide 

example usages of the BODs7

. 

Table 1 presents possible mappings between several of these 

standards. 

Table 1. Example mapping of common business processes 

Common 

Business 

Processes 

Normative 

Category 

Normative Sub 

Category 

EDIFACT 

including 

sub-sets 

X12 

including 

sub-set 

RosettaNet 

Partner 

Interface 

Process 

CII 

(HWSW

001A) 

OAG BODs 

Distribute 

Dispatch 

Instructions 

Procurement 

Management 

Transportation 

and 

Distribution 

INSDES 862, 858 PIP3B1 165_sync_sh

ipschd_001 

Notify Of 

Advance 

Shipment 

Procurement 

Management 

Transportation 

and 

Distribution 

DESADV 856, 869 PIP3B2 0520 165_sync_sh

ipschd_001 

Besides the above, SCOR and DCOR present process reference 

models for any supply chain. 

 

 and amend. 

 3 http://www.x12.org

4 http://www.stylusstudio.com/edifact

 5 http://eidx.comptia.org 

6

 http://www.rosettanet.org

 7 http://www.openapplications.org 

SCOR: Supply-Chain Operations Reference is a process reference 

model that has been developed and endorsed by the Supply-Chain 

Council (SCC). The SCC is an independent, not-for-profit, global 

corporation with membership open to all companies and 

organizations interested in applying and advancing the state-ofthe-art in supply and design chain management systems and 

practices. SCOR has been adopted as the cross-industry de facto 

standard diagnostic tool for supply chain management8

. It is a 

hierarchical model that has five major building-block processes: 

plan, make, source, deliver, and return. 

DCOR: The Design Chain Operations Reference-model 

(DCOR)9

. The newest model from the SCC, the DCOR-model 

captures the SCC’s Technical Development Steering Committee’s 

consensus view of design chain management. The structure is 

based on the same hierarchical philosophy as SCOR, but with five 

different building-block processes: plan, research, design, 

integrate,

5. OUR APPROACH: MANUFACTURING 

INFORMATION NETWORKS (MINS) 

As noted above, future manufacturing networks will be 

dynamically created from global resources (see Figure 2). 

Orchestration, cooperation, coordination, and distributed 

decision-making will be critical to their success. The execution of 

these functions, in turn, will depend on the creation of an 

infrastructure that automates, as much as possible, the exchange 

of required manufacturing- and business-related knowledge. We 

call such an infrastructure a manufacturing information network 

(MIN). A MIN (see Figure 3) is created every time an application 

needs to find or exchange information. 

Conceptually, the MIN will constitute another “layer” of open 

cyberspace, sitting atop the Internet and other evolving Web 

technologies. As such, it will be independent of any particular 

enterprise software applications. Such an infrastructure will 

enable the complete virtualization of and ubiquitous access to 

global manufacturing resources allowing information to be 

exchanged anywhere, anytime, on any device. The primary 

feature of the MIN is composability. 

Composability is a system design principle that deals with 

component inter-relationships. A high degree of composability 

means the system has recombinant components that can be 

selected and assembled in arbitrary ways to satisfy user 

requirements. A composable component must be self-contained 

(modular), self-descriptive, and be able to integrate easily with 

other components in the system. 

The key to achieving this capability is to link these various 

components together in arbitrary ways to exchange the 

information necessary to meet business needs. 

The primary components of the MIN include services, 

repositories, brokers, and registries (See Figure 2). 

8

http://www.supplychain.org/cs/root/scor_tools_resources/scor_model/scor_model 

9

http://www.supplychain.org/cs/root/scor_tools_resources/designchain_dcor/dcor_mo

dels 

256
Services: The goal of the services is to be discovered and used as 

frequently as possible and by as many different actors. A service 

must be engineered for interoperability and designed to live in a 

completely open environment where they will not know who their 

potential partners will be in advance. This means, at a minimum, 

they must publish complete (register with the Service Registry), 

semantically rich descriptions and representations of what they do 

(their capabilities), the information they need to do it (their 

inputs), and the information they provide when they are done 

(their outputs). Ultimately, if the descriptions and representations 

are not easily understood, a service will not get used. 

A number of different services are envisioned: 

• Services that facilitate real-time information sharing and 

collaboration between enterprises, such as reasoning, searching, 

discovery, composition, assembly, and delivery of semantics 

automatically. 

• Services that leverage emerging Web technologies for enabling 

a new generation of information-based applications that can selfcompose, self-declare, self-document, self-integrate, selfoptimize, self-adapt, and self-heal. 

• Services that support knowledge creation, management, and 

acquisition to enable knowledge sharing between virtual 

organizations. 

• Services that help connect islands of interoperability by 

federating, orchestrating, or providing common e-business 

infrastructural capabilities such as digital signature management, 

certification, user profiling, identity management, and libraries of 

templates and interface specifications. 

• Services that support the use of mashup technologies such as 

verification of credentials; reputation management; assessment of 

e-business capabilities; assessment of collaboration capabilities; 

facilities for data sourcing, integrity, security and storage; 

contracting; registration and labeling; and payment facilities, 

among others. 

Figure 2. MIN Concept 

Interoperability Framework

Interoperability

A2 A3

A4

A5

A6 A7 A8

A1

I

(New Application)

I

I

Services Knowledge Repositories Brokers Registries

Figure 3. Composable-On-Demand MINs 

Knowledge Repositories: Knowledge Repositories continuously 

capture, store, and analyze all manufacturing-related information, 

for example, the knowledge of assets, manufacturing facilities/ 

capabilities of an organization or enterprise. Participating 

applications can then query or browse both structured and 

unstructured information in order to retrieve and update 

information. Besides being dynamic, knowledge repositories must 

cater for explicit form of knowledge to be able to retrieve context 

sensitive data. 

Brokers: Brokers can also be referred to as the MIN infrastructure 

bureau services. Depending on the demand and request, the 

broker identifies the service component that fills the need, locates 

it, and plugs it into the framework. The broker’s function is to 

select and assemble components belonging to different 

applications into integrated processes; for example, for order 

fulfillment. This integration is analogous to the formation of 

virtual enterprises from separate enterprises. Component 

technology provides seamless communication between 

applications residing in the different supply-chain partners. 

Registries: Registries can be thought of as advertisement services 

or yellow pages. They can also be useful to locate knowledge 

repositories and services. 

6. RESEARCH ISSUES 

To address the development of the above discussed composable 

MIN and its corresponding infrastructure, we need structured 

research into the conditions/requirements for interoperability in 

these networks. The following research questions will have to be 

investigated: 

x an interoperability framework in the context of MIN 

x specific roles of a MIN component like brokers, 

services, registries, will have to be investigated as part 

of the framework 

x minimum requirements for an application to participate 

in MIN (for service provider and service requester) 

x level of information transparency required to participate 

in MIN 

x roles of an interpreter/ translator for new application 

services 

257
x common vocabulary requirements for interoperability 

x level of intelligence that will make these application 

systems adaptive and self configuring (implies an 

application to be either context-aware, adaptive or 

anticipated based on experience) 

x specific use cases of manufacturing and business 

processes (scenarios or transactions) 

There are undertakings at NIST to develop and demonstrate an 

open, standards-based, testing and integration infrastructure that 

enables the automated exchange of manufacturing information 

among suppliers [3]. This infrastructure will provide the 

foundation for the new types of collaboration and management 

described above as a number of NIST-supported economic impact 

studies claim that such an infrastructure does not exist today [4]. 

7. CONCLUSION 

In this paper, we presented an approach towards information 

networks that supports composable manufacturing. We identified 

a need for a MIN infrastructure that provides a mechanism for 

information acquisition, sharing, delegation of tasks, and decision 

making between the various entities. We speculate on how the 

future of MINs may evolve as composable on demand MINs. 

Correspondingly we presented and discussed the issues and 

prerequisites that need to be addressed to support interoperability 

in such MINs. 

Semantic interoperability may be the key to MINs of the future. 

Adopting semantic interoperability for product-process automates 

information flow in an extended enterprise among different levels 

of information resources. Future research is on composable MIN 

and architectures to enable the way manufacturing organizations 

use information technology (computers, networks, information 

systems, data, algorithms, and decision support) to make their 

manufacturing processes more effective. 

8. ACKNOWLEDGEMENTS 

The authors wish to acknowledge Steven Fenves, Eswaran 

Subramanian and Nenad Ivezic for participating and contributing 

to discussions pertaining to the Manufacturing Information 

Networks. 

DISCLAIMER 

No approval or endorsement of any commercial product by the 

National Institute of Standards and Technology is intended or 

implied. 

9. REFERENCES 

[1] Mahesh, M., Ong, S.K., Nee, A.Y.C., Fuh, J.Y.H., and 

Zhang, Y.F. 2007. Towards A Generic Distributed and 

Collaborative Digital Manufacturing. Robotics and 

Computer Integrated Manufacturing, International Journal of 

Manufacturing and Product and Process Development. 23, 3, 

(June 2007), 267-27. 

DOI=http://dx.doi.org/10.1016/j.rcim.2006.02.008 

[2] Sriram, R.D. 2002. Distributed and Integrated Collaborative 

Engineering Design. Sarvan Publishers, Maryland. 

[3] Li, M.S., Jones, A. 2008. An information infrastructure for 

next generation Global enterprises, International MultiConference on Engineering and Technological Innovation: 

IMETI 2008. Orlando. Florida. USA. 

[4] Comparisons and Analyses of U.S. and Global Economic 

Data and Trends: Globalization: Trends and Impact Factors 

of Globalization of Manufacturing Input Factors on Future 

U.S. Manufacturing Capability. National Institute of 

Standards and Technology. U.S. Department of Commerce 

2004. 

http://www.sri.com/policy/csted/reports/nist/NIST_SUBD_G

lobalization.pdf

258
3D Reconstruction of Rough Terrain for USARSim 

Using a Height-map Method

G. Roberts 

 Intelligent Systems Division, 

National Institute of Standards 

& Technology, 100 Bureau 

Drive, MS 8230, Gaithersburg, 

MD 20899 USA. 

1-301-975-3434, 

gael.roberts@nist.gov 

S. Balakirsky 

Intelligent Systems Division, 

National Institute of Standards & 

Technology, 100 Bureau Drive, 

MS 8230, Gaithersburg, MD 

20899 USA. 

1-301-975-4791, 

stephen.balakirsky@nist.gov

S. Foufou

Laboratoire Electronique, Informatique et Image (LE2i 

Lab). UMR CNRS 5158, University of Burgundy, 21000, 

Dijon, FRANCE. 

00-333-8039-3805, 

sfoufou@u-bourgogne.fr

ABSTRACT 

In this paper, a process for a simplified reconstruction of rough 

terrains from point clouds acquired using laser scanners is presented. The main idea of this work is to build height-maps which 

are level gray-scale images representing the ground elevation. 

These height-maps are generated from step-fields which can be 

represented by a set of side-by-side pillars. Although height-maps 

are a practical means for rough terrain reconstruction, it is not 

possible to represent two different elevations for a given location 

with one height-map. This is an important drawback as terrain 

point clouds can show different zones representing surfaces above 

other surfaces. 

In this paper, a methodology to create several height-maps for the 

same terrain is described. Experimental results are shown using 

the high-fidelity physics-based framework for the Unified System 

for Automation and Robot Simulation (USARSim). 

Keywords 

3D Reconstruction, height-map, step-field, point cloud, USARSim. 

1. INTRODUCTION 

The usefulness of simulation systems for developing agent control 

systems is well established. The role of the simulation is to provide convincing sensor measurements as input to the control system and to accurately model the system’s response to actuator 

outputs (physics, dynamics, and statics). An important enabler 

that allows the simulation system to meet these requirements is 

the existence of an accurate model of the real world. 

One aspect of this world model is its representation of the ground 

surface, or a height-map. The required complexity of the ground 

surface representation is directly related to the agent’s application 

and target environment. For example, an agent that is required to 

operate in a flat-floored environment with no overhanging obstacles may only require occupancy information in its model. More 

complex environments that include uneven terrain may require a 

2.5D model (a single elevation value per unit area). Even more 

complex environments that include overhanging obstacles or 

multi-level terrain may require a full 3D model (multiple elevation values per unit area). 

This paper addresses the automatic creation of height-maps from 

data collected with laser scanners. The overall objective is to be 

able to recreate complex 3D terrains such as those that may be 

found at disaster sites (partially destroyed buildings, large 

amounts of debris, etc.) for use in simulation and in reconstructed 

physical representations. While the general techniques developed 

in this paper should be applicable to the general problem, the 

specific output formats have been tailored for the Unified System 

for Automation and Robotics Simulation (USARSim) framework 

[1]. 

USARSim was initially developed in 2002 as a low cost (under 

$40) robotics simulator at Carnegie Mellon University (CMU) 

and the University of Pittsburgh [2]. In 2005, USARSim management was handed off to the National Institute of Standards & 

Technology (NIST) and it became an open source project hosted 

on the Sourceforge network (www.sourceforge.net/projects/usarsim). USARSim is based on the UnReal Game Engine from Epic 

Games1

 and provides a high-fidelity, physics based simulation 

environment for robotic development. One of the unique features 

of USARSim lies in its validated sensor and robot models [3]. In 

addition to its use as a research tool, USARSim is also used as the 

basis for the RoboCup Rescue Virtual Competition as well as the 

 (c) 2008 Association for Computing Machinery. ACM acknowledges 

that this contribution was authored or co-authored by a contractor or 

affiliate of the U.S. Government. As such, the Government retains a 

nonexclusive, royalty-free right to publish or reproduce this article, or to 

allow others to do so, for Government purposes only. 

PerMIS’08, August 19-21, 2008, Gaithersburg, MD, USA 

ACM ISBN 978-1-60558-293-1/08/08.

1

 Certain commercial software and tools are identified in this paper in order to explain our research. Such identification does not 

imply recommendation or endorsement by the authors, nor does it 

imply that the software tools identified are necessarily the best 

available for the purpose. 

259
IEEE Virtual Automation and Manufacturing Competition. More 

information on USARSim may be found in [4]. 

The remainder of this paper is laid out as follows: Section 2 recalls some preliminary definitions regarding the dataset, stepfields, and height-maps. The relation between our work and other 

works is explained in Section 3. Section 4 gives the general approach adapted in this work. Section 5 details the proposed algorithm for terrain reconstruction using height-maps. Some experimental results are shown and discussed in Section 6. Section 7 

concludes and discusses about future extensions of this work. 

2. PREREQUISITE 

This section indicates the type of data used in this project and 

gives some fundamental definitions. 

The purpose of this work is to reconstruct models of rough terrains for use in a simulator. Laser based scanners are used to acquire 3D numerical data (point clouds) representing the ground. 

Point clouds may be complex, containing ground, surfaces, and 

heaps of objects. Point clouds are muddled, contain no texture, 

and their points are not uniformly distributed in space. 

In this work, the complexity of point clouds representing realworld scenes is intentionally avoided by only considering point 

clouds generated artificially. These point clouds are simpler but 

keep approximately the same characteristics (muddled, not textured, not uniform) as those acquired from real-world scenes. 

These artificial point clouds are generated as follows: a scene is 

created with different simple objects (planes, spheres, cylinders 

...) and points are randomly put onto the surface of each object 

using their equation. At the end, noise is added to make the clouds 

more realistic. 

Two important models are calculated for each point cloud: a stepfield model and a height-map model. A step-field can be represented by a set of side-by-side pillars (see Figure 1) and is computed as follows: starting from a horizontal plane, side by side 

pillars are placed with predefined dimension (height * width * 

depth). These pillars will all have identical width and depth, but 

their height will vary according to the configuration and properties of the point cloud. More details regarding the construction of 

these pillars are given later. 

The height-map model, also called CEM (Cartesian Elevation 

Map) or elevation map, is a gray scale picture (based on 256 levels of gray) which represents the height information of the studied 

terrain (see Figure 2). The lighter the color of a pixel is, the higher 

the elevation of the terrain is for the location represented by this 

pixel. 

3. RELATED WORK 

Since the beginning of mobile robot development, researchers 

have been striving to find ways for the platforms to navigate 

through various terrains. Work has even been performed on classifying the difficulty of terrain for robotic traversal. The general 

idea of our work is to find an adequate representation of rough 

terrains that will allow simulations of robots to be used to create 

and evaluate algorithms that will allow mobile robots to be more 

or less autonomous on rough terrains. 

Because robots come in many different shapes, sizes and abilities, 

simulation is a useful tool that allows one to predict which types 

of robots will be best-suited for particular types of terrain under 

consideration. Simulation is also an efficient way to test the impact of algorithm changes on the effectiveness of a given platform. There are two main types of ground mobility: walking robots [5, 6] and rolling robots (with tracks or wheels). Despite a 

large effort in the area of walking robots, they are not completely 

adequate for the ground studied for this paper. The reason for this 

is the rocky and uneven nature of a disaster site. Consequently, 

rolling robots which are also the subject of studies as regards their 

efficiency for rough terrains are used [7, 8, 9]. 

The terrains are created from a cloud of points. These reconstructions are an important area of computer graphics and there are 

many methods of 3D reconstruction from point clouds. Among 

these methods, which have the objective of creating a mesh, there 

are the Delaunay triangulation (which is joined to the Voronoi 

diagram) [10, 11, 12], related methods such as Ball-Pivoting 

(pivot of a sphere) [13] or other methods such as the one from 

Chang et al. [14]. All these methods give very good constructions, 

but the results are often very costly in memory. 

To resolve this problem, other research aims at simplifying the 

obtained meshing. These simplifications consist in reducing the 

number of polygons in a meshing by grouping polygons according 

to certain criteria such as the orientation of polygons or their configurations [15, 16, 17]. Although these mesh simplifications give 

reasonable results, the processes to do this are very costly in 

memory compared to the creation of height-maps as discussed in 

the next paragraph. 

Other methods for creating ground representations use heightmaps. The concept of height-map is used for several studies including the crossing possibilities of grounds or the construction of 

obstacles on a ground [18, 19]. Height-maps are useful for path 

planning and collision avoidance [20], they are also used to represent surfaces having a low-level of detail such as landscapes (e.g., 

video games). 

4. THE APPROACH TO THE PROBLEM 

The purpose of this work is to create a 3D terrain model that will 

be used in a simulator, consequently the simplest possible construction is necessary in order to reduce the computation costs 

during simulation. Therefore, in order to have a good simulation, 

it is very important to have a very simple scene because the Frame 

Per Second (FPS) is taken into consideration. For a complex scene 

with big meshed objects, the FPS will be too low for effective 

rendering and the simulation will certainly be too slow. 

Fig. 2: Example of 

height-map 

Fig. 1: Example of 

step-field 

Our simulator utilizes the Unreal 3D engine, thus the editor of this 

engine is used to construct the 3D models either by importing 

them as meshed scenes or by generating a height-map from point 

clouds. However, it is only considering the use of height-maps to 

avoid having bad FPS during the simulation. 

260
5. ALGORITHM DESCRIPTION 

The algorithm operates in two steps: (i) compute the step-field 

from the point cloud, (ii) and then compute the height-map. Several height-maps may be created for the same scene in order to 

have various layers representing surfaces (or objects) because 

these surfaces can be positioned one on the top of the other. 

5.1. Step-fields elaboration 

Having acquired the point cloud, a virtual horizontal plane P(x,y) 

is created: 

P(x,y) = Zmin – D 

Where Zmin represents the coordinates of the lowest point of the 

cloud on the Z axis, and Drepresents a small distance defined by 

the user. Therefore, the plane will be “Dunits” below the point 

cloud. This plane is bounded by the cloud on the X and Y axes. 

Then a grid on this plane is created. Each compartment of this 

grid represents the possible base of a future pillar. The side sizes 

of each compartment will be equal to the dimension of the pillar 

sides. The size of a compartment is given by the user. Thus, the 

dimensions of the grid (length * width compartments) are a function of the plan size and the compartments size. 

A pillar is created in each compartment situated under a nonempty subset of points. The height of this pillar is the average of 

the heights (Z-components) of the points of the subset. The obtained set of pillars defines the step-field of the scene (terrain), 

and will be used to construct the height-map. 

5.2. Height-map construction 

The height-map is built from the step-field. To this end, each pillar created is correlated with a pixel of a gray-scale image. If a 

pillar has a width of 10 cm, a pixel of the image will also represent a zone of 10 cm in reality. One should notice that if there was 

beforehand a grid of 64*64 compartments on the initial plane, 

there will be a height-map of 64*64 pixels. 

Height-map being an image of 256 levels of gray, the maximal 

height (Hmax) of the pillars is put in correspondence to the highest 

level of the scales of gray (that is 256). Other heights (h) of pillars 

will be represented by a proportional gray level g, such that: 

g = h * 256 / Hmax.  

We note that the simulator constrains the height-map to have a 

number of pixels equal to a power of 2 for each of its sides. For 

that purpose, padding is added around the height-map obtained 

previously. This padding will have a value equal to 0 on the scale 

of the gray-levels. (see Figure 2). 

5.3. Construction of different layers 

A layer can be assimilated to one height-map or to one surface in 

the 3D reconstruction. 

5.3.1. Why different layers? 

The purpose of creating different layers is to rebuild surfaces 

which are above other surfaces. Effectively, in a point cloud, several objects heaped upon each other can be represented. A perspective scan of a table is a perfect simple example of this situation, because in the associated point cloud, there is the surface of 

the ground and the top surface of the table. 

A height-map is a gray scale picture and with only one gray color. 

It is not possible to represent different elevations. Thus, different 

surfaces (or elevations) cannot be represented for a given location 

with only one height-map. 

5.3.2. The process 

With one step-field, one height-map is constructed, and with one 

height-map, one surface is constructed for the simulator. So, in 

order to have different surfaces in the final 3D model, it is necessary to construct different step-fields for the same scene. 

As presented in Section 5.1, a plane is placed below the point 

cloud and it is subdivided into a grid. Each compartment of the 

grid is potentially the base of several pillars. Since the height of a 

pillar is equal to the average of the Z-coordinates of the points 

above it, to construct different pillars at the same location the 

points above the compartment are portioned according to their 

elevations into different subsets. Then, the height of each pillar 

will be equal to the average of the Z-coordinate of the points of 

one particular subset. Grouping the obtained pillars into different 

sets gives different step-fields. The pillars of the same compartment cannot be placed in the same set (every step-field is composed of pillars from different compartments). 

Consequently, if there are X sets of points, there will be X pillars 

for the same location. The number of pillars can be different from 

one compartment to another. The number of layers equals the 

maximum number of pillars created on the grid for one compartment. 

5.3.3. Classification of pillars 

When pillars are created for one compartment of the grid, the first 

created pillar is placed in the first layer, the second pillar in the 

second layer and so on. This placement of this pillar leads to layers containing pillars not according to their heights, but according 

to their creation rank. A pillar which should be in step-field number N can be in step-field number N-1. As a consequence, the 

built surfaces will not be regular and a pillar replacement process 

is needed to classify each pillar in the adequate layer. 

To classify the pillars, the average elevation of each layer is computed. Then, pillars having heights close to the average of a particular layer are moved to this layer. This process is repeated several times until stability is reached. 

6. EXPERIMENTAL RESULTS 

Some experimental results are presented and discussed in this 

section,. Figures 3, 4, 5, and 6 show different reconstruction 

cases. Figures 3.a, 4.a, 5.a, and 6.a show the point clouds and 

Figures 3.b, 4.b, 5.b, and 6.b show the associated computed reconstruction. Textures that appear on these reconstructions represent the layers found on the reconstructed surfaces. 

In the first example (see Figure 3.a and Figure 3.b), there are 3 

horizontal overlaid planes. A point in a plane does not have the 

same elevation as a point in another plane. By this fact, at the 

creation of the step-field, it is easy to classify the pillars according 

to their elevations for each layer, and one may notice remark that 

the associated height-maps are very homogeneous (there is one 

height-map for each surface). Of course this is the perfect case 

where the reconstructed layers (Figure 3.b) correspond to the 

surfaces of the initial planes. 

261
Fig. 3.a: Point cloud representing 3 planes 

Fig. 3.b: Construction representing 3 planes

The second example (Figure 4.a) represents a scene that is a little 

more complicated. There are the three planes from Figure 3.a 

above which a fourth inclined plane is positioned. This fourth 

plane crosses the elevation of the two highest horizontal planes. 

Figure 4.b displays the associated construction, where one can see 

that the three parallel planes are constructed correctly, but the 

inclined plane presents some discrepancies. This inclined plane is 

constructed with three different layers because the pillars are classified according to their elevations. Since the inclined plane 

crosses the elevations of the two other planes, the pillars for the 

inclined plane are classified in different layers. This classification 

may lead the pillars of the inclined plane to be positioned in the 

same layer as the pillars of the other planes with approximately 

the same elevation. 

Notice that the reconstruction of the inclined surface is not continuous. That is explained by the fact that the inclined plane is 

reconstructed with three layers, and although no data are lost, the 

continuity of the surface at this location is lost, which creates a 

discontinuity in the 3D model. The 3D model is used to manipulate a robot in a simulator, and the created holes have the size of 

the pillars (a small size). Thus the robots can cross over these 

holes and there is no real impact for the simulation. 

Fig. 4.a: Point cloud representing 4 planes 

Fig. 4.b: Construction representing 4 planes 

The third example (see Figure 5) is more complicated than the 

second example where the inclined plane does not only cross the 

elevation of others surfaces, but also crosses one of these planes. 

The same problem as previously is noticed (the holes because of 

the discontinuity) and the construction is more complicated too. 

Actually, even the horizontal planes are built with several layers 

but the 3D reconstruction is still correct. 

The fourth example (see Figure 6) presents a more complex scene 

where a cylindrical object is positioned on an horizontal plane. 

The relevance of this scene is to show how one object (the cylinder) which presents a surface above itself is reconstructed. The 

algorithm cuts the object surface into two parts (see Figure 6.b) in 

order to create two different layers for the same object. 

During the process of creating the ground, there are edge effects. 

It is during the process of creation of a 3D scene from heightmaps that there is a loss of information. This is due to the fact that 

a pixel of the height-map represents a vertex and not a compartment of the surface in the simulator. This fact has the effect of 

cutting down the side of the surfaces. Consequently, if there is a 

ground (or a height-map) which is strewed with holes, these holes 

will be increased in the final reconstruction, and if the surface is 

too thin, it will totally disappear. 

262
Fig. 5.a: Point cloud representing 4 planes with intersection 

Fig. 5.b: Construction representing 4 planes with intersection 

Fig. 6.a: Point cloud representing a cylinder onto a plane 

Fig. 6.b: Construction representing a cylinder onto a plane 

7. CONCLUSION 

We have presented a method to build a simplified 3D scene from 

point clouds using height-maps. The use of several height-maps 

allows us to reconstruct in a very simplistic way different scenes, 

which could have had a heavy and high cost mesh based reconstruction. Furthermore, the elaboration of overlapped height-maps 

representing grounds to be analyzed permits one to simplify the 

reconstruction of overlapped surfaces. This new reconstruction 

method gives satisfactory results for relatively simple scenes. 

However, height-maps based reconstruction methods are still 

limited for ground representations, which become complex by the 

presence of several kinds of objects. The height-maps method 

works very well for the generation of grounds having few discontinuities, but fails with complex grounds with many discontinuities or with important variations. A future work is to validate this 

method in two different ways. The first is to create a terrain as 

similar as possible with the reality. The second way is to compare 

the similarity between the behaviors of a robot on the terrain in 

the simulation and in the real world. Namely, the second way is 

more important than the first one. 

The objective is to reconstruct real rough terrains for a simulation, 

thus we can have very complex scenes. In these scenes, we can 

differentiate what we call the simple parts of the scene and the 

complex parts of the scene. To differentiate these two sorts of 

parts, the local density of points and the shape of the representation of the points are taken in consideration. In this way, a smooth 

shape will be assimilated to a simple part, and a small area with 

much variation will be assimilated to a complex part. In order to 

improve our algorithm, we envisage combining the overlapped 

height-maps method (for the simple parts of the ground) with a 

simple mesh-based method (for the complex parts of the ground). 

Actually, we can also define the boundary between a simple and a 

complex part with the effectiveness of local reconstructions using 

the overlapping height-maps method. 

8. REFERENCES 

[1] Carpin, S.; Lewis, M.; Wang, J.; Balarkirsky, S.; Scrapper, C.; 

USARSim: a robot simulator for research and education. Proceedings of the IEEE 2007 International Conference on Robotics and 

Automation, Page(s):1400-1405 

[2] Balaguer, B.; Balakirsky, S.; Carpin, S.; Lewis, M.; Scrapper, 

C.; “USARSim: A Validated Simulator for Research in Robotics 

and Automation”, Workshop on “Robot Simulators: Available 

Software, Scientific Applications, and Future Trends” at 

IEEE/RSJ 2008. 

[3] Carpin, S.; Stoyanov, T.; Nevatia Y.; Lewis, M.; Wang, J.; 

Quantitative Assessments of USARSim Accuracy. Proceedings of 

PerMIS 2006, NIST Special Publication 1062, August 2006. 

[4] Usarsim homepage: http://sourceforge.net/projects/usarsim 

(Accessed: 2008) 

[5] Pongas, D.; Mistry, M.; Schaal, S.; “A Robust Quadruped 

Walking Gait for Traversing Rough Terrain”, Robotics and 

Automation 10-14 April 2007 Page(s):1474 – 1479. 

[6] Rebula, J.R.; Neuhaus, P.D.; Bonnlander, B.V.; Johnson, M.J.; 

Pratt, J.E.; “A Controller for the LittleDog Quadruped Walking on 

Rough Terrain”, Robotics and Automation, 2007 IEEE International Conference on 10-14 April 2007 Page(s):1467 – 1473. 

[7] Fukuda, T.; Zhang, X.; Hasegawa, Y.; Matsuno, T.; Hoshino, 

H.; “Preview posture control and impact load control of rough 

terrain vehicle with interconnected suspension”, Intelligent Robots and Systems, 2004. (IROS 2004). Proceedings. 2004 

263
IEEE/RSJ International Conference on Volume 1, 28 Sept.-2 Oct. 

2004 Page(s):761 - 766 vol.1, 

[8] Udengaard, M.; Iagnemma, K.; “Kinematic analysis and control of an omnidirectional mobile robot in rough terrain”, 

Intelligent Robots and Systems, 2007. IROS 2007. IEEE/RSJ 

International Conference on Oct. 29 2007-Nov. 2 2007 

Page(s):795 – 800. 

[9] Nakamura, S.; Faragalli, M.; Mizukami, N.; Nakatani, I.; Kunii, Y.; Kubota, T.; “Wheeled robot with movable center of mass 

for traversing over rough terrain”, Intelligent Robots and Systems, 

2007. IROS 2007. IEEE/RSJ International Conference on Oct. 29 

2007-Nov. 2 2007 Page(s):1228 – 1233. 

[10] Ledoux, H.; “Computing the 3D Voronoi Diagram Robustly: 

An Easy Explanation”, Voronoi Diagrams in Science and Engineering, 2007. ISVD '07. 4th International Symposium on 9-11 

July 2007 Page(s):117 - 129. 

[11] Tse, R.; Gold, C.; Kidner, D.; “Using the Delaunay Triangulation/ Voronoi Diagram to extract Building Information from 

Raw LIDAR Data”, Voronoi Diagrams in Science and Engineering, 2007. ISVD '07. 4th International Symposium on 9-11 July 

2007 Page(s):222 – 229. 

[12] Labatut, P.; Pons, J.-P.; Keriven, R.; “Efficient Multi-View 

Reconstruction of Large-Scale Scenes using Interest Points, Delaunay Triangulation and Graph Cuts”, Computer Vision, 2007. 

ICCV 2007. IEEE 11th International Conference on 14-21 Oct. 

2007 Page(s):1 – 8. 

[13] Bernardini, F.; Mittleman, J.; Rushmeier, H.; Silva, C.; 

Taubin, G.; “The ball-pivoting algorithm for surface reconstruction”, Visualization and Computer Graphics, IEEE Transactions 

on Volume 5, Issue 4, Oct.-Dec. 1999 Page(s):349 – 359. 

[14] Ming-Ching, C.; Leymarie, F.F.; Kimia, B.B.; “Surface Reconstruction from Point Clouds by Transforming the Medial Scaffold”, 3-D Digital Imaging and Modeling, 2007. 3DIM '07. Sixth 

International Conference on 21-23 Aug. 2007 Page(s):13 – 20. 

[15] Hua-Hong, C.; Xiao-nan, L.; Ruo-tian, L.; “Surface Simplification Using multi-edge mesh collapse”, Image and Graphics, 

2007. ICIG 2007. Fourth International Conference on 22-24 Aug. 

2007 Page(s):954 - 959. 

[16] Qu, L.; Meyer, G. W.; “Perceptually Guided Polygon Reduction”, Visualization and Computer Graphics, IEEE Transactions 

on Volume 14, Issue 5, Sept.-Oct. 2008 Page(s):1015 – 1029. 

[17] In Kyu, P.; Sang Wook, L.; Sang Uk, L.; “Shape-adaptive 3D 

mesh simplification based on local optimality measurement”, 

Computer Graphics and Applications, 2002. Proceedings. 10th 

Pacific Conference on 9-11 Oct. 2002 Page(s):462 – 466. 

[18] Asada, M.; “Building a 3D world model for mobile robot 

from sensory data”, Robotics and Automation, 1988. Proceedings., 1988 IEEE International Conference on 24-29 April 1988 

Page(s):918 – 923, vol.2. 

[19] Asada, M.; “Map building for a mobile robot from sensory 

data”, Systems, Man and Cybernetics, IEEE Transactions on Volume 20, Issue 6, Nov.-Dec. 1990 Page(s):1326 – 1336. 

[20] Gutmann, J.S.; Fukuchi, M.; Fujita, M.; “A Floor and Obstacle Height Map for 3D Navigation of a Humanoid Robot”, 

Robotics and Automation, 2005. ICRA 2005. Proceedings of the 

2005 IEEE International Conference on 18-22 April 2005 

Page(s):1066 – 1071. 

264
Using Virtual Scans to Improve Alignment Performance in

Robot Mapping

Rolf Lakaemper

Temple University

Philadelphia, PA, USA

lakamper@temple.edu

Nagesh Adluru

Temple University

Philadelphia, PA, USA

nagesh@temple.edu

ABSTRACT

We present a concept and implementation of a system to integrate low level and mid level spatial cognition processes for

an application in robot mapping. Feedback between the two

processes helps to improve performance of the recognition

task, in our example the alignment of laser scans. The low

level laser range scan data (’real scans’), are analyzed with

respect to mid level geometric structures. The analysis leads

to generation of hypotheses (Virtual Scans) about existing

real world objects. These hypotheses are used to augment

the real scan data. The core mapping process, called Force

Field Simulation, iteratively aligns the augmented data set

which then in turn is re analyzed to confirm, modify, or

discard the hypotheses in each iteration. Experiments with

scan data from a Rescue Robot Scenario show the applicability and advantages of the approach.

1. INTRODUCTION

This article demonstrates how the integration of low level

spatial cognition processes (LLSC) and mid level spatial cognition processes (MLSC) can help to improve the performance of spatial recognition tasks in robotics. We are using

the area of robot perception for mobile rescue robots, specifically alignment of 2D laser scans, as a showcase to demonstrate the advantages of the integration of LLSC and MLSC

processes. Alignment of data, e.g. acquired from multiple

robots from different positions, is a required task for environment mapping. The basic task of mapping is to combine

spatial data usually gained from laser range devices, called

’scans’, to a single data set, the ’global map’. The global

map represents the environment as scanned from different

locations, even possibly scanned by different robots (’multi

robot mapping’), usually without knowledge of their pose

(= position and heading).

We apply our LLSC/MLSC system to map an environment from Urban Search and Rescue Robots. Mapping is a

requirement for these robots to perform their main task: to

autonomously detect victims in disaster areas (e.g. tsunami,

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earthquake or terrorist attack). The goal is to assist the rescue teams generating location and best access path. Typically multiple robots are deployed in the area to cooperatively map the disaster area. Currently their applicability is

limited due to the extreme constraints to robot mapping in

such an environment: single scans have little overlap, no additional sensor information, e.g. odometry, is reliably available, and none or just a few landmark features are present.

In robot cognition, MLSC processes infer the presence of

mid level features from low level data based on regional properties of the data. In our case, we detect the presence of

simple mid level objects, i.e. line segments and rectangles.

The MLSC processes model world knowledge, or assumptions about the environment. In our case, we assume the

presence of (collapsed) walls and other man made structures. If possible wall-like elements or elements somewhat

resembling rectangular structures are detected, our system

generates the most likely ideal model as a hypothesis, called

’Virtual Scan’. Virtual Scans are generated from the ideal,

expected model in the same data format as the raw sensor

data, hence Virtual Scans are added to the original scan

data indistinguishably for the low level alignment process;

the alignment is therefore performed on an augmented data

set.

In robot cognition, LLSC processes usually describe feature extraction based on local properties like spatial proximity, e.g. based on metric inferences on data points, like

edges in images or laser reflection points. In our system

laser scans (virtual or real) are aligned to a global map using mainly features of local proximity using the LLSC core

process of ’Force Field Simulation’ (FFS). FFS was recently

introduced to robotics [20]. In FFS, each data point can

be assigned a weight, or value of certainty. It also does

not make a hard, but soft decision about the data correspondences as a basis for the alignment. This is achieved

by computation of a correspondence probability to multiple

neighboring points, based on weight, distance and direction

of underlying linear structures. Mainly this feature makes

FFS a natural choice over its main competitor, ICP [2, 24],

for the combination with Virtual Scans (however, the general

idea of Virtual Scans is applicable to both approaches). The

weight parameter can be utilized to indicate the strength of

hypotheses, represented by the weight of virtual data.

FFS is an iterative alignment algorithm. The two levels

(LLSC: data alignment by FFS, MLSC: data augmentation)

are connected by a feedback structure, which is repeated in

each iteration:

• The FFS-low-level-instances pre-process the data. They

265
find correspondences based on low level features. The

low level processing builds a current version of the

global map, which assists the mid-level feature detection

• The mid level cognition module analyzes the current

global map, detects possible mid level objects and models ideal hypothetical sources possibly being present in

the real world. These can be seen as suggestions, fed

back into the low level system by Virtual Scans. The

low level system in turn adjusts its processing for reevaluation by the mid level systems.

Figure 1: LLSC/MLSC feedback. The LLSC module works on the union of real scans and the Virtual

Scan. The MLSC module in turn re-creates a new

Virtual Scan based on the result of the LLSC module.

In such a system, MLSC processes steer LLSC processes introducing higher knowledge to enable spatial inferences the

LLSC system is not able to draw by itself. However, the

MLSC system also needs assistance of the LLSC for two

reasons: MLSC systems concentrate on higher information

which needs LLSC pre-processed data (e.g. a set of collinear

points is passed to the MLSC as a single line segment). But

also LLSC processes have to support the suggestions stated

by the MLSC. Since MLSC introduces higher knowledge,

it is dangerous to focus on spatial mid level inferences too

early. Feedback with the LLSC system enables more careful evaluation of plausibility (see also final note in section

’Experiments’). The following example will illustrate the

Figure 2: Alignment using Virtual Scans (VS). Top

row: Alignment without VS. The LLSC misalignes

the scene due to lack of global information. Bottom row: two iterations using VS. The hypothetical

rectangle createa a the VS add global information,

leading to correct alignment. The VS are newly created in each iteration.

approach: Figure 2, top left, assumes 2 scans, e.g. taken

from robots in 2 different positions. A typical LLSC alignment process like ICP or FFS tries to find correspondences

between single points in the scans, and to superimpose the

scans in an optimal way, e.g. minimizing the summed distances between corresponding points. These approaches assume the existence of overlapping features in scans. Like in

this example, such a constraint is often not met, and the

assumption leads to wrong results. The LLSC alignment

process works on a local basis, hence it is not able to detect

a possible rectangular feature. Figure 2 illustrates the result of an alignment process with (bottom row) and without

(top row) Virtual Scans. In the illustration of our approach

in fig.2, bottom, an MLSC process detects a rectangular

structure and adds an optimal model to the data set. The

LLSC module aligns the augmented data. The hypothesis

now directs the scans to better location. In each iteration,

the relocated real scans are analyzed to adjust the MLSC

hypothesis, LLSC and MLSC assist each other in a feedback

loop.

2. RELATED WORK IN SPATIAL COGNITION AND ROBOT MAPPING

The potential of MLSC has been largely unexplored in

robotics, since recent research mainly addressed LLSC systems. They show an astonishing performance: especially

advances in statistical inferences [5, 10, 13] in connection

with geometric modeling of human perception [6, 9, 25] and

the usage of laser range scanners contributed to a breakthrough in robot applications, with the most spectacular results achieved in the 2005 DARPA Grand Challenge where

several autonomous vehicles were able to successfully complete the race [26]. But although the work on sophisticated

statistical and geometrical models like extended Kalman Filters (EKF),e.g. [12], Particle Filters [10] and ICP (Iterative Closest Point) [2, 24] utilized in mapping approaches

show impressive results, their limits are clearly visible, e.g.

in the aforementioned rescue scenarios. These systems are

still based on low level cognitive features, since they construct metric maps using correspondences between sensor

data points. However, having these well-engineered low level

systems at hand, it is natural to connect them to MLSC processes to mutually assist each other.

The knowledge in the area of MLSC in humans, in particular in spatial intelligence and learning, is advancing rapidly

[7, 14, 27]. Research in AI models such results to generate generic representations of space for mobile robots using

both symbolic, e.g. [16], and non symbolic, e.g. [8], approaches. Each is trying to identify various aspects of the

cognitive mapping process. Naturally, SLAM (Simultaneous

Localization and Mapping [4] is often used as an application

example [23]. In [28], a spatial cognition based map is generated based on High Level Objects. Representation of space

is mostly based on the notion of a hierarchical representation of space. Kuipers [16] suggests a general framework for

a Spatial Semantic Hierarchy (SSH), which organizes spatial

knowledge representations into levels according to ontology

from sensory to metrical information. SSH is an attempt

to understand and conceptualize the cognitive map [15], the

way we believe humans understand space. More recently,

Yeap and Jefferies [29] trace the theories of early cognitive

mapping. They classify representations as being space-based

and object-based. Comparing to our framework, these classifications could be described being related to LLSC and

High Level Spatial Cognition (HLSC), hence the supposed

LLSC/MLSC system would relate closer to space-based sys266
tems.

In [1], the importance of ’Mental Imagery’ in (Spatial)

Cognition is emphasized and basic requirements of modeling

are stated. Mental Images invent or recreate experiences resemble actually perceived events or objects. This is closely

related to the ”Virtual Scans” described in this proposal.

Recently, Chang et al. [3] presented a predictive mapping

approach (P-SLAM), which analyzes the environment for

repetitive structures on the LLSC level (lines and corners)

to generate a ”virtual map”. This map is either used as a

hypothesis in unexplored regions to speed up the mapping

process or as an initialization help for the utilized particle

filters when a region is first explored. In the second case

the approach has principles similar to the presented Virtual

Scans. The impressive results of P-SLAM can also be seen

as proof of concept of integrating prediction into robot perception.

The problem of geometric robot mapping is based on aligning a set of scans. On the LLSC level the problem of simultaneous aligning of scans has been treated as estimating sets

of poses [22]. The underlying framework for such a technique is to optimize a constraint-graph, in which nodes are

features, poses and edges are constraints built using various

observations and measurements.

There are numerous image registration techniques, the

most famous being Iterative Closest Point (ICP)[2], and its

numerous variants to improve speed and converge basins.

Basically all these techniques do search in transformation

space trying to find the set of pair-wise transformations of

scans by optimizing some function defined on transformation space. The techniques vary in defining the optimization functions that range from being error metrics like ”sum

of least square distances” to quality metrics like ”image distance”. ’Force Field Simulation’ (FFS), [20], minimizes a

potential derived from forces between corresponding data

points. The Virtual Scan technique presented in this paper

will interact with FFS as underlying alignment technique.

3. SCAN ALIGNMENT USING FORCE FIELD

SIMULATION

The understanding of FFS is crucial to the understanding of the presented extension of the FFS alignment using

Virtual Scans. We will give an overview here. FFS aligns

single scans Si obtained by robots, typically from different

positions. We assume the scans to be roughly pre-aligned

(see fig.7), e.g. by odometry or shape based pre-alignment.

This is in accord with the performance comparison between

FFS and ICP described in [19]. FFS alignment, in detail

described in [20] is able to iteratively refine such an alignment based on the scan data only. In FFS, each single scan

is seen as a non-deformable entity, a ’rigid body’. In each

iteration, a translation and rotation is computed for each

single scan simultaneously. This process minimizes a target

function, the ’point potential’, which is defined on the set of

all data points (real and Virtual Scans: FFS can not distinguish). FFS solves the alignment problem as optimization

problem utilizing a gradient descent approach motivated by

simulation of dynamics of rigid bodies (the scans) in gravitational fields, but ”replaces laws of physics with constraints

derived from human perception” [20]. The gravitational field

is based on a correspondence function between all pairs of

data points, the ’force’ function. FFS minimizes the overlaying potential function induced by the force and converges

towards a local minimum of the potential, representing a locally optimal transformation of scans. The force function is

designed in a manner that a low potential corresponds to a

visually good appearance of the global map. As scans are

moved according to the laws of motion of rigid bodies in a

force field, single scans are not deformed.

Fig. 3 shows the basic principle: forces (red arrows) are

computed between 4 single scans (the 4 corners). FFS simultaneously transforms all scans until a stable configuration is

gained.

With S1, S2 being two different scans, the force between

two single data points vi ∈ S1 and uj ∈ S2 is defined as a

vector

V (v1, v2) = M(v1, v2) vi − uj

vi − uj (1)

Its magnitude V (vi, uj ) = M(vi, uj ) is defined as:

M(vi, uj ) = 1

σt

√2π

e



− vi,uj 2

2σ2

t



wiwj cos(∠(vi, uj )) (2)

with parameters σt, wi, wj , ∠(vi, uj ) defined as follows:

∠(vi, uj ) denotes the angle between the directions of points,

which is defined as the angle between directions of assumed

underlying locally linear structures. See fig. 4, left, for an

example, which especially shows the influence of the cosineterm in eq.2: forces are strong between parallel structures

only. In eq.2, the forces are strongly depending on σt, which

is a parameter steering the radius of influence. With σt decreasing during the iterative process, FFS changes the influence of each data point from global to local. In addition, the

weight wi, wj (or mass) determines the influence of points

vi, uj . The weight is a parameter which can e.g. express the

certainty about a point, or it can model the feature importance. We utilize this feature of FFS to model the strength

of hypothesis in the Virtual Scans. Hence in eq.2 the interfacing between LLSC and MLSC can be seen directly:

distance and cosine term refer to LLSC, while the weights

are derived from MLSC (in case of the Virtual Scans).

To compute the resulting movement from the forces of all

point pairs between different scans, FFS re-assigns a constant mass to all data points and applies Newton’s law of

movement of rigid bodies in force fields. Constant mass

causes data points participating in stronger force relations

to influence the transformation stronger than those responding to weaker forces. For a single transformation step see fig.

4, right.

The step width Δt of FFS is determinded by a ’cooling

process’. Δt It is monotonically decreasing, allowing the

system in early iterations to jump out of local minima, yet

to be attracted by local features in later steps. The interplay between σt and Δt is an important feature of FFS. See

figures 7 and 8 for an example of the performance of FFS

on a laser range data set.

FFS is closely related to simultaneous ICP. A performance

evaluation of both algorithms [19] showed similar results.

In general, FFS can be seen as more robust with respect

to global convergence with non near optimal initialization,

since the point relations are not built in a hard (nearest

neighbor) but soft(sum of forces) way. Also the inclusion

of weight parameters makes it a natural decision for our

purposes of extension using Virtual Scans.

267
Figure 3: Basic principle of FFS. Forces are computed between 4 single scans. Red arrows illustrate

the principle of forces. The scans are iteratively

(here: two iterations) transformed by translation

and rotation until a stable configuration is achieved.

Figure 4: FFS example. Left: Forces (green) between two rigid structures (brown, black). The

black and brown lines connect the actual data set for

display reasons only. The figure shows a magnification of the upper left corner of fig. 7, right. Right:

example of force and movement. Dotted lines show

2 scans (black, brown) and their forces (green) in iteration t. Solid lines show the resulting transformed

scans at iteration t + 1.

4. CREATING VIRTUAL SCANS: MID LEVEL

ANALYSIS

The analysis module detects line segments and rectangles

in each iteration of the FFS alignment. Both detection steps

work on the entire point set of the current global map, i.e.

the union 

i Si of all points of the real scans Si.

4.1 Lines

The usage of lines for our Virtual Scan approach is motivated by the world knowledge assumption of scanning a man

made environment (e.g. a collapsed house): although these

environments often locally don’t show major linear elements

any longer, a global view still often reveals an underlying

grid structure. In our line detection, we use the classic line

detection approach of Hough transform [11], since it detects

globally present linear structures. Hough transform does not

only show location and direction of a line, but also the number of participating data points. We use this value to compute a certainty-of-presence measure, i.e. the strength of the

line hypothesis. We only use lines above a certain threshold

of certainty. We will specify below how the detected lines

are utilized to create the Virtual Scan.

4.2 Rectangles

For rectangle detection, we use an approach described in

[17]. This approach needs line segments as input, which

model the underlying point data. Each line segment is translated into the ’S,L,D space’ (Slope,Length,Distance), which

simplifies the detection of appropriate (rectangular like) configurations of four near parallel and near perpendicular segments. To use this approach, the laser data has to be modeled by underlying line segments. Since line segments rely on

local linearity of the underlying data points, global Hough

detection is not feasible. A recently published technique [21]

from robot mapping, using a statistical approach, ’Extended

Expectation Maximization’, is specifically tailored to model

laser scan data with line segments. To speed up the rectangle

detection process, we detect line segments in each single scan

once before the FFS process. Hence, for rectangle detection,

we superimpose the data represented the pre-computed line

segments line segments according to the FFS transformation

of the underlying scan, rather than data points. Due to yet

imprecise single scan alignment during the early FFS process, single lines in the environment are frequently presented

by clusters of line segments, rather than the required single

line segments. We merge similar lines in a cluster to a single prototype using a line merge approach described in [18],

see figure 5. The rectangle detection module then predicts

location, dimension and certainty-of-presence of hypothetical, ideal rectangles present in the data set of line segments.

The certainty, or strength of the hypothesis is derived from

properties (segment length, perpendicularity) of participating rectangle-generating line segments. This value is used to

create the weight of the ideal rectangle in the Virtual Scan.

Figure 5: Rectangle detection. a) Global map

built by line segments of all single scans. b) result

of global line merging c) red: detected rectangles

(magnification of area encircled in b)

4.3 Creating a Virtual Scan

A Virtual Scan is a set of virtual laser scan points, superimposed over the entire area of the global map. The

detected line segments and rectangles are ’plotted’ into the

Virtual Scans, i.e. they are represented by point sets as if

they would be detected by a laser scanner. We assume a

virtual laser scanner that represents each line and rectangle

by a set of points, sub sampled equidistantly according to

the point density of the underlying point data in the original

data set.

An important feature of the Virtual Scan is, that each

point in the Virtual Scan is assigned a weight, being the

strength of hypothesis of a virtual structure it represents.

Utilizing this feature, we benefit from the weights steering

the FFS alignment. As defined in eq.2, the weight wi, wj

directly influences the alignment process; stronger points,

i.e. points with higher value wi, have a stronger attraction.

Hence, a strong hypothesis translates into a locally strongly

attractive structure. The hypothesis value reflects the belief

into the hypothesis relative to the real data; all data points

of the real data are assigned a ’normal’ weight of 1.

5. ALIGNMENT USING VIRTUAL SCANS:

ALGORITHM

The algorithm describes the interplay between LLSC (FFS)

and the MLSC analysis. Si, i = 1..n, denotes the real scan

268
Figure 6: Virtual Scans in an early stage of FFS. a)

global map b) the Virtual Scan consisting of points

representing detected lines and rectangles c) superimposition of real data and Virtual Scan. This is the

data used in the next FFS iteration.

data, consisting of n scans. V [t] is the Virtual Scan in iteration t. Init: t = 1, V [0] = ∅, create set of line segments Li

for each scan Si

—————————————————–

1) Perform FFS on 

i=1..n Si ∪V [t−1], resulting in transformations T[t]

i for each scan Si=1..n

2) Form global map G of points and GL of line segments,

superimposing the transformed scans and their line segment

representation: G = 

i=1..n T[t]

i (Si), GL = 

i=1..n T[t]

i (Li)

3) Detect set of lines L in G, set of rectangles R in GL

4) Create Virtual Scan V [t]

. V [t] contains scan points representing the elements of L and R.

5) Compute parameters σt and Δt for the FFS process

6) Loop: goto 1, or end if FFS converged (stable global

map).

—————————————————–

6. EXPERIMENTS AND RESULTS

6.1 NIST Disaster Area

This data set consists of 60 single laser scans, taken from

15 different positions in 4 directions (N,W,S,E) with 20◦

overlap. It can be interpreted as a scene scanned by 15

robots, 4 scans each. No order of scans is given. The

scans resemble the situation of an indoors disaster scenery,

scanned by multiple robots. The scans have little overlap

and no distinct landmarks. The initial global map was computed using a shape based approach described in [19]. See

fig. 7 for example scans and the initial map. We used the

initial global map for two different runs of FFS, once with

Virtual Scans, once without. The experiment was performed

to demonstrate the increase in alignment performance using

Virtual Scans. The increase in performance was evaluated

by visual inspection, since for this data set no ground truth

data is available. Comparing the final global maps of both

runs, the utilization of Virtual Scans leads to distinct improvement in overall appearance and mapping details, see

fig.8. Overall, the map is more ’straight’ (compare e.g. the

top wall), since the detection of globally present linear structures (top and left wall in fig.8) adjusts all participating single segments to be collinear. These corrections advance into

the entire structure. More objectively, the improvements

can be seen in certain details, the most distinct encircled

in fig.8, bottom right. There especially the rectangle in the

center of the global map is an excellent example for a sitFigure 7: The NIST disaster area data set. Left: 6

example scans (from a total of 60). Crosses show each

robot’s position. Right: 60 scans superimposed using a

rough pre-estimation, building the initial global map.

uation where correct alignment is not achievable with low

level knowledge only. Only the suggested rectangle from the

Virtual Scan (see fig.8, top left) can force the low level process to transform the scan correctly. Without the assumed

rectangle the low level optimization process necessarily tried

to superimpose 2 parallel sides of the rectangle to falsely appear as one (fig.8,bottom right).

Comparison of fig.8, top left, and fig.6 shows the effect of

feedback between the core FFS alignment process and the

map analysis to create Virtual Scans. Figure 6 shows iteration 5 of the same experiment. Objects and object locations

differ between the 2 Virtual Scans. Fig. 8 has discarded

some hypotheses (objects) present in fig. 6, e.g. some of the

rectangles. Other hypotheses are modified, e.g. the top wall

is adjusted.

Note: The proposed system handles errors caused by premature belief in MLSC features by implementing the feedback principle, which evaluates a single MLSC-hypothesis.

It is known that single hypothesis systems introducing higher

knowledge tend to be not robust. Under certain circumstances this behavior could also be observed in experiments

with our system. However, this single hypothesis system already significantly improves the alignment performance and

therefore highlights the advantages of LLSC/MLSC connection. It can easily be embedded into a multiple hypotheses

framework, e.g. particle filters, which will also be part of

future work.

7. CONCLUSION AND OUTLOOK

The presented implementation of the alignment process

FFS in feedback with MLSC recognition modules could significantly improve the results for the alignment task. The

implementation proves the applicability of the presented concept for the combination of LLSC and MLSC processes.

In this implementation, already the detection of simple elements (lines, rectangles) could improve the performance.

These elements modeled assumptions of indoor disaster areas. Future implementations will work with different assumptions to adjust to outdoor disaster settings.

8. REFERENCES

[1] S. Bertel. Thomas barkowsky, dominik engel, christian

freksa. computational modeling of reasoning with

mental images: basic requirements. D. Fum, F. del

269
Figure 8: Alignment of NIST data set (initial alignment

see fig. 6). Top left: after 10 iterations with detected line

and rectangular objects plotted into the Virtual Scan

(red). Top right: Final result using Virtual Scans, after

100 iterations. MLSC objects are not shown for clarity

of display. Compare to Bottom Right: final result of

alignment without Virtual Scans. Encircled areas show

examples of improvement using Virtual Scans. Bottom

left: The center rectangle could only be aligned correctly

using MLSC information. Compare to motivational example fig. 2

Missier, A. Stocco (Eds.), Proceedings of the 7th

International Conference on Cognitive Modeling

ICCM06, 2006.

[2] P. Besl. N. mckay. a method for registration of 3.d

shapes. IEEE PAMI, 14(2), 1992.

[3] H. J. Chang. C.s.george lee and y.h. lu and y.c.hu.

p-slam: Simultaneous localization and mapping with

environmental structure prediction. IEEE

Transactions on Robotics, Vol.23, No.2, April 2007.

[4] G. Dissanayake. H. durrant-whyte and t. bailey. a

computationally efficient solution to the simultaneous

localization and map building (slam) problem.

ICRA2000 Workshop on Mobile Robot Navigation and

Mapping, 2000.

[5] A. Doucet. N. defreitas, n. gordon. sequential monte

carlo methods in practice. Springer, 2000.

[6] D. J. Field. A. hayes, r.f. hess. contour integration by

the human visual system: evidence for a local

association field. Vision Research, 33, pages 173–193,

1993.

[7] C. Freksa. M. knauff, b. krieg-brueckner, b. nebel, t.

barkowsky. spatial cognition iv: Reasoning, action,

interaction. Springer, 2004.

[8] T. Ghiselli-Crippa. Hirtle s.c., munro, p. connectionist

models in spatial cognition. The Construction of

Cognitive Maps, Kluwer Academic Publishers. 1-51,

pages 87–104, 1996.

[9] W. Grimson. Object recognition by computer: The

role of geometric constraints. Boston, MA: MIT Press,

1991.

[10] G. Grisetti. C. stachniss, burgard w. improving

grid-based slam with rao-blackwellized particle filters

by adaptive proposals and selective resampling. ICRA,

2005.

[11] P. V. C. Hough. Methods and means for recognizing

complex patterns. US patent 3,069,654, 1962.

[12] S. Huang. G. dissanayake. convergence analysis for

extended kalman filter based slam. IEEE International

Conference on Robotics and Automation, 2006.

[13] D. C. Knill. W. richards. perception as bayesian

inference. New York: Cambridge, 1996.

[14] G. J. M. Kruijff. H. zender, p. jensfelt, h. i.

christensen. situated dialogue and spatial

organization: What, whereE and why? ˇ Int. J. of

Advanced Robotic Systems, 2007.

[15] B. J. Kuipers. The cognitive map: ’could it have been

any other way?’. Spatial Orientation: Theory,

Research, and Application. New York: Plenum Press,

pages 345–359, 1983.

[16] B. J. Kuipers. The spatial semantic hierarchy.

Artificial Intelligence 119, pages 191–233, 2000.

[17] D. Lagunovsky. Ablameyko s. fast line and rectangle

detection by clustering and grouping. Proc. of

CAIP’97, Kiel, Germany, 1997.

[18] R. Lakaemper. L. j. latecki, d. wolter. geometric robot

mapping. Int. Conf. on Discrete Geometry for

Computer Imagery (DGCI), 2005.

[19] R. Lakaemper. A.nuechter, n.adluru. performance of

6d lum and ffs slam. Workshop on Performance

Metrics and Intelligent Systems (PerMIS),

Gaithersburg, MD, August 2007.

[20] R. Lakaemper. N.adluru, l.j.latecki, r.madhavan. multi

robot mapping using force field simulation. Journal of

Field Robotics, Special Issue on Quantitative

Performance Evaluation of Robotic and Intelligent

Systems, 2007.

[21] L. J. Latecki. R. lakaemper. polygonal approximation

of laser range data based on perceptual grouping and

em. IEEE Int. Conf. on Robotics and Automation

(ICRA), Orlando, Florida, May 2006.

[22] F. Lu. Milios, e. globally consistent range scan

alignment for environment mapping. Auton. Robots,

4(4), pages 333–349, 1997.

[23] A. Martinelli. A. tapus, k.o. arras, r. siegwart.

multi-resolution slam for real world navigation.

Proceedings of the 11th International Symposium of

Robotics Research, Siena, Italy, 2003.

[24] A. Nuechter. K. lingemann, j. hertzberg, h. surmann,

k. pervoelz, m. hennig, k. r. tiruchinapalli, r. worst, t.

christaller. mapping of rescue environments with

kurt3d. Proceedings of the International Workshop on

Safety, Security and Rescue Robotics (SSRR

’05),Kobe, Japan, June 2005.

[25] A. Pentland. Perceptual organization and the

representation of natural form. AI Journal, Vol. 28,

No. 2, pages 1–38, 1986.

[26] e. a. Thrun. Stanley: The robot that won the darpa

grand challenge. Journal of Field Robotics 23(9),

pages 661–692, 2006.

[27] D. Uttal. Seeing the big picture: Map use and the

development of spatial cognition. Developmental

Science, 3, pages 247–286, 2000.

[28] S. Vasudevan. V. nguyen, r. siegwart. towards a

cognitive probabilistic representation of space for

mobile robots. Proceedings of the IEEE International

Conference on Information Acquisition (ICIA),

Shandong, China, pages 20–23, August 2006.

[29] W. K. Yeap. M.e. jefferies. on early cognitive

mapping. Spatial Cognition and Computation 2(2),

pages 85–116, 2001.

270
The role of Bayesian bounds in comparing SLAM

algorithms performance

Andrea Censi

Control & Dynamical Systems

California Institute of Technology

ABSTRACT

It is certainly hard to establish performance metrics for intelligent systems. Thankfully, no intelligence is needed to

solve SLAM at all. Actually, when we cast the SLAM problem in the Bayesian framework, we already have a formula

for the solution — SLAM research is essentially about finding good approximations to this computationally monstrous

formula. Still, SLAM algorithms are difficult to analyze formally, partly because of such out-of-model ad hoc approximations. This paper explains the role of Bayesian bounds in

the analysis of such algorithms, according to the principle

that sometimes it is better to analyze the problem than the

solutions. The theme is explored with particular regard to

the problem of comparing algorithms using different representations and different prior information.

1. INTRODUCTION

In this paper I will often compare localization and SLAM.

By “localization” I mean the problem of estimating the pose

of the robot given a known, perfect map. Localization can

be seen as a problem of the kind y = f(x) where x is

the pose (or the trajectory) of the robot, y are the sensor measurements, and a known function f encodes both

the sensor model and the known map (which is “hidden”

inside f). For most sensors, noise can be modeled as an additive stochastic term. The other piece of information we

have is some relation between successive poses, for example given by odometry, and usually described by a certain

distribution p(xk|xk−1). SLAM, instead, is a problem of

the kind y = f(x,m), where f is still thought as a known

function, and m, the map, is some parameterization for f.

This relation in the literature is usually written in the form

p(y|x,m), but in this context it will be useful to highlight

the functional relation between y and x,m.

There are many qualitative differences between localization and SLAM. On a superficial level, it is clear that “estimate x and m” is much more difficult than “estimate x”.

But there are subtler points. For one thing, while we know

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the physical meaning of x, what exactly is the map m?

One possible pragmatic answer is that the map is that

which, together with the pose of the robot, allows to predict

the observations, through a certain function f. But this answer is not entirely satisfying: in this problem, it is literally

true that “the map is not the territory”1; the design of a

SLAM algorithm must deal up-front with the map-territory

abstraction, which manifests itself as two main problems:

the problem of representation, and the problem of the prior.

There is a “geometric” representation issue: unstructured

maps are inherently infinite-dimensional, and yet the designer must chose a finite-dimensional approximated representation, such as occupancy grids [7], the Normal distribution transform [2], or other similar variations [9]. There is

also a representation problem for probability distributions:

in theory one should estimate the full distribution p(x,m|y)

which implies keeping track of the correlation between the

pose and every part of the map. While this is relatively

straightforward for landmark-based SLAM (a big covariance

matrix), it is quite a problem keeping track of the correlation of the pose and, say, each cell of an occupancy grid

(Rao-Blackwellized particle filters essentially work by not

considering this correlation).

Another important problem is that of the prior: correct

Bayesian inference needs the knowledge of the prior p(m),

and the posterior density p(m|y) can vary almost arbitrarily as a functional of p(m). This distribution encodes all

the information we know about the environment: What

is the average size of the rooms? Is it structured (walls,

corners, etc.), unstructured (cave-like), or is the robot outdoors? How many bathrooms are there in a typical suburban

Pasadena house? These are all examples of prior knowledge,

from measurement space to high-level semantic information,

which should be encoded in the prior.

All modern SLAM research is well grounded in a probabilistic framework, but for SLAM algorithms it is not easy

to prove the typical properties of estimators, like unbiasedness, efficiency, and so on: there are no SLAM algorithms

working with dense sensors and maps for which it is possible

to guarantee a given accuracy in a given environment. The

main reason is that, for efficiency reasons, SLAM algorithms

are a carnival of reasonable approximations, and this makes

their analysis difficult.

I argue that in this context it is fruitful to study Bayesian

bounds for SLAM: sometimes it is easier to study the problem than a particular solution to it. This theme has not

1Remark by Alfred Korzybski, 1879-1950, linguist and

philosopher.

271
been approached in the literature; this paper gives a first

exploratory look at it, with particular regard to the problem

of comparing SLAM methods which use different representations and those which use different prior information on

the map.

The remainder of this paper is organized as follows. Section II recalls some basic notions of estimation theory. Section III touches on some of the reasons it is hard to analyze

SLAM algorithms formally. Section IV illustrates the use of

Bayesian bounds in SLAM. Section V discusses a practical

example.

2. PROPERTIES OF ESTIMATORS

In the Bayesian formalization, a SLAM algorithm is nothing but an estimator of x and m: “performance metrics” are

just the usual properties one looks for in an estimator.

Basic properties of an estimator are its bias, its variance, and the mean squared error (MSE) which takes into

account both bias and variance. In some fields, an estimator is called robust if it tolerates out-of-model errors. For

example, the vanilla linear-least-squares estimator is not robust to outliers, as any one of them can lead the estimate

astray.

There are two different meanings associated to “consistency” in the literature. A consistent(1) estimator is one

whose estimate converges in probability to the true value,

as the number of observations grows to infinity. A consistent(2) filter is one that it is not overconfident; that is, it

is not too optimistic about the quality of its estimate.

Intuitively, an estimator is statistically efficient2 if it

makes use of all the information contained in the data; formally, it is efficient if it reaches the Cram ́er–Rao Bound

(CRB).

2.1 The Cramér-Rao bound

There are many results about theoretical bounds for the

performance of estimators [13]. The Cram ́er-Rao inequality is a classic one, and the proof is surprisingly easy and

enjoyable [3].

Cram ́er-Rao inequality. If the density p(y, x) satisfies

some regularity conditions [3], then for any unbiased estimator xˆ,

cov[xˆ] ≥ (I[x])−1 (1)

The n × n symmetric matrix I [x], called Fisher’s information matrix (FIM), is defined as3

I[x] = E

j∂ log p(y, x)

∂x

t ∂ log p(y, x)

∂x

ff

(2)

In the case of a Gaussian measurement model: y ∼ N (f(x), Σ),

the FIM is

I[x] = ∂f

∂x

T

Σ−1 ∂f

∂x (3)

There is an extension to the case of biased estimators, for

which it is possible to prove a bound that can be lower or

2which has nothing to do as with computationally efficient. 3A more correct but cumbersome expression for the FIM

would be I[x](x), in the sense that it is the information for

[x], but it also depends on the particular point (x) being considered. We will drop the functional dependence throughout

the paper.

higher than (1):

cov[xˆ] ≥

»

I+

d

dxbiasxˆ (x)

–

(I[x])−1

»

I+

d

dxbiasxˆ (x)

–t

This result is however not practically useful because one

needs to know the function biasxˆ (x) which in general is not

known.

The bound depends on the particular “true” value of x

which is considered fixed but unknown. In general, there

is no guarantee that this bound is tight, except in special

cases, for example when the model is linear with Gaussian

noise (y = f(x) = Lx + 
).

There are tighter bounds that consider higher-order derivatives of the density; unfortunately the computations quickly

become convolute: see [13] for details.

3. WHY IS IT HARD TO ANALYZE SLAM

ALGORITHMS?

In estimation theory there are a number of ready-made

results for the “canonical” estimators: for example, we know

that the maximum-likelihood estimator is consistent(1) while

it is not efficient. This kind of results are not usable in

SLAM, because SLAM algorithms is that they are often

crude ad-hoc approximations to one of the canonical estimators, and while it might be intuitive that “almost” a ML

estimator would be “almost” consistent, it is difficult to assess the impact of the approximations on the quality of the

estimate.

It is interesting to give an example of where exactly these

approximations are introduced. In the Bayesian framework,

one already knows the solution, and the problem is just of

matter of making its computation efficient: many papers

start with the formula for the Bayesian filter, and then start

to demolish it using the dreaded approximation symbol “
”

until there is something which is actually computable. As a

typical example of this practice — to not smear the work of

others — I will take my paper [5]: it is about global localization and its use inside SLAM for loop closing. We start with

the usual formula for the Bayesian filter, and then we make

the assumptions that for small distances the scan matching

estimate can be considered overly precise (the distribution

is equivalent to a Dirac delta) with respect to, say, the finite

resolution of the grid. This completely reasonable assumption makes it hard to analyze the algorithm: it seems to

work splendidly, but we cannot say how this approximation

makes its performance differ from the exact algorithm.

A canonical example of theoretically sound, but hard to

analyze, estimators are particle filters. Pretty much the only

results that one can get is that everything is fine when the

number of particles goes to infinity, but nothing is guaranteed for a finite computation [6]. The answer to the question

of how many particles does one actually need is usually very

fuzzy [8]. Additionally, there is a whole line of research involved with something that is, essentially, “cheating”: using

more relaxed observation models to deal with the problem of

having just so many particles (see for example [11] and references therein); although this makes the filter more robust

and computationally efficient, it is yet another out-of-model

approximation that makes the analysis difficult.

It should be noted that not even for landmark-based SLAM

it is possible to do correct inference, even though the state

space is finite-dimensional. In fact, methods like the Ex272
tended Kalman Filter (or the Information filter [12]) work

by doing some kind of linearization, hence they are very far

from correct inference. Linearization is a necessary evil, but

it completely destroys the structure of the problem: in a

certain sense, a linearized filter is not solving the original

problem anymore. As a consequence, it can be shown that

the EKF is not consistent(2) with respect to the original

problem (see for example [10, 1]).

4. BAYESIAN BOUNDS FOR SLAM

In the PerMIS context, Bayesian bounds and the CRB in

particular have many uses:

• The CRB provides a lower bound for accuracy that is a

baseline for comparing the actual experimental results.

• It allows to verify the realism of accuracy claims: an

algorithm claiming an accuracy below the CRB would

be clearly wrong.

• In some cases, when it is tight, it provides the actual,

or asymptotic, accuracy of canonical estimators like

the ML.

4.1 The “easy” case: CRB for localization

The paper [4] studied the CRB for the case of 2D localization with range-finders. In that case, the observation are

a set of ranges {ρ ̃i}, each corresponding to a direction φi.

The equation y = f(x) becomes in this case:

ρ ̃i = r(x, y, θ + φi) + 
i i = 1 ...n (4)

where 
i is a Gaussian noise with variance σ2

i , and r is the

“ray-tracing” function: r(x, y, ψ) is the distance from point

(x, y) to the first obstacle in direction ψ. The FIM depends

on the geometry of the environment: in the following αi

is the surface orientation at the point intercepted by the

i-th ray, and βi is the angle of incidence, defined as βi 

αi − (θ + φi):

I[x] = Xn

i

1

σ2

i cos2 βi

" v(αi)v(αi)

t ri sin βiv(αi)

∗ r2

i sin2 βi

#

(5)

4.2 The CRB for SLAM

Assume we have a Gaussian independent measurements

according to the model y = f(x,m)+. The FIM for SLAM

can be written as

I[x,m] = " I[x] I[x|m]

∗ I[m]

#

(6)

The upper left block I(x) is exactly the same as the FIM for

localization, so it is (5) in the case of range finders. Here x

should properly be a parameterization of the whole trajectory; however, for simplicity, we let x be a single pose (this

models a sort of “one-shot” SLAM).

The term I[x] represents the achievable accuracy for localization; that is, assuming m known. Analogously, there

is an interesting interpretation of the block I[m]: it represents the achievable accuracy for mapping, that is how precise can the reconstruction of m be if we assume x known.

The term I[x|m] represents the mutual information that x

gives about m and vice versa. The upper-right block I[x|m]

represents the “simultaneous” in Simultaneous Localization

and Mapping.

The CRB is the inverse of the FIM:

cov[xˆ,mˆ ] ≥ (I[x,m])−1 (7)

and must be interpreted as a bound on the joint covariance

of x and m, given one sensor reading. The bound (7) depends on the particular representation used for m. This is

bad, because one would want to compare the performance

of SLAM algorithms that use different representations.

However, it can be shown that the upper left block of

[I(x,m)]−1 is independent of the representation of m, in

the sense that it is invariant to a change of variable m =

g(m). The upper-left block is given by (I[x/m])−1 where

I[x/m] is a non-standard but useful notation:

I[x/m] I[x] − I[x|m] (I[m])−1 I[x|m]

t

The correct interpretation of I[x/m] is as the information in

the data about x, after considering that the nuisance parameter m is unknown. Note that if x and m were “orthogonal”

(I[x|m] = 0), then one would have I[x/m] = I[x].

Formally, we prove the following proposition:

Proposition 1: Assume a model of the kind y = f(x, w).

Then the CRB for x is independent of a 1-to-1 reparametrization w → m = p(w).

Proof: Suppose we do a reparametrization w → m. The

new sensor model is a function g of m:

y = g(x,m) = f(x, p−1

(m))

The FIM for x is

I[x/m] = I[x] − I[x|m] (I[m])−1 I[x|m]

t (8)

Assuming a normalized covariance for the measurements

(σ2 = 1), the elements in (8) are given by

I[x|m] = ∂g

∂x

t ∂g

∂m I[m] = ∂g∂m

t ∂g

∂m

Now note that the chain rule says that

∂g

∂x = ∂f∂x

∂g

∂m = ∂f∂w

∂

∂mp−1

(m) = ∂f

∂w

»

∂p(w)

∂w

–−1

Let J ∂p(w)

∂w to obtain

I[m] = J −t ∂f

∂w

t ∂f

∂w J −1 = J −t

I[w]J −1

and

I[x|m] = ∂g

∂x

t ∂f

∂w J −1 = I[x|w]J −1

By substituting these in (8), one obtains:

I[x/m] = I[x]−

ˆ

I[x|w]J −1 ̃ ˆJ −t

I[w]J −1 ̃−1 ˆ

I[x|w]J −1 ̃t

= I[x] − I[x|w] (I[w])−1 I[x|w]

t = I[x/w]

This result makes sense: no matter what exotic representation one uses for estimating the map, still there is a

well-defined bound for the accuracy of x.

273
align along green line

docking station

(a) Docking task

(x, y, θ)

global reference frame

(b) Unobservable representation

(−δ/2, 0) x (δ/2, 0)

y

(c) Rectangular assumption

α2

(−δ/2, 0)

α1

y

x (δ/2, 0)

(d) Polygonal assumption

Figure 1: (a): The robot must execute a simple docking task. (b): Expressing the pose of the robot

and of the walls in an absolute frame of reference makes the representation unobservable. (c) shows a

possible representation, with the only unknown being the width of the docking station. (d) augments this

representation by introducing the possibility of not perpendicular walls.

In the context of PerMIS, this suggests that a correct way

of evaluating a SLAM algorithm is by comparing its accuracy in estimating the posterior of x with the well-defined

CRB: implicitly, this will also assess the accuracy of the

map. This has some practical consequences: one only needs

the ground truth for x, and it is possible to compare the

accuracy of algorithms using different map representations.

Unfortunately, this result is not useful to treat the case of

different prior information. That would be the case in which

the two representations w and m belong to two sets that

cannot be put in a 1-to-1 correspondence. The example in

the next section illustrate such a case and shows that the

prior information on the map does influence the achievable

accuracy for the pose.

5. AN EXAMPLE

The purpose of this example is to show in detail a practical

computation of the CRB in a SLAM setting, and to illustrate

the impact of different prior information for the map on the

achievable accuracy for the pose.

5.1 Scenario

Suppose we are designing a mobile robot which must execute a docking task, perhaps to attach to its battery charger.

The docking station geometry is not completely known: for

example, it might be known that it is rectangular, but the

precise dimensions are not known. This is a practical case in

which the robot must do SLAM: estimate both the geometry

of the docking station and its position inside it.

We are interested in how accurately such task can be accomplished given the robot’s range-sensor sensor accuracy,

the geometry of the environment, and the a-priori information.

We consider three cases:

1. (Fig. 1(a)) The robot knows the docking station is rectangular, with a known geometry. The robot must dock

at the middle of the side, properly orientated.

2. (Fig. 1(c)) The robot knows the docking station is rectangular, but it does not know the width δ.

3. (Fig. 1(d)) The robot knows the docking station is

polygonal.

The first case corresponds to localization; the other two are

SLAM with different prior hypotheses. Notice that the three

cases are progressive generalizations: if we denote by Mi

the sets of possible worlds in the i-th case, we have that

M1 ⊂ M2 ⊂ M3.

5.2 Steps for the analysis

The CRB analysis follows these steps:

1. Find a parametrization of the map m and of the poses

which is observable.

2. Write all measurements as a function y = r(x,m) and

compute the FIM.

3. Decide which variables are known, completely unknown,

or unknown with some a priori information, and obtain the CRB for a chosen subset of the state which is

of interest.

The computations are not difficult, but pretty tedious: this

is an excellent case for which one should use a computer

aided algebra system; Appendix I shows the Mathematica

notebook used.

5.3 Parameterizing the world

Even if not strictly necessary, it is better to work with

a representation of the world which is fully observable. To

achieve this, it suffices to choose the reference frames correctly: SLAM with relative measurements is not observable,

if global coordinates are chosen. For example, Fig. 1(b)

shows a unobservable way to parametrize the environment:

a relative distance sensor can only observe the distance between itself and the walls, but not their absolute position.

It is convenient to choose the variable of interest among

the state variables. Because we assume the task is to align

along the middle of the front edge, we put the reference

frame at its midpoint, and we call δ the total length (Fig. 1(c)).

In 2D it is a good choice to use the polar representation of

lines: {(x, y)| cos(α)x + sin(α)y = ρ}. In this environment,

the lines on the sides pass through the points (−δ/2, 0) and

(δ/2, 0): this gives another constraint between α and ρ. Assuming α as the independent variable, we obtain for the first

line ρ1 = cos(α1)δ/2, and similarly for the other. (Thanks to

274
1.0 1.2 1.4 1.6 1.8 2.0 0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Δ m

ΣxΣsens

CRB for x versus Δ

(a) CRB for x as a function of δ

15 10 5 0 5 10 15 0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Α1  Α2 deg

ΣxΣsens

CRB for x versus Α1Α2

(b) CRB for x as a function of α1

0.2 0.1 0.0 0.1 0.2 0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

x m

ΣxΣsens

CRB for x versus x

(c) CRB for x as a function of x

Figure 2: Changes in the CRB for x as a function of small perturbations of the other variables.

Proposition 1, the representation does not matter, hence we

could have chosen ρ1 as the independent variable). Fig. 1(d)

shows the resulting parametrization m = (δ, α1, α2) for the

full SLAM case.

5.4 Writing the measurements equation

Suppose the i-th ray is colliding with the j-th line, which

has coordinates (αj , ρj ). We should find the expression for

the “ray-tracing function” r(x, y, φ) for a line expressed in

polar coordinates (α, ρ). A bit of geometry shows that the

distance from point (x, y) to the line (α, ρ) along direction

φ is

r(α,ρ)(x, y, φ) = cos(α)x + sin(α)y − ρ

cos(α − φ)

The measurement equation is written for each ray i:

yi = r(αi,ρi)(x, y, θ + φi) + 
i

where (αi, ρi) is the line intercepted by the ray, (x, y, θ) is

the robot pose, and φi is the orientation of the ray in the

robot frame.

Group all the measurements in an equation

y = r(x, y, θ, δ, α1, α2)

and compute the FIM using (3).

5.5 Computing the CRB

To compute the CRB given the global FIM, one should

divide the variables into three groups:

1. The variables of interest xi for which one wants to

compute the CRB.

2. The variables considered known xk.

3. The other unknown variables xn, called nuisance variables, which are not of interest but the fact of them

being unknown affects the achievable accuracy for the

variables of interest.

In the three scenarios, the division is as follows:

Case interest (xi) known (xk) nuisance (xn)

1 x, θ δ, α1, α2 y

2 x, θ α1, α2 y, δ

3 x, θ y, δ, α1, α2

By doing permutations if necessary, rewrite the FIM as:

I[xi

, xn, xk] =

2

4

I[xi] I[xi|xn] I[xi|xk]

∗ I[xn] I[xn|xk]

∗ ∗ I[xk]

3

5

Variables that are considered known are effectively ignored

and their rows/columns can be cancelled from the matrix.

We are left with

I[xi, xn] = » I[xi

] I[xi|xn]

∗ I[xn]

–

To compute the CRB for the variables of interest, do not

invert the whole matrix, just compute the upper left block

of `I[xi

, xn]

 ́−1

, which in Section IV was shown to be computed as `

I[xi

/xn]

 ́−1

.

5.6 Results

The full details for the computation are provided in the

Mathematica notebook in Appendix I. In the following, σsens

is the accuracy of the sensor and serves as a scale parameter.

We obtain for the first case (localization):

σ[x] ≥ 0.49 σsens σ[θ] ≥ 0.90 σsens

and for the case of unknown δ:

σ[x] ≥ 0.49 σsens σ[θ] ≥ 0.91 σsens

It appears that not knowing δ does not have much impact in

the accuracy for estimating x. It is usually not immediate to

interpret these results. In this case, one intuitive explanation

might be that the robot needs to align halfway through the

front edge by observing the distances to the left and right

walls; even if there is an error in the estimate for δ, this error

is evenly distributed on the left and right side, and it does

not impact the accuracy of the task (the small variation is

due to second-order couplings between the variables).

The results for the full SLAM case are:

σ[x] ≥ 1.94 σsens σ[θ] ≥ 0.98 σsens

In this case, not knowing α1, α2 has a serious repercussion

on the accuracy on x.

Further insights on the process can be gained by considering a variation of the parameters. Suppose we start with

a rectangular docking station (α1 = α2 = 0). If we want

to improve the accuracy on the task, would it be better to

increase δ? Fig. 2(a) shows that it is: if the sides are further away, they are a better localizing reference. Fig. 2(b)

275
shows that, if possible, it is better to design a docking station which is slightly triangular (α1 = −α2 < 0). Fig. 2(b)

shows that the accuracy for x is maximum at the middle of

the environment (x = 0) so it would not pay to change the

docking position.

6. CONCLUSIONS AND OUTLOOK

The study of the FIM provides good insight into the SLAM

process. The CRB is a necessary component in every experimentalist’s toolkit. In the PerMIS context, the CRB

for SLAM suggests that the right way of comparing SLAM

algorithms is by comparing the accuracy in the posterior

estimate of x. This is also the most practical way and it

bypasses the problem of comparing algorithms that use a

different representation for the map.

However, it should be understood that, in general, the

CRB is not a tight bound, in the sense that it can be optimistic. As a rule of thumb, the more the problem is nonlinear, the more the CRB is optimistic. In the case of localization with range-finders, in [4] it has been shown that

the CRB is quite tight. A similar experimental investigation

should be completed for SLAM, and other sensors should be

considered as well.

7. REFERENCES

[1] T. Bailey, J. Nieto, J. Guivant, M. Stevens, and

E. Nebot. Consistency of the EKF-SLAM algorithm.

In IEEE/RSJ Intern. Conf. on Intelligent Robots and

Systems (IROS), 2006.

[2] P. Biber and W. Strasser. The Normal distributions

transform: a new approach to laser scan matching. In

IEEE/RSJ Intern. Conf. on Intelligent Robots and

Systems (IROS), 2003.

[3] G. Casella and R. L. Berger. Statistical Inference.

Duxbury Press, 1990.

[4] A. Censi. On achievable accuracy for range-finder

localization. In Proceedings of the IEEE International

Conference on Robotics and Automation (ICRA),

pages 4170–4175, Rome, Italy, Apr. 2007.

[5] A. Censi and G. D. Tipaldi. Lazy localization using

the Frozen-Time Smoother. In Proceedings of the

IEEE International Conference on Robotics and

Automation (ICRA), Pasadena, CA, May 2008.

[6] D. Crisan and A. Doucet. A survey of convergence

results on particle filtering for practitioners. IEEE

Trans. Signal Processing, 50(3):736–746, 2002.

[7] A. Elfes. Using occupancy grids for mobile robot

perception and navigation. IEEE Computer, 22(6),

1989.

[8] D. Fox. Adapting the sample size in particle filters

through KLD-sampling. International Journal of

Robotics Research, 22, 2003.

[9] G. Grisetti, C. Stachniss, and W. Burgard. Improved

techniques for grid mapping with Rao-Blackwellized

particle filters. IEEE Transactions on Robotics,

23(1):34–46, Feb. 2007.

[10] S. Huang and G. Dissanayake. Convergence and

consistency analysis for Extended Kalman Filter based

SLAM. IEEE Transactions on Robotics,

23(5):1036–1049, Oct. 2007.

[11] P. Pfaff, C. Plagemann, and W. Burgard. Gaussian

mixture models for probabilistic localization. In

Intern. Conf. on Robotics and Automation (ICRA),

Pasadena, CA, 2008.

[12] S. Thrun, D. Koller, Z. Ghahramani,

H. Durrant-Whyte, and A. Ng. Simultaneous

localization and mapping with sparse extended

information filters. International Journal of Robotics

Research,, 23(7-8), 2004.

[13] H. L. V. Trees and K. L. Bell. Bayesian Bounds for

Parameter Estimation and Nonlinear

Filtering/Tracking. Wiley-IEEE Press, 2007.

276
APPENDIX

A. MATHEMATICA CODE

This is the model of a range finder: distance to the line (a,r) from point (x,y) in direction f.

In[1]:= range@a_, r_, x_, y_, f_D := HCos@aD x + Sin@aD y - rL ê Cos@a-fD;

These are the three lines (R=Right, L=Left, U=Up):

In[2]:= rangeR@x_, y_, f_D := range@a1, Cos@a1D d ê 2, x, y, fD;

rangeL@x_, y_, f_D := range@a2, -Cos@a2D d ê 2, x, y, fD;

rangeU@x_, y_, f_D := range@p ê 2, 0, x, y, fD;

Because we don‘t want to write here a full-fledged ray-tracer, we make the hypothesis that rays 1,2 intersect line on the right, rays 3,4 intersect the line in front, rays 5,6

intersect the line on the left. The analysis is valid only in such interval.

In[5]:= Y = 8 rangeR@x, y, q+f1D, rangeR@x, y, q+f2D,

rangeU@x, y, q+f3D, rangeU@x, y, q+f4D, rangeL@x, y, q+f5D, rangeL@x, y, q+f6D<;

Computing the FIM is a easy but tedious task, we are happy in letting Mathematica do the derivations for us. The vector vars chooses the order of variables in the matrix.

In[6]:= vars = 8x, y, q, d, a1, a2<;

FisherInformation@Y_, vars_D := Transpose@D@Y, 8vars<DD.D@Y, 8vars<D;

fim = FisherInformation@Y, varsD;

To compute the Cramér-Rao Bound correctly, we need to take into account nuisance parameters. 

In[9]:= iCRB@fim_, varOfInterest_, varNuisance_D := H

VarIndexes@v_D := Flatten@Map@Flatten@Position@vars, ÒDD &, vDD;

inte = VarIndexes@varOfInterestD; nuis = VarIndexes@varNuisanceD;

If@ Length@varNuisanceD > 0, fim@@inte, inteDD - fim@@inte, nuisDD.Inverse@fim@@nuis, nuisDDD.fim@@nuis, inteDD,

fim@@inte, inteDD D

L;

CRB@fim_, vars_, nuisances_D := Inverse@iCRB@fim, vars, nuisancesDD;

CRBdesc@fim_, vars_, nuisances_D := H mat = CRB@fim, vars, nuisancesD;

Map@s@vars@@ÒDDD ¥ Hmat@@Ò, ÒDDL^H1 ê 2L ssens &, 81, 2<DL;

To evaluate the FIM and CRB, we must decide a true state:

In[12]:= trueState =

8a1 Ø 0.1, a2 Ø -0.1, d Ø 1.5, x Ø 0.1, y Ø 0.5, qØp ê 2 + 0.1, f1 Ø -p ê 2, f2 Ø -p ê 3, f3 Ø -p ê 4, f4 Ø p ê 4, f5 Ø p ê 3, f6 Ø +p ê 2<;

In the case of localization, we assume the variables a1, a2, d are known:

In[13]:= CRBdesc@fim ê. trueState, 8x, q<, 8y<D

Out[13]= 8s@xD ¥ 0.489147 ssens, s@qD ¥ 0.897132 ssens<

In the first example of SLAM, we assume d is not known; that is, it is a nuisance parameter.

In[14]:= CRBdesc@fim ê. trueState, 8x, q<, 8y, d<D

Out[14]= 8s@xD ¥ 0.489148 ssens, s@qD ¥ 0.910006 ssens<

In the last example, a1, a2, d are not known:

In[15]:= CRBdesc@fim ê. trueState, 8x, q<, 8y, d, a1, a2<D

Out[15]= 8s@xD ¥ 1.93523 ssens, s@qD ¥ 0.980067 ssens<

This is the code to create the graphs in the last figure:

In[16]:= p1 = Plot@HCRB@fim ê. 8a1 Ø b Hp ê 180L, a2 Ø -b Hp ê 180L< ê. trueState, 8x<, 8d, a1, a2, y, q<DL^H1 ê 2L, 8b, -15, 15<

, Frame Ø True, PlotRange Ø 8-0.5, 3<,

AxesLabel Ø 8"a1 = -a2 HdegL", "sxêssens"<, AxesOrigin Ø 80, 0<, PlotLabel Ø "CRB for x versus a1=-a2"D;

In[17]:= p2 = Plot@HCRB@fim ê. 8d Ø d< ê. trueState, 8x<, 8d, a1, a2, y, q<DL^H1 ê 2L, 8d, 1, 2<,

Frame Ø True, PlotRange Ø 8-0.5, 3<,

AxesLabel Ø 8"d HmL", "sxêssens"<, AxesOrigin Ø 81.5, 0<, PlotLabel Ø "CRB for x versus d"D;

In[18]:= p3 = Plot@HCRB@fim ê. 8x Ø d< ê. trueState, 8x<, 8d, a1, a2, y, q<DL^H1 ê 2L, 8d, -0.25, 0.25<,

Frame Ø True, AxesLabel Ø 8"x HmL", "sxêssens"<,

PlotLabel Ø "CRB for x versus x", AxesOrigin Ø 80, 0<, PlotRange Ø 8-0.5, 3<D;

In[19]:= Export@"crb1.pdf", p1D; Export@"crb2.pdf", p2D; Export@"crb3.pdf", p3D;

277
Map Quality Assessment 

Asim Imdad Wagan1, Afzal Godil1, Xiaolan Li1,2

1

National Institute of Standards and Technology 2

Zhejiang Gongshang University 

{wagan, godil, lixlan}@nist.gov 

 

ABSTRACT

The maps generated by robots in real environment are usually 

incomplete, distorted, and noisy. The map quality is a quantitative 

performance measure of a robot's understanding of its 

environment. Map quality also helps researcher study the effects 

of different mapping algorithms and hardware components used. 

In this paper we present an algorithm to assess the quality of the 

map generated by the robot in terms of a ground truth map. To do 

that, First, localized features are calculated on the pre-evaluated 

map. Second, nearest neighbor of each valid local feature is 

searched between the map and the ground truth map. The quality 

of the map is defined according to the number of the features 

having the correspondence in the ground truth map. Three feature 

detectors are tested in terms of their effectiveness, these are the 

Harris corner detector, Hough Transform and Scale Invariant 

Feature Transform. 

Categories and Subject Descriptors

I.2.9 [Robotics]: Robot Map Quality. 

General Terms

Algorithms 

Keywords

Harris corner detector, Scale Invariant Feature Transform, Hough 

Transform 

1. INTRODUCTION 

Assessing the map quality generated by the robots is one of the 

useful ways to assess the capability of a robot's understanding of 

its surrounding environment. Robot map quality is one of the 

quantitative measures which can be helpful in determining which 

robots will perform better in the field. When a robot moves, it 

generates the map which helps in its localization and planning. 

Normal image noise measures are not suitable to assess the map 

quality because the differences in maps are structural in nature. To 

assess these kinds of maps we had assumed that the quality is 

defined not in terms of overall image but on the structural detail 

contained inside the image. This can be observed in the ground 

truth image as shown in figure 1 while one test map is shown in 

figure 2 which was generated by the robot. So we consider a map 

as accurate even if there is noise and distortions present but it 

contains all the salient details of the ground truth.

There is not much work done in this field. Most of the work done 

is either in the field of image quality measure or in the range data 

quality measure for moving robots. The initial work was done by 

Chandran et al in [12] and [13]. Their method measures the 

quality of the map from 3D point cloud generated from the robot. 

This point cloud is further classified into plausible and suspicious 

patches using the conditional random fields. The number of 

suspicious patches is used to calculate the quality. Although this 

method seems promising but it is dependent upon the mapping 

where the data generated is in 3D point cloud format. The testing 

was done with data generated from 3D laser scanners. 

In [14] the authors have used the polylines to model the shapes 

from the robot generated maps and utilization of these models for 

the solution of the SLAM problem. Although this paper is not 

directly related with the map quality problem but it provides an 

interesting insight into map generation which can be used to 

identify different parts of the map. As identification of different 

regions inside the map can be helpful in assessing the map 

quality. 

Recently a manual map evaluation toolkit," Jacob's Map Analysis 

Toolkit" has been suggested by [16]. This application provides the 

manual map viewer which is designed in a way to help the quality 

assessor to judge the quality of the map by overlapping the maps 

over each other. This toolkit also provides a simple measure to 

assess the map quality based on evolutionary algorithms. 

However, using the evolutionary algorithms does not guarantee 

that the results for the map quality will be similar when used each 

time. 

Another recent development is the usage of localized features for 

map quality assessment [17]. Authors have used the rooms as the 

localized features. They propose an algorithm to detect the rooms 

and then find the map quality using these localized features. But it 

is not necessary that a map will always contain features such as 

rooms and room like structures. Most of the time the robot 

generated maps do not contain lines but the collection of point 

clouds generated from the sensors. In that case, it will be difficult 

to identify rooms. 

Our proposed algorithm is based on techniques which try to cover 

most of the short comings found in other algorithms. There are 

still many cases where our algorithm can fail. The reason to use 

multiple features is that if one kind of algorithm fails in some 

specific type of map, there are still two other options to judge the 

map quality correctly. 

Some of the limitations are because of inherent nature of the 

algorithms used which will be discussed later in this paper. 

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278
Rest of our paper discusses our algorithm which consists of three 

separate sub parts. Our algorithm can be described in following 

steps: 

1. Generation of the localized features on the map. 

2. Similar features are identified in Target image and 

ground truth image. 

3. Quality is calculated from the final number of matched 

features. 

Figure 1. Ground Truth Map. 

Figure 2. Robot generated Map 

2. MAP QUALITY 

2.1 Introduction 

Measuring the map quality is a very difficult task because it is 

difficult to define quality in terms of the image. There can be 

different criteria to define the map quality. Some of them can be 

based on the noise generated in the maps and on the other side 

some can be based on the rotation and translation observed in the 

generated map. There can be many ways to define the map 

quality. But one important factor which we want to measure in the 

map quality for robot is the structural details in the map, so 

although there might be some other noise in the map it is assumed 

that any map is accurate if it thoroughly represents all the 

important structure features when compared to the ground truth. 

So to assess this measure we cannot use the noise to signal ratio 

or some other measures. We are proposing a novel method to 

assess the map quality based on three separate algorithms each 

corresponding to different type of features found in the map. 

These are Harris Corner Detector, Hough Transforms and Scale 

Invariant Feature transform. These measures will gives us three 

values which can be used to assess the quality of the map in three 

different terms. 

2.2 Harris based algorithm 

Our first algorithm is defined on the principals of closest point 

matching. Let us assume we are given two images to compare 

named X and Y. To compare these images we need to find interest 

points in these images. These images are binary so we have 

limited choice in selecting the interest point algorithms. Most of 

the interest point detectors work on gray scale or color images. 

The interest points should be useful with enough detail so that 

they can be compared with points in other image. 

Corner detectors are effective in case we have binary images so 

we have chosen Harris corner detector [8] [9]. This algorithm is 

very effective in capturing corners and is effectively invariant to 

rotation, scale, illumination variation and image noise. This is a 

desirable metric which will enable us to deal with minor noise, 

rotation and scale problems in the map, see figure 3. 

Figure 3. Harris corner detector 

After calculating the interest point using the Harris corner 

detector, we use the closest point matching process to generate the 

vector maps which are later used for calculating the quality 

metric. To generate the vector map we find the corners which are 

closest to the point under consideration and then use that point in 

map and find its closest point in the ground truth and eliminate 

those points from both maps with increase in the value for true 

points matched counter for the map quality. 

2.3 Hough based algorithm 

To account for the structural detail we have used Hough transform 

[5] [6] to transfer the map from Euclidean space to Hough space. 

This has the benefit of identifying lines in the image. These lines 

are compared according to the position of lines as points in the 

Hough space. Hough space is created by exchanging the 

Euclidean coordinates with the parameterized values form the 

parametric form of the equation of the line. 

r(θ ) = x cosθ + y sinθ (1) 

This helps in identifying lines easily as in the Hough space the 

points with large values will be highly likely to represent the lines. 

This same process can be repeated to generate the space for circle 

and other geometrical objects detection. A variation of the Hough 

transform which is known as the generalized Hough transform, 

can be used to detect different type of arbitrary shapes in the 

279
image. This can be used to detect lines, squares (rooms etc), circle 

(roundabouts etc) in the map which will be a more generalized 

way to calculate the map quality. 

After detection of these features the matching features can be 

located in the ground truth map and compared for the map quality 

as described in the last section. 

2.4 Scale Invariant Feature Transform 

Scale Invariant Feature Transform (SIFT) was introduced by the 

David Lowe in [15]. Since then SIFT based localized feature have 

gained prominence among researchers due to there invariability to 

rotation scale and even dynamic changes. To assess the map 

quality we have proposed an algorithm based the SIFT. SIFT 

feature are calculated from extrema detection by finding the 

extrema points from difference of Gaussian images as shown in 

equation 2, where the Gm and Gn represent the Gaussian filters at 

multiple scales and I is the original image. These points are 

further processed to find out the stable point under various 

conditions like edge response and low contrast point elimination. 

DOG(I) (G * I) (G * I) = m − n (2) 

SIFT points detection is the first part of the process, after 

detection usually a descriptor is calculated and stored for each 

point so that it can be used to compare point from different 

images. The length of the SIFT detector is equal to 128 elements, 

which is basically the directional histogram of the local region. 

Figure 4. SIFT features on ground truth and robot generated 

maps. 

For our algorithm we have used the following procedure: 

1- First the entropy [18] of the image is calculated so that 

important regions with high entropy are identified. As our maps 

are binary images it is necessary to convert them into multiple 

scales with more information so that useful features are 

calculated. 

2- This image is passed on to the SIFT for feature detection and 

descriptor calculation, see figure 4 for an example of SIFT 

features. 

2.5 Closest Point Matching 

Closest point matching is performed by finding the closest point 

to the corresponding interest points in one image to another. Each 

point in the ground truth is mapped in a one to one fashion 

between the ground truth image and the target image. To keep 

points from matching to a point which is extremely far, the 

matching is performed only for the points which exist below a 

specified threshold. So it generates a displacement map for each 

point from one image to another image. The obvious benefit is the 

localized identification of the object interest points. 

The closest point match can be described by equation 3. 

Match = Dis(FV(P(x,y))- FV(P (x, y ))) θ (3) 

Where equation 3 describes that the match is the point which is 

equivalent to the point in one map to the corresponding region in 

another map under an specified threshold, where FV is the feature 

vector of the P(x,y) and Dis is the distance between two 

corresponding feature vectors. Only in the case of the SIFT 

features the comparing criteria is based on the calculated 

descriptors. 

Figure 5. Map showing displacement of interest points.

Figure 6. Displacement in test image.

2.6 Vectorial Space 

The displacement or vector map calculated in the last step 

provides much more information regarding the kind of distortion 

which appeared in the image. This way this vector map is a 

localized distortion map in the image. This can be done in both 

directions to identify the missing features which were not 

captured and extra features which don't really exist. The figure 5 

shows the displacement of closest points in ground truth while the 

vectorial space is shown in figure 6 for the test image. 

2.7 Quality Measure 

The map quality measure is calculated using the ratio between the 

set of features. The map quality can be defined mathematically as 

q = RMF /GTF (4) 

where RMF are the number of valid feature points found in the 

robot generated map while GTF are the number of feature points 

in the ground truth map. 

The map quality obtained from the set of test images (as show in 

Figure 8) is shown in Table 1 and figure 7. 

Image quality assessment is difficult [7] [10] because for each 

case there can be different criteria to define the quality. For these 

robot generated maps the most important quality measure is the 

amount of features or landmarks (points, lines, etc) which are 

contained in the generated map. That is why we have based our 

quality measure on the feature having same shapes. We have not 

280
used the texture and color information because the maps are only 

binary images. 

Table 1. Quality values obtained with different algorithms. 

Map Hough SIFT Harris 

1 0.61818 0.52966 0.68981 

2 0.74545 0.55085 0.81481 

3 0.41818 0.47175 0.35648 

4 0.58182 0.50000 0.67593 

5 0.47273 0.41102 0.84722 

6 0.50909 0.40395 0.71759 

7 0.49091 0.39407 0.40741 

8 0.30909 0.45763 0.24074 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

12345678

Map Number

Quality

Hough SIFT Harris

Figure 7. Comparative view of different algorithms.

A very subtle issue is with the finding of the quality of the maps 

when they are the subset of a larger map. The ground truth is 

assumed to be the superset of all the maps so it contains all the 

features and information. So to assess the quality of the map 

which is smaller than the ground truth, we have to identify the 

subset from ground truth for which the map was generated. This 

remains an issue with this algorithm although for maps which are 

equivalent to the ground truth the algorithm gives fairly accurate 

results. 

Only other remaining issue is the utilization of the threshold. 

Utilization of threshold can be a problem because we will not be 

able to match features if the maps are not aligned as in the case of 

Harris and Hough transform but this is not the case for SIFT 

based detector because it can detect matches even if they are far 

away, independent of scale, rotation and dislocation. Although for 

the Harris and Hough alignment of the map remains an important 

point. Alignment can be achieved by a startup marker that 

identifies a stable point between the robot generated map and the 

ground truth. A map can be considered more accurate if it 

consistently shows good performance in all three measures. 

3. LIMITATIONS 

This system is only suitable for offline-measurement for the 

quality of the maps. As per definition the measure of quality is 

very difficult to define because requirements on which the map 

quality is based can be changed according to the need. 

This algorithm measures the quality only on the basis of the 

information content of the image. These maps only contain bilevel images without any additional information. Map distortions 

and noise are not considered because the information is intact 

even with the added noise. 

Some of the limitations which are observed are due to the type of 

maps used for processing. If the map has signal noise, such as, a 

jagged line or map with distortions, most likely the Harris corner 

detector will find lots of corners which could give erroneous 

results. Also Hough transform will fail for the case when point 

cloud data is separated quit far apart. Similarly for the SIFT case, 

if there is too much noise in the maps, this will introduce 

additional features which can cause problems during comparison 

of the features, because closely related features will give similar 

results. 

Figure 8. Maps used for the comparison. 

4. CONCLUSION 

We have tested our algorithm on the test map images generated by 

robots. The map images are also augmented with additional set of 

artificially created images to check the quality. 

In conclusion, we have devised an automated method to calculate 

the quality of the maps generated by the robot. We have used the 

Harris corner detector to detect the interest points while we have 

used Hough transforms to detect lines, another important 

localized feature which we have used is scale invariant feature 

transform (SIFT). In the end we propose the three measures that 

can define the map quality in three separate terms. We also 

provide a vectorial map that basically tells us the local distortions 

found in the image. 

281
ACKNOWLEDGMENTS 

We would like to acknowledge Chris Scrapper and Raj Madhavan 

for their help and the map data. We would also like to thank the 

SIMA program and the IDUS program for supporting this work. 

REFERENCES 

[1] B. Girod, “What's wrong with mean-squared error,” Digital 

Images and Human Vision, A. B. Watson, Ed. Cambridge, 

MA: MIT Press, 1993, pp. 207-220. 

[2] P. C. Teo and D. J. Heeger, “Perceptual image distortion,” in 

Proc. SPIE, vol. 2179, 1994, pp. 127-141. 

[3] A. M. Eskicioglu and P. S. Fisher, “Image quality measures 

and their performance,” IEEE Trans. Commun., vol. 43, pp. 

2959-2965, D 

[4] M. P. Eckert and A. P. Bradley, “Perceptual quality metrics 

applied to still image compression,” Signal Processing, vol. 

70, pp. 177-200, Nov. 1998. 

[5] J. Illingworth and J. Kittler, “A survey of the Hough 

transform,” Computer Vision, Graphics, and Image 

Processing 44, no. 1 (1988): 87-116. 

[6] D. H. Ballard, “Generalizing the Hough transform to detect 

arbitrary shapes,” Pattern Recognition 13, no. 2 (1981): 111-

122. 

[7] Z. Wang and A. C. Bovik, “A universal image quality 

index,” IEEE Signal Processing Letters, vol. 9, pp. 81-84, 

Mar. 2 

[8] C. Harris and M. Stephens, “A combined corner and edge 

detector,” Alvey Vision Conference 15 (1988): 50. 

[9] M. Trajkovic and M. Hedley, “Fast corner detection,” Image 

and Vision Computing 16, no. 2 (1998): 75-87. 

[10] Z. Wang, A. C. Bovik, and L. Lu, “Why is image quality 

assessment so difficult,” in Proc. IEEE Int. Conf. Acoustics, 

Speech, and Signal Processing Orlando, FL, vol. 4, May 

2002, pp. 3313-3316. 

[11] J. L. Mannos and D. J. Sakrison, “The effects of a visual 

fidelity criterion on the encoding of images,” IEEE Trans. 

Inform. Theory, vol. IT-4, pp. 525-536, 1974. 

[12] M. Chandran and P. Newman, “Motion Estimation from 

Map Quality with Millimeter Wave Radar,” Intelligent 

Robots and Systems, 2006 IEEE/RSJ International 

Conference on (2006): 808-813. 

[13] Manjari Chandran-Ramesh and Paul Newman, Assessing 

Map Quality using Conditional Random Fields, International 

Conference on Field and Service Robotics (FSR), Chamonix, 

July 2007. 

[14] D. Wolter and L. J. Latecki, “Shape matching for robot 

mapping.” Proceedings of 8th Pacific Rim International 

Conference on Artificial Intelligence, Auckland, New 

Zealand, August (2004). 

[15] D. G. Lowe, "Distinctive image features from scale-invariant 

key points", IJCV, vol. 2, no. 60, pp. 91-110, 2004. 

[16] Ioana Varsadan, Andreas Birk, and Max Pfingsthorn, 

"Determining Map Quality through an Image Similarity 

Metric", RoboCup 2008: Robot WorldCup XII, L. Iocchi, H. 

Matsubara, A. Weitzenfeld, C. Zhou (Eds.) Lecture Notes in 

Artificial Intelligence (LNAI), Springer. 

[17] Johannes Pellenz,Dietrich Paulus, “Mapping and Map 

Scoring at the RoboCupRescue Competition “ , Robotics 

Science and Systems Workshop, 2008. 

[18] Gonzalez, R.C., R.E. Woods, S.L. Eddins, Digital Image 

Processing Using MATLAB, New Jersey, Prentice Hall, 

2003, Chapter 11. 

[19] C. J. van Rijsbergen (1979) Information Retrieval (London: 

Butterworths) 

[20] Kondrak, G., Marcu, D. and Knight, K. (2003) "Cognates 

Can Improve Statistical Translation Models" in Proceedings 

of HLT-NAACL 2003: Human Language Technology 

Conference of the North American Chapter of the 

Association for Computational Linguistics, pp. 46--48 

282
Introduction to Biological Inspiration for Intelligent 

Systems

Gary Berg-Cross 

Engineering, Management and Integration 

Potomac, MD 20854 

301-424-9256 

Gary.berg-cross@em-i.com and gbergcross@gmail.com

Abstract 

This paper serves as a short introduction for the special PerMIS 

session on Biological Inspiration (BI) for Intelligent Systems. The 

paper is organized into 4 parts. Part 1 provides a brief 

introduction to the idea and history of bio-inspiration for 

computation. Part 2 discusses the increased relevance of biounderstanding and presents a few examples of increased biounderstanding in cognitive areas. Part 3 provides examples of 

alternate focuses and levels of bio-reality that BI can take. Finally 

Part 4 notes some potential challenges in BI for intelligent 

systems. 

Categories and Subject Descriptors

F.1 COMPUTATION BY ABSTRACT DEVICES, I.2.9 

Robotics, K.2 HISTORY OF COMPUTING 

General Terms

Performance, Design, Experimentation 

Keywords 

Biological Inspiration, Developmental Robotics, Intelligent 

Systems, Dual Cognitive Systems 

1. INTRODUCTION

 Biology has long “inspired” computation and cognitive models 

through examples and principles. A representative sampling from 

the origins of digital computation includes classic discussions in 

various disciplines involved in the study of cognitive systems, 

namely biology/neuroscience, developmental sciences, 

psychology, philosophy and artificial intelligence. Notable 

examples might start with Alan Turing, whose role in algorithmic 

computation and symbolic processing is well known. Turing is 

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less known for using interaction as way of naturally educating 

“intelligent machines” (Turing, 1950). He pointed out that one 

might want to develop an intelligent machine by “simulating the 

child’s mind” the way it develops interactively in nature. This is 

similar to Piaget’s approach to understanding cognitive growth as 

multi-cellular organisms grow in complexity from relatively 

simple initial states. In this model a child’s mind provides a 

relatively simple state that we might understand as a step to 

understanding the full range of natural computing. Another biomodel for computation is to relate it directly to the function of the 

nervous system and its hierarchy of sub-components. Thus, the 

way neurons assemble into computational networks has been a 

common source of designs starting with the famous example from 

research on how neural networks might support logical calculation 

(McCulloch & Pitts, 1943). This work develops the idea of a 

brain-computer analogy, something that “inspired” John von 

Neumann’s subsequent work on the logical design of digital 

computers. Such brain analogies to automata were Also part of the 

Dartmouth Summer Research Project on Artificial Intelligence in 

1956. However the bulk of work continuing into the 60s was less 

bio-inspired and viewed thinking as a form of symbolic 

computation. This moved computer science away from natural 

computing to a human engineering one where computation 

processes are “optimized” by an architect rather than selected 

from natural, evolutionary processes. This is not necessarily a 

fatally flawed approach since it is reasonable to believe that 

significant progress in symbolic computing can occur without the 

application of principles derived from the study of biology. 

Computation may follow some general principles like gases and 

organic tissue and need not always imitate biological processes or 

our idea of mental operations. On the other hand, it is not obvious 

that human engineers have an adequate understanding of problems 

and computational approaches to build-in solutions before a 

system is operating and can be gauged against and adapt to 

problems. Indeed, the human brain is currently the only known 

entity capable of exhibiting the type of general aptitudes & 

capabilities we target for many intelligent systems. These include 

some integrated form of capabilities such as adaptive/creative 

problem solving, language/communications processing, integrated 

planning, creative, and multi-level, goal directed learning. 

Nevertheless the computational path has followed a more abstract 

approach with computational class of machines technically 

referred to as 'automata'. Underlying the approach is that 

computation is effectively equivalent to the products of thinking 

and can be modeled within the domain of the mechanical rather 

than what we think we understand from the biological. Some 

doubts about this simple view have crept into the discussion 

recently. 

283
2. THE INCREASED RELEVANCE OF BIOUNDERSTANDING 

While there is an early history of inspiration from biology to 

computational system, the nature of this inspiration lessened as 

traditional algorithmic computational systems became the 

dominant example of computation. However this trend has 

slowed recently and biological inspiration seems increasingly 

relevant for two reasons. The first is due to broad advances in 

biological understanding and the second is the accumulation of 

problems with the traditional automata approach. There is much to 

say on the first point where we have recently experienced notable 

advances across a broad range of biological sciences. Some 

argue that we have reason to believe that “we are on the advent of 

being able to model or simulate biological systems multiple levels 

(Coates, 2007).” The way it works is shown in Figure 1. An 

increased understanding of bio-reality leads to better hypotheses 

to guide experimentation which turn can validate models of 

underlying mechanisms. Robotics researchers increasingly agree 

that models from biology and self-organization provide valuable 

insights for the 

engineering of autonomous robots. These models may help to 

understand complicated and non-obvious underlying neural 

dynamics, which in turn can serve as basis for simulation, robotic 

experimentation etc. Taken as whole all of this can then be used to 

design and build more robust and intelligent systems. For 

example, improved bio-inspiration might lead to significant 

progress in computing by applying adaptive principles that are 

derived from the enhanced study of biology. For example, more 

abstractly biological models (e.g. ethological, neurophysiological, functional & anatomical organization etc.), may 

suggest what data is critical to gather to validate both traditional 

computational models and bio-inspired cognitive models. 

Scientists studying artificial intelligence have traditionally 

separated physical behavior and sensory input, but recent work 

stresses a more biological hybrid approach (Berg-Cross, 2004). 

These can provide some understanding of deep relations between 

cognition, environment and embodiment. For example, 

experiments involving real and simulated robots suggest that the 

relationship between physical movement and sensory input can be 

important to developing intelligent systems (IS). Tests involving 

both real and simulated robots have shown that feedback between 

sensory input and body movement is crucial to successfully 

navigating the surrounding world. Understanding this relationship 

may help engineers build more adaptive and intelligent robotic 

systems. Among the more rigorous summaries discussing useful 

issues are Wooley and Lin (2005) and de Castro and Von Zuben 

(2004). Wooley and Lin (2005) discuss how a biological system 

may operate according to general principles that have applicability 

to our now traditional non-biological computing problems such as 

security and autonomy. By studying an appropriate biological 

system and its characteristics, research may develop an 

understanding of the relevant principles that can be used to 

handle a traditional computer problem. Among the notable 

characteristics biological systems exhibit and whose principles 

may be relevant are: Metabolism, Growth/Development, 

Reproduction, Adaptability, Autonomy/Self-maintenance, Selfrepair, Reactivity, Evolution and Choice. Wooley and Lin (2005) 

note, for example, one value of considering biological models is 

that all biological organisms have some mechanisms for things 

like self-repair, a characteristic related to autonomy and of value 

to approaches to computer security: 

“in the sense that it classifies and eliminates pathogens 

and repairs itself by replacing damaged cells without the 

benefit of any centralized control mechanism. Given the 

growing security burden placed on today’s computer 

systems and networks, it will be increasingly desirable 

for these system and networks to manage security 

problems with minimal human intervention.“ Wooley 

and Lin (2005) 

This illustrates how biology can be relevant to computing as 

principles emerge directly from the study of biological 

phenomena. The second reason to look to the biological realm for 

inspiration is that traditional systems have proven fragile, difficult 

to maintain and subject to catastrophic failure. A bio-development 

hypothesis suggests why the engineering of Intelligent Systems 

sometimes fail. In biological systems the adaptive nature of 

behavior derives a very indirect relationship between the 

properties of the interacting elements and the emergent results of 

the interactions. Thus, as Nolfi et al (2008) says, “behavioral 

systems can hardly be designed while they can be effectively 

developed through self-organizing methods in which properties 

emerging from interactions can be discovered and retained 

through an adaptive process based on exploration and selection.“ 

In contrast to engineered systems, biological ones represent 

powerful cognitive architectures for managing complexity in a 

robust and sometimes even an elegant manner. An example of 

this is computer vision, where some visual tasks (e.g, 

segmentation and motion) aren’t well handled perhaps due to the 

over simplified way classical models have been developed. To 

handle this gap, some current research lines are going back to 

more biologically “plausible” models of visual perception based 

on an understanding, modeling and simulation of the mechanisms 

observed in neural processes within the brain. 

284
3. DIFFERENT DIRECTIONS & LEVELS 

FOR BIO-INSPIRATION 

Intelligent robotics, like animals are behaving systems with 

sensors and effectors that easily be embedded in the physical 

world. Both have sensors and actuators and require an 

autonomous control system that enables them to successfully 

carry out various tasks in a complex, dynamic world. It is pretty 

natural to see the study of autonomous robots as analogous to the 

study of animal behavior (Dean 1998). But there are many 

variations on how to proceed from this broad analogy. For 

example in “Biorobotics” autonomous agents have been used as 

empirical models of simple behavioral patterns to study the 

influence of morphology on adaptive behavior. Alternatively the 

bio-characteristic of interaction with the environment can be 

combined with the idea of development to study how intelligence 

emerges. A panel at last year’s PerMIS called “Can the 

Development of Intelligent Robots be Benchmarked? 

Concepts and Issues from Developmental/Epigenetic 

Robotics” (Berg-Cross et al 2007) made a start on describing 

emerging this subfield of AI. As described there developmental 

robotics (DR) studies how autonomous robots can learn to acquire 

behavior and knowledge on their own, based in their interactions 

with an “environment”. A major benefit of this view of intelligent 

systems to that it removes engineer bias (Blank, Kumar, & 

Meeden 2002) and opens up the possibility of adaptive 

intelligence – a major topic at prior PerMIS workshops. Among 

other things the DR panel session discussed what primitive 

capabilities should be built into an intelligent system. Blank, 

Marshall and Meeden (Berg-Cross et al 2007) described their 

developmental algorithmic design using core ingredients of 

abstractions, anticipations, and self-motivations. This design is 

proposed to allow a mobile robot to incrementally progress from 

sensory-motor activities through levels of increasingly 

sophisticated behavior. This design attempts to answer the 

question of how to learn and represent increasingly complex 

behavior in a self-motivated, open-ended way. 

Another direction BI takes is a more faithful biological realism of 

the central nervous system and in particular the brain. Recent 

work such DARPA’s BICA program is illustrative of recent 

efforts to emphasize “Bio-neural Realism” and “develop 

integrated psychologically-based and neurobiology-based 

cognitive architectures that can simulate human cognition in a 

variety of situations.” Among the Phase I projects perused in 

DARPA’s BICA program was the development of cognitive 

theories that could map cognitive functions to neurological 

functions and provide an inspiration for the emerging field of 

developmental robotics. Figure 2 illustrates the two parts of such 

neuroscience related efforts to fully understand neural processes 

and their relations to mental processes. On the left are models of 

brain/CNS system reality and on the right are corresponding level 

of cognitive activities, from simple to complex that might map to 

the operations of some levels. As shown in the Figure CNS 

components span sizes at the molecular (such as DNA)/ synapse 

level to structures 105

 larger. Corresponding time for functional 

activity can span the order of nanoseconds to seconds or longer. A 

neuroscience theory to simultaneously handel all these level 

would be a single bio-physical/chemical theory and obviously 

such a “theory of everything” does not currently exist. Nor can 

one expected one that integrates most of these levels in the near 

future. At this stage of computational modeling we can understand 

animal/human behavior by studying computer models of a subset 

of levels. For example, one current model of the brain suggests 

how neurons are organized into basic functional units and operate 

much like microcircuits in a computer. The model proposes that in 

the cortex, neurons are organized into these functional units are 

roughly cylindrical volumes 0.5 mm wide by 2 mm high, each 

containing about 10,000 neurons that are connected in an intricate 

but consistent way. Each microcircuit, known as the neocortical 

column is repeated millions of times across the cortex and the 

model can be tested by the larger computer systems currently 

available (IBM Blue Brain Project, 2005). It remains to be seen if 

this neural circuit-cortical model is correct and if our current 

hardware is up to simulating such large models. There are 

obviously many other biological issues to consider in modeling 

the CNS, but there are also many related issues to consider on the 

cognitive-behavioral side too. Some of these are summarized in 

the concluding section. 

4. SOME CHALLENGES IN BIOINSPIRATION OF INTELLIGENT 

SYSTEMS

There is considerably evidence that humans reasoning and 

cognition is based on two distinct processing systems with 

different evolutionary histories. Essentially the dual cognitive 

processes theory proposes that higher animal brains have two 

mental systems that compete in humans for control of reasoned 

actions. There is a range of experimental psychological evidence 

supporting this view, as summarized in Stanovich (2004), 

although this dichotomy may oversimplify the evolutionary nature 

of the divide (Evans 2008). For example, there is evidence for the 

presence of higher-level cognition in many species which Toates 

285
(2006) argues may have developed into human consciousness. In 

the standard theory there are two cognitive systems. System 11

 is 

the evolutionarily older one which is common to many animals 

and is characterized by stimulus-bound, heuristic processes that 

are fast, automatic, effortless and unconscious (Stanovich 1999). 

System 1 is thought to be made up of a set of relatively 

autonomous/modular subsystems that include both innate input 

modules and domain-specific knowledge that is constructed by 

one or more general learning mechanism. System 22

 is 

evolutionarily recent with higher, more controlled processes that 

are slow, deliberative, and conscious – making them more 

characteristic of humans and other primates. System 2 permits 

abstract reasoning and hypothetical thinking, but is constrained by 

modular working memory capacity. Dual processing challenges 

classical ideas of monolithic control which seems important for 

characterizing the plasticity and robustness of human reasoning as 

a broad interplay between an automatic and belief-based system 

(Berg-Cross et al. 2007). But we have scant research on the 

interplay of System 1 and System 2 adaptive mechanisms 

"designed" by natural selection to solve the kinds of problems 

faced by human. Thus, we do not yet have adequate models of 

cross-linkage between specialized intelligences and those with 

wider reaching domain-generality. This is in part due to the 

fragmentary nature of the evolutionary data on which to base our 

theories. The harmonization of dual cognitive processes may have 

evolved through a still unknown, complex selection path. 

Developmental and epigenetic robotics may be one way to 

investigating a path that characterizes the robust interplay between 

an easily believed perception-based system and a more 

cognitively demanding logic-based reasoning system of human 

reasoning. This views intelligence as a developed phenomena that 

balances multiple reasoning mechanisms, together with scruffy 

modules of knowledge which learn to deal with situations that are 

only partial predictability, due to dynamics, and the absence of 

precisely defined states. Berg-Cross (2004, 2006) has suggested 

that a multi-level, hybrid architecture, based on a cognitively 

realistic foundation, could approximate human performance for 

this class of problems. To be practical such an architecture would 

build on the existing agent models, semantic web technology and 

standards, as well as a reasonably adequate knowledge and 

domain models. 

In concluding it may be worth suggesting that designing 

intelligent systems based on slavish adherence to bio-cognitive 

“realism” at this level of understanding is likely to yield systems 

with strengths and weaknesses in an attempt to harmonize the two 

processes. Thus it may a dual cognitive process inspired approach 

to developing an IS could yield some greater ability to integrate 

information from many sources and effective coupling of “higherlevel” cognition with perception. However, it may yield 

integration this with a relatively high error rate and slow 

responses compared to what is possible with digital processing 

time scales. Effectively large memory may be achieved using 

“experience” and a constructionist approach to memory that 

 

1

 System 1 is a neutral term. Other labels are experiential, 

heuristic, implicit and associative. 

2 Non neutral labels include: rational, analytic, systematic, 

explicit and rule-based.

integrates “relevant” past experience with the present “situation”. 

But we lack adequate theories to handle such distributed and quite 

fallible memory representations. For example we don’t know 

how to handle interferences from broadly distributed memories. 

And human reasoning is often biased by stereotypical judgments 

(built in pre-judgments we call biased) that is influenced by a 

limited set of experiences. And we don’t know how to balance 

the fast, modular a-logical/un-analytic processes that seem to be 

built in for typical situation prediction and understanding. In this 

regard we have a interesting road ahead which is well summarized 

by Evans (2006): 

“If the conscious, analytic system is at best only partially 

in control and in competition with not one but several 

implicit systems, how come everything works so well? 

Understanding how generally adaptive behavior can result 

from such an apparently chaotic cognitive architecture is 

one of the great challenges for cognitive science.” 

5. REFERENCES 

[1]. Barto, A; Singh, S.; and Chentanez, N. (2004). 

“Intrinsically motivated learning of hierarchical collections of 

skills. “In 3rd International Conference on Development and 

Learning. 

[2]. Berg-Cross, G. (2004). “Developing Rational-Empirical 

Views of Intelligent Adaptive Behavior “ Performance Metrics 

for Intelligent Systems. PerMIS Proceedings 2004. 

[3]. Berg-Cross, G.; Fu W.; and Kwon A. (2004). "A 

Cognitive-based Agent Architecture for Autonomous Situation 

Analysis" Performance Metrics for Intelligent Systems. PerMIS 

Proceedings 2007. 

[4]. Blank, D.; Kumar, D.; and Meeden, L. (2002). Bringing 

up robot: Fundamental mechanisms for creating a self 

motivating, self-organizing architecture. In Proc. of the 

Growing Up Artifacts that Live workshop at Simulation of 

Adaptive Behavior 2002. 

[5]. Coates, Christopher; (2007); “ The Air Force ‘In Silico’ 

-- Computational Biology in 2025, DTEC Report No.(s): ADA474845; Nov 2007; 49 pp.de Castro, L. N. and Von Zuben, F. 

J. (2004) Recent Developments in Biologically Inspired 

Computing, , Idea Group Publishing. Dean J. (1998) “Animats 

and what they can tell us. “ Trends in Cognitive Sciences

2(2):60–67.

[6]. Gunning D. (2005) “Biologically-Inspired Cognitive 

Architectures” (BICA), 

[7]. http://www.darpa.mil/IPTO/programs/bica/bica_phase1.

asp

[8]. IBM Blue Brain Project (2005), 

http://bluebrainproject.epfl.ch/

[9]. McCulloch, W. S. and Pitts, W. H. (1943). “A logical 

calculus of the ideas immanent in nervous activity. “ Bulletin of 

Mathematical Biophysics, 5:115-133. 

[10]. Nolfi, N., Ikegami,T. and Tani, J., “Behavior as a 

Complex Adaptive System: On the role of Self-Organization in 

the Development of Individual and Collective Behavior”, 

Adaptive Behavior, Vol. 16, No. 2-3, 101-103 (2008) 

286
[11]. Prince, C., Helder, N. A., and Hollich, G. J. (2005). 

“Ongoing emergence: A core concept in epigenetic robotics.” 

In Proceedings of the fifth international workshop Epigenetic

Robotics, pages 63–70. 

[12]. Schlesinger, M., Amso, D. & Johnson S. (2007) 

Simulating Infants’ Gaze Patterns during the Development of 

Perceptual Completion., Proceedings of the Seventh 

International Conference on Epigenetic Robotics: Modeling 

Cognitive Development in Robotic Systems. Lund University 

Cognitive Studies, 135. 

[13]. Stanovich, K. E. (1999). Who is Rational? Studies of 

Individual Differences in Reasoning. Mahway, NJ: Lawrence 

Elrbaum Associates. 

[14]. Stanovich, K. E. (2004). The robot's rebellion: Finding 

meaning the age of Darwin. Chicago: Chicago University

Press. 

[15]. Toates, F., (2006 ) “A model of the hierarchy of 

behaviour, cognition, and consciousness.”, Consciousness and 

Cognition, Mar;15(1):75-118.Torres-Huitzil, C., Girau B. and 

Castellanos-Sanchez, D., (2005) “Digital Implementation of a 

Bio-inspired Neural Model for Motion Estimation”, 

International Joint conference on Neural Networks, IJCNN05.

[16]. Turing, A. (1950), ‘Computing Machinery and 

Intelligence.’, Mind 59(236), pp. 433–460. 

[17]. Wooley, J. C., and Lin, H. S. (2005) “Biological 

Inspiration for Computing.” In: Catalyzing Inquiry at the 

Interface of Computing and Biology, Computer Science and 

Telecommunications Board, The National Academies Press, 

John C. Wooley and Herbert S. Lin, editors. 

287
Applying Developmental-Inspired Principles to the Field of 

Developmental Robotics 

Gary Berg-Cross 

Engineering, Management and Integration 

Potomac, MD 20854 

301-424-9256 

Gary.berg-cross@em-i.com and gbergcross@gmail.com

ABSTRACT 

Bio-inspired principles of development and evolution are a 

special part of the bio-models and principles that can be 

used to improve intelligent systems (IS). Such principles 

are central to cognitive developmental robotics (DR) and its 

effort to understand cognition by imitating development. 

DR approach takes inspiration from nature process so that 

engineered intelligent systems may create solutions to 

problems in way similar to what is believed to occur with 

biologics in their natural environment. This paper uses a 

three-level, bio-inspired framework to illustrate 

methodological issues in DR research. I stress the 

importance of using bio-realistic developmental principles 

to guide research keeping models and implementation 

separate to avoid the possible of falling into a Ptolemaic 

paradigm of endless tweaking of models. Several of 

Lungarella’s design principles for developmental robotics 

are discussed as constraints on intelligence as it emerges 

from a ecologically balanced, three-way interactions 

between an agents’ control systems, physical embodiment, 

and the external environment. 

Categories and Subject Descriptors 

F.1 COMPUTATION BY ABSTRACT DEVICES, I.2.9 

Robotics, K.2 HISTORY OF COMPUTING. 

General Terms

Performance, Design, Experimentation. 

Keywords 

Bio-inspiration, developmental robotics, bio-realism, Ptolemaic 

paradigm, embodiment. 

Permission to make digital or hard copies of all or part of this 

work for personal or classroom use is granted without fee 

provided that copies are not made or distributed for profit or 

commercial advantage and that copies bear this notice and the full 

citation on the first page. To copy otherwise, to republish, to post 

on servers or to redistribute to lists, requires prior specific 

permission and/or a fee. 

PerMIS’08 August 19-21, 2008, Gaithersburg, MD, USA 

ACM ISBN 978-1-60558-293-1/08/08...$5.00. 

1. INTRODUCTION 

As noted in Berg-Cross (2008) efforts to make synthetic/artificial 

systems more intelligent increasingly borrow from biologicallyinspired models in part due to advanced understanding in the 

relevant domains. Indeed the bio-adaptive nature of intelligence in 

realistic environments has been discussed previously at PerMIS 

meetings and is well summarized by Freeman (2003): 

“Why do brains work this way? Animals and 

humans survive and flourish in an infinitely 

complex world despite having finite brains. Their 

mode of coping is to construct hypotheses in the 

form of neural activity patterns and test them by 

movements into the environment. All that they can 

know is the hypotheses they have constructed, 

tested, and either accepted or rejected. The same 

limitation is currently encountered in the failure of 

machines to function in environments that are not 

circumscribed and drastically reduced in 

complexity from the real world. Truly flexible and 

adaptive intelligence operating in realistic 

environments and cannot flourish without 

meaning.” 

Over the last few years embodied, development thinking has 

emerged in the form of a “new robotics” partly in response to lack 

of progress with the information processing paradigm which 

currently seems ill-suited to come to grips with natural, adaptive 

forms of intelligence. But part of the question on bio-inspiration 

for intelligent systems (IS) involves epistemological and 

methodological questions of the risks of such inspiration to 

improve our understanding and implementations. Following an 

introduction the development as an inspiration some of these 

general methodological issues are broached and some biodevelopmental principles from the literature discussed as 

important constraints on unbridled influence. 

2. DEVELOPMENTAL ROBOTICS 

METHODS 

One sub-set of this work is developmental robotics (DR), with 

various names depending on the emphasis1

. Developmental 

 

1

 Terms besides Developmental Robotics include the more 

general BioRobotics, the more specific ones of Cognitive 

Developmental Robotics, Epigenetic Robots and Evolutionary 

Robotics 

288
Robotics (DR) is an emerging experimental science inspired by 

increased understanding of the importance of a developmental 

stance . That is, DR uses “synthetic” experimental studies of 

development as a core idea e.g. Piagetian stage-theory processes 

involving prolonged epigenetic development to elucidate general 

mechanisms of intelligence development, starting with proposed 

cognitive development mechanisms. While the idea may not be 

new, using present day robotic technology embedding neural 

systems as building blocks we now have the unique opportunity 

to test challenging hypotheses representing complex principles of 

cognitive development in realistic environments. Such embedded, 

bio-adaptive nature of intelligence, responding to environmental 

challenges was recently discussed at a PerMIS Special Session on 

Epigenetic/ Developmental Robotics (Berg-Cross, 2007). The 

session discussed how research leverages our increased 

understanding of the mechanisms underlying development using 

computational models of development, cognitive architecture and 

neural models. The session included, as an example, the work of 

Blank, Marshall and Meeden (2002) who describe a 

developmental, algorithmic design using core ingredients of 

abstractions, anticipations, and self-motivations. This design is 

designed to allow a mobile robot to incrementally progress from 

sensory-motor activities through levels of increasingly 

sophisticated behavior and it also attempts to answer the question 

of how to learn and represent increasingly complex behavior in a 

self-motivated, open-ended way. Self motivation is hypothesized 

as an important link between “low level” cognitive phenomena, 

such as pattern formation and higher complexities (such as 

concept formation, plans, the emergence of simple syntactic 

categories, e.g. action names) are research topics. DR often takes 

such constructivist perspective to study how higher processes 

emerge via self-organize for general-purposes as skill and 

knowledge is learned from environmental interactions. The 

overall DR research program is synthetic and iterative: initially, 

robot technology is used to instantiate and investigate models 

originating from developmental sciences, and results eventually 

feeds back to new hypotheses about the nature of development 

and intelligence. The resulting improved models can then be 

used to construct better robotic systems by exploiting insights 

gained from deeper understanding of developmental mechanism. 

A major attraction of DR is this combination of developmentinspired principles combined with progressive, empirical methods 

for validating derived hypotheses. A simple four part version of 

the methodology is summarized in Figure 1 starting with a 

cognitive developmental model based on “developmental sources” 

such as prior research and/or theory. To mimic development we 

also start with a realistic approach to some innate substrates (e.g. 

 

 

motivation, attention), a cognitive design that may afford 

emergence through interactions with some realistic environment. 

Model-based hypotheses can be empirically tested in a 2nd step by 

building a robot (embodiment) that is situated and can develop 

certain capabilities though interaction with the environment. One 

example is Piaget’s hypothesis on the importance of sensorymotor interaction, staged competence learning and the sequential 

lifting of constraints over a developmental path. Such hypotheses 

suggest robotic “development” studies that can checked against 

behavioral stages (periods of growth and consolidation) followed 

by transitions (phases where new behavior patterns emerge) that 

we observe in children. The next section discusses some of the 

issues that influence design, modeling and experimentation within 

DR in an attempt to improve the overall process. 

3. A SCIENTIFIC FRAMEWORK FOR DR 

Generally, DR methods follow a basic hypothetical-deductive 

framework of a scientific method and its characteristic dual 

sources of inspirations from observations and prior theory and a 

central use of models. Webb (2001) provides a useful three-level, 

general frame (Figure 2) to discuss some of the bio-inspiration 

issues. We can approximately call the levels running from 

bottom to top bio-reality, model-based experimentation, and 

embodied implementation. Taken together they integrate 

hypotheses, models and robots as a scientific device to learn about 

& understand the “bio-reality” of developmental phenomena such 

as adaptive learning. It is worth noting in passing that the right 

side of the figure that compares target behavior, predicted 

behavior and the embodied behavior achieved as part of the actual 

experiment. This is often the topic of PerMIS papers and provides 

the general model-experimental context for these measurements. 

289
We can understand the bio-modeling in many types of DR studies 

using this framework, starting at the lower level, which grounds 

itself in the reality of biological “target systems” that exist in the 

world. In DR studies are targets are typically human 

infants/children whose behavior is known for certain 

circumstances at certain developmental “stages”. For example, 

there is the sequence seem from inaccurate reaching reflex to 

accurate visual target fixation and learning reaches that 

correspond to visual targets. It is commonly observed that 

visually guided reaching is the earliest “accurate” reaching 

behavior to occur. Infants spend notable time observing their 

hands around 12 weeks and by 15 to 20 weeks are performing 

“visually guided” reaching. This bottom level is experimentally 

related to the second (middle) level which is essentially part of the 

first step shown in Figure 1 where “sources” are used to set a 

hypothesized mechanism that can be tested via the robot 

mechanism experiments of steps 2 and the developmental 

structures of step 3. An example model at this level is 

Scassellati’s (2001) shared attention model whose source was the 

more the general developmental theories of children’s cognitive 

abilities (Baron-Cohen, 1995). In Scassellati’s hypothesis there 

are modular processes such as “Eye Direction Detector” which 

can determine the angle of gaze of an individual, usually the 

parent, and extrapolate to find an object of gaze interest. 

Complementing this is an “Intentionality Detector” observes 

other’s motion patterns and attributes the simple intentional states 

of desire and fear to animate objects. Finally a “Shared Attention 

Mechanism” produces representations of attentional states and 

allows a child to observe highly salient objects that are under 

consideration by the observing child. All of this can be 

implementation as shown in the upper level of Figure 3 by a 

robotic system, whose behavior now simulates the gaze behavior 

of young children. 

Webb’s (2001) framework nicely illustrates some of the problems 

that may arise in such DR efforts. One of them is that they 

sometimes attempt to test and validate a bio-mechanistic 

hypotheses based on particular models (e.g. models of neural 

circuits for particular regions of the brain) but then use related 

neural networks as the implementation method to test such 

models. That is Source models at level 2 and Implementation at 

level 3 are effectively the same and we have circular validation. 

Or they may “simulate” virtual implement an embodied robot 

rather than physically implement it and tweak parameters in the 

simulation to make it fit observation. This is hardly a real 

validation as the model at level 2 and the test at level 3 are both 

mathematical models and connection to the real world has been 

skipped. That is, there are problems with some circular aspects of 

how researchers may define source, mechanisms, implementations 

and how close performance must be and to what level of detail it 

is tested in some of the work. Of particular interest are questions 

that can be generated from Webb’s (2001) framework such as: 

• whether all “biases” are eliminated simply by letting a 

system develop from general capabilities since one still 

has to pick some innate substrate, relevant biological 

levels, and relevant environments. 

o There are many competing view of what is 

“real” vs. hypothesized concepts & principles 

e.g. sensori-motor schemas are the source of 

more abstract schemas. 

• Related to this is the issue of relevance & realism: do 

models test and generate hypotheses that are biodevelopmentally applicable? 

• When collections of distributed, specialized neural 

models are the source of inspiration multiple 

“hierarchical units” need to be modeled - neuron to nets 

to circuits to brains. 

• Generality: what range of bio-developmental systems & 

phenomena can the model represent? 

o If adaptive mechanisms are included in the 

model, there may be long chains of 

environmental interactions that may be 

needed to carry through a realistic experiment. 

Some of these issues interact with the issue of performance, for 

example, the issue of levels. We have trouble comparing target, 

expected and actual performance since the amount of detail to do 

this starting at the lowest “level” exceeds not only our ability to 

build such distributed specialized networks but even to simulate 

them. And the physical levels have correspondingly different 

time scales on which they work, so integrating these scales within 

a robot implementation is explicitly handled Lungarella (2004). 

Performance definition is a central issue as Webb (2001) notes, 

arguing that we need to consider more than a naive match of 

behavior. When a direct comparison of the development of higher 

processes is attempted, the possible variability going into the 

match between various behaviors is considerable. Researchers 

have to consider whether the behaviors need to be identical 

(indistinguishable by some interpretive criteria) or merely similar 

(again by some interpretive criteria). Indeed Deakin (1990) argues 

that a behavioral match is never sufficient evidence for drawing 

conclusions about the accuracy or relevance of a model. 

This seems to be particularly true when the target is adaptive 

behavior which may respond to chains of small changes in the 

environment where time is important. There are an enormous 

range and number of variables to consider. An overall problem is 

that researches may “finesse” these problems in various ways 

such simplifying performance accuracy assumptions, tweaking 

simulations etc. (Webb, 2001). It may make the models and 

implementations take on a Ptolemaic character (Gary Berg-Cross, 

2003). By that I mean that the current state of work (in both IS 

and related, if simpler, problem fields) seems a bit like a 

Ptolemaic paradigm. As noted above mathematical models can be 

used as sources in DR. Such models are a bit Ptolemaic in that 

they break complex intelligent behavior into known neat, related 

components that are bit analogous to Ptolemy’s “perfect circular 

motions”. It is a system of step by step complexity build by 

cycles/epicycles with certain perfect cognitive 

290
process/mechanisms as the functional/circular primitives. Bioinspired to begin with we accept heuristic devices for their 

practical computational usefulness and ease of implementation. 

Such core functions are added to in an ad hoc (rather than biodevelopment constrained way) as required to obtain any desired 

degree of performance and accuracy. Using large combinations of 

constructions we are able to measure performance in some small 

problem domain for some of the agreed upon intelligent behaviors 

within the standards of observational accuracy. The ultimate 

concern is that, like a Ptolemaic system, when we encounter 

anomalies, parameters can all-to -easily be modified to account 

for them. Thus the model becomes more an after-the-event 

description then a deep capture of the underlying problem. Such 

descriptions may be very useful, making it possible to 

economically summarize a great amount of brute observational 

data, and to produce empirical predictions, but they often prove to 

be brittle, do not scale and might not be fruitful to further 

predictive IS research. The field seems to understand this 

potential downside of some of these issues and has begun to 

develop some principles to constrain and guide the work. In the 

next section we consider some of Lungarella’s principles (2004) 

that can help, behind the scenes, adding realistic constraints as 

part of DR experimentation. 

4. DEVELOPMENTAL PRINCIPLES 

WITHIN AN EMBODIED, INTERACTIVE 

MODEL 

Lungarella (2004) has outlined a broad set of bio-development 

principles that DR can employ to guide research. He proposes that 

we embed these within a developmental framework the interactive 

coupling of three things - control, body, and environment as 

shown in Figure 4. This coupling reflects principles of ecological 

balance between the three factors. Such balancing of embodied 

intelligent systems includes adaptation to natural constraints from 

gravity, friction, energy limitations, living with damage, etc.

This reflects what Lungarella (2004) calls the principle of “cheap 

design” which means that the design of a developmental agent 

must be parsimonious, and must opportunistically exploit the 

physics of the system-environment interaction, as well as the 

constraints of an agent’s ecological niche. Building on this is the 

principle of developmental “design for emergence” of higher 

cognition. This principle says that when engineering agents one 

should not design them completely for target behavior, but instead 

design should endowed an agent with more general ability that 

will let higher abilities emerge. For example, as in Blank et al 

(2002) they should self-direct the exploration of their own 

sensory-motor capabilities, and have some realistic capabilities to 

enhance their limited initial behavioral repertoire, and acquire a 

cognitive-experiential history. A related principle is that of 

“ecological balance”, which can be understood in terms the 3 part 

coupling model. For balance an agent’s complexity or behavioral 

diversity has to match the complexity of the environment as 

measured against the agent’s sensory apparatus. Thus when 

designing or developing an agent for a particular task 

environment, a balance is required between the complexity of the 

sensor, motor, and control system. This happens naturally in 

natural environment through selection, but has to be through in 

design - a difficult problem since the coupling of the three 

elements is not obvious. This happens more readily in nature as 

understood by Lungarella’s “value principle”, which provides a 

substrate repertoire of motivated learning & adaptive behavior. A 

motivation substrate is needed for a developmental process to take 

place and for an autonomous agent to behave adaptively in the 

real world, along with a set of mechanisms for self-supervised 

learning. This substrate provides values that shape the 

development of the agent’s control and bodily structure. 

Principles for the embodiment add important constraints since 

embodiment implies far than just some limiting physical 

constraints to an organism. embodiment is a challenge that 

actively supports and promotes intelligent information processing. 

It encourages agents to exploit the dynamics of the interaction 

between an embodied system and their environment. It thus 

directly supports the selection and processing of information by 

coupling with the agent control systems and interaction within the 

environment (Pfeifer and Bongard, 2006). They argue that “ 

artificial evolution together with morphogenesis is not only ‘nice 

to have’ but is in fact a necessary tool for designing embodied 

agents.” This coupling is different from non-biological views of 

computation in that it favors the developmental emergence of 

stable computational patterns, including adaptivity and robustness 

against changing environments and indeed the corporal changes of 

development or damage. Lungarella (2004) has formalized how 

embodiment affects agent processing as the principle of 

“information self-structuring” (active perception). As part of 

sensory activity an agent is not passively exposed to information 

from its surrounding environment. Due to its particular 

morphology, and through its actions on the environment; it 

actively structures, selects, and exploits such information. This 

reflects what Lungarella (2004) calls the “starting simple” 

principle for development. We don’t start with a high level model 

but an unfolding hybrid with a gradual and well-balanced increase 

of both the agent’s internal complexity (perceptual and motor) and 

its external complexity (regulated by the task environment or an 

instructor). This speeds up the learning of tasks and the 

acquisition of new skills, compared to an agent that is complex 

from the onset. From this perspective, behavior informs and 

shapes cognition as it is the outcome of the dynamic interplay of 

physical and information theoretic processes, and not the end 

result of a control process (computation) that can be understood at 

any single level of analysis. Instead there emerges an emphasis 

on a general understanding of cognitive aspects. 

291
5. SUMMARY 

I have discussed some of the bio-developmental thinking that 

inspires work to understand and develop more intelligent systems. 

A major benefit argued for a DR view of intelligent systems (IS) 

to that it removes engineer bias (Blank, Kumar, & Meeden 2002) 

inherent in artificial design. There is a good deal to this criticism, 

based on problems we see with engineered systems. On the other 

hand bio-inspiration might be considered to have some biases of 

its own based on chance events along the evolutionary path. In 

addition DR research is still influences by interpretations of 

reality and selection among the complexity of bio-reality. For 

example researchers may select some levels of the neural system 

to emulate and some design selections are driven by the sheer 

practicality of the time scales involved in phenomena as outlined 

in Berg-Cross (2008). I have noted a number of research issues in 

such inspiration including the, challenge of integrating levels of 

bio-reality and cognitive levels; the mixing of models with 

implementation especially when mathematical simulations are 

used; and problems with handling the degree of behavioral 

similarity that constitutes validation of hypotheses. Indeed there 

remains a serious difference of opinion on how to proceed based 

on models. One group which I’ll call “neat formalists” believes in 

centering on models as expressed by Barto (1991) that “the 

complexity of animal behavior demands the application of 

powerful theoretical frameworks” (and “nervous systems are 

simply too complex to be understood without the quantitative

approach that modeling provides”). Another group, that I’ll call 

scruffy empiricists, are represented by Croon and van de Vijver 

(1994) who are uncomfortable with “developing formalized 

models for phenomena which are not even understood on an 

elementary level is a risky venture: what can be gained by casting 

some quite gratuitous assumptions about particular phenomena in 

a mathematical form?” 

Advice for the current stage of work DR researchers might be 

follow such principles rather than trying to tweak particular 

results against target behavior. That is, they should be concerned 

with: “building a complete, but possibly rough or inaccurate 

model, than with strict accuracy per se” (Webb, 2002). This 

would be a complete system that connects action and sensing to 

achieve a task in an environment, even if this limits the individual 

accuracy of particular parts of the model because of necessary 

substitutions, interpolations etc. . The direction proposed herein 

is not to slavishly follow bio-inspiration. Rather we should 

proceed with a developmental approach using developmental 

principles based on our understanding of how intelligence 

develops. A final note is an observation that I add as Gary’s 

principle. It’s based on the observation of the large, 

interdisciplinary nature of the teams now working on bio-inspired 

robots which stand in some contrast to the simple application 

development teams of the past. Due to the inherent complexity of 

cognitive systems, interdisciplinary teams are required where 

biological, theoretic and robotic systems are studied at different 

levels of granularity. This suggestion is simply that successful 

developments will require a considerable, explicit expertise in the 

development team to understand what is implicit in the agent to be 

developed. 

6. REFERENCES 

[1]. Baron-Cohen, S.. Mindblindness MIT Press, 1995. 

[2]. Berg-Cross, G. (2003), “A Pragmatic Approach to 

Discussing Intelligence in Systems”, PerMIS Proceedings 

2003. 

[3]. Berg-Cross, G. (2007), Panel discussion “Can the 

Development of Intelligent Robots be Benchmarked? 

Concepts and Issues from Epigenetic Robotics”, PerMIS 

Proceedings 2007. 

[4]. Berg-Cross, G. (2008) “Introduction to biological 

inspirations for intelligent systems”, PerMIS Proceedings 

2008. 

[5]. Croon, M. A. & van de Vijver, F. J. R. (1994) Introduction. 

In: Viability of mathematical models in the social and 

behavioural science, ed. M. A. Croon & F. J. R. van de 

Vijver. Swets and Zeitlinger. 

[6]. Deakin, M. (2000) “Modelling biological systems.” In: 

Dynamics of complex interconnected biological systems”, 

ed. T. L. Vincent, A. I. Mees & L. S. Jennings. Birkhauser. 

[7]. Freeman W. (2002), “On Communicating with Semantic 

Machines”, PerMIS Proceedings, 2002. 

[8]. Lee, M., Meng Q. and Chaom F. “Developmental Robotics 

from Developmental Psychology” 

[9]. Lungarella., M. (2004 ) “Exploring Principles Toward a 

Developmental Theory of Embodied Artificial Intelligence”, 

Ph.D. Disertation, Zurich. 

http://www.ifi.uzh.ch/ailab/people/lunga/Download/PhDThe

sis/thesis040504_complete.pdf

[10].Pfeifer R, and Bongard, J. C. (2006) How the body shapes 

the way we think—A new view of intelligence. Cambridge 

(Massachusetts): MIT Press. 

[11].Scassellati (2001) “Foundations for a Theory of Mind for a 

Humanoid Robot” Ph.D. Dissertaion, MIT, 

http://www.cs.yale.edu/homes/scaz/papers/scassellatiphd.pdf. 

[12].Webb, B. (2001) “Can robots make good models of 

biological behaviour?” BEHAVIORAL AND BRAIN 

SCIENCES (2001) 24, 1033–1050. 

292
Overcoming Barriers to Wider Adoption of Mobile Telerobotic 

Surgery: Engineering, Clinical and Business Challenges 

Gerald R. Moses, PhD 

MASTRI Center, University of 

Maryland Medical Center 

22 S. Greene Street 

Baltimore, MD 21201 

410-328-8431

gmoses@smail.umaryland.edu

Charles R. Doarn, MBA 

University of Cincinnati Advanced 

Center for Telemedicine and Surgical 

Innovation

231 Albert Sabin Way 

Cincinnati, Ohio 45267

513 558 6148 

 charles.doarn@uc.edu 

Blake Hannaford, PhD & Jacob 

Rosen, PhD 

Biorobotics Laboratory, University of 

Washington

Dept. of Electrical Engineering

Seattle, Washington 

206 543 2197 

http://brl.ee.washington.edu

ABSTRACT

A portable robotic telesurgery network could remove the 

geographic disparity of surgical care and provide expert surgical 

support for first responders to traumatic injury. This is 

particularly relevant to battlefield medicine where surgical 

intervention is currently not available to the most perilous fighting 

circumstances. Similar utility applies to the peacetime healthcare 

mission. The authors identify the potential advantage to 

healthcare from a mobile robotic telesurgery system and specify 

barriers to the employability and acceptance of such a system. 

This presentation will describe a collaborative effort to design and 

develop one or more portable robotic systems for telesurgery and 

develop those systems through successful animal trials. Recent 

advances in engineering, computer science and clinical 

technologies have enabled prototypes of portable robotic surgical 

platforms. Specific challenges remain before a working platform 

is suitable for animal trials, such as the inclusion of imageguidance and automated tasks

Other barriers to the development of mobile robotic surgical 

platform will be described. These include technical challenges of 

refinement of robotic surgical platforms, reduction of weight, 

cube, complexity and cost, and expansion of applications of 

technology to several procedures. Clinical challenges involve the 

protection of patient rights and safety, selection of surgical 

procedures appropriate for the system, the application of surgical 

skill to evaluate hardware and the application of surgical lore to 

software programs. Finally, business challenges include 

resolution of intellectual property considerations, legal liability 

aspects of telesurgery, patient safety and HIPPA, reimbursement 

and insurance issues, FDA approval of the final product and 

development of a commercialization plan. 

Keywords

Surgery, robotic telesurgery, access to surgical care. 

1. INTRODUCTION

The past decade has witnessed the growth of both interest in and 

capability of telesurgery systems. These developments are based 

in great measure upon enabling of technologies related to 

engineering, computer science, robotics, telecommunications, 

medical informatics, and surgery [1]. Barriers to the conduct of 

telesurgery have been identified and to some extent ameliorated 

[2]. The physical barriers of latency, visual discrepancy, roundtrip delay, jitter and limited bandwidth have been studied and 

measured as quality of service indicators [3,4]. Additional 

challenges include strong business cases for wider adoption in 

clinical practice. 

Various demonstrations have shown the possibility and potential 

of telerobotic systems; including the conduct of the first 

transcontinental telesurgery in the United States, the conduct of 

collaborative experiments with NASA within the NASA Extreme 

Environments Mission Operations (NEEMO) program, the 

refinement of prototype microsurgery equipment as a model for 

portable surgery systems, robotic laser tissue welding, robotic 

replacement for surgical scrub technicians, control of timedelayed telesurgery, and the use of high altitude platforms for 

transmission of telesurgery signals [5,6,7,8]. 

2. THE CHALLENGE OF FUNDING 

Various working groups have identified the lack of 

multi/interdisciplinary collaboration as a barrier that could be 

overcome by funding specifically targeted to improve 

interdisciplinary research, design and commercialization. Failure 

to resolve intellectual property issues could impair and potentially 

stop development of robotic surgery. The lengthy and costly IP 

battle waged between Computer Motion and Intuitive Surgical 

exemplifies how intellectual property litigation can consume 

resources that could be used for further system development. 

Permission to make digital or hard copies of all or part of this work for 

personal or classroom use is granted without fee provided that copies are 

not made or distributed for profit or commercial advantage and that copies 

bear this notice and the full citation on the first page. To copy otherwise, 

or republish, to post on servers or to redistribute to lists, requires prior 

specific permission and/or a fee. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA. 

Copyright 2008 ACM 978-1-60558-293-1...$5.00. 

293
It was estimated by a Defense Department working group that 

funding in excess of $380M would be required to advance robotic 

surgical assistants to the point of “crossing the chasm” into early 

acceptance, from the perspective that we are now at the stage of 

“early adopters”. This places the effort in the realm of “Grand 

Challenges” on par with the National Nanotechnology Initiative, 

where many believe it rightly belongs. Early reports do 

demonstrate that these surgical robots can allow the performance 

of safer, faster surgery, but the technology is tightly bound to 

economies of scale as long as the current designs and poor 

business practices are utilized.

The primary hurdles that need to be overcome in order to even 

begin addressing the roadmap include funding; the resistance of 

funding agencies to fund, and academia to support, large-scale, 

distributed, multidisciplinary teams; the culture and 

communication barriers between the disparate groups that would 

need to collaborate; industry’s resistance to open architectures 

and large-scale collaboration. The “Grand Challenge” of 

developing surgical robotics should begin with a “grand” meeting 

where the relevant technologies, their current state, and the 

roadmap are described. Any future effort to plan a strategic 

roadmap for telesurgery research funding must engage all of the 

stockholders. Relevant federal agencies such as NIBIB, NIH, 

NSF, FDA, NIST, stakeholders from industry, academia and 

professional and standards organizations would need to join the 

community of clinicians and scientists who seek to advance 

telesurgery as a vital force in the provision of health care.

3. CURRENT STATUS OF TELESURGERY 

For nearly a decade, the Department of Defense medical research 

agencies have explored the development of a portable robotic 

telesurgery system. Both the Defense Advanced Research 

Projects Agency (DARPA) and the Telemedicine and Advanced 

Technology Research Center (TATRC) have invested 

considerable resources in this investigation. The DARPA Trauma 

Pod project demonstrated that a single surgeon located outside of 

the operating environment could control multiple surgical 

assistant robotic functions. TATRC’s support to several projects 

demonstrated that live animal telesurgery could be performed 

safely and effectively over the Internet, that telesurgical 

manipulation could be accomplished across great distances and 

into extreme environments and that alternative modes of 

transmitting signals could support robotic telesurgical tasks and 

movements.

The development of the current M7 “Army Arm” for robotic 

telesurgery demonstrated the possibility of a portable robotic 

surgery system. This system was constructed by SRI 

International from an earlier ophthalmic telepresence 

microsurgery model. 

Figure 1. The M7 Surgical Robotic System 

Similarly, progress was made in a robotic C-Arm system, named 

RAVEN, by the University of Washington HIT Lab. The 

development of a surgical robotic arm by MD Robotics in 

Toronto, Canada rounded out a significant North American effort 

to expand capabilities in the realm of medical robotics for 

telesurgery. MD had proven success as a company that develops 

robotic arms for space exploration, and had applied space-based 

robotic lore to produce a prototype single-arm system. 

Figure 2. The RAVEN robotic surgery system. 

In addition to the engineering and computer science related 

challenges, there are non-technical challenges that impede the 

implementation of a mobile telesurgery system. There is a need 

for industry and political arena representatives to establish a 

nation-wide communications network capable of supporting 

telesurgery. Also, licensure, privacy, liability and third-party 

payer issues must be addressed to enable wider adoption of 

telecollaboration and its effective use. Robust business models 

will offer greater adoption across a broader spectrum. 

Given the current nature of support to mobile robotics and the 

reduction in DOD funding there has been slowdown in 

development of mobile robotic surgery systems. What is needed 

now is clarification of DIRECTION of research efforts and 

restoration of momentum for research and development. 

294
4. POSSIBILITIES AND DIRECTION 

Our presentation will address the identification and description of 

challenges to the development of portable telerobotic surgery, 

then articulate specific actions to overcome those challenges. The 

long-term goal of this and related research is the development of a 

portable telerobotic surgery system, capable of permitting surgical 

intervention across distances and into extreme and remote 

environments. That goal will likely be attained by the engagement 

of a multidisciplinary team of engineers, surgeons, computer 

scientists and informaticists to build on developing technologies 

to create the portable telerobotic surgery system. The 

multidisciplinary team would then need to address the technical 

challenges of quality of service over a telecommunication system 

and other systems to reduce latency and jitter of the signal. It is 

anticipated that animal trials would be conducted, leading up to a 

human surgical event within five years. The ultimate goal of the 

project is to enhance patient safety and quality of care by way of 

distributed surgical intervention. 

Because the problems related to the development of a portable 

telesurgical system are many and varied, the contributions of 

collaborators can take many forms. There is the singular 

challenge of developing a robotic surgery system that is 

considerably smaller and lighter than current, commercial 

hospital-based systems. The reduction in weight and cube must be 

accomplished without degradation of efficiency and accuracy of 

robotically-controlled aspects. Once a master-slave system has 

been developed, the two parts must be connected over a secure, 

efficient and unfailing transmission link, which guarantees 

robustness, reliability, redundancy, minimal or zero latency, and 

quality of service. Various transmission modes have been 

explored, including the use of the Internet with enhanced 

connectivity to ensure quality of signal and an airborne platform 

capable of “bouncing” signals across distances. 

Before this endeavor of developing a portable robotic telesurgery 

system can be attempted, a roadmap for its attainment must be 

drawn. That roadmap should identify the currently known 

obstacles to success and predict some likely obstacles to be 

encountered. The purpose of this presentation is to identify the 

barriers to success and chart alternative routes to the long-term 

goal.

5. A ROADMAP FOR RESEARCH 

We propose to develop a comprehensive strategic roadmap for 

investment of research dollars for the development of a portable 

robotic telesurgery system, one that leads to animal trials within 

one year of completion. Our plan of work is to convene a 

conference of recognized experts in robotic telesurgery with the 

objective of crafting specific guidance for development, testing 

and refinement of a robotic telesurgery system. We predict that 

several physical barriers to telesurgery will be identified; their 

characteristics will need to be defined. These include control 

latency, visual discrepancy, round-trip delay, jitter, bandwidth 

and quality of service. Our plan is to understand the nature of 

these barriers and develop solutions to them. We anticipate also 

that non-physical barriers will be identified and hypothesize that 

they will include the need for a refined nation-wide 

communications network, resolution of privacy and 

confidentiality issues, acceptance of a broad license-to-practice, 

clarification of legal and regulatory matters and creation of an 

electronic medical record 

The methodology of the study will begin with an extensive review 

of related research and background literature related to robotic 

telesurgery. Findings from recent experiments throughout the 

world will be considered in framing the research and development 

challenge. We will conduct discussions with scientists, surgeons, 

and engineers who understand robotics, telecommunications, and 

surgery, then expand our investigation to include related factors 

of intellectual property, device development as approved by the 

FDA, medical reimbursement, security and confidentiality of 

data, and patient safety. 

We will obtain information and guidance from experts in two 

ways; first by means of convening a strategic planning 

conference; second by direct interview. The conference will 

address developments in robotic form, factor and function; 

effector structure and function requirements; controller 

ergonomics and haptics; integration with imaging; quality of 

service in signal transmission; and preparation for testing a 

prototype robotic telesurgery system by way of animal trials. 

Individual direct interviews will expand on the topics of 

establishing and maintaining intellectual property, resolution of 

business practices and patent registration arising from 

collaborative product development, informing the FDA of plans 

for both product development and animal trials, conducting 

discussions with CMMS and third-party payers regarding 

reimbursement of eventual health care services delivered by way 

of telesurgery. 

The deliverable from the research effort will be a comprehensive 

report with specific targets and timelines for research and 

development leading to the establishment of a functional and safe 

robotic telesurgery system. 

6. REFERENCES 

[1] Cleary K and Mun SK, “OR 2020, The Operating Room

 of the Future”, Workshop Report, March 2004.

[2] Curley K and Moses G, “Innovation by Committee” 

Reigniting Surgical Robotics Research and 

Development”, Surgical Innovation, December, 2005, 

12(4), 291-95. 

[3] Curley K, Broderick T , Marchessault R, Moses G, 

Taylor R, Grundfest W, Hanly E, Miller B, Gallagher 

A, Marohn M., “An Integrated Research Team (IRT) 

meeting for Surgical Robotics – The Next Steps, 

TATRC Report, No. 04-03, 2005, January. 

[4] Doarn C, Broderick T, Harnett B, Marchessault, Moses 

G and Anvari M, “Telesurgery and Telerobotics: Where 

we Need to Focus Research” Meeting Summary, 2004, 

May. 

[5] Hanly E, Marohn M, Schenkman N, Miller B, Moses G, 

Marchessault R and Broderick, T, “Dynamics and 

295
Organizations of Telesurgery”, European Surgery, Vol 

37, No. 5, Oct, 2005. 

[6] Hanly RJ, Miller BE, Herman BC, Marohn MR, 

Broderick TJ, Shih SP, Sterbis, JR, Doarn CR, Harnett 

B, Hasser CJ, Talamini MA, Moses GR, Marchessault 

R. Schenkman NS. Remote Robotic Surgery Using the 

Public Internet: Cheap Transcontinental Telesurgery. 

11th

Annual Meeting and Exposition of the American 

Telemedicine Association, San Diego, CA. May 2006.

Telemed and E Health 2006; 12(2):223.

[7] Hoffman L, Doarn CR, Harnett B, Moses G, Broderick 

 TJ. “Recent Advances in Robotic Telesurgery and 

 Applications to Battlefield Trauma”, 2nd

 Annual 

 Meeting of the Association of Academic Surgeons. 

 Phoenix, AZ. February 2007. 

[8] Harnett BM, Doarn CR, Rosen J, Hannaford B, 

Broderick TJ. Evaluation of Unmanned Airborne 

Vehicles and Mobile Robotic Telesurgery in an 

Extreme Environment. Telemed J E Health 2007; 

14(6):537-42.

296
 Calibration of a Computer Assisted Orthopedic Hip 

Surgery Phantom

Daniel Sawyer 

NIST 

100 Bureau Drive 

Gaithersburg, MD20899 

(301) 975-5863 

dssawyer@nist.gov 

Nick Dagalakis 

NIST 

100 Bureau Drive 

Gaithersburg, MD20899 

(301) 975-5845 

dagalaki@nist.gov 

Yong Sik Kim 

NIST 

100 Bureau Drive 

Gaithersburg, MD20899 

(301) 975-8081 

yong@nist.gov 

Craig Shakarji 

NIST 

100 Bureau Drive 

Gaithersburg, MD20899 

(301) 975-3545 

shakarji@nist.gov 

ABSTRACT

Orthopedic surgeons have identified a need for calibration 

artifacts (phantoms) to establish the traceability (to the SI unit of 

length) of measurements performed with Computer Assisted 

Orthopedic Surgery (CAOS) systems. These phantoms must be 

lightweight, easy to transport and simple to use. In collaboration 

with medical professionals, National Institute of Standards and 

Technology (NIST) researchers have developed a family of 

novel CAOS phantoms designed to meet the metrology needs of 

this critical segment of the US healthcare industry. The 

phantoms function as a surrogate hip joint and pelvis and can be 

measured with CAOS systems using the same technique 

employed to measure a patient’s hip joint and pelvis for 

replacement surgery. The phantoms contain a mechanical ball 

joint, which functions as a substitute for a patient’s hip joint and 

small holes, referred to as target holes, for receiving the 

measuring probe of CAOS systems. The location of the 

mechanical ball joint and the relative positions of the target 

holes are measured using the CAOS system and the results 

compared to the known values for these quantities. The results 

of this comparison are then used to verify the CAOS system 

performance specifications. In order to determine the known 

values for the critical dimensions of the phantom, the 

mechanical ball joint location and target hole positions are 

measured with a Coordinate Measuring Machine [1] (CMM), 

which is more accurate than CAOS Systems. This paper will 

report on the calibration of the NIST prototype phantom using a 

CMM and simulation tools at NIST. 

Keywords 

computer assisted surgery, computer assisted orthopedic 

surgery, hip arthroplasty, phantom, calibration.

1. INTRODUCTION 

The NIST operating room artifact (known as the phantom)[2][3] 

is designed to evaluate the measurement performance of threedimensional coordinate measuring instruments that are used for 

Computer Assisted Orthopedic Surgery (CAOS). The intent of 

this report is not to describe the development and use of the 

phantom. (See [2] and [3].) Instead, this report provides a 

description of the critical features of the NIST phantom with 

only enough details about its construction to clearly describe the 

calibrated dimensions and their general intent. Further, this 

document will not provide the values of the results of the 

measurements. Such information is not part of the description of 

the measurement procedures. Finally, a description of a novel 

tool for calculating the task specific measurement uncertainty 

for all of the measurements performed is provided [4]. 

The phantom is comprised of two independent parts. The base 

is the primary support structure and is the “L” shaped part 

depicted on the right-hand side of figure 1 and shown in the 

photograph of figure 2. The femur bar is removable and 

connected to the base via a magnetic ball socket; it has 

kinematic constraints similar as to the human femur bone 

relative to the pelvis, which is depicted on the left-hand side of 

figure 1. 

The base and femur bar are constructed of INVAR with a 

coefficient of thermal expansion of 1.30 Pm · m-1 · qC-1 and 

include three types of calibrated features. First, there are small 

holes (approximately 1 mm in diameter and 1.4 mm in depth) on 

the base of the phantom, referred to as target holes. Collectively, 

these target holes function as a three-dimensional point 

coordinate artifact. The base has target holes aligned along two 

nominally orthogonal axes and additional target holes aligned 

along a semicircular path about the intersection of these axes. 

This paper is authored by employees of the United States Government 

and is in the public domain. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA 

ACM ISBN 978-1-60558-293-1/08/08.

297
(See figure 3.) The three-dimensional coordinates of these target 

holes are provided as part of the phantom calibration and when 

referenced to the appropriate coordinate frame (see the next 

section) these known values can be used to evaluate the 

performance of CAOS systems in point coordinate 

measurements. 

Second, a stainless steel magnetic kinematic ball nest is bolted 

to the base; it is designed to firmly hold a highly spherical 

38.1 mm diameter stainless steel sphere. The coordinates of the 

center location of the sphere placed in the kinematic nest, along 

with its measured diameter, are included in the calibration 

report. This kinematic ball nest functions as a surrogate hip 

socket. When fitted with the sphere on the femur bar, CAOS 

systems can measure the ball center location in a manner 

consistent with operating room procedures. The calibrated value 

for the ball center can then be used to evaluate the performance 

of the CAOS system in determining the location of the center of 

rotation. This is similar in practice to determining the center of 

rotation of a patient’s hip joint. 

Finally, the angles between three sets of planes are also 

provided. CAOS systems are often configured with a 

supplemental cutting blade and spatula tools. When these tools 

are present, the sides of the tools will be brought into contact 

with these surfaces and their angular orientation recorded by 

CAOS systems. The calibrated value for the angles between 

each set of planes can be compared to the CAOS measured 

angles to determine the tool angular positioning performance. 

In all cases, the measured coordinates provided as part of the 

calibration report are relative to a common coordinate frame. 

The details for establishing this common or part-coordinate 

frame and the method employed to inspect each of the calibrated 

features are included in the applicable section of this paper. 

Calibration of the phantom features was performed using a 

Coordinate Measuring Machine (CMM) with active part 

temperature compensation and the task specific measurement 

uncertainty was evaluated using Pundit/CMM software1

[3]which incorporates a measurement uncertainty tool 

developed at NIST [4]and following NIST Technical Note 

1297, Guidelines for Evaluating and Expressing the Uncertainty 

of NIST Measurement Results. 

2. PART COORDINATE FRAME 

Referring to figure 2, the part-coordinate frame origin is located 

at the center of the bottom plane of the target hole labeled

Origin. The X-axis is defined as the line that passes through the 

origin and the bottom center of the target hole labeled X20. The 

X-Y plane contains the X-axis and the bottom center of target 

hole Y15. And finally, the Y-axis lies nominally along the 

direction of the line from the origin through the bottom center of 

target hole Y15. It’s important to note that the coordinate frame 

as drawn in figure 2 is misleading as the part-coordinate frame’s 

X- and Y-axes lie along the bottom of the target holes and, 

consequently, the part coordinate frame’s X- and Y-axes are 

inside the part. 

3. TARGET HOLE MEASUREMENTS 

During calibration, the phantom is positioned with the X- and Yaxes in the X-Y plane of the NIST Resource Engineering 

Incorporated1 (REI) CMM. This class of CMM is a standard 

commercial grade CMM. (Volumetric performance number [6] 

is approximately 10 μm.) The center of each target hole is 

designated by its X and Y coordinates. These centers are 

determined by measuring 4 points distributed along a circular 

path around the interior of the cylindrical bore that forms the top 

two thirds of the target hole. The Z coordinates are then 

obtained by probing vertically, towards the bottom of the target 

hole, with the probe positioned in the center of the target hole. 

(Uncertainties associated with the non-perpendicularity of the 

target hole axis and the X-Y plane have been assessed and are 

included in the uncertainty statement that is part of the phantom 

calibration report.) 

Figure 1. The image on the left is a depiction of a patient 

pelvis along with a femur bone and an artificial ball joint. 

Comparing this to the NIST phantom and femur bar on the 

right side of the figure, it is easy to recognize the motivation 

for the construction of the measurement artifact. 

Unlike the CAOS systems, which use pinpoint probes, CMMs 

use spherical probes with finite diameters. Consequently, the 

measured coordinate obtained using a CMM represent the center 

of the probe. As a consequence, the Z coordinates had to be 

corrected for the effect of the probe tip radius to be consistent 

with the coordinates measured by the CAOS systems. 

The target holes with names that begin with R are labeled 

from R15 through R75 in figure 3. These target holes are labeled 

using integer increments of 15. The number following R in the 

name corresponds to the approximate angle in degrees that a 

vector through the origin and the target hole makes with the Xaxis, as shown in figure 3. 

 

1

 Certain commercial products and processes are identified in 

this paper to foster understanding. Such identification does not 

imply recommendation or endorsement by the National Institute 

of Standards and Technology, nor does it imply that the products 

and processes identified are necessarily the best available for the 

purpose. 

298
4. SPHERE MEASUREMENT (CENTER

OF ROTATION) 

A sphere with 38.1 mm nominal diameter was measured while 

positioned in the kinematic ball nest. (See figure 2 below.) The 

sphere was measured with five points; one on the pole and 4 

points distributed approximately 15° above the equator. This 

measured quantity represents the center of rotation when the 

femur bar is attached to the phantom base. There is 

approximately a 3 μm difference in diameter between the size of 

the sphere attached to the femur bar and the sphere used during 

calibration. The effects of the difference in size of the two 

spheres are included in the uncertainty analysis, and the 

expanded uncertainty provided in the calibration report reflects

the effect of this difference. 

5. ANGLE MEASUREMENT 

Three sets of planes were measured and the angle between the 

calculated surface normals is reported for each set of planes. The 

planes were measured using 5 points: 4 points in each of the 

corners of the plane and one point in the approximate center. 

These planes are shown in figures 4 and 5. 

R30 

R15 

R45 

R60 

R75 

| 15

| 30

| 45

| 60

R30 | 75

R15 

R45 

R60 

R75 

| 15

| 30

| 45

| 60 | 75

Figure 3. The target holes with names that begin with R

are labeled from R15 through R75. These target holes are 

labeled using integer increments of 15. The number 

following R in the name corresponds to the approximate 

angle in degrees that a vector through the origin and the 

target hole makes with the X-axis, as shown in figure 2b. 

Origin 

X1 

X20 

Y15 

Y1 

R15 

R30 

R75 

X Axis 

Y Axis 

Z Axis 

Y15

Origin (0,0,0)

X

Y

Y14

Y13

Y12

Y11

Y10

Y09

Y08

Y07

Y06

Y05

Y04

Y03

Y02

Y01

X05 X04X03 X02 X01

X20X19X18X17X16 X10X09X08X07X06

X15 X14X13X12X11

Y15

Origin (0,0,0)

X

Y

Y14

Y13

Y12

Y11

Y10

Y09

Y08

Y07

Y06

Y05

Y04

Y03

Y02

Y01

X05 X04X03 X02 X01

X20X19X18X17X16 X10X09X08X07X06

X15 X14X13X12X11

Figure 2. The coordinate of each target hole is defined as the 

point in its bottom center. The names for the target holes are 

labeled X1 through X20. They are labeled sequentially from the 

origin through point X20. The numbering is the same for the YAxis, although there are fewer target holes along this axis. 

6. MEASUREMENT UNCERTAINTY 

Because of the versatility of CMMs, the calculation of 

measurement uncertainty for the broad array of measurements 

they can perform is a challenging task. This challenge is a result 

of the large number of factors that affect the accuracy of CMM 

measurements. Specifically, CMM hardware errors, environmental effects, form errors in the feature under inspection and 

the number and distribution of points used to inspect the feature 

all affect the accuracy of the measurements performed. In 

response to this challenge, industry has developed some tools to 

simulate the measurement task while varying the parameters that 

characterize these factors. To calculate these critical 

components of uncertainties for the measurements described in 

this paper, NIST used one such tool, PUNDIT/CMM [4]. This 

software tool implements a technique called Simulation by 

Constraints [5] to estimate the components of the measurement 

uncertainty mentioned above. In the software, all of these effects 

are modeled and varied and the measurement process simulated. 

299
In particular, the determination of the uncertainty in the X and Y 

target hole coordinates is complicated by the fact that the 

cylindrical portion of the target hole is neither perfectly 

cylindrical nor orthogonal to the X-Y plane. In fact, the angle 

and shape of each target hole varies slightly due to 

manufacturing inaccuracy. Clearly, the number and the 

distribution of points along the surface of the cylindrical portion 

of the target hole affect the value of calculated coordinates. In 

order to include the variation of the axis direction and the form 

error, 4 of the target holes were measured using a large number 

of points (approximately 26 points total). The data was then 

evaluated and information about the characteristic form error in 

the cylindrical surface and the variation of the target hole axis 

direction was entered into the uncertainty software. Further, the 

bottoms of the target holes are not perfectly flat and smooth. To 

obtain information for input into the simulation software, a large 

number of points were measured along the bottom surface of the 

target hole. The software then uses this information to vary the 

form of the surface for each measurement simulation. The 

variation in the simulation results characterizes these important 

components of the measurement uncertainty. 

| 60

| 45

| 17.5

Figure 4. The angle between the adjacent planes labeled in the 

figure is provided to evaluate the angular measurement 

performance of CAOS systems when fitted with a 

supplementary cutting tool. 

Figure 5. The femur bar shown with the sphere attached. 

The sphere shown in Figure 3 is removed and replaced with 

the sphere shown here allowing the femur to be rotated 

much like a hip joint. 

The simulation tool is also used to determine which points 

should be measured. That is, potential users of the phantom 

specified the required uncertainties for the calibration before 

300
hand. As typical CAOS point coordinate measurement 

uncertainty is on the order of 1 mm, it is desirable for the 

calibration uncertainty to be on the order of 0.1 mm. 

Consequently, the number and distribution of the points used to 

calibrate each of the features of the phantom were determined 

using the simulation software. Specifically, the uncertainty 

software was used to perform experiments to find more efficient 

procedures to calibrate parts given a required uncertainty. That 

is, it would not be an efficient use of measurement and 

programming time to measure a large number of points on each 

surface if the required uncertainties do not warrant such effort. 

By using the simulation tool, sampling points can be increased 

or decreased and the measurement simulation performed to 

determine if the required level of accuracy is obtained. In fact, to 

obtain the required level of accuracy, only measurements of a 

circular feature on the cylindrical surface of the target hole are 

required. This greatly simplified the measurement programming 

and significantly reduces the measurement time. 

7. CONCLUSION 

We have described the methods, procedures and tool used to 

calibrate the critical dimensions of the NIST phantom artifact. 

Field-testing of the prototype phantom artifact has led to 

proposed refinements in the phantom artifact design. However, 

the methods and procedures described here may be used to 

develop a measurement strategy to calibrate future designs of 

this important artifact. 

8. REFERENCES 

[1] John A. Bosch, Coordinate Measuring Machines and 

Systems, Marcel Dekker, Inc., 1995 

[2] http://www.orthosupplier.com/bonezone/online/2007/fall/e

ditorial_dagalakis.pdf 

[3] http://www.isd.mel.nist.gov/medical_devices/PerMIS_OR_

CAOHS_Artfct_Vs32.pdf 

[4] http://www.metrosage.com/pundit.htm 

[5] S.D. Phillips, B. Borchardt, D. Sawyer, et al., The 

Calculation of CMM Measurement Uncertainty via the 

Simulation by Constraints, Proceedings of the ASPE, 1997, 

pages 443-446 

[6] ANSI/ASME B89.4.1-1997 Methods for Performance 

Evaluation of Coordinate Measuring Machines 

301
HLPR Chair – A Novel Patient Transfer Device 

Roger Bostelman 

National Institute of Standards 

and Technology 

100 Bureau Drive MS 8230 

Gaithersburg, MD 20899 

301-975-3426 

roger.bostelman@nist.gov 

James Albus (retired)

National Institute of Standards 

and Technology 

100 Bureau Drive MS 8230 

Gaithersburg, MD 20899 

301-975-3420 

james.albus@nist.gov 

Joshua Johnson 

Florida Gulf Coast University 

10501 FGCU Blvd., South 

Fort Myers, FL 33965-6565 

(239) 590-1000 

joshua.johnson@nist.gov

ABSTRACT

In this paper, we briefly describe the design of the Home Lift, 

Position and Rehabilitation (HLPR) Chair, invented at the 

National Institute of Standards and Technology (NIST), 

Manufacturing Engineering Laboratory (MEL) under the 

Healthcare Mobility Project. The HLPR Chair was designed to 

provide independent patient mobility for indoor tasks, such as 

moving to and placing a person on a toilet or bed, and lift 

assistance for tasks, such as accessing kitchen or other tall 

shelves. These functionalities are currently out of reach of most 

wheelchair users. One of the design motivations of the HLPR 

Chair is to reduce back injury, typically an important issue in the 

care of this group. Static and dynamic stability tests of the HLPR 

Chair prototype were also recently completed and are also 

described here. The tests followed the appropriate and current 

wheelchair standards and provide suggestions for improvement to 

these standards. While the Healthcare Mobility Project has 

recently ended, stability test methods of a lift wheelchair, such as 

the HLPR Chair, potentially overlap into forklift standard stability 

test methods and could be useful to the manufacturing industry. 

General Terms

Design, Performance, Experimentation, Standardization. 

Keywords

HLPR Chair, wheelchair standards, stability, forklift, static, 

dynamic. 

1. INTRODUCTION 

Reference [1] says “today, approximately 10 percent of the 

world’s population is over 60; by 2050 this proportion will have 

more than doubled” and “the greatest rate of increase is amongst 

the oldest old, people aged 85 and older.” She follows by adding 

that this group is subject to both physical and cognitive 

impairments more than younger people. These facts have a 

profound impact on how the world will maintain the elderly 

independent as long as possible from caregivers. Both physical 

and cognitive diminishing abilities address the body and the 

mental process of knowing, including aspects such as awareness, 

perception, reasoning, intuition and judgment. Assistive 

technology for the mobility impaired includes the wheelchair, lift 

aids and other devices, all of which have been around for decades. 

However, the patient typically or eventually requires assistance to 

use the device; whether it’s someone to push them in a 

wheelchair, to lift them from the bed to a chair or to the toilet or 

for guiding them through cluttered areas. With fewer caregivers 

and more elderly, there is a need for improving these devices to 

provide them independent assistance. 

There has been an increasing need for wheelchairs over time. 

L.H.V. van der Woude [2] states that mobility is fundamental to 

health, social integration and individual well-being of humans. 

Henceforth, mobility must be viewed as being essential to the 

outcome of the rehabilitation process of wheelchair dependent 

persons and to their successful (re-)integration into society and to 

a productive and active life. Thrun [3] said that, if possible, 

rehabilitation to relieve the dependence on the wheelchair is ideal 

for this type of patient to live a longer, healthier life. Van der 

Woude continues stating that many lower limb disabled subjects 

depend upon a wheelchair for their mobility. Estimated numbers 

for Europe and USA are 2.5 million and 1.25 million, 

respectively. The quality of the wheelchair, the individual work 

capacity, the functionality of the wheelchair/user combination, 

and the effectiveness of the rehabilitation program do indeed 

determine the freedom of mobility. 

Just as important as wheelchairs are the lift devices and people 

who lift patients into wheelchairs and other seats, beds, 

automobiles, etc. The need for patient lift devices will also 

increase as generations get older. When considering if there is a 

need for patient lift devices, several references state the positive, 

for example: 

• “The question is, what does it cost not to buy this equipment? 

A back injury can cost as much as $50,000, and that’s not even 

including all the indirect costs. If a nursing home can buy these 

lifting devices for $1,000 to $2,000, and eliminate a back injury 

that costs tens of thousands of dollars, that’s a good deal,” [4] 

• 1 in every 3 nurses becomes injured from the physical exertion 

put forth while moving non-ambulatory patients; costing their 

employers $35,000 per injured nurse. [5] (c) 2008 Association for Computing Machinery. ACM acknowledges 

that this contribution was authored or co-authored by a contractor or 

affiliate of the U.S. Government. As such, the Government retains a 

nonexclusive, royalty-free right to publish or reproduce this article, or to 

allow others to do so, for Government purposes only. 

PerMIS'08, August 19-21, 2008, Gaithersburg, MD, USA 

ACM ISBN 978-1-60558-293-1/08/08.

• 1 in 2 non-ambulatory patients falls to the floor and becomes 

injured when being transferred from a bed to a wheelchair. [6] 

• "Nursing and personal care facilities are a growing industry 

where hazards are known and effective controls are available," 

said OSHA Administrator John Henshaw. "The industry also 

ranks among the highest in terms of injuries and illnesses, with 

rates about 2 1⁄2 times that of all other general industries..." [7] 

302
• “Already today there are over 400,000 unfilled nursing 

positions causing healthcare providers across the country to 

close wings or risk negative outcomes. Over the coming years, 

the declining ratio of working age adults to elderly will further 

exacerbate the shortage. In 1950 there were 8 adults available 

to support each elder 65+, today the ratio is 5:1 and by 2020 the 

ratio will drop to 3 working age adults per elder person.” [8] 

Wheelchairs and patient lift devices have been built and are 

commercially available today. What has not been built, prior to 

the HLPR Chair, is a combined: intelligent, powered, liftwheelchair, geared towards home use that can provide 

independent or dependent patient transfer to beds, chairs, and/or 

toilets while also providing a support structure for rehabilitation. 

Similarly, there are no standards for such devices. [9] Therefore, 

NIST MEL developed the HLPR Chair to investigate this type of 

patient transfer device while advancing standards in this area. Of 

particular concern for safe operation of a device like HLPR Chair 

is its stability. The question here is: can the device meet current 

wheelchair standards and are there new standards that can be 

suggested for these devices as they become commercialized? 

This paper includes the HLPR Chair: design, specifications and 

recent static stability test descriptions and results. Conclusions 

and references close the paper. References [10, 11, 12, and 13] 

provide in-depth discussion of the HLPR Chair design and 

capabilities. 

2. HLPR CHAIR DESIGN 

The HLPR Chair [10, 11, 12, 13] prototype, shown in Figure 1, is 

based on a manual, steel, inexpensive, off-the-shelf, and sturdy 

forklift. The forklift includes a U-frame base with casters in the 

front and rear and a rectangular vertical frame. The lift and chair 

frame measures 58 cm (23 in) wide by 109 cm (43 in) long by 193 

cm (76 in) high (when not in the lift position) making it small 

enough to pass through even the smallest, typically 61 cm (24 in) 

wide x 203 cm (80 in) high, residential bathroom doors. The 

HLPR Chair frame could be made lighter with aluminum instead 

of steel. 

The patient seat structure is a double, nested and inverted L-shape 

where the outer L is a seat base frame that provides a lift and 

rotation point for the inner L seat frame. The L frames are made 

of square aluminum tubing welded as shown in the photograph. 

The outer L is bolted to the lift device while the inner L rotates 

with respect to the seat base frame at the end of the L as shown in 

Figure 1. The frame’s rotation point is above the casters at the 

very front of the HLPR Chair frame to allow for outside 

wheelbase access when the seat is rotated 180o and is the main 

reason access to other seats is available. Drive and steering 

motors, batteries and control electronics along with their 

aluminum support frame provide counterweight for the patient to 

rotate beyond the wheelbase. When not rotated, the center of 

gravity remains near the middle of the HLPR Chair. When 

rotated to 180o with a 136 kg (300 lb) patient on board, the center 

of gravity remains within the wheelbase for safe seat access. 

Heavier patients would require additional counterweight. 

The HLPR Chair is powered similarly to typical powered chairs 

on the market. Powered chairs include battery powered, drive and 

steer motors. However, the HLPR Chair has a tricycle design to 

simplify the need to provide steering and drive linkages and 

provide for a more vertical and compact drive system design. The 

drive motor is mounted perpendicular to the floor and above the 

drive wheel with chain drive to it with maximum speed set to 0.7 

m/s (27 in/s). The steering motor is coupled to an end cap on the 

drive motor and provides approximately 180o rotation of the drive 

wheel to steer the HLPR Chair. The front of the robot has two 

casters mounted to a U-shaped frame. 

3D imaging camera 

Color camera 

Rotation point 

Torso lifts 

Patient controls 

Retractable seat 

Retractable footrest 

Lift Actuator 

Casters 

Steel forklift frame Wheel encoders (1 of 2) 

Drive/Steering motors and wheel 

Batteries 

Load washer (future) 

Outer L-Frame 

 Inner L-Frame 

Figure 1: HLPR Chair Prototype 

Steering is a novel single wheel design hard stopping the wheel at 

just beyond 180o for safety of the steering system. Steering is 

reverse Ackerman controlled as joystick left rotates the drive 

wheel counterclockwise and joystick right rotates the drive wheel 

clockwise. The steering rotation amount can be limited by the 

amount of drive speed so as not to roll the frame during excessive 

speed with large steering rotation. 

Access to and from the HLPR Chair, lift, and rehabilitation 

configurations, as well as autonomous control efforts and designs 

are described in detail in [10, 11, 12, 13]. Two prototypes of the 

HLPR Chair have been built where the first version is used to 

study stability and autonomous control. The second was built to 

study ergonomics and manufacturability of the seat and sling 

designs. 

3. HLPR CHAIR SPECIFICATIONS 

Current specifications for the HLPR Chair are listed in Table 1. 

Weight was measured unloaded using a spring scale. Maximum 

payload was designed into the seat and frame structures. The 

manufacturer’s specifications of the manual forklift and lift 

actuator lists 227 kg and 454 kg (500 lb and 1000 lb), 

respectively. Maximum speed can be adjusted via the drive 

amplifier but has been set at 0.7 m/s (28 in/s). A conservative tilt 

estimate is shown in the table as 0.06 rad (10o) as determined 

using a CAD model of the HLPR Chair as previously shown in 

303
[13]. However, Stability tests, explained in Section 4, note a 

larger static tilt in some orientations. A future test of the battery 

per-charge range is expected. 

Table 1: HLPR Chair Specifications. 

4. STABILITY TESTS 

A test platform measuring 2.4 m x 1.2 m (8 ft x 4 ft) was recently 

designed and built, as shown in Figure 2, to perform static 

stability tests on the HLPR Chair. The platform, made of 

extruded aluminum framing and plywood base, was lifted with a 

hoist on one end. Safety straps attached to the facility structure 

were attached to the HLPR Chair during all tests. Slip prevention 

bars were also attached to the platform to prevent HLPR Chair 

from slipping down the ramp as the platform was tilted. 

 

Figure 2: Static Stability Test Set-up. 

For stability tests, we needed to verify safe operating parameters 

of HLPR Chair, including: maximum safe loading capabilities and 

angle of operation, braking/retardation capabilities, and lift height 

in relation to the payload. We followed existing wheelchair 

(patient mobility and transfer application) and forklift 

(manufacturing application) standards as a basis for the 

development of the stability tests. For wheelchair standards, we 

studied various ANSI/RESNA (American National Standards 

Institute)/(Rehabilitation Engineering and Assistive Technology 

Society of North America) and ISO (International Organization 

for Standardization) standards. Those standards were: 

• ANSI/RESNA WC/Vol. 1-1998 Wheelchairs- Volume 1: 

Requirements and test methods for wheelchairs (including 

scooters) 

• ISO 7176-1 Wheelchairs- Part 1: Determination of static 

stability 

• ISO 7176-2 "Wheelchairs- Part 2: Determination of dynamic 

stability of electric wheelchairs. 

For manufacturing, we studied the ISO 1074 Counterbalanced 

fork-lift trucks - Stability Tests standard. 

In the static stability tests the discrete tip angle was measured by 

placing a piece of paper under the tipping wheel as suggested by 

the above standards. When the paper could easily be removed 

from beneath the wheel, the angle was recorded. The test was not 

designed to measure mechanical failure or device durability using 

a payload of 114 kg (250 lbs). Instead, the discrete tip angle in 

the most and least stable configuration was tested. Factors 

included: load/lift height, load orientation, and HLPR orientation 

on the test platform. Load height was chosen to be a medium 

height of 1.3 m (4.2 ft) and a high height of 1.8 m (5.9 ft), the 

highest the HLPR Chair can lift. Figure 3 shows a series of 

example test configurations including the forward, lateral and rear 

configurations. Figure 4 shows a series of load or seat 

orientations including forward, side and rear orientations. Results 

of the static stability test are shown in Table 2. 

Figure 3: Photos of example test configurations, including: 

(left) forward, (middle) lateral, and (right) rear 

Safety Devices configurations. 

Hoist 

HLPR with 

payload 

Platform 

Slip Prevention 

 

Figure 4: Load/Seat Orientations of the HLPR Chair with 

respect to the frame including: (left) forward, (middle) side, 

and (right) rear orientations. 

304
Table 2: Static Stability Test Results. 

In future dynamic stability tests, we will be looking for loss of 

contact of the load-bearing wheels when the platform angle 

relative to horizontal is at 0, 0.05, 0.1, and 0.15 rad (0o, 3o, 6o, and 

9o, respectively). Results will be based on the severity of the lost 

wheel (drive, caster or stabilizer) contact with the ground as 

follows: 

• 3 – No Tip 

• 2- Transient Tip (lifting wheels lose contact then drop back 

onto the test plane 

• 1- Stuck on Anti-tip device 

• 0- Full Tip (device is π/2 (90°) or more from original 

orientation) 

Dynamic tests will include: 

• Rearward dynamic stability on a ramp 

• Forward dynamic stability on a ramp 

• Lateral dynamic stability on a ramp 

• Lateral dynamic stability while turning in circles 

• Lateral dynamic stability while turning suddenly 

• Dynamic stability while traversing a step 

Suggestions for changes or additions to current standards, 

regarding static stability tests, include: 

• “Loose” tie-down supports for the vehicle base to the ramp 

allowing wheel lift from the ramp without catastrophic tip, 

• Safety straps to support structures near or at the top of the 

lift-wheelchair, 

• Duplicate tests for aligned-seat-with-base-frame and various 

misaligned-seat-with-base-frame configurations. 

• The standard reads that the operator can currently use a sheet 

of paper beneath the lifted wheel caused by the tilted 

platform. Instead, suggested text stating to “use a paperretractor device (e.g., spring or rubber-band) attached to the 

paper under the wheel” will allow a safer, single operator for 

the static tests. 

Once dynamic tests are completed, further suggestions to 

wheelchair standards can be made. 

5. CONCLUSION 

The HLPR Chair has been prototyped in two versions. Static 

stability tests were completed on the first HLPR Chair prototype. 

The results proved higher than expected tilt angles. The second 

prototype has been loaned to the Florida Gulf Coast University as 

an example device for their Bio-Engineering Product Design 

Course. Improvements to the HLPR Chair design are the subject 

of the course. Future plans are to perform dynamic stability tests 

and to transfer the HLPR Chair design to the healthcare industry 

and to the manufacturing industry for semi-autonomous forklift 

control research. 

 18.4o (0.32 rad)__

 17.8o (0.31 rad)__

 17.3o (0.30 rad)__

 8.0o (0.14 rad)__

 8.1o (0.14 rad)__

 8.7o (0.15 rad)__

 >25o (>0.44 rad)_

 >25o (>0.44 rad)_

 >25o (>0.44 rad)_

12.9o (0.23 rad)__

12.7o (0.22 rad)__

12.2o (0.21 rad)__

4.9o (0.09 rad)__ 6. REFERENCES 4.8o (0.09 rad)__ [1] Pollack, Martha, Intelligent Technology for Adaptive Aging,

Presentation, AAAI-04 American Association for SArtificial 

Intelligence Conference Keynote Address, 2004. 

5.1o (0.09 rad)__

>25o (>0.44 rad)

>25o (>0.44 rad)

>25o (>0.44 rad) [2] L.H.V. van der Woude, M.T.E. Hopman and C.H. van 

Kemenade, Biomedical Aspects of Manual Wheelchair 

Propulsion: The State of the Art II, Volume 5, Assistive 

Technology Research Series, 1999, 392 pp., hardcover. 

[3] Thrun, Sebastian, Visit to Stanford University to discuss 

healthcare mobility devices, August 2006. 

[4] Marras, William, Lifting Patients Poses High Risk for Back 

Injuries, Ohio State University, 

http://researchnews.osu.edu/archive/resthome.htm, 1999. 

[5] Blevins, Healthcare Statistics: Blevins Medical, Inc., 

http://www.patientlift.net/282164.html, 2006. 

[6] U.S. Bureau of Labor Statistics, from Blevins website: 

http://www.patientlift.net/282164.html, 1994. 

[7] John Henshaw, http://www.osha.gov/SLTC/nursinghome/ 

solutions.html, Occupational Safety and Health 

Administration, 2005 

[8] Wasatch Digital iQ, InTouch Health's Remote Presence 

Robot Used by Healthcare Experts, http://www.wasatch 

digitaliq.com/parser.php?nav=article&article_id=43, Santa 

Barbara, CA & Salt Lake City --(Business Wire)--June 16, 

2003. 

[9] Bostelman, Roger; Albus, James, Survey of Patient Mobility 

and Lift Technologies Toward Advancements and Standards,

NISTIR #7384, 2006. 

[10] Bostelman, R., Albus, J., HLPR Chair – A Service Robot for 

the Healthcare Industry, 3rd International Workshop on 

Advances in Service Robotics, Vienna, Austria, July 7, 2006. 

[11] Roger Bostelman, James Albus, Tommy Chang, Tsai Hong, 

Sunil K. Agrawal, Ji-Chul Ryu, HLPR Chair: A Novel Indoor 

Mobility-Assist and Lift System, Proceedings of IDETC/CIE 

2007, ASME 2007 International Design Engineering 

Technical Conferences & Computers and Information in 

Engineering Conference, Las Vegas, Nevada, September 4-7, 

2007. 

[12] Bostelman, R., Albus, J., Sensor Experiments to Facilitate 

Robot Use in Assistive Environments, Proc. of the 1st 

International Conference on Pervasive Technologies Related 

to Assistive Environments (PETRA), Athens, Greece, July 

15-19, 2008. 

[13] Bostelman, R., Albus, J., Chang, T., Recent Developments of 

the HLPR Chair, Proc. of the 10th edition of the International 

Conference on Rehabilitation Robotics (ICORR 2007), 

Noordwijk aan Zee, Netherlands, June 13-15, 2007. 

305
Robotic Navigation in Crowded Environments: 

Key Challenges for Autonomous Navigation Systems 

James Ballantyne Salman Valibeik Ara Darzi Guang-Zhong Yang

Department of Biosurgery and Surgical Technology 

Institute of Biomedical Engineering 

Imperial College London 

London, United Kingdom 

ABSTRACT 

Crowded environments provide significant challenges for 

autonomous navigation systems. The robot must be fully aware of 

its surroundings and incorporate this knowledge into its decisionmaking and planning processes. The purpose of this paper is to 

outline major challenges that an autonomous navigation system 

needs to overcome to enable effective navigation in crowded 

environments such as hospital wards. We will discuss several key 

components of autonomous navigation systems to include 

localization and mapping, human-robot interaction, and dynamic 

object detection. 

Categories and Subject Descriptors

I.2.9 [Artificial Intelligence]: Robotics – Autonomous Vehicles, 

Sensors 

General Terms

Navigation Algorithms, Performance, Reliability, Verification. 

Keywords

Robotic navigation in crowded environments. 

1. INTRODUCTION 

Autonomous navigation systems aim to provide seamless 

integration of robots into everyday life. The robot must fully 

understand the environment and sense alterations and potential 

problems. Furthermore, interaction between humans and robots 

provides an important link that allows humans to help in difficult 

navigation situations. This paper outlines the current challenges 

that autonomous navigation systems must overcome before full 

immersion is possible. 

Developing accurate environment maps is one of the most 

difficult challenges for autonomous navigation systems. An 

accurate representation of the environment improves the 

capabilities of the robot in navigation and dealing with dynamic 

objects. The pre-requisite of the task is correct map creation while 

maintaining an accurate estimate of the pose of the moving robot. 

This is commonly referred to as the Simultaneous Localization 

and Mapping (SLAM) problem. The inclusion of dynamic objects 

can cause difficulties to SLAM, and therefore may require 

additional information to simplify the problem. 

One such source of information is Human-Robot Interaction 

(HRI), which can play a valuable role in preventing the robot 

from getting lost in crowded and highly congested areas. 

However, there are many difficulties involved in achieving 

successful human guided navigation including robust 

identification of human and human gestures. An effective means 

of establishing such communication can come from the 

identification of facial expression and eye-gaze. To this end, 

localizing the person with attention is necessary. This requires the 

detection and tracking of objects such as the face, eyes, hands, as 

well as the posture of the whole body. In a crowded environment, 

however, this is difficult due to scene complexity, constant 

occlusions of objects, and changes in lighting conditions due to 

inter-reflection and shadows. 

In SLAM, dynamic objects are the primary reason for failures if 

the majority of features tracked belong to the dynamic objects. 

Without the effective use of temporal information, the system can 

have difficulties in distinguishing dynamic and static parts of the 

environment. Therefore, dynamic object detection is essential. In 

a crowded environment, this also entails the segmentation of 

different moving objects as each of them can have different 

motion characteristics. In the following sections, we will review 

some of our approaches in dealing with the problems mentioned 

above. In particular, we will discuss issues related to motion 

planning and its dependency on SLAM, HRI, and dynamic object 

detection. 

2. SYSTEM HARDWARE SETUP 

To demonstrate our methods for navigation in crowded 

environments, a Mesa-Imaging SR-3000 [1] Time-of-Flight

camera and a Point Grey DragonFly2 [2] digital camera mounted 

on an ActivMedia PeopleBot [3] were used. The system set-up is 

Permission to make digital or hard copies of all or part of this work for illustrated in Figure 1. 

personal or classroom use is granted without fee provided that copies are 

not made or distributed for profit or commercial advantage and that copies 

bear this notice and the full citation on the first page. To copy otherwise, 

or republish, to post on servers or to redistribute to lists, requires prior 

specific permission and/or a fee. 

PerMIS’08, August 19–21, 2008, Gaithersburg, MD, USA. 

ACM ISBN 978-1-60558-293-1...$5.00.

The time-of-flight camera provides 4D information at frame rates 

up to 30fps. The sensor provides a pixel array of size 176×144, 

where each pixel provides x, y, z, and intensity information. The 

field of view of the camera is about 48 by 40 degrees of visual 

angle. We used a time-of-flight camera over the traditional laser 

range finder due to its compact size and high frame rate. The 

digital camera provides 648×488 RGB color images at 30 fps. For 

the HRI experiment, we used a lens with adjustable focal length 

306
between 3.5–8mm, while for SLAM, we used a fisheye lens with 

a 1.78 mm focal length. 

Figure 1. Experimental Setup; an Activmedia PeopleBot 

equipped with a Mesa-Imaging SR-3000 time-of-flight 

camera (right) and a Point Grey DragonFly2 camera (left) are 

used. 

3. LOCALIZATION AND MAPPING 

In an ideal situation, robots need to create accurate maps of the 

environment without the use of prior knowledge. SLAM has 

received significant attention [4, 5, 6, 7, 8, 9, 10, 11] in recent 

years and existing techniques can efficiently map large 

environments with high accuracy if the environment is static. 

Crowded environments present many difficulties for SLAM due 

to its reliance on static landmarks. The following example 

demonstrates the limitations of the existing solutions in a crowded 

and congested environment. Range-based SLAM systems are 

capable of mapping large-scale environments, both indoors and 

outdoors. However, these environments typically only have 

limited moving objects. Figure 2 shows both the scan line (top 

row) and intensity image (bottom row) taken from the time-offlight camera for a short video sequence, which gives insight into 

the fundamental challenge for range-based SLAM systems. The 

majority of the scan corresponds to dynamic objects (circled in 

red). This prevents scan matching algorithms from functioning 

correctly, thus forcing the system to fall back to odometry 

readings. In the initial map-building phase, scan-matching failures 

prevent the understanding of the environment due to a lack of 

knowledge of its location. Furthermore, even when the static 

objects exist in one frame, there is no guarantee that they will be 

visible in the next. 

Vision-based systems provide an alternative to range-based 

methods. They aim to identity landmarks in the environment for 

reliable matching to help determine the location of the robot in the 

environment. The key to feature-based methods is to identify high 

quality features that are easily recognizable from varying 

orientations and illumination conditions. For our investigation, we 

used an implementation of MonoSLAM [6], which has shown 

favorable results for indoor environments based only on 

Figure 2. The top row provides scan lines taken from the time-of-flight camera. A red circle identifies the dynamic areas of the 

environment, which were manually segmented. This short sequence illustrates the problem for range-based systems, where the lack of 

static information prevents scan matching. 

307
monocular vision. The system uses Shi and Tomasi feature 

detection [12] to identify salient regions. The acquired sequences 

were captured from a fisheye lens because features can remain 

visible for longer periods of time. 

Figure 3 illustrates some select image frames from two different 

sequences. The top row corresponds to the current image taken 

from the camera, while the bottom row illustrates the estimated 

movement as determined by the SLAM algorithm. The first 

sequence involved the robot travelling down a corridor with no 

dynamic objects in the field-of-view, while the second sequence 

shows the corresponding scene with a crowd of people. 

It is evident that the SLAM approach maintained an accurate 

estimation of the robot’s motion in the static scene. However, the 

system failed to track the movement of the robot accurately in the 

crowded environment. This occurred because the majority of 

features corresponded to the dynamic objects. As the objects 

moved, the system was not able to maintain enough features for 

accurate tracking. Even with a large field of view based on the 

fisheye lens, the static features remained scarce and many of 

which corresponded to the ceiling and lights, which could cause 

further problems if lighting condition changed. 

Figure 3. Top: a short sequence taken from a moving robot in a static scene. The SLAM algorithm correctly tracks the forward 

movement of the robot down the corridor. Bottom: a similar sequence but with a group of people in the corridor. In this case, the 

majority of tracked features belong to the moving people and for this reason the SLAM algorithm is unable to function during the 

initial map-building phase. 

The above results illustrate the main difficulties of the existing 

SLAM implementations in crowded environments. The main 

difficulties are involved in the initial map-building phase where 

the amount of usable sensor information is limited. In such 

situations, we propose the use of HRI and dynamic object 

detection to help with this initial phase in SLAM. HRI would 

allow humans to guide the robot through congested areas of the 

environment where it would be able to track its estimated position 

based on the movement of the person. Dynamic object detection 

could further improve the SLAM algorithm by segmenting out the 

dynamic information, leaving only static data for environment 

mapping. 

4. HUMAN-ROBOT INTERACTION 

Human guided navigation is used to allow the robot to learn from 

humans about a specific environment such that the domain 

specific knowledge acquired can be used for subsequent 

308
Figure 4. A probabilistic framework for face and gesture association. Top: the result of face detection (labeled with yellow rectangles). 

Middle: potential hand gestures identified with green rectangles. Bottom: data association based on normalized likelihood. In (a) and 

(b), the likelihood is correctly computed, whereas in (c) and (d) the correlation fails and further visual cues are required for correct data 

association. 

(a) (b) (c) (d) 

navigation. Currently, there are a number of difficulties involved 

in achieving successful human guided navigation. The main 

difficulty is in the robust identification of humans and 

establishing effective communication via visual cues involving 

facial expression, hand gestures and posture of the body. Face 

detection is a common method for identifying humans based on 

its distinctive geometrical and color features and limited pose 

variability with respect to other parts of the body [13, 14, 15]. 

However, existing methods are sensitive to illumination, size and 

orientation changes. Furthermore, the presence of multiple people 

in the environment can significantly increase the complexity of 

the algorithm. 

For commanding the robot, hand gesture detection is desirable as 

it best represents human-machine interaction [16, 17, 18]. This 

allows the robot to identify different gestures suitable for HRI. 

Most dynamic and static hand gesture recognition techniques rely 

on finding large hand silhouettes [18, 19], which is difficult in a 

crowded scene. To facilitate the association of hand silhouettes 

with the right person and his/her face, we have used a statistical 

method based on a fast and accurate face detection system as 

described by Kienzle et al [20]. Initially, we trained the system 

by segmenting the correlated faces and hands based on an 

observation factor O defined as: O = [Fwidth, Fheight, Hwidth, Hheight, 

D]. Where Fwidth and Hwidth represent the face and hand width, 

Fheight and Hheight indicate the face and hand height, 

and specifies the distance between the face and hand. The 

training data involves different gestures and movements. When a 

face was detected, we stored feature information for the hand 

silhouettes according to the observation factor. This then allows 

the creation of a Gaussian Mixture Model (GMM) to describe the 

statistical description of the gesture space given a detected face. 

D

For real-time deployment, the mean and covariance matrices can 

be used to identify the likely position of the hands after face 

detection. Figure 4 illustrates some example results from the 

GMM based on a real-time footage. Figures 4 (c) and (d) illustrate 

potential problems arisen in a crowded and dynamic environment. 

The correlation between hands and face was wrongly identified 

due to a large number of potential hand silhouettes. In contrast, 

Figures 4 (a) and (b) provide the correct correlation between the 

face and hand due to a less complicated environment. This 

highlights the difficulty of HRI in a crowded environment. 

5. DYNAMIC OBJECT DETECTION 

Another key component for autonomous navigation systems in 

crowded environments is dynamic object detection. This requires 

the system to segment the scene into static and dynamic objects. 

Segmentation can potentially help alleviate some of the 

drawbacks of SLAM. In our work, we have attempted two 

methods for dynamic object detection. Since our main sensor is 

309
range based, we have mainly focused on range-based frame 

differencing techniques. 

The goal of frame differencing is to distinguish static and 

dynamic objects by comparing the current frame with the 

previous one. The underlying principle regards the scene as static, 

therefore specifying objects as dynamic requires finding current 

occupied space that was previously unoccupied. We chose frame 

differencing due to its speed and low computation complexity. 

The focus of our investigation of dynamic object detection is how 

to enhance the power of SLAM. It should be noted that our intent 

is to detect the dynamic aspects of the scene on a frame-to-frame 

basis, although long-term tracking should further enhance the 

robustness of the results. As an example, we implemented a two 

dimensional system as described by Prassler et al [21]. The 

method used Time-Stamping Maps (TSM) to compare cells 

occupied in the current map, TSMt, against the previous map, 

TSMt-1. Any cells with no correspondence were considered 

dynamic. To prevent false moving object detection, groups of 

cells were created by linking neighboring cells. Then, if the 

majority of a group was moving, the whole group was marked as 

moving. 

To identify potential problems in crowded environments, we 

gathered sequences of images with a group of people in front of 

the robot while it performed simple rotations and translations. 

Figure 5 provides an example of five frames where the robot 

performed a small rotation to the right. The top row shows the 

scan line from the time-of-flight camera, while the bottom row 

shows the intensity image of the scene. This short sequence 

demonstrates the challenge of the detection systems in a crowded 

environment, where global and local motion separation is 

necessary. During rotation, static objects were highlighted as 

moving for two reasons. First, new information entered the field 

of view that was not visible in the previous image. Second, 

previously occluded objects became visible as other objects 

moved. 

The main problem stems from the lack of understanding of the 

robot motion. Since, the majority of the scene was moving, it was 

difficult to determine the robot’s motion. This prevented the 

correct projection of the previous frame into the current frame’s 

reference point. Thus, there are both false and missing detections. 

Figure 5. Top: the local occupancy grid from the time-of-flight camera. Bottom: the full scene as seen through the camera’s viewpoint. 

Cells colored in red correspond to detected dynamic objects in the environment. This short sequence illustrates the key challenge of 

handling both local and global motion. The figure shows incorrect labeling of both static and dynamic parts of the environment. 

As a second example, we implemented a 3D system where we 

performed a straight comparison of the current and previous 

images using 3D information taken from the time-of-flight 

camera. The algorithm worked as follows: 

1) Grab the current image. 

2) Project the previous image into the current field of 

reference. 

3) Mark pixels as moving if there is a difference in depth 

between current and previous. 

4) Perform a flood-filling algorithm to highlight the full 

object. 

To project the previous image into the current frame of reference, 

we first converted the depth map to the world coordinate system 

using the estimated pose from odometry. Then, we computed a 

reverse projection onto the current coordinate system using the 

method described by Stipes et al [22]. Finally, we compared each 

pixel in the projected image against the current image. Any pixels 

that did not match within a certain threshold (0.1m for this study) 

were marked as dynamic. The final step highlighted the full object 

using a flood-filling algorithm based on depth. 

The top row of Figure 6 presents three consecutive frames to 

highlight one of the problems for 3D frame differencing. As the 

robot rotates to the right with several moving objects, the system 

incorrectly labeled objects due to inaccuracies in the estimated 

pose, which causes errors in the reverse projection. 

The bottom row of Figure 6 highlights the second difficulty for 

the frame differencing algorithms and dynamic object detection, 

which is the cancellation of global and local motion causing 

310
missing dynamic objects. The above examples outline the 

importance of global and local motion separation. 

6. MOTION PLANNING 

The final component for an autonomous navigation system is the 

perceived intelligence of the robot. The goal of any path planning 

system is to devise efficient and effective plans to complete any 

given task. The system must do this in such a way to avoid 

running into objects whether static or dynamic. The path planning 

system mainly consists of local and global navigation. Local 

navigation, often called reactive control, learns or plans local 

paths using only the current sensory input and no prior knowledge 

of the environment. Global navigation, often termed as deliberate 

control, learns or plans global paths using the system’s current 

knowledge of the environment. 

Local navigation or reactive control systems mainly devise plans 

to navigate locally. The system uses only the current sensory 

input without any prior knowledge of the environment. The 

system performs tasks such as obstacle avoidance and point-topoint moving. Some examples of reactive control approaches are 

potential fields [23] and virtual force fields [24]. 

These basic reactive control systems can be extended to full 

behavioral systems [25, 26, 27, 28, 29] where the goal is to design 

a list of acceptable behaviors for the robot. Examples of 

behavioral control architectures are fuzzy logic, neural networks, 

evolutionary computation, and reinforcement learning. The major 

hurdle for reactive systems is the lack of prior knowledge. 

The effectiveness of local navigation relies on the understanding 

of dynamic objects. It is not feasible for the system to determine 

safe paths through the environment without fully understanding 

the motion of other objects involved. If accurate dynamic 

detection methods are available, intelligent local avoidance 

systems can be created, such as the system by Berg et al [30]. 

Figure 6. Top: an illustration of the errors introduced due to global motion in a crowded environment based on 3D frame differencing. 

Bottom: errors introduced due to global and local motion, where the two cancel out each other, thus preventing the correct 

identification of moving objects. 

HRI provides alternative ways to improve local navigation. With 

increasing complexity of the environment, even advanced 

dynamic object detection system can fail. Furthermore, the 

unpredictability of humans can further disrupt local navigation. 

Therefore, a reliable HRI system can safely help a robot navigate 

through even the most complex environments. 

Global navigation or deliberate control systems attempt to 

generate global paths based on the current knowledge of the 

environment. These systems are concerned with generating paths 

or plans for the robot to complete any given task. The success of 

the global planner relies on the assumption that the environment 

map is accurate. Without an accurate map, the robot is unable to 

complete any given task due to lack of knowledge of its 

surroundings. With a full representation of the environment, there 

are many available planning algorithms. Both Latombe [31] and 

LaValle [32] give comprehensive reviews of potential solutions. 

Therefore, without an accurate SLAM system, global navigation 

is difficult to achieve. 

7. FUTURE WORK 

This paper illustrates some of the key challenges for robotic 

navigation in crowded and congested environments. We have 

concentrated our discussion on the initial phase of autonomous 

navigation for understanding the environment. It has been shown 

that the SLAM approach is challenging for both the range and 

vision based systems due to the lack of sufficiently accurate static 

information in the scene at any given time. Dynamic objects (e.g., 

people within the scene) can further confuse the system. To avoid 

these difficulties, it is useful to incorporate explicit HRI to rule 

out some of the intrinsic ambiguities in navigation. To this end, 

the reliable of tracking human gesture, expression is necessary. 

311
8. REFERENCES 

[1] Mesa-Imaging, "http://www.mesa-imaging.ch." 

[2] "Point Grey Research," 

http://www.ptgrey.com/products/dragonfly/index.asp. 

[3] "Mobile Robots: ActivMedia Robotics," 

http://www.activrobots.com/. 

[4] Hähnel., D., Burgard, W., Fox, D. and Thrun, S., "An 

efficient FastSLAM algorithm for generating maps of largescale cyclic environments from raw laser range 

measurements," in IEEE/RSJ International Conference on 

Intelligent Robots and Systems (IROS), Las Vegas, NV, 

USA, 2003, pp. 206-211. 

[5] Thrun, S., Liu, Y., Koller, D., Ng, A., Ghahramani, Z. and 

Durrant-Whyte, H., "Simultaneous Localization and 

Mapping with sparse extended information filters," 

International Journal of Robotics Research, vol. 23, pp. 693-

716, 2004. 

[6] Davison, A. J., Reid, I. D., Molton, N. D. and Stasse, O., 

"MonoSLAM: Real-Time Single Camera SLAM," IEEE 

Transactions on Pattern Analysis and Machine Intelligence, 

vol. 29, pp. 1-16, 2007. 

[7] Montemerlo, M., Koller, S. T. D. and Wegbreit, B., 

"FastSLAM 2.0: An improved particle filtering algorithm for 

simultaneous localization and mapping that provably 

converges," in International Conference on Artificial 

Intelligence (IJCAI), Acapulco, Mexico, 2003, pp. 1151-

1156. 

[8] Murphy, K., "Bayesian map learning in dynamic 

environments," in Conference on Neural Information 

Processing Systems (NIPS), Denver, CO, USA, 1999, pp. 

1015-1021. 

[9] Montemerlo, M., Thrun, S., Koller, D. and Wegbreit, B., 

"FastSLAM: A Factored Solution to the Simultaneous 

Localization and Mapping Problem," in National Conference 

on Artificial Intelligence, Edmonton, Alberta, Canada, 2002, 

pp. 593-598. 

[10] Grisetti, G., Tipaldi, G. D., Stachniss, C., Burgard, W. and 

Nardi, D., "Fast and Accurate SLAM with RaoBlackwellized Particle Filters," Robotics and Autonomous 

Systems, vol. 55, pp. 30-38, 2007. 

[11] Eliazar, A. and Parr, R., "DP-SLAM: Fast, robust 

simultaneous localization and mapping with predetermined 

landmarks," in International Conference on Artificial 

Intelligence (IJCAI), Acapulco, Mexico, 2003, pp. 1135-

1142. 

[12] Shi, J. and Tomasi, C., "Good Features to Track," in IEEE 

International Conference on Computer Vision and Pattern 

Recognition, 1994. 

[13] Li, S. Z. and Zhenqiu, Z., "FloatBoost learning and statistical 

face detection," Pattern Analysis and Machine Intelligence, 

IEEE Transactions on, vol. 26, pp. 1112-1123, 2004. 

[14] Chengjun, L., "A Bayesian discriminating features method 

for face detection," Pattern Analysis and Machine 

Intelligence, IEEE Transactions on, vol. 25, pp. 725-740, 

2003. 

[15] Ming-Hsuan, Y., Kriegman, D. J. and Ahuja, N., "Detecting 

faces in images: a survey," Pattern Analysis and Machine 

Intelligence, IEEE Transactions on, vol. 24, pp. 34-58, 2002. 

[16] Xia, L. and Fujimura, K., "Hand gesture recognition using 

depth data," in Automatic Face and Gesture Recognition, 

2004. Proceedings. Sixth IEEE International Conference on, 

2004, pp. 529-534. 

[17] Hasanuzzaman, M., Ampornaramveth, V., Tao, Z., Bhuiyan, 

M. A., Shirai, Y. and Ueno, H., "Real-time Vision-based 

Gesture Recognition for Human Robot Interaction," in 

Robotics and Biomimetics, 2004. ROBIO 2004. IEEE 

International Conference on, 2004, pp. 413-418. 

[18] Ying, W. and Huang, T. S., "Hand modeling, analysis and 

recognition," Signal Processing Magazine, IEEE, vol. 18, pp. 

51-60, 2001. 

[19] Yuanxin, Z., Haibing, R., Guangyou, X. and Xueyin, L., 

"Toward real-time human-computer interaction with 

continuous dynamic hand gestures," in Automatic Face and 

Gesture Recognition, 2000. Proceedings. Fourth IEEE 

International Conference on, 2000, pp. 544-549. 

[20] Kienzle, W., Bakir, G., Franz, M. and Schölkopf, B., "Face 

Detection - Efficient and Rank Deficient," 2005. 

[21] Erwin Prassler, J. S., Alberto Elfes, "Tracking Multiple 

Moving Objects for Real-time Robot Navigation," 

Autonomous Robots, vol. 8, pp. 105-116, April 2000. 

[22] Stipes, J. A., Cole, J. G. P. and Humphreys, J., "4D Scan 

Registration with the SR-3000 LIDAR," in IEEE 

International Conference on Robotics and Automation 

(ICRA), Pasadena, CA, USA, 2008. 

[23] Khatib, O., "Real-time obstacle avoidance for manipulators 

and mobile robots," International Journal of Robotics 

Research, vol. 5, pp. 90-98, 1986. 

[24] Borenstein, J. and Koren, Y., "Real-time Obstacle avoidance 

for fast mobile robot," IEEE Transactions on Systems, Man, 

and Cybernetics, vol. 19, pp. 1179-1187, 1989. 

[25] Zhu, A. M., Yang, S. X., Wang, F. J. and Mittal, G. S., "A 

neuro-fuzzy controller for reactive navigation of a behaviorbased mobile robot," Lecture Notes Computer Science, vol. 

3498, pp. 259-264, 2005. 

[26] Thrun, S., "Probabilistic algorithms for robotics," in AI 

Magazine. vol. 21, 2000, pp. 93-109. 

[27] Kondo, T. and Ito, K., "A Reinforcement learning with 

evolutionary state recruitment strategy for autonomous 

mobile robots control," Robotic Autonomous Systems, vol. 

46, pp. 111-124, 2004. 

[28] Chen, C., Li, H.-X. and Dong, D., "Hybrid Control for Robot 

Navigation," in IEEE Robotics & Automation Magazine, 

2008. 

[29] Chen, C. L. and Chen, Z. H., "Reinforcement learning for 

mobile robot: From reaction to deliberation," Journal of 

System Engineering Electronics, vol. 16, pp. 611-617, 2005. 

[30] Berg, J. V. D., Patil, S., Sewall, J., Manocha, D. and Lin, M., 

"Interactive navigation of multiple agents in crowded 

environments," in Proceedings of the 2008 symposium on 

Interactive 3D graphics and games, Redwood City, CA 

USA, 2008, pp. 139-147. 

[31] Latombe, J.-C., Robot Motion Planning. Norwell, MA, USA: 

Kluwer, 1991. 

[32] LaValle, S. M., "Planning Algorithms [Online]," in 

http://planning.cs.uiuc.edu/, 2006. 

312