Terrain Representation Methods in VR Environment
Koji Makanae

Morio Nakahara

Miyagi University
1 Gakuen, Taiwa, Miyagi, Japankoji@makalab.org

Graduate student, University of Tsukuba
Tsukuba, Ibaraki, Japan
nakahara@image.esys.tsukuba.ac.jp

Abstract
This paper describes methods for visual 3D representation using VR technology and introduces the terrain representation methods that the authors have developed and some of the application systems using those methods.
Furthermore the tangible terrain representation system which has been worked on is shown against the problems of conventional methods. The paper also discusses possibilities of further development of terrain representation systems, positioning 3D terrain representation systems.
Keywords
Terrain representation, Tangible display, Virtual Reality, DEM, VR-CAD

1. INTRODUCTION
Recent advances in the development and disseminationof spatial information have made it possible to obtain anduse various types of spatial information easily. It is also
becoming possible to obtain and use topographic information on a global scale. Topographic information is inmany cases provided in the form of mesh data such asUSGS Digital Elevation Models (DEM) . Such information may be provided by, for example, representing different elevations and slopes with different colors, generating contours from mesh data, generating shaded-relief
maps automatically or using bird's-eye views prepared byprojection transformation for 3D representation. Thesemethods, however, represent terrains in two dimensions
on the computer display, instead of as three-dimensional
objects as in the real world. These representation methods, therefore, make it difficult to understand topographic relief intuitively. To solve this problem, the authors have been working on the research and development of methods for representing virtual terrain surfaces
defined on the computer by applying virtual reality (VR)technology and of systems that can be realized by applying those methods.
This paper describes methods for visual 3D representation using VR technology and introduces the terrain representation methods that the authors have developed andsome of the application systems using those methods.
The paper also discusses possibilities of further development of terrain representation systems, positioning 3Dterrain representation systems.
2. VR-BASED VISUAL 3D REPRESENTATIONMETHOD
Virtual reality (VR) is a technology to experience a realistic virtual world defined on the computer. The technology uses an interface making effective use of stereoscopic visualization made possible by means of the two

human eyes in order to visually enhance the degree ofreality.
The mechanism by which a human visually recognizes
the three-dimensional configuration of an object involves
two types factors: physiological factors and psychological factors. Physiological factors, which are due to thefunctions of the human eye, include the focus adjustment
function of the lens, eye convergence, binocular parallax
and monocular motion parallax. Psychological factors,
which help reconstruct 3D images from experience, areclassified either as geometric or optical. Among thesefactors, binocular parallax, which is one of the physiological factors, is generally thought to be most importantin 3D perception.
The stereoscopic visualization technology used in thefield of virtual reality is based mainly on 3D perception
caused by binocular parallax. If the locations of the eyesof a human viewer are determined in a virtual space defined on the computer, a pair of perspective images justlike images that would be perceived by the two humaneyes can be obtained by applying computer graphics(CG) technology. By giving the perspective images thus
obtained to the two eyes of a human viewer, the viewer
can be made to perceive the images as a 3D object. Devices for giving different images to the left and right human eyes have been developed during the evolution ofvirtual reality technology. Representative examples ofsuch devices are stereoscopic eyeglasses with liquid crystal shutters, 3D displays, head-mounted displays (HMD)
and immersive displays.
1.

Stereoscopic eyeglasses with liquid crystal shutters
A stereoscopic eyeglasses system with crystal liquid
shutters provides different images to the left and righteyes by displaying images for the left and right eyes
alternately at high speed on a single CRT display andsynchronizing those images with the liquid crystal
shutters of the stereoscopic glasses. Because the display area is fixed on the display system, the user is
not allowed to move around.
2.

3D display system:
A 3D display makes it possible to have stereoscopic
views with the naked eye by using binocular parallax
and eye convergence. Like the stereoscopic eyeglasses method, this method does not allow the user
to move around. Recent advances in technology,
however, have been rapidly making inexpensive systems available on the market.

3.

Figure 1 The configuration of HRPS

3D display system:
A 3D display makes it possible to have stereoscopic
views with the naked eye by using binocular parallax
and eye convergence. Like the stereoscopic eyeglasses method, this method does not allow the user
to move around. Recent advances in technology,
however, have been rapidly making inexpensive systems available on the market.

4.

3D display system
A representative example of an immersive display
system is an IPT (immersive projection technology)
device called the "CAVE" (Cave Automatic VirtualEnvironment) developed by the University of Illinois[Cruz93]. In the CAVE, 3D images can be projected
onto about 3m by 3m screens placed at the left andright and at the front of the user and on the floor sothat the user can immerse herself or himself into the3D visualization environment. The CAVE is advantageous because it provides a wider field of view thanthe HMD and does not require image generation synchronized with movement, so problems such as a delay in image generation do not occur.

In recent years, research and development efforts associated with mixed reality, which aims to integrate virtual
space and real space have also been underway. One ofthese efforts is the research and development of tangibleinterface. The MIT Media Laboratory, for example, hasdeveloped a system called "Illuminated Clay," which
projects information onto a terrain surface created withclay [Piper02].
3. TERRAIN REPRESENTATION AND DESIGNSUPPORT SYSTEMS DEVELOPED TO DATE
The authors have been working to develop terrain representation methods making use of VR technology andconstruct design support systems using these methods.
This paper describes (1) a road design support systemthat uses stereoscopic visualization of aerial photographsand (2) a terrain representation and urban space modelingsystem that uses an HMD, both of which have been developed by the authors, along with problems of thesesystems.

Figure 2 Interface of HRPS
3.1 Highway Route Planning System Using
Stereoscopic Visualization of Aerial Photographs
Makanae[Makanae02] has developed a system (HRPS;Highway Route Planning System) that acquires terrain
images through the stereoscopic visualization of aerial
photographs and enables road design. Aerial photographimages taken into the computer in the form of digital
information are shown on the display of a stereoscopic
viewer (CrystalEyes2 manufactured by Stereo Graphics,Inc.) as information that can be visualized stereoscopically (Figure 1). A coordinate system identical to thestereoscopic visualization space obtained by aerial photograph orientation is defined on the computer, and roaddesign is conducted in this 3D virtual space. Parametriccurves (B-spline) are used to define road alignments, andcontrol points are located within the space so that theiralignments can be defined easily.
Figure 2 shows the interface of the system. A 3D modelof each road structure is automatically generated according to the alignment defined on the aerial photograph,and plans, longitudinal profiles and perspectives can bedisplayed.
An advantage of this system is that it allows an engineer
who is good at interpreting topographic characteristics(e.g., landslides) from aerial photographs to directly determine road alignments with the assistance of a roaddesign module that uses parametric curves. This is particularly advantageous in, for example, designing mountain roads under poor topographic conditions. By making
direct use of aerial photographs, unnecessary mapping
processes can be eliminated. A problem with this systemis the applicability of road alignments determined byusing parametric curves to the current design standard.
Another problem is that the relationship between con-structed road structures and the terrain surface represented in a virtual 3D visualization space cannot be computed.
3.2 Terrain representation method using HMD:VR-CAD system
In the conventional drawing-based space design method,
the designer constructs 3D configurations in his or her
mind while preparing drawings. VR technology, however,makes it possible to define any 3D virtual space on thecomputer. The VR-CAD system developed by Makanae[Makanae03] enables the designer to immerse himself or
herself into a virtual space constructed on the computer.
In the virtual space, the designer can exist on any scale:the designer can enter the space either as a correctly
scaled human figure or as a giant. The system also enables the designer to conduct 3D design without relying
on the 2D/3D conversion capability of the designer.
The system consists of a head-mounted display (HMD)
and 3D position sensors (Figure 3). By combining theHMD and a position sensor, the position and orientationof the head can be measured and appropriate images canbe displayed so that the design has a 360-degree field ofview both in the horizontal direction and in the verticaldirection.
Since the system is intended for use in constructing large
structures such as roads, terrain information is essential.
Elevation data (50 m mesh) in Digital National Land Information are used as 3D terrain models for terrain representation in the virtual space. The modeling input interface of the VR-CAD system has a 3D mouse and keyboard equipped with a position sensor. These devices
enable 3D modeling of such features as buildings (rectangular prisms, cylinders), roads and trees by simple
operations. Known problems of the design interface of
this system include the difficulty in perceiving the position of the 3D cursor and the difficulty in comprehending
the relative positions of the terrain surface and the objectof interest [Makanae03].

Figure 3 The configuration of VR-CAD
of 64 actuators (8×8) and projecting an aerial photographonto the screen. Mesh data of Digital National Land Information(Japan) are used as terrain data, and the heightof each actuator is determined according to the mesh datavalues.
Figure 5 shows an example of a terrain represented byusing the system. The terrain model onto which an aerial
photograph is projected is a touchable terrain model. As
the next steps, the authors are thinking of evaluating thevalidity of the terrain representation system and constructing design support systems for roads and otherstructures by adapting the existing system.
5. OUTLOOK FOR TERRAIN REPRESENTATIONSYSTEMS

Difficulty in comprehending the relative positions of
the terrain surface and the object of interest

The ongoing development and dissemination of spatial
information are making it increasingly easier to obtainand use digital terrain information. Obtained terrain information, however, can only be displayed in a limitedarea of a flat display device. Consequently, it is difficult
to give the viewer a sense of three-dimensionality and asense of scale. The authors have been working on thedevelopment of the systems described in Sections 3 and 4.
Requirements for a terrain representation system identified in view of the problems encountered in connection
with the development of those systems are as follows:

Need for a special stereoscopic visualization device1.

Limited field of viewNot usable for group work

4. DEVELOPMENT OF TANGIBLE TERRAIN
REPRESENTATION SYSTEM
Problems of the terrain representation and design support
systems include the following:

Believing that the introduction of a tangible interface
helps solve these problems, the authors have been working on the construction of a tangible terrain representation system.
Figure 4 shows the configuration of the terrain representation system. As shown, the system represents a terrain
surface by controlling the shape of a stretchable screen
used to represent the terrain surface by means of a total

Recognition of the three-dimensionality of terrain
surfaces is easy.

2.. The user does not need to wear any special device
such as stereoscopic glasses or HMDs.
3. Reconstructed terrain surfaces can be matched withdigital information.
4. Various types of information can be superimposed.
The first requirement is one of the basic requirements fora terrain representation system, so it is necessary to makea higher degree of three-dimensional recognition possible.
The second requirement is listed here because the use ofA

BCDEFGHSELECTED
ON-LINEFigure 4 The configuration of the terrain representation system.
special equipment may cause fatigue or sickness, making
many hours of use difficult. The use of special equipment
should be avoided as much as possible. The third requirement is important because in order to develop an
application system, it is necessary to extract a particularpoint on a virtual terrain surface in digital form. The
fourth requirement is also important because the terrain
representation system can be used effectively by superimposing not only aerial photographs but also other datasuch as land use data and city plans on the reconstructedterrain surface.
Examination of these requirements indicates that the following systems are thought to be promising in the coming years:
1. Tangible terrain representation system
The tangible terrain representation system that the authors are currently developing can satisfy all of the four
requirements listed above. The system, however, is stillat the development stage, and it is necessary to further
enhance the resolution of terrain representation and develop equipment and devices that can be easily used evenby non-expert users. It is also necessary to develop apointing device for use on a virtual terrain.
2. Terrain representation system using rapid prototyping
Recent advances in CAD/CAM technology has madepossible fast advances in rapid prototyping technology tomake real 3D models from resin or other materials inaccordance with 3D data prepared as CAD data. In recentyears, this technology has been increasingly used to maketerrain models more easily than by other methods. Problems of terrain representation systems of this type include
the difficulty in getting feedback from completed terrain
models to electronic information and the necessity of thedevelopment of pointing devices as in the case of tangible terrain representation systems described above 1.
3. Terrain representation system with 3D display
A 3D display enables the user to have three-dimensionalrecognition without using special equipment. A terrain
representation system with a 3D display is being developed and used at the authors' laboratory, and the system
has proved effective in giving a strong sense of threedimensionality. The system satisfies the first, second andfourth requirements mentioned above although the degree of strength varies among individuals. A problem ofFigure 5 An example of a terrain

this system concerns the matching of the virtual terrain
surface and digital terrain information (related to thethird requirement mentioned above), so it is difficult toindicate a particular point on the terrain surface accurately.
6. CONCLUSION
This paper has introduced a number of methods for reconstructing terrains from digital terrain information thatthe authors have developed, and application systems using the terrain representation methods. The paper has
also identified requirements for a terrain representation
system to be used as a GIS tool and has described terrain
representation systems that are likely to prove useful inthe coming years.
At present, the representation of digital terrain information is restricted by 2D display devices. With further advances in representation and control technology madepossible by the progress of VR technology and robotics,
however, more realistic and easier 3D terrain representation will become possible. The authors believe that advances in terrain representation technology can contribute to not only research in the fields of technology andscience such as geography, geology and civil engineering
but also CAD interfacing in the field of construction, andalso to a wide range of other applications such as geographic education.
7. REFERENCES[Cruz93] C. Cruz-Neira, D.J.Sandin, Defanti, T.A. Surroud-Screen Projection-Based Virtual Reality: The
Design and Implementation of the CAVE. Proceedings of SIGGRAPH’93, 135-142, 1993.
[Makanae02]K. Makanae. Stereoscopic Systems for 3-D
Highway Route Planning on Aerial Photo-graphs, International Journal of Design Sciences & Technology,
Vol.9-1, 15-22. Europia Productions, 2002.
[Makanae03]K.Makanae. Development of the VR-CAD
System for Landscape and Town Planning. Proceedings of the CONVR2003, Virginia Tech, 114-121,2003.
[Piper02]B.Piper, C.Ratti, H.Ishii. Illuminating Clay: A
3-D tangible interface for landscape analysis. In Proceedings of the Conference on Human Factors in
Computing Systems (CHI’02) 20–25 April, Minneapolis, 2002.