bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Method of Image Mosaicking and Its Application to Cultural Heritage Representation
Authors: Cortelazzo G.M. , Lucchese L.
Published: March 2003

This paper presents an original two‐step procedure for estimating projective transformations between pairs of images: first, the transformation between the images is approximated as an affine transformation; second, this estimate is refined into that of a projective transformation. This strategy for matching projective views is computationally very efficient. The proposed method can be applied both to mosaicking of high resolution images of planar textured objects (e.g., frescoes and paintings), with subpixel accuracy, and to construction of panoramic images. Practical examples of mosaicking of cultural heritage imagery obtained by using the presented procedure are discussed in the paper.
Fast Lines: a Span by Span Method
Authors: Boyer V. , Bourdin J.J.
Published: March 2003

Straight line’s scan conversion and drawing is a major field in computer graphics. Algorithm’s time computation is very important. Nowadays, most of research papers suggest improvements of the DDA method that was first presented by J. Bresenham. But other approaches exist as well like combinatory analysis and linguistic methods. Both of them use multiple string copies that slow down the efficiency of the algorithms. This paper proposes a new algorithm based on a careful analysis of the line segments’ properties some of them previously unused. Our algorithm is proved significantly faster than previously published ones.
Metis – An Object‐Oriented Toolkit for Constructing Virtual Reality Applications
Authors: Turner Russell , Li Song , Gobbetti Enrico
Published: March 2003

Virtual reality systems provide realistic look and feel by seamlessly integrating three‐dimensional input and output devices. One software architecture approach to constructing such systems is to distribute the application between a computation‐intensive simulator back‐end and a graphics‐intensive viewer front‐end which implements user interaction. In this paper we discuss Metis, a toolkit we have been developing based on such a software architecture, which can be used for building interactive immersive virtual reality systems with computationally intensive components. The Metis toolkit defines an application programming interface on the simulator side, which communicates via a network with a standalone viewer program that handles all immersive display and interactivity. Network bandwidth and interaction latency are minimized, by use of a constraint network on the viewer side that declaratively defines much of dynamic and interactive behavior of the application.
Modeling and Rendering Escher‐Like Impossible Scenes
Authors: Savransky Guillermo , Dimerman Dan , Gotsman Craig
Published: March 2003

Inspired by the drawings of “impossible” objects by artists such as M.C. Escher, we describe a mathematical theory which captures some of the underlying principles of their work. Using this theory, we show how impossible three‐dimensional scenes may be modeled and rendered synthetically.
Reflectance Models with Fast Importance Sampling
Authors: Neumann László , Neumann Attila , Szirmay‐Kalos László
Published: March 2003

We introduce a physically plausible mathematical model for a large class of BRDFs. The new model is as simple as the well‐known Phong model, but eliminates its disadvantages. It gives a good visual approximation for many practical materials: coated metals, plastics, ceramics, retro‐reflective paints, anisotropic and retro‐reflective materials, etc. Because of its illustrative properties it can be used easily in most commercial software and because of its low computational cost it is practical for virtual reality. The model is based on a special basic BRDF definition, which meets the requirements of reciprocity and of energy conservation. Then a class of BRDFs is constructed from this basic BRDF with different weight functions. The definition of such weight functions requires the user to specify the profile of the highlights, from which the weight function is obtained by derivation. It is also demonstrated how importance sampling can be used with the new BRDFs.
External Memory View‐Dependent Simplification
Authors: El‐Sana Jihad , Chiang Yi‐Jen
Published: March 2003

In this paper, we propose a novel external‐memory algorithm to support view‐dependent simplification for datasets much larger than main memory. In the preprocessing phase, we use a new spanned sub‐meshes simplification technique to build view‐dependence trees I/O‐efficiently, which preserves the correct edge collapsing order and thus assures the run‐time image quality. We further process the resulting view‐dependence trees to build the meta‐node trees, which can facilitate the run‐time level‐of‐detail rendering and is kept in disk. During run‐time navigation, we keep in main memory only the portions of the meta‐node trees that are necessary to render the current level of details, plus some prefetched portions that are likely to be needed in the near future. The prefetching prediction takes advantage of the nature of the run‐time traversal of the meta‐node trees, and is both simple and accurate. We also employ the implicit dependencies for preventing incorrect foldovers, as well as main‐memory buffer management and parallel processes scheme to separate the disk accesses from the navigation operations, all in an integrated manner. The experiments show that our approach scales well with respect to the main memory size available, with encouraging preprocessing and run‐time rendering speeds and without sacrificing the image quality.
Robust Motion Watermarking based on Multiresolution Analysis
Authors: Kim Tae‐hoon , Lee Jehee , Shin Sung yong
Published: March 2003

Digital watermarking is one of commonly used solutions for copyright protection. A watermark should be imperceptible and robust to various attacks. In this paper, we address watermarking for motion data. Our watermarking scheme is based on two well‐known ideas, so called multiresolution representation and spread spectrum. We embed a watermark into a motion signal by perturbing large detail coefficients of its multiresolution representation, and extract the watermark by analyzing perturbation of coefficients from a suspected signal. For more effective watermark extraction, we align suspected motion data to the original using dynamic time warping. Our scheme has merits of spread spectrum such as the resilience to common signal processing as well as the robustness to time warping.
Fast Volume Rendering and Data Classification Using Multiresolution in Min‐Max Octrees
Authors: Dong Feng , Krokos Meleagros , Clapworthy Gordon
Published: March 2003

Large‐sized volume datasets have recently become commonplace and users are now demanding that volume‐rendering techniques to visualise such data provide acceptable results on relatively modest computing platforms. The widespread use of the Internet for the transmission and/or rendering of volume data is also exerting increasing demands on software providers. Multiresolution can address these issues in an elegant way. One of the fastest volume‐rendering alrogithms is that proposed by Lacroute & Levoy 1 , which is based on shear‐warp factorisation and min‐max octrees (MMOs). Unfortunately, since an MMO captures only a single resolution of a volume dataset, this method is unsuitable for rendering datasets in a multiresolution form. This paper adapts the above algorithm to multiresolution volume rendering to enable near‐real‐time interaction to take place on a standard PC. It also permits the user to modify classification functions and/or resolution during rendering with no significant loss of rendering speed. A newly‐developed data structure based on the MMO is employed, the multiresolution min‐max octree, M 3 O, which captures the spatial coherence for datasets at all resolutions. Speed is enhanced by the use of multiresolution opacity transfer functions for rapidly determining and discarding transparent dataset regions. Some experimental results on sample volume datasets are presented.
Integrating Occlusion Culling and Levels of Detail through Hardly‐Visible Sets
Authors: Andújar Carlos , Saona‐Vázquez Carlos , Navazo Isabel , Brunet Pere
Published: March 2003

Occlusion culling and level‐of‐detail rendering have become two powerful tools for accelerating the handling of very large models in real‐time visualization applications. We present a framework that combines both techniques to improve rendering times. Classical occlusion culling algorithms compute potentially visible sets (PVS), which are supersets of the sets of visible polygons. The novelty of our approach is to estimate the degree of visibility of each object of the PVS using synthesized coarse occluders. This allows to arrange the objects of each PVS into several Hardly‐Visible Sets (HVS) with similar occlusion degree. According to image accuracy and frame rate requirements, HVS provide a way to avoid sending to the graphics pipeline those objects whose pixel contribution is low due to partial occlusion. The image error can be bounded by the user at navigation time. On the other hand, as HVS offer a tighter estimation of the pixel contribution for each scene object, it can be used for a more convenient selection of the level‐of‐detail at which objects are rendered. In this paper, we describe the new framework technique, provide details of its implementation using a visibility octree as the chosen occlusion culling data structure and show some experimental results on the image quality.
Rendering Natural Waters
Authors: Premože Simon , Ashikhmin Michael
Published: March 2003

Creating and rendering realistic water is one of the most daunting tasks in computer graphics. Realistic rendering of water requires that the sunlight and skylight illumination are correct, the water surface is modeled accurately and that the light transport within water body is properly handled. This paper describes a method for wave generation on a water surface using a physically‐based approach. The wave generation uses data from the oceanographical observations and it is controlled by intuitive parameters such as wind speed and wind direction. The optical behavior of the water surfaces is complex but is well‐described in the ocean science literature. We present a simple and intuitive light transport approach that is easy to use for many different water types such as deep ocean water, muddy coastal water, and fresh water bodies. We demonstrate our model for a number of water and atmospheric conditions.
An Adaptive Sampling Scheme for Out‐of‐Core Simplification
Authors: Fei Guangzheng , Cai Kangying , Guo Baining , Wu Enhua
Published: March 2003

Current out‐of‐core simplification algorithms can efficiently simplify large models that are too complex to be loaded in to the main memory at one time. However, these algorithms do not preserve surface details well since adaptive sampling, a typical strategy for detail preservation, remains to be an open issue for out‐of‐core simplification. In this paper, we present an adaptive sampling scheme, called the balanced retriangulation (BR), for out‐of‐core simplification. A key idea behind BR is that we can use Garland's quadric error matrix to analyze the global distribution of surface details. Based on this analysis, a local retriangulation achieves adaptive sampling by restoring detailed areas with cell split operations while further simplifying smooth areas with edge collapse operations. For a given triangle budget, BR preserves surface details significantly better than uniform sampling algorithms such as uniform clustering. Like uniform clustering, our algorithm has linear running time and small memory requirement.
Formal Specification in the Revision of GKS: An Illustrative Example
Authors: Duce D.A. , Damnjanovic L.B.
Published: March 2003

The first ISO/IEC standard for computer graphics, the Graphical Kernel System (GKS) was published in August 1985. In accordance with ISO/IEC procedures, GKS is now being reviewed and revised. This paper describes how formal specification techniques are being used by the authors to analyse key parts of proposals being made for changes to the framework of GKS to bring the standard into line with the requirements of applications and the operating environment likely to be found in the mid‐1990's.
Geometric and Group‐theoretic Methods for Computer Graphic Studies of Islamic Symmetric Patterns
Authors: Abas S. J. , Salman A.
Published: March 2003

Over the last several years the authors have used computer graphics to generate, study and analyze more than 300 Islamic geometrical repeat patterns. These patterns offer a rich source for exploitation by artists and are also of interest to mathematicians, crystallographers, architects, archaeologists and others. They can serve as elegant test beds for research into hierarchical programming and texture mapping. The paper discusses the evolution of classical geometric methods for Islamic patterns and goes on to develop algorithms based on group theory for efficient generation of all crystallographic repeat patterns using modern computer graphics.
Visual Composition and Multimedia
Authors: de Mey Vicki , Breiteneder Christian , Dami Laurent , Gibbs Simon , Tsichritzis Dennis
Published: March 2003

Multimedia applications can be seen as sets of autonomous parts, independent yet capable of working together. This assumption allows for the construction of multimedia applications in a “connectionist” fashion. In this paper we describe mechanisms for the visual composition of multimedia applications. These mechanisms allow for quick and flexible application construction by direct manipulation with reference to multiple composition models. An object‐oriented framework for multimedia systems will be introduced throughout the paper.
HAGI, a High‐level Application/Graphics Interface
Authors: Hsu Y. H. , Kuo Y. S.
Published: March 2003

HAGI is an object‐oriented graphics system developed on top of the X window system. In addition to providing facilities that structured graphics systems such as GKS usually have, HAGI supports a high‐ level graphics paradigm with the following features:

In addition to graphical objects, the system provides a class of application objects with a higher level of abstraction than graphical objects.

Graphics manipulation operations can be issued simplyfrom application objects without explicitly referring to specific graphical objects. Thus graphics manipulation appears to be transparent to application programmers.

Graphical objects are designed to encompass more semantics, thus are at a level close to the application. For example, they useflexible visual objects to determine their visual appearance.

HAGI provides such a high‐level application/graphics interface by maintaining a dependency relationship between graphical objects and application objects.
A Functional Approach to the Visual Simulation of Gaseous Turbulence
Authors: Sakas Georgios , Westermann Rüdiger
Published: March 2003

This paper presents a functional method for the visual simulation of 2‐D or 3‐D turbulent gaseous motion by using time‐varying fractals. The used function incorporates results from the “spectral theory of turbulence”, thereby providing a physics‐based approach adapted to the needs of computer graphics. The involved turbulence function is band‐limited, continuous, differentiable, anisotrop, and smooth, provides different fractal dimensions along each axis, may be evaluated locally with different parameters, and requires only minimal storage space, thus supporting an implementation on large parallel processing networks with small nodes. Inhomogeneity in the form of local disturbances of the turbulence field may also be easily considered. The parameters used to describe turbulent motion are rather intuitive, so that they may be utilized easily by users. Examples for modeling different types of clouds and fire are given.
Template‐Based Volume Viewing
Authors: Yagel Roni , Kaufman Arie
Published: March 2003

We present an efficient three‐phase algorithm for volume viewing that is based on exploiting coherency between rays in parallel projection. The algorithm starts by building a ray‐template and determining a special plane for projection ‐ the base‐plane. Parallel rays are cast into the volume from within the projected region of the volume on the base‐plane, by repeating the sequence of steps specified in the ray‐template. We carefully choose the type of line to be employed and the way the template is being placed on the base‐plane in order to assure uniform sampling of the volume by the discrete rays. We conclude by describing an optimized software implementation of our algorithm and reporting its performance.
A line clipping algorithm and its analysis
Authors: Krammer Gergely
Published: March 2003

One of the classical problems of Computer Graphics: line clipping against a rectangle is revisited. Coordinate raster refinement and some unusual forms of the parametric equation of the line are used to develop formulae for a line clipping algorithm. The algorithm is first presented in a form, where clarity of presentation is the prime concern. It is then transformed into one big nested branch, which after optimisation is assumed to be the most efficient form with a heavy cost on size. It is assumed that any mathematical consideration of the clipping problem would after a similar optimisation lead to a branching structure of equal complexity and speed. Line clipping thus belongs to the class of problems for which after a proper mathematical and logical analysis automatic program transformations may do the rest.

This work has been supported by a grant from the Hungarian Academy of Sciences, Project No. OTKA 2572/1991
Area Sampling Buffer: Tracing Rays with Z‐Buffer Hardware
Authors: Sung Kelvin
Published: March 2003

An algorithm that allows the use of z‐buffer hardware in assisting area sampling for a ray tracing style renderer is described. The implementation issues involved in discretizing the sampling area and light source area are discussed and solutions are proposed. The effects of the hardware‐assisted ray tracing approach on frame‐buffer systems and image synthesis processes are considered.
Reference, Synthesis and Constraint Satisfaction*
Authors: Pineda Luis A.
Published: March 2003

In this paper we discuss two kinds of constraint satisfaction problems that arise in the context of geometric modelling, In particular in the modification of 2‐D wire‐frame diagrams that are subject to an arbitrary number of geometrical and topological constraints. We argue that problems in this domain can be classified in two categories that we shall call problems of reference and problems of synthesis. Since Sutherland's Sketchpad program [16], a large number of systems have addressed constraint satisfaction in terms of the representation of constraints sets as equation systems, which in turn are solved by numerical methods like local propagation, relaxation and Gaussian elimination. Here, we present an alternative framework. We argue that conceptualising constraint satisfaction as symbolic rather than “numerical” problems helps to clarify the notion of “constraint”, simplify solution methods, and to explain the intuitive inferential processes underlying the modification of drawings in the course of interactive drafting sessions. The theory presented in this paper has been tested with an experimental computer program called Graflog [5, 8, 9, 10, 11, 12]. The program has been implemented during the last four years, and has evolved through several stages. The current version is implemented in terms of two Unix‐processes connected by Unix‐pipes. The first is a “C” program running X windows, and handles the external aspects of the interaction. The second is a Prolog program supporting the representational structures and interpreters of the system.
A Development Environment for Constructing Graph‐Based Editing Tools
Authors: Chen M. , Townsend P. , Wang C.Y.
Published: March 2003

Scientists and engineers use numerous kinds of graph notations to model various objects in the real world and their relationships in an abstract pictorial form. However, developing a specific graph editing tool for each of these notations is often very costly in terms of time and resources. This paper outlines a design of a suitable development environment for constructing graph‐based editing tools, based on the requirements analysis of such an environment derived from a survey of more than 60 different graph notations.
The Graphical Translation of English Text into Signed English in the Hand Sign Translator System
Authors: Holden E.J. , Roy G.G.
Published: March 2003

Signed English is a manual interpretation of English using fingerspelling and signs. A prototype of the Hand Sign Translator (HST) system was developed to graphically translate English into Signed English, using two‐handed animation. The HST consists of a practical interface that aims to help users learn Signed English, and the translation process where English text is transformed into a series of images that represent corresponding signs. This paper describes the translation process which involves two stages; the input environment and the animation process. The input environment consists of text analysis in order to extract corresponding kinematic data from the database, named English‐Sign Dictionary (ESD). The data is then used as an input to the animation process, Firstly, the skeleton models of keyframe images and their in‐between poses are calculated. Secondly, appropriate volume models are applied in order to surround the surface of skin. Then the shapes that are suitable for painting are generated, and finally images are drawn and rendered using a smooth animation technique.
PRIP – A Parallel Raster Image Processor
Authors: Van Campenhout Jan M. , Lasure Roeland
Published: March 2003

Like colour video displays and laser printers, laser photoplotters are raster scan devices. For such devices, the pixel stream representing the image must be generated in real time, and in the (scan line) order required. However, the typical size of the images photoplotters produce is an order of magnitude higher than that of video displays and laser printers, precluding the use of full‐size bitmap memories. These requirements pose particular implementation problems for the raster image processor generating the pixel stream.

The parallel RIP system presented here is aimed at high‐resolution laser photoplotters, and features a largely scalable performance ranging from 40 to several hundred megapixels per second. It is built with standard components such as graphics microprocessors and VRAM memories. Its architecture is that of a distributed memory multiprocessor system with a global ring‐like topology. And most importantly, it can be programmed using the traditional sequential programming paradigm. Only minor additions are needed to sequential graphical algorithms to be executable on the system with an arbitrary number of processors.

A prototype 8‐processor PRIP system has been built and tested generating printed circuit board images for a direct imaging photoplotter. The prototype exhibits a near‐linear speedup with respect to a monoprocessor solution. Architectural simulations indicate that the system can be expanded to well over 10 processors.
Using Multimedia to Support Cooperative Editing
Authors: Santos A. , Tritsch B.
Published: March 2003

By Cooperative Editing we mean the coordinated manipulation of information by a group of authors. During the editing process the (co‐)authors need to communicate their ideas, drafts and constraints (remotely or face‐to‐face) until a final version of the information is achieved. For the different phases of this process ‐ discussion of ideas, editing, cross‐checking ‐ different media or media integration are adequate. Furthermore, analysing the transition from individual work to group work, within different human activities, two pitfalls are often detected if computer support is considered: a) technological communication difficulties, especially if the group is remotely located on heterogeneous hardware, associated with a fall in productivity and frequent social inadequacies of the group's computer support; b) the lack of integrated media processing tools available for group editing.

In order to solve these problems, we suggest that Multimedia can be applied in two ways: to effectively support the necessary group communication links; and to enhance the expressiveness of the information edited. To test this statement we have been conceptualising and implementing a prototype system. Most of the techniques involved can be used in other tools that need multimedia capabilities or that support other specific types of group activities.

The innovative aspects of the work are the use of multimedia techniques to support demanding applications, possibly on cross‐platforms, and the integration of several concepts to support cooperation.
A Declarative Design Method for 3D Scene Sketch Modeling
Authors: Donikian Stéphane , Hégron Gérard
Published: March 2003

In this paper, we present a dynamic model associated with an intelligent CAD system aiming at the modeling of an architectural scene sketch. Our design methodology has been developed to simulate the process of a user who tries to give a description of a scene from a set of mental images. The scene creation is based on a script which describes the environment from the point of view of an observer who moves across the scene. The system is based on a declarative method viewed as a stepwise refinement process. For the scene representation, a qualitative model is used to describe the objects in terms of attributes, functions, methods and components. The links between objects and their components are expressed by a hierarchical structure, and a description of spatial configurations is given by using locative relations. The set of solutions consistent with the description is usually infinite. So, either one scene consistent with this description is calculated and visualized, or reasons of inconsistency are notified to the user. The resolution process consists of two steps: firstly a logical inference checks the consistency of the topological description, and secondly an optimization algorithm deals with the global description and provides a solution. Two examples illustrate our design methodology and the calculation of a scene model.
Accurate and Consistent Reconstruction of Illumination Functions Using Structured Sampling
Authors: Drettakis George , Fiume Eugene
Published: March 2003

The study of common classes of diffuse emitters, such as planar convex polygons, reveals several interesting properties of the functions of illumination these emitters cast on receiver surfaces. Some properties, such as the position of the maximum and the curvature are of particular interest for sampling and reconstruction of illumination across receivers. A computationally efficient approach is presented that identifies these properties, and uses them to select samples of illurnination. In addition these properties are used to determine upper bounds on the error due to linear and quadratic interpolants. These bounds are then used to adaptively subdivide the non‐uniform sampling grid, resulting in accurate reconstruction. Results show that the method reduces the error compared to uniform approaches, and produces more consistent animated sequences.
Automatic Reconstruction of Buildings from Stereoscopic Image Sequences
Authors: Koch Reinhard
Published: March 2003

A vision–based 3‐D scene analysis system is described that is capable to model complex real–world scenes like streets and buildings automatically from stereoscopic image pairs. Input to the system is a sequence of stereoscopic images taken with two standard CCD Cameras and TV lenses. The relative orientation of both cameras to each other is known by calibration. The camerapair is then moved throughout the scene and a long sequence of closely spaced views is recorded. Each of the stereoscopic image pairs is rectified and a dense map of 3‐D suface points is obtained by area correlation, object segmentation, interpolation, and triangulation. 3‐D camera motion relative to the scene coordinate system is tracked directly from the image sequence which allows to fuse 3‐D surface measurements from different viewpoints into a consistent 3‐D model scene. The surface geometry of each scene object is approximated by a triangular surface mesh which stores the suface texture in a texture map. From the textured 3‐D models, realistic looking image sequences from arbitrary view points can be synthesized using computer graphics.
Spanning a C1‐Surface over a Given Wireframe
Authors: Tokumasu Shinji , Harashima Ichirou , Nakajima Norihiro
Published: March 2003

A problem of spanning a surface of C1 continuity (C1‐surface) over a given wireframe is introduced. By exploiting the concept of a super surface patch introduced in an earlier paper, we proved the existence of an approximate, yet practical solution of the problem. That is, we presented a method or a procedure, by which to span a C1‐surface over the wireframe. This technique is intended to be utilized as a flexible surface generation method for the 3D shape design in the industrial world.
A Library for Developing PHIGS Programming Tools in a PEX Environment
Authors: Wainer Michael , Tan Ting
Published: March 2003

The merger of three‐dimensional graphics with the X Window System has recently been standardized by adapting PHIGS, the Programmer's Hierarchical Interactive Graphics System, to the X Window System with PEX, the PHIGS Extension to X. The standard programming library for PEX has been defined to be identical to PHIGS PLUS allowing PHIGS programs to port directly to the X environment. X uses a client server model to run applications as client processes which communicate with a server to perform graphical display and input. For improved performance, the PEX extension defines new server resources to reduce network traffic and to take advantage of graphics hardware existing on high‐end servers. A side effect of this distributed model of computation is a distribution of PHIGS structures leading to a relaxation of the exclusive access which a PHIGS application usually maintains over its Central Structure Store.

We exploit the distributed nature of a PEX/PHIGS client's Central Structure Store to provide access to it for other applications besides the originating PEX/PHIGS client. We refer to these other applications as tools since one of our primary goals is to create development tools for PHIGS programmers. Rather than concentrate on particular debugging tools, we focus upon easing the process of actually developing tools. Our goal is to supply a collection of routines which can be used by PHIGS programmers to create custom tools or other programs which require access to the graphics data of remote PHIGS processes.

Our Tool Development Library provides the PHIGS programmer a small number of management routines which orchestrate the connection and mapping to the data of one or more remote PHIGS applications. Manipulation of remote PHIGS structures is accomplished just as easily as local operations and is performed using standard PHIGS calls. The remote application being accessed requires no changes to its source code. Obvious uses for the Tool Development Library are in the construction of PHIGS tools such as structure browsers, editors and debugging aids. Less obvious is the potential for developing collections of cooperating graphics applications which share graphics data.
Experiments in the Parallel Computation of 3D Convex Hulls
Authors: Claret A.R. , Day A.M.
Published: March 2003

Two parallel implementations of a 3D convex hull algorithm are reported. The paper considers a MIMD distributed memory architecture and the implementations are carried out on the Meiko Computing Surface using T800 transputers and the programming languages Occam and C. The first method uses a simple parallel geometric decomposition strategy and produces encouraging results. With the second approach a parallel generic Divide‐and‐Conquer kernel is incorporated. This is an example of the algorithmic skeleton approach to parallel programming and involves run‐time, dynamic allocation of work to processors. The resulting performances for both methods are measured and compared.
Making Shaders More Physically Plausible
Authors: Lewis Robert R.
Published: March 2003

There is a need to develop shaders that not only “look good”, but are more physically plausible. From physical and geometric considerations, we review the derivation of a shading equation expressing rejected radiance in terms of incident radiance and the bidirectional reflectance distribution function (BRDF). We then examine the connection between this equation and conventional shaders used in computer graphics. Imposing the additional physical constraints of energy conservation and Helmholtz reciprocity allows us to create variations of the conventional shaders that are more physically plausible.
Wavelet Projections for Radiosity
Authors: Schröder Peter , Gortler Steven J. , Cohen Michael F. , Hanrahan Pat
Published: March 2003

One important goal of image synthesis research is to accelerate the process of obtaining realistic images using the radiosity method. Two important concepts recently introduced are the general framework of projection methods and the hierarchical radiosity method.

Wavelet theory, which explores the space of hierarchical basis functions, offers an elegant framework that unites these two concepts and allows us to more formally understand the hierarchical radiosity method.

Wavelet expansions of the radiosity kernel have negligible entries in regions where high frequency/fine detail information is not needed. A sparse system remains if these entries are ignored. This is similar to applying a lossy compression scheme to the form factor matrix. The sparseness of the system allows for asymptotically faster radiosity algorithms by limiting the number of matrix terms that need to be computed. The application of these methods to 3D environments is described in4. Due to space limitations in that paper many of the subtleties of the construction could not be explored there. In this paper we discuss some of the mathematical details of wavelet projections and investigate the application of these methods to the radiosity kernel of a flatland environment, where many aspect are easier to visualize.
3D Visualization for 2D GIS: an Analysis of the Users' Needs and a Review of Techniques*
Authors: Giertsen Christopher , Lucas Anne
Published: March 2003

Most of the existing geographical information systems (GIS) make limited use of algorithms for advanced computer graphics and visualization. One explanation is that few attempts are made to identify the visualization needs for different uses of GIS, and to couple such needs to the available algorithms. Another explanation is that most GIS are designed to handle two‐dimensional (20) data with few obvious relationships to three‐dimensional (30) visualization.

In an attempt to provide a better understanding of the application of visualization in GIS, we propose a conceptual framework linking several aspects of the two fields. At the user‐level, we link different uses of GIS to different categories of audience and presentation styles. At the level of implementation, we first propose different ways to create 3D data for visualization from 2D GIS data, and then we review algorithms and techniques for 3D visualization with respect to support of different presentation styles.
Fast Dynamic Tessellation of Trimmed NURBS Surfaced1
Authors: Abi‐Ezzi Salim S. , Subramaniam Srikanth
Published: March 2003

Trimmed NURBS (non‐uniform rational B‐splines) surfaces are being increasingly used and standardized in geometric modeling applications. Fast graphical processing of trimmed NURBS at interactive speeds is absolutely essential to enable these applications. which poses some unique challenges in software, hardware, and algorithm design. This paper presents a technique that uses graphical compilation to enable fast dynamic tessellation of trimmed NURBS surfaces under highly varying transforms.

We use the concept of graphical data compilation. through which we preprocess the NURBS surface into a compact, view‐independent form amenable for fast per‐frame extraction of triangles. Much of the complexity of processing is absorbed during compilation. Arbitrarily complex trimming regions are broken down into simple regions that are specially designed to facilitate tessellation before rendering. Potentially troublesome cases of degeneracies in the surface are detected and dealt with during compilation. Compilation enables a clean separation of algorithm‐intensive and compute‐intensive operations, and provides for parallel implementations of the latter. Also, we exercise a classification technique while processing trimming loops. which robustly takes care of geometric ambiguities and deals with special cases while keeping the compilation code simple and concise.
AGRELs and BIPs: Metamorphosis as a Bezier curve in the space of polyhedra
Authors: Rossignac Jarek , Kaul Anil
Published: March 2003

The metamorphosis between two user‐specified objects offers an intuitive metaphor for designing animations of deforming shapes. We present a new technique for interactively editing such deformations and for animating them in realtime. Besides the starting and ending shapes, our approach offers easy to use additional control over the deformations. The new Bezier Interpolating Polyhedron (BIP) provides a graphics representation of such a deforming object formulated mathematically as a point describing a Bezier curve in the space of all polyhedra. We replace, in the Bezier formulation, the traditional control points by arbitrary polyhedra and the vector addition by the Minkowski sum. BIPs are composed of Animated GRaphic ELement (AGRELs), which are faces with constant orientation, but with parametrized vertices represented by Bezier curves. AGRELs were designed to efficiently support smooth realtime animation on commercially available rendering hardware. We provide a tested algorithm for automatically computing BIPs from the sequence of control polyhedra and demonstrate its applications to animation design.
Volume Rendering on Non‐regular Grids
Authors: Tabatabai Behnam , Sessarego Emanuela A. , Mayer Harald F.
Published: March 2003

In this article we present the principle methods for volumerendering of non‐regular grids as used in the Finite Element Method or the Method of Control Volumes. Besides linear element types, the methods discussed here also cover the handling of commonly used non‐linear element types but little considered in the Computer Graphics community. The very basic operation in the whole rendering process, namely the interpolation of the geometry and function values is fully based on the element type specific shape functions, ensuring a consistent mathematical treatment of the object in the sense of the underlying numerical simulation. We discuss the implications of this approach and propose optimizations justified by general assumptions on the qualify of the simulation model.
A Method for Displaying Metaballs by using Bézier Clipping
Authors: Nishita Tomoyuki , Nakamae Eihachiro
Published: March 2003

For rendering curved surfaces, one of the most popular techniques is metaballs, an implicit model based on isosurfaces of potential fields. This technique is suitable for deformable objects and CSG model.

For rendering metaballs, intersection tests between rays and isosurfaces are required. By defining the higher degree of functions for the field functions, richer capability can be expected, i.e., the smoother surfaces. However, one of the problems is that the intersection between the ray and isosurfaces can not be solved analytically for such a high degree function. Even though the field function is expressed by degree six polynomial in this paper (that means the degree six equation should be solved for the intersection test), in our algorithm, expressing the field function on the ray by Bézier functions and employing Bézier Clipping, the root of this function can be solved very effectively and precisely.

This paper also discusses a deformed distribution function such as ellipsoids and a method displaying transparent objects such as clouds.
Improved Visualisation of Marine Data: Algae and Acid Rain
Authors: Day A.M. , Turner S.M. , Arnold D.B.
Published: March 2003

Recent studies have shown a connection between seasonal phytoplankton activity and generation of atmospheric sulphur products known to contribute towards acid rain [1]. Although anthropogenic sources of sulphur dioxide and sulphate dominate in acid &position on land surfaces, for some less industrialised areas of Europe, during the summer, there may be a significant contribution from natural marine sources.

This paper describes briefly the nature of the marine processes thought to be taking place and survey cruises in the Southern North Sea used to collect data. Such field studies pose peculiar difficulties in both collection and processing of data. A critique on the nature of data generated under such conditions is included and some implications drawn for visualisation and interpretation techniques. Some initial results, with basic interpolation and approximation techniques, are compared. The paper concludes with suggestions on the way in which the research projects described are intended to befurther developed.
GKS‐9x: The Design Output Primitive, an Approach to a Specification.
Authors: Nehlig Ph. W. , Duce D. A.
Published: March 2003

This paper describes an approach to the formal definition of the design primitive introduced in the revision of the ISO/IEC computer graphics standard, GKS. The paper starts with a general description of the design primitive and then describes the specification (which is given in the Z notation) and the motivation for the approach taken in some detail. The paper concludes with a reflection on the contribution of this work, and the descriptive style adopted an the GKS revision, to the role of formal description in the presentation of graphics standards.
The Design and Specification of a Visual Language: An Example for Customising Geographic Information Systems Functionalities
Authors: Paterna' F. , Campari I. , Scopigno R.
Published: March 2003

In this paper the design of a visual program editor and its specification using formal grammars are discussed. We consider an environment to specify, analyse and execute visual programs for a Geographical Information System (GIS). The lack of sophisticated user interfaces is one of the major drawbacks to Geographical Information Systems, particularly for people without a sound background in computer science. The use of a visual language approach is useful in order to hide the plethora of basic GIS functions, while providing ready‐ to‐use tools to solve users' tasks. The visual environment provides users with higher level interfaces; it is based on the module concept, which is conceived as a software building block that implements a solution to a general basic task and is presented to the user through an interactive frame. Complex GIS queries can be carried out by interconnecting modules into flow networks, using a direct manipulation approach.
Deriving Spectral, Reflectance Functions of Computer‐Simulated Object Colours
Authors: Schettini R.
Published: March 2003

A method is presented which, given the RGB values of a colour stimulus displayed on a given cathode ray tube (to which a CIE XYZ triple corresponds), makes it possible to find a spectral reflectance function characterizing an object colour. Such an object when “illuminated” by a given illuminant produces a metameric spectral power distribution, that is, one with the same XYZ tristimulus values. The method is useful in the colorimetric matching of colours on different media or supports.
Computation of Offset Curves by the Huygens Principle
Authors: Mikheev A. , Nozik M. , Rubinstein J.
Published: March 2003

A new algorithm for computing offset curves is proposed. The algorithm is based on the Huygens principle for propagating wave‐fronts. It automatically avoids the topological singularities that appear in conventional methods. The algorithm is simple to implement and it does not require any multiplication or other floating number operations.
Multiresolution Tiling
Authors: Meyers David
Published: March 2003

This paper describes an efficient method for constructing a tiling between a pair of planar contours. The problem is of interest in a number of domains, including medical imaging, biological research and geological reconstructions. Our method, based on ideas from multiresolution analysis and wavelets, requires O(n) space and appears to require O(n log n) time for average inputs, compared to the O(n2) space and O(n2 log n) time required by the optimizing algorithm of Fuchs, Kedem and Uselton1. The results computed by our algorithm are in many cases nearly the same as those of the optimizing algorithm, but at a small fraction of the computational cost. The performance improvement makes the algorithm usable for large contours in an interactive system. The use of multiresolution analysis provides an efficient mechanism for data compression by discarding wavelet coefficients smaller than a threshold value during reconstruction. The amount of detail lost can be controlled by appropriate choice of the threshold value. The use of lower resolution approximations to the original contours yields significant savings in the time required to display a reconstructed object, and in the space required to store it.
An Algorithm for Perspective Viewing of Objects Represented by Octrees
Authors: Aref Walid G. , Samet Hanan
Published: March 2003

A new algorithm is presented for viewing three‐dimensional objects, represented by an octree, from an arbitrary location. The algorithm generates aperspective view of the objects while eliminating hidden surfaces. The viewer can be located anywhere inside or outside the objects. The algorithm presented in this short notefixes an artifact that is generated by a previously published algorithm due to Meagher when the viewer is located in certain regions in space. The new algorithm traverses the octree in a back‐to‐front order and recursively chooses correct orders for visiting the sons of non‐leaf nodes.
Fast Generation of Leakproof Surfaces from Well‐Defined Objects by a Modified Marching Cubes Algorithm
Authors: Roll Stefan , Haase Axel , von Kienlin Markus
Published: March 2003

Local surface reconstruction by the Marching Cubes algorithm and its derivatives has a well known ambiguity, which prevents constructed surfaces from being closed and simple. We investigate this ambiguity assuming that a 3D image samples well‐defined objects. In this case it is justified to aim at tiling of extracted object voxels rather than at reconstructing iso surfaces. Compared to iso surface reconstruction, our algorithm provides essentially the same level of confidence with respect to surface location at a lower computational cost. We present a leak detection and mending scheme which resolves the Marching Cubes ambiguity and guarantees a well‐defined behaviour with respect to which objects are covered by which surface. We detail how to implement our leak mending method within a completely tabulated Marching Cubes algorithm. We finally give an example of how the adapted algorithm is of benefit to a recently developed 3D MR spectroscopy technique.
Fractals and Quasi‐Affine Transformations
Authors: Nehlig P. W. , Reveilles J.‐P.
Published: March 2003

In the continuum , contracting affine transformations have a unique fixed point. It is well known that this property is not preserved by dicretization and that the dynamics of discretized functions are very complicated. Discrete geometry allows us to start a theory for these dynamics and to illustrate some of their features by pictures. These pictures, rendered by a simple algorithm, reveal a very large spectrum of fractal structures, from the simplest to the intricatest.