University of west Bohemia, Pilsen, Czech Republic

February 14 - 18, 1995

******************** V O L U M E I ************************** GENERATING A MODEL OF PLANT USING NURBS Bedrich BenesCTU, Fac.of Electrical Eng., Dept. of Computer Science Karlovo nam.13, 131 25 Prague, Czech Rep. e-mail benes@sgi.felk.cvut.cz Abstract is not available. Keywords: Computer Graphics, NURBS, ModellingONE METHOD OF THE HUMAN BODY MODEL ANIMATION R. Berka, I. JelinekDepartment of Computers Faculty of Electrical Engineering Czech Technical University Karlovo nam. 13 121 35 Prague Czech Republic e-mail: berka@cs.felk.cvut.cz jelinek@cslab.felk.cvut.cz In the first part of the paper we show a new approach to the modelling of the human body. The modelling of the human body has two parts - the model structure description (the model of the human body we call "figure") and the model motion control. The second part of this article is devoted to methods of the figure's structure formal description and to control of the figure's behavior. For this purpose we have proposed a special formal language FDL (Figure Description Language). The next part informs on the implementation our ideas in program VITALIATOR. The implementation is consistently based on the object oriented approach. In the last part of our contribution we discuss questions connected with control of all actor's body parts and parallel movement control of more figures. Keywords : computer animation, object-oriented graphics, human body animation, modellingAN APPROACH TO DRAWING FAIR PLANE OPEN CURVES Marcelo Cordeiro Bernardes, Wu Shin-Ting, Itala M.L.D'OttavianoDCA - FEE - UNICAMP, CLE/IFCH - UNICAMP e-mail: {ting,mcb}@dca.fee.unicamp.br itala@cle.unicamp.br In this paper an approach for interpolating a given sequence of points by a fair plane curve is presented. Since the fairness concept is subjective, a non classical modelling tool - fuzzy sets - is used and interactive facillities are provided. Some results of our implementation are included.A PARALLEL APPROACH TO HIERARCHICAL RADIOSITY Christian A. Bohn, Robert GarmannGerman National Research Center for Computer Science Dept. Visualization and Media Systems design Sankt Augustin, Germany e-mail : bohn@viswiz.gmd.de, garmann@ls7.informatik.uni-dortmund.de A parallel algorithm solving the radiosity equation is presented. It is based on the hierarchical approach (HR) [5] and realized on a massively parallel supercomputer - the Connection Machine 5. Our algorithm considers the HR approach as a process that manipulates a huge graph structure. Simulated annealing is used in the graph's rearranging procedure to achieve a good work-ballance and nearly optimal communication costs. The implementation shows a significant step to faciliate the aplication of a radiosity solver, produced on one hand by the few user-support that HR needs, on the other hand by the fast calculation times the parallel implementation offers. On 64 processors we obtained a speed-up of 8.4. Keywords : Computer Graphics, Scientific Visualisation, Hierarchical radiosity, Rendering, Simulation, Parallelization, Message Passing, Supercomputer, Architecture.FAST COLOUR SHADING J.J.BourdinDepartement d'Informatique Universite Paris-8 2,rue de la Liberte 935 26 Saint-Denis 02 - France e-mail: jj@aristote.univ-paris8.fr Colour shading a region of the plane is the action of filling its interior with continuously varying colours. Some classic methods are presented. This paper proposes an original approach to colour shading. A condition of smoothness is given. A region is modeled as a support and a chromatic function. Various shapes of shading are presented. Incremental computing and benchmarks are also discussed. In addition, we solve the problem of good visual smoothing for an angular colour shading. Keywords : Shading, colour shading, 2D Graphics, Computer graphics, fundamental algorithmsSTUDY OF ITERATIVE PROCESSES IN COMPUTER GRAPHIC'S PROBLEMS Jean-Marc Brun, Sebti Foufou, Abdelaziz Bouraz, Philippe ArthaudLISPI /LIGIA bat.710 Universite Claude Bernard LYON 1 43 Bd du 11 Novembre 1918 69 622 Villeurbanne Cedex Coretech International 27-29, Bd du 11 Novembre 1918 B.P. 2131 69 622 Villeurbanne Cedex The convergency of iterative processes can exhibit unexpected behaviour. In this paper an analysis of the convergency of the iterative processes is made through the aplication of the Newton method to the polynomial equations resolution. This leads to the definition of a dynamic relaxation scheme applied to computer graphics. Keywords : Iterative processes, convergency, relaxation, equations, graphics.THE INTERACTION OF THEORY AND PROCEDURE IN FRACTAL GEOMETRY Stephan D. CaseyDepartment of Mathematics and Statistics The American University 4400 Masachusetts Ave., N.W. Washington, D.C. 20016-8050 e-mail:scasey@american.edu This article discusses the interplay in fractal geometry occuring between computer programs for developing (approximation of) fractal sets and the underlying dimension theory. The computer is ideally suited to implement the recursive algorithms needed to create these sets, thus giving us a laboratory for studying fractals and their corresponding dimensions. Moreover, this interaction between theory and procedure goes both ways. Dimension theory can be used to classify and understand fractal sets. This allows us, given a fixed generating pattern, to describe the resultant images produced by various programs. We will also tie these two perspoectives in with the history of the subject. Three examples of fractal sets developed around the turn of the century are introduced and studied from both classical and modern viewpoints. Then, definitions and sample calculations of fractal and Hausdorff-Besicovitch dimensions are given. Finally, dimension theory is used to clasify images.TEXTURE, DISPLACEMENT AND IMMERSION : A MODEL FOR TREE RENDERING Miguel Chover, Roberto Vivo, Ricardo Quiros, Xavier LLuchDepartamento de Informatica, Universidad Jaume I. Campus de Penyeta Roja, 12071 Castellon, Espana Tel. ++34 64 345771, fax ++34 64 344858 e-mail chover@inf.uji.es Departamento de Sistemas Informaticos y Computacion Universidad Politecnica. Camino de Vera s/n 46071 Valencia, Espana This paper presents a new method to generate realistic details on tree surfaces and structures. The method combines texture, displacement and immersion techniques. We use an extension of L-systems, namely random L-Systems, to construct the tree, and represent its structure of branches using parametric surfaces (cones). Adding displacement at the surface level by means of 2D and 3D functions, and deviation at the structure level by immersion in a 3D function, we perturb the surface definition. The parametric definition of the surface is adequate to apply textures and reduces the spatial cost of the previous tree representations. In addition, the proposed technique can even manage further detail than previous ones.DYNAMIC SUBDIVISION IN RADIOSITY Eric Dubuis, Hanspeter BieriInstitut fur Informatik und angewandte Mathematik Universitat Bern, Langgasstrasse 51, 3012 Bern, Switzerland e-mail dubuis@iam.unibe.ch, bieri@iam.unibe.ch This paper presents a fast radiosity algorithm for illuminating scenes containig large piecewise polygonal surfaces. Dynamic subdivision is based on the well known Adaptive Subdivision, introduced by M.Cohen et.al.[3]. During the illuminating process, patches in areas with high intensity gradients are refined. Contrary to Adaptive Subdivision, the presented algorithm subdivides patches not in a static way. The patch hierarchy is dynamic and adapted to the respective state of the illumination process. To take a decision concerning path subdivision, more information about the gathered energy of a patch is considered than with Adaptive Subdivision. The results show that this new algorithm can lead to remarkable speedups compared to Adaptive Subdivision.SPEEDING UP PROGRESIVE RADIOSITY BY OVERSHOOTING Martin FedaTechnical University of Vienna Institute of Computer Graphics Karlsplatz 13/186-2 Vienna, Austria e-mail feda@cg.tuwien.ac.at Overshooting techniques have proven to significantly speed up the convergence of radiosity computation. Similar methods (overrelaxation) have also been widely used in numerical mathematics to speed up iterative solution methods for linear equation systems, e.g. Gauss-Seidel iteration. This paper gives a comprehensive description of all overshooting techniques. Advantages and disadvantages of the different techniques are also described.ATTRACT - ITERATIVE VISUALIZATION OF DYNAMICAL SYSTEMS Eduard Gröller, Herbert OppolzerTechnical University Vienna Institute of Computergraphics Karlsplatz 13/186/2 A-1040 Vienna, Austria Tel.+43(1)58801-4582 FAX +43(1)5874932 e-mail groeller@cg.tuwien.ac.at herbert@cybercafe.co.at An interactive program for visualizing the long term behavior of dynamical systems, e.g., attractors and bifurcation diagrams is presented. The program allows an easy specifications of a set of formulas and constants which describe a dynamical system. This set of equations is then used for displaying the geometrical structure of the long term development of dynamical system. The user defines the assignment of variables of the dynamical system to at most three spatial axes and one colour axis. Viewing parameters, e.g., point of view, zoom, rotation angle, can again be changed interactivelly. The program is intended to provide researchers working on dynamical systems with a fast visual analusis and experimentation tool. Keywords : visualization, dynamical system, interactivity, attractor, bifurcation diagram.COMBINING CLUSTER ANALYSIS AND CONTINUOUS ISOSURFACE COLOURING IN A TOOL FOR DATA EXPLORATION Johan HangmanSSKKII, University of Göteborg 41298 Göteborg, Sweden e-mail hagman@ling.gu.se The paper shows how two powerfull techniques for supporting data exploration of multidimensional data can be combined in a tool for this purpose. The techniques, cluster analysis and graphics visualization, are briefly presented and discussed as modules of a prototype. Its preformance is illustrated by experiments resulting in cluster configurations where the value distribution of "underlying" dimensions are visualized with colors or shades of grey.NON-PHOTOREALISTIC SHAPE CUES FOR VISUALIZATION Peter HallDepartment of Computer Science PO Box 600 Victoria University of Wellington New Zealand e-mail peter@comp.vuw.ac.nz Visualization applications often need to display objects that are both three dimensional and coloured. The objects may be represented either by surfaces or by volumes. The motivation behind such displays is to demonstrate two or more independent variables at once. So one variable may determine object shape and anotehr variable may determine the distribution of colour. A lighting model is needed to provide cues for visual shape recognition. Conventional lighting models provide these cues by altering colour. Hence a conflict arises when this approach is adopted because the total color variation is made up of two components that are perceptually indistinguishable. There are variations that show the distribution of a variable, and global variations caused by the lighting model. It might be said that a side effect of the light model is to distort the information represented by colour. This paper offers a solution to this problem be replacing the conventional lighting model with a structured lighting model of the kind used in machine vision context. The proposed solution simulates the shadow of a regular, planar grid on the surface of an object. Improved shape cues can be obtained by using a grid that is sensitive to lighting conditions, this generates a cross-hatch shading effect. The notion of a planar grid easily generalises to three dimensions, where it can be used not only with surfaces, but also with volumes. The benefit of the method is that colour is effected only locally, and in well defined places; the remaining colour is readily identifable and faithfully represents underlying data. In addition, the method in either of its forms is simple to incorporate into existing renderers. The method is demonstrated with results obtained from a computation fluid dynamics application. Both coloured iso-surfaces and coloured volumes are shown.ADVANCED DESIGN SOFTWARE FOR THE INJECTION MOULDS DESIGN BASED ON SOLID MODELLING TECHNIQUES Ir. T. S. HuangDivision of Production engineering, Machine design and Automation Faculty of Engineering, Department of Mechanical Engineering Katholieke Universiteit Leuven Celestijnenlaan 300B B-3001 Heverlee Belgium This paper describes a CAD software that focuces on computer-aided design for injection moulds using solid modelling techniques. The ultimate goal of this CAD software is to enable the designer to do various mould design works. It consists of two main modules, geoetric modelling and mould design. The former consists of a set of functions which can be used to create solid primitives and execute Boolean operations and the latter is able to support the design of standard mould components and some further applications such as the automatic determination of undercut, parting lines and parting surfaces, core and cavity plates, etc. This software is now implemental on a Unigraphics CAD/CAM system and operated in a dialogue mode to communicate with the user. Keywords : Solid modelling, three-dimensional convex hull, Injection moulds, Undercuts, Parting lines and parting surfaces.OPTIMIZING PATH TRACKING USING NOISE REDUCTION FILTERS Henrik Wann Jensen, Niels Joergen ChristensenDept. of Graphical Communication Technical University of Denmark fax : +45 45 93 83 17 phone : + 45 45 93 41 66 e-mail : igkhwj@unidhp.uni-c.dk, igkncj@unidph.uni-c.dk The problem of global illumination can be solved using path tracing. Unfortunatelly path tracing gives very noisy images. This noise is mostly caused by the indirect illumination reflected diffusely. The common way to reduce the noise is to use more samples/rays per pixel. However, tho convergence speed in path tracing makes this strategy very costly. In this paper we propose a technique in which light reflected diffusely two times is separated from the final solutin. This light is filtered by different noise reduction filters and then added to the remaining solution. In this way we avoid blurring the image and at the same time we are able to reduce the noise level significantly. Keywords : Global illumination, path tracing, noise reduction, filtering.GRAPHSUPPORT : INTERACTIVE MODELLING WITH COMPUTER GRAPHICS IN ASSISTING DESIGN Ö. KaraçaliUniversity of Technology, Loughborough, England e-mail O.karacali@lut.ac.uk This paper explains a novel approach that the dsesigner can be supported by interactive object modifications with graphics system. An engineering application, called GraphSupport system is identified and relations to the software support aspect is discussed. An example of industrial product in interactive modelling with objects is applied to GraphSupport to aid engineering design. Simple, yet versatile, information and functional modelling methods are introduced , allowing variants and views of the product to be represented and modified in a solid modelling environment.EFFICIENT FILTER COMPUTATIONS WITH SYMMETRIC MATRIX KERNELS Manfred KoppInstitute of Computer Graphics, Visualization and Animation Group Technical University of Vienna Karlsplatz 13/186-2, A-1040 Wien e-mail m.kopp@ieee.org, http://www.cg.tuwien.ac.at/~kopp/ This paper presents an algorithm for filter calculations using symmetric matrix kernels. This algorithm outperforms traditional methods for kernels larger than or equal to 5x5 on machines based on RISC designs, where the time needed to calculate an adittion equals the time needed for multiplication. The algorithm is based on a decomposition of the kernel matrix into several kernel matrices of decreasing size, which can be computed very fast because of spatial coherence. A comparison with traditional methods shows the efficiency of the presented approach. Keywords : image processing, anti-aliasing, filtering, symmetric matrix kernels, spatial coherence.PARAMETRIZING SUPERQUADRICS Helwig Löffelmann, Eduard GröllerInstitute of Computer Graphics Technical University of Vienna A-1040 Karlsplatz 13/186/2 Superquadrics are well known and often used 3D surface objects in computer graphics. They are used for modelling parts of scenes that are then rendered using photorealistic synthesis algorithms (e.g., ray tracing) . For some techniques, like texturing, which are part of these rendering methods, the type of the parametrization of such a surface has to be chosen carefully and is not intuitively obvious at first sight. There are cases, where the straightforward extension of quadric parametrizations to superquadrics do not produce satisfying results. We therefore investigate a number of different parametrizations in combination with the corresponding formulas, and point out some significant differences between them. Keywords : Conics, Superconics, Quadrics, Superquadrics, ParametrizationsTOPOLOGICAL OPERATIONS FOR NON-MANIFOLD MODELING David Marcheix, Stefka GueorguievaProcessing non-manifold topologies (abbreviated as NMT) plays a primary role in current development of solid modelling applications. Euler operators are a powerfull tool for creation of valid boundary representations of solids. By contrast with the manifold domain, where topological operators are well understood and implemented, there is a lack of elaboration of their non-manifold counterparts. In this paper we work out a basis of Euler-like operators for construction, maintenance and manipulation of boundary schemes of non-manifold objects. The presented algorithms are implemented for a NMT data structure and experimental results are discussed in the context of the completeness and soudness of the NMT operators. Keywords : geometric modelling, non-manifold topology, boundary representation, Euler operators, data structures, algorithms.AN AVERAGE-CASE COMPLEXITY OF RAY TRACING ALGORITHMS Gabor Marton, Laszlo Szirmay-KalosDepartment of Process Control Technical University of Budapest Budapest, Müegyetem rkp.9/R, H-1111, Hungary e-mail marton@seeger.fsz.bme.hu A theoretical framework for analyzing average-case time and storage complexity of ray tracing acceleration techniques is introduced by means of homogeneous spatial Poisson point processes. Then, as a demonstrative example of its application, the expected query time of the widely known techique based on a regular spatial grid is analyzed. Finally, an interpretation of the results is presented within the context of probability theory.USER-COMPUTER INTERACTION : COGNITIVE PROPERTIES OF ICONS FOR MULTIDIMENSIONAL DATA ANALYSIS Antonio Messina, Laura Moltedo, Silvana Contento, Roberto NicolettiDipartimento di Fisica "A.Righi", Universita di Bologna Instituto per le Applicazioni del Calcolo "M.Picone" , Roma Dipartimento di Psicologia, Universita di Bologna Dipartimento di Scienze Biomediche, Universita di Modena Italy In the graphical environment, icons (i.e. symbols or pictorial representations analogous to physical objects, actions or functions) are generally more informative and easier to manipulate than verbal labels. Because icon should resemble the functions they represent, pre-testing should be done to determine whether the user understands what the icons are supposed to symbolize. In the present work we aimed at establishing whether the criteria adopted to shape the icons of a graphic tool for the analysis of multidimensional field (MUDI3) were shared by the user. Method, procedure and results are presented and discussed.ON SCENE COMPLEXITY DEFINITION FOR RENDERING Ludovit Niepel, Jozef Martinka, Andrej Ferko, Pavol EliassDepartment of Computer Graphics and Image processing Comenius University, 842 15 Bratislava, Slovakia e-mail niepel, ferko, elias@fmph.uniba.sk Jozef.Martinka@st.fmph.uniba.sk This paper introduces one way how to define mathematically correct way the complexity of the polygonal scene for rendering. This complexity allows to compare previously uncomparable rendering algorithms via computing the complexity of various scenes, and give the more rigid solution of other related problems. The advantages of this unified approach are discussed.PARALLEL ADAPTIVE RAY_TRACING Irena Notkin, Craig GotsmanDepartment of Computer Science Technion - Israel Institute of Technology Haifa 32000, Israel e-mail {cyrus|gotsman}@cs.technion.ac.il We describe a dynamic task allocation algorithm for ray tracing by adaptive progressive refinement on a parallel computer. Parallelization of adaptive ray tracing is difficult because of the inherent sequential nature of the sample location generation process, which is optimized (and different) for any given scene. We report on experimental results obtained from our implementation of this algorithm on a Meiko parallel computer. The three performance measures of the algorithm, namely, load-balance, speedup, and image quality, are shown to be good.TUNNING RENDERED LINE-DRAWINGS Bernhard Preim, Thomas Strothottee-mail {bernhard|tstr}@isg,cs.uni-magdeburg.de Normally rendered imagesare the polished output of rendering software and are, by definition, "perfect". However, as we think about rendering abstractions of the underlying models, rather than photorealistic images, it becomes evident that user involvement is necessary to tune the rendered images to his or her satisfaction. In this paper we outline methods to tune rendered images. We concentrate on-line drawings, as these are most readily edited to make the modelled object appear more abstract. Rather than having user edit individual lines, our emphasis lies on studying, what users really want to achieve, and how we can support them more directly to attain these effects. This emphasis is used to guide the design of the user-interface to the system for tuning line-drawings. We present a tool which allows high-level intent-based interaction to generate line-drawings from rendered 3D-models. Included in the system are editting facilities to fine-tune and thereby individualizing line-drawings. High-level interaction draws on statistical methods to distribute over the rendered image. We show how the interaction can be improved if information about the model is available to the image editor. Keywords : Non-photorealistic images, line-drawings, architectual sketches, human-computer interaction.PHOTO-REALISTIC GRAPHICS FOR EMERGENCY LIGHTING VISUALISATION Thomas Ramstad, Alan ChalmersDepartment of Computer Science University of Bristol Bristol, BS8 1TR United Kingdom In an emergency situation it is vital that people are rapidly able to identify the exits. This is particularly important when the visibility of the sign can be significantly reduced, for example in a smoke filled room. There are several factors which contribute to a sign's visibility : the colour of the sign, luminance, size of letters, the location of the sign in the room and of course how engulfed the room is with smoke. It is also important to determine the visibility in clear and dark conditions. This paper describes a visualisation system under development which uses photo-realistic computer graphics techniques and parallel processing to provide an interactive tool for emergency lighting designers. The system will enable designers to investigate different positioning and illumination of emergency lighting under a variety of environmental conditions.VISUALIZATION OF SMOOTHED PARTICLE HYDRODYNAMICS Rene T. RauWSI/GRIS, Universität Tübingen Auf der Morgenstelle 10 D-72076 Tübingen, Germany Today smoothed particle hydrodynamics (SPH) play an important role in the computation of gas dynamical processes appearing in astrophysics and other fields. Nevertheless the visualisation techniques for this particle based model are still rudimentary. In order to visualize the density and pressure appearing in the simulation correctly we investigated the simulation in more detail. By this investigation we show that a splatting based visualization technique displays the volume density and pressure used in the simulation exactly. Furthermore we conclude that in our situation splatting is the only reasonable technique and is superior to other techniques such as raycasting. Finally, our visualization method enables the scientist to control the result of the simulation especially with few particles and gives high quality rendering at every state of the research process.******************** V O L U M E II **************************MULTIMEDIA INTERFACE FOR ADVANCED MATHEMATICS: OTTER 3.0 AS A CASE STUDY John F. RichardsonNCCOSC Code 44201 53560 Hull Street San Diego, Ca. 92152 United States e-mail richards@marlin. nosc.mil This paper describes a multimedia interface for the OTTER theorem proving system. This interface is implemented using an advanced multimedia authoring system based upon the SUPERCARD program. SUPERCARD is a Hypercard type system that basically solves most of the problems prevoiusly existing in Hypercard. This interface described in this paper is designed for the Macintosh computer although multimedia authoring systems exist for Unix and PC based systems. The primary purpose of this interface is to provide a "Macintosh look and feel" environment for the OTTER theorem proving system. The interface provides this look and feel through the use of hypermedia objects called cards. These cards serve as backdrops for interactive graphics and controls made available to the user for interacting with the theorem power. The secondary purpose of the interface is to provide a natural environment for navigating within the theoretical realms of Automated Reasoning, Logic Programming, Theorem proving and mathematics. The interface seeks to restructure the rules and symbols of the above realms into more "user friendly" and "intuitive" rules and symbols for use by students and general mathematicians. The interface also seeks to make it easier on experts in the field of Automatic theorem proving. Keywords : Multimedia, Automatic Theorem Proving, Expert Systems, Animation, HypermediaFLOW VISUALIZER Harald RuckserInstitut für Informatik Abteilung für graphishe und parallele Datenverarbeitung Universität Linz, Altenbergerstrasse 69, 4040 Linz Austria In this paper a new system for visualization of combined scalar and vector fields is presented. The methods implemented in this system are based on the use of combination AVOs (abstract visualization objects) consisting of arrows, spheres, isosurfaces, streamlines and cylinders. These AVOs improve the understanding of correlations between the spatial distributions of one vector and up to three scalar quantities, and enable simple forms of topological filtering. Furthermore, new clasification methods for visualization methods and AVOs are introduced, which, among others, describe the dimensionality of the data that a single AVO displays (DD - displayed dimensions). An extended model of the visualization process reveals important details of the microstructure of visualization, its transformational phases and objects.AN ARCHITECTURE OF MULTIMEDIA PLATFORM FOR INTEGRATED AUDIO-VISUAL DATA PROCESSING Ok-Keun Shin*, Hyun-Ki Kim and Young-Do ChaeElectronics and Telecommunications Research Institute Korea (* e-mail okshin@kiet.etri.re.kr) In this paper, we introduce an experimental hardware architecture of a multimedia data processing system called ComBiStation, whose applications area includes multimedia authoring, CSCW and video conferencing. The platform comprises most commonly needed multimedia processing functions: audio-visual data capture, playback, multistandard compression as well as interleaving of compressed audio visual data. The proposed architecture minimizes the CPU overhead that might be caused by multimedia data processing and assures the fluent data flow among system components. We begin with overall architecture of the whole system, and then audio-visual data capture/display unit and multistandard compression unit are discussed. Implementation issues and future works are also discussed. Keywords : Multimedia Platform, Compression, CSCW, Video ConferencingDITHERING AS A METHOD FOR IMAGE DATA COMPRESSION Pavel Slavik, Jan Prikryle-mail slavik@cslab.felk.cvut.cz, prikryl@sgi.felk.cvut.cz Abstract is not available. Keywords : data compression, dithering, parallel processingASPECT GRAPHS OF THREE_DIMENSIONAL SCENES Eduard SojkaDepartment of Computer Science Technical University of Ostrava ul.17.listopadu, 708 33 Ostrava-Poruba Czech Republic e-mail eduard.sojka@vsb.cz The paper presentes a new approach to the theory of aspect graphs. This approach is based on the presumption that an equivalence relation can be introduced on the set of images of a given scene. The equivalence relation induces the decomposition of the set of images, which is infinite, into the finite number of classes. Similarly, also the space surrounding the scene is decomposed into the classes. From every point of certain class, equivalent images of the scene are perceived. The aspect graph is the graph that contains the information about these classes and the relations between them. Presented theory enables to put the approaches published earlier into the unifying framework. The paper also presents an example in which the general theory of aspect graphs is applied to the three-dimensional problem. Also an algorithm for computing the decomposition of space into the classes is proposed. Keywords : Aspect graph, visual potential graph, visibilityDISCRETE RAY TRACING HIGH RESOLUTION 3D GRIDS Nilo Stolte, Rene CaubetInstitut de Recherche en Informatique de Toulouse 118, Route de Narbonne 31062 - Toulouse - France e-mail stolte@irit.fr This article suggests a new approach to discrete Ray-Tracing in which a two step three-dimensional DDA and an octree are used. A very important problem regarding this kind of Ray Tracing, also known as Raster Ray Tracing, is the amount of memory required to store the 3D raster grid which will contain the discretized scene to be visualized. Since the resolutin of this grid is huge because the voxel is assumed to be approximatelly the size of a pixel on the screen, it is l imited by the maximum amount of memory of today's machines. Although using an octree and assuming that the majority of space will be empty, as such is the case in most scenes, an important memory saving is achieved. This memory saving helps using discrete Ray Tracing in normal workstations. It is shown that the special octree presented here doesn't slow down Ray Tracing significantly and even competes with normal discrete Ray-Tracing. It is also shown that in critical cases this octree will not occupy much more space than a normal 3D grid. Another important problem is the bottleneck caused by the three dimensional DDA in such huge resolution grids. This problem is solved by dividing these grids into two low resolution ones. The process can be divided in two steps where optimal times of three-dimensional DDA are achieved. This is shown through the comparative tests with the single step process. Keywords : Ray-Tracing, Discrete Ray_tracing, Raster Ray-Tracing, Octree, Three-dimensional DDA, VoxelON CONVERGENCE AND COMPLEXITY OF RADIOSITY ALGORITHMS Laszlo Szirmay-Kalos and Gabor MartonDepartment of Process Control Technical University of Budapest Budapest, Müevetem rkp. 11,H-111 Hungary e-mail szirmay@fsz.bme.hu This paper evaluates and compares the convergence and complexity characteristics of radiosity algorithms with a special emphasis on randomized methods. Keywords: Radiosity method, complexity evaluation, randomized algorithmsVEGA : VIENNA ENVIRONMENT FOR GRAPHICS APPLICATIONS Robert F. Tobler, Helwig Löffelmann, Werner PurgathoferInstitute of Computer Graphics Technical University of Vienna A-1040 Karlsplatz 13/186/2 e-mail rft@cg.tuwien.ac.at, helvig@cg.tuwien.ac.at, wp@cg.tuwien.ac.at This paper presents a software development environment for rendering applications. The main parts of this environment are a set of rules concerning the coding style, a set of tools to maintain source files and a number of libraries providing graphics functionality. The environment has been succesfully used in a number of internal projects, dealing with rendering.A ROBUST OBJECT MODELING SYSTEM USING A RANGE FINDER Takashi Wada, Tatsuro Nakamura, Kaoru SuzukiKansai Research Lab. Toshiba 8-6-26 Motoyoma-Minami-machi, Higashi-Nada-ku, Kobe, 658 Japan Multimedia Engineering Lab. Toshiba 209, Suhiro-chou, Ome, Tokyo, 198 Japan e-mail wada@krl.toshiba.co.jp, tatsuro@mmfive.pms.mmlab.toshiba.co.jp suzuki@krl.toshiba.co.jp This paper presents a robust object modeling system that generates an object model from multiviewing range data. The purpose of the system is to obtain an exact model, overcoming a noise problem in range data. Our system computes object existence in voxel space by integrating observations form multi-viewpoints. The noise in range data is excluded by this integration process. Then, a triangular mesh is efficiently obtained by using adjacent relationships between voxels. Finally, a fine object model is acquired by associating brightness values in color image with the vertex on the mesh. Experiments are performed for plural real objects (dolls and a cup) and effectiveness of the system is shown.FREE FORM SURFACE CONSTRUCTION USING GREGORY PATCHES Shouqing Zhang, A.L.Thomase-mail: S.Zhang@central.sussex.ac.uk This paper deals with the construction of a free form surface by using both triangular and rectangular Gregory patches. The input is a set of 3D points associated with normal values at each point. All the control points needed for Gregory patch can then be calculated automatically to achieve the G1 continuity between neighbouring patches within surface. Keywords: Gregory patch, Triangular and Rectangular shape, G1 continuityEMPLOYING CONSTRAINTS TO FONTS Borut Zalik, Fiaz Hussain and Nikola GuidUniversity of Maribor Faculty of Technical Scienes Department of Computer Science Smetanova 17, SI-62000 Maribor Slovenia e-mail zalik@uni-mb.si, fiaz@dmu.ac.uk This paper gives a new approach for describing the outlines of characters. It uses geometric constraints to model characteristics of fonts. Such an approach is known to have applications in the area of rasterization, where so-called hints are introduced to maintain character legibility at low resolutions. In order to promote flexibility and performance, the technique outlined uses the principle of localised constraints. Its basic features are highlighted via its application on the Bezier cubic curve. Keywords : Bezier, constraint-based design, feature-based design, constraint solving, font, hints, rasterisation.TEXTURE CLASSIFICATION BY NEURAL NET IN MEDICAL SONOGRAPHY V. Cerny, L. Fekete, R. ZajacInstitute of Physics, Comenius University Mlynska dolina, 842 15 Bratislava, Slovakia Department of Urology, Medical Faculty Hospital Hlboka 7, 811 05 Bratislava, Slovakia e-mail cerny@fmph.uniba.sk We have developed a simple neural net classifier to evaluate textural informational content in the sonographic medical images. The net is trained on a set of texture patterns from sonographic images of testes. The samples in the set were classified by the supervisor into two classes: "normal" and "tumor". After training the performance was 85% correctly classified images. We are in the stage of collecting data for the independent test set of samples.A NOTE TO THE STRUCTURE OF BRESENHAM SLICE ALGORITHM Tomas Hruz, Ivo PovazanSlovak Technical University Faculty of Mechanical Engineering Namestie Slobody 17 812 31 Bratislava, Slovakia Institute of Control Theory and Robotics Slovak Academy of Sciences Dubravska cesta 9 842 37 Bratislava, Slovakia e-mail hruz@cvt.stuba.sk, utrrpova@savba.savba.sk This paper gives a complete analysis of the structure of segments (spans) of points with a constant y-coordinate, which are observed in the Bresenham Slice algorithm. In particular, we show that this structure is related to the greatest common divisor of the end-point coordinates.SCIENTIFIC VISUALIZATION WITH MAPLE Jiri HrebicekWaterloo MAPLE software GmbH, Heidelberg Abstract is not available.CATIA SOLUTIONS VERSION 4 - THE OVERVIEW OF THE CAD/CAM/CAE SYSTEM Ing. Miroslav KralIBM Czech Republic CATIA Solutions Version 4 builds on more than a decade of proven marketplace success for CATIA, which currently has more than 4 000 customers of all sizes worldwide in industries ranging from general manufacturing to aerospace, automotive and customer goods. CATIA is internationally recognized as an industry leader because it has benefited so many users and because of its comprehensive, integrated approach to the entire product design, manufacture and support process.REDUCING THE NUMBER OF SHADOW RAYS IN BIDIRECTIONAL PATH TRACING Eric P. Lafortune, Yves D. WillemsDepartment of Computer Science Katholieke Universität Leuven Celestijnlaan 200A, 30001 Heverlee, Belgium e-mail Eric.Lafortune@cs.kuleuven.ac.be Bidirectional path tracing is a fairly new Monte Carlo algorithm for physically based rendering. Introduced as a generalisation of path tracing, the algorithm traces paths for each pixel, not only from the eye point but also from the light sources. It subsequently links the intersection points on the respective paths by means of shadow rays. Each shadow ray determines if a lighting contribution has to be added to the estimate of the radiance of the pixel. In this paper we present a technique which reduces the number of shadow rays that are traced effectivelly. The resulting slight increase in the variance of the stochastic process can be undone by taking more samples. Practical tests show that the approach yields a reduction of the variance for the same amount of work.SIMULATING FEATURE-BASED MODELLING IN PROGRAMMING-BY-EAMPLE PARAMETRIC CAD Evgueni N. Loukipoudis and Jan A.A. MelkebeekDepartment of Electrical Power Engineering University of Gent Sint-Pietersnieuwstraat 41, B-9000 Gent, Belgium As an alternative to the development of a full feature-based CAD system, we suggest a fairly simple extension to a system that possesses parametric capabilities so that feature-based modelling interface is simulated. We use programming-by-example in defining features by parametric programs following a purely procedural approach. The parametric programs constitute the feature model which is built up in a bottom-up manner. The structuring of the object in features allows modifications to the parametric description in a graphical manner. Some problems related to the use of feature in an engineering system for the purpose of simulation and analysis as well as the handling of duality and comlementarity in a feature model are discussed. We have restricted our approach to 2D models and have implemented Electric Machinery specific features into 2D CAD system.STEREOGRAPHIC VISUALIZATION OF TURBULENT PIPE FLOWS USING ANALYPHS WITH TWOFOLD CENTRAL PROJECTION Wolfgang Messner, Walter HuberTechnische Universität München Institut für Informatik Lehrstuhl für Ingenieuranwendungen in der Informatik D-80290 München, Germany e-mail messner,huberw@informatik.tu-muenchen.de The size of velocity-vector fields obtained from numerical solutions of the Navier-Stokes equations for three-dimensional, time varying and turbulent flows is extremely large. Stereographic systems can intuitively depict the small depth movements and relations between fluid particles that standard perspective projections fail to. As expensive high-end-stereographics systems aim at one user one computer and are therefore not suitable for demonstration purposes in lectures, the anaglyphic method is applied for visualizing turbulence in a stereographic movie to a large number of people. A solution to overcome the effect of ghosting, which has been a major drawback in the use of anaglyphs, is introduced. A twofold central projection was found to be superior to standard on-axis projections in graphics harware allowing an easy representation of objects in front of and behind the projection plane and thus enhancing the stereoscopis effect. The visualization system deals with the small fluctuations of the velocity about its mean values (i.e. the so called rms values) to depict real turbulence in a pipe flow at reynolds number Re approx.7000.SOUND MAPPINGS FOR SURFACE VISUALIZATION Rosane Minghim and A.R.ForrestUniversity of East Anglia School of Information Systems Norwich NR4 7TJ UK e-mail rm@sys.uea.ac.uk, forrest@sys.uea.ac.uk This paper is concerned with the development of a system to support Scientific Visualization by utilising the sound channel. The mappings presented here are intended to support understanding and interaction with surface data. This is done by using sound signals associated with methods of analysis of surfaces to help the interpretation of surface shape, data, and classification. Several examples of sound mappings are presented and the implications for data interaction are discussed.A PARALLEL RADIOSITY SYSTEM FOR LARGE DATA SETS David Stuttart, Adam Worrall, Derek Paddon and Claire WillisDepartment of Computer Science University of Bristol Bristol, BS8 1TR, UK e-mail derek@compsci.bristol.ac.uk The radiosity method gives realistic results for syhtnesising images based on diffuse light interaction; however, the method is also very computationally expensive. Here we present a system for parallelising a progressive refinement radiosity method using a ray casting approach. The system decomposes the environment into two distinct entities, the model geometry and the radiosity sample points. These are then distributed amongst the processors and message passing communication protocols and caching methods are introduced to enable the system to cope with very large models while maintaining a high processing rate.COMPUTER ANIMATION AND HUMAN ANIMATORS Philip J. WillisComputing Group, School of Mathematical Sciences University of Bath Claverton Down. Bath BA2 7AY, UK e-mail P.J.Willis@bath.ac.uk There is often a gap between what technology can deliver and what users want. Sometimes this is because of fundamental technological constraints but often it is because technologists do not address the realities of user needs and expectations before attempting to solve the problem. The talk will describe our approach to computer animation and some of the pitfalls of trying to address a community which is visually more literate than typical computer graphic people, while being far less computer oriented. Keywords : computer animation, animationLOAD BALANCING FOR PARALLEL RAYTRACER ON VIRTUAL WALLS Jiri Zara, Ales Holecek, Jan Prikryl, Jan Burianek, Knut Menzele-mail zara@cs.felk.cvut.cz, holecek@sgi.felk.cvut.cz, prikryl@sgi.felk.cvut.cz, xburiane@sgi.felk.cvut.cz, knut@uni-paderborn.de Dynamic load balancing of parallel ray-tracing algorithm based on spacial subdivision is discussed. We attempt to find the load balancing method with the fastest respond on the load extreams in the system. An optimal architecture of the computational system based on three level process hierarchy is proposed. The scene partitioning is based on Virtual Walls. Keywords : computer graphics, rendering, parallel algorithm, ray-tracing, load-balancingGEOMETRIC MODELLING IN A THREE-DIMENSIONAL ENVIRONMENT G.J. Clapworthy, R.A. NobleDepartment of Computer & Information Sciences De Montfort University Hammerwood Gate Kents Hill Milton Keynes, MK7 6HP e-mail gclapwor@dmu.ac.uk Computer animators have long had difficulties in defining and controlling the shape of deformable objects during motion. In the context of human figure animation, a new form of surface description has been developed. Murugaiyan \& Clapworthy [1], which allows the surface to be manipulated by adjustment of a single parameter. The form of the surface deformations produced by the operations is under the control of the user. The mathematical structures used are extensions of NURBS, but have a greater flexibility at the cost of marginally-increased overheads. The development of this tool enables the surface modelling of a deformable object to be speeded up considerably, and the paper describes a geometric modeller currently under construction which will use this facility to produce the desired object by 'virtual sculpting', a process analogous to the production of real objects from clay. In this, the user is able to pull and push the surface shape to produce either rounded or shaped surface indentations or protrusions by direct interaction with the surface. The object is viewed stereoscopically and at present shutter glasses are used. These have the attendant problem of ghosting, but this can be removed by a subtract-from-background algorithm, Noble [2]. Ongoing work at De Monfort university [3,4] will eventually allow enhancement using autostereoscopic displays and eye tracking. The object is oriented in three dimensions using a spaceball and the surface operations are controlled using a mouse. The reduction in the number of paremeters employed in the surface description enables the operations on the surface to be performed by the use of the mouse buttons. Thus, the shape of the object is defined by simple 'point and click' operations providing an extremely rapid, interactive method of surface construction. It is anticipated that this modelling system could be used in a number of areas of work, including Virtual Reality. While the tool is still at the developmental stage, the paper lays out the complete conceptual basis for its construction and implementation.USING OF DISCRIMINATORY ANALYSIS TO PATTERN RECOGNITION OF TACTILE PATTERN Jaromir VolfCzech Technical University Faculty of Mechanical Engineering Technicka 4, 166 07 Prague 6 Czech Republic Tel.:+422 24 35 27 37, fax +422 24 31 02 92 e-mail volf@fsid.cvut.cz This papre described a new method of tactile pattern recognition. The method can be used a numeric regulator, too. This method is based on the discriminatory analysis. The computation is going through all system of pattern classes. This corresponds to classical computing process, which is used in the discriminatory analysis. The Ivanovic deviation is used as discriminatory function. The m dimensional vector is impute and the method can classify into n groups of patterns. Pattern recognition can work at a real time. Keywords : discriminatory analysis, tactile, pattern, image, pattern recognitionCOMPARISON OF SOME RAY GENERATORS FOR RAY TRACING VOLUMETRIC DATA Milos SramekInstitute of Measurement Science Slovak Academy of Sciences Dubravska cesta 9 842 19 Bratislava, Slovak Republic Ray tracing is a popular technique for rendering not only analytical objects, but also volumetric data, either synthetized or measured. Different techniques for the ray definition by traversal of the voxel space were designed. The first part of the paper is an overview of ray tracing or ray casting algorithms for the volume data. Stress is laid upon exploiting various kinds of speed up techniques. In the second part, we compare some of these approaches in a computer experiment. Further we show that an appropriate choice of background traversal algorithm can significantly shorten computation time of the exact ray-surfrace intersection point.GRAPHICAL REPRESENTATION OF RULES IN AN OBJECT-ORIENTED ENVIRONMENT Kenneth Messa, Bogdan Czejdo, Erick VillalobosDepartment of Mathematics and Computer Science Loyola University New Orleans, LA U.S.A. In this paper a graphical representation of rules is proposed. The graphical rules are formulated based on Extended Entity-Relationship (EER) diagrams. Such diagrams are compiled into an object-oriented language code that is included as a component of the developed software system. Other components can be directly coded in an object-oriented language or generated using other graphical tools. We identify and discuss two types of graphical rules : class graphical rules and instance graphical rules. The syntax and semantics of both types of graphical rules are discussed. The graphical rules can contain object-oriented code in addition to graphical diagrams. The methods of integration of diagram and object-oriented code are described.