- EG1989 Proceedings (Technical Papers)

# EG1989 Proceedings (Technical Papers)

## Permanent URI for this collection

Accelerated Radiosity Method for Complex Environments

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Xu, Hau

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Peng, Qun-Sheng

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Liang, You-Dong

Pixel Selected Ray Tracing

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Akimoto, Taka-aki

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Mase, Kenji

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Hashimoto, Akihiko

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Suenaga, Yasuhito

The Macro-Regions: An Efficient Space Subdivision Structure for Ray Tracing

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Devillers, Olivier

The Structure of Tube - A Tool for Implementing Advanced User Interfaces

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Hill, Ralph D.

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Herrmann, Marc

A VLSI Chip for Ray Tracing Bicubic Patches

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Bouatouch, Kadi

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Saouter, Yannick

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Candela, Jean Charles

Components, Frameworks and GKS Input

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Duce, D. A.

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Ten Hagen, P.J.W.

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Van Liere, R.

Two Object-Oriented Models to Design Graphical User Interfaces

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Hübner, Wolfgang

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Gomes, Mario Rui

On the Software Structure of User Interface Management Systems

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Burgstaller, Johann

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Grollmann, Joachim

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Kapsner, Franz

Visualisation of Digital Terrain Data

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Thiemann, Rolf

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Fischer, Joachim

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Haschek, Guido

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Kneidl, Gerald

A Parallel Image Computer with a Distributed Frame Buffer: System Architecture and Programming

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Potmesil, Michael

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McMillan, Leonard

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Hoffert, Eric M.

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Inman, Jennifer F.

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Farah, Robert L.

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Howard, Marc

Deformation of Solids with Trivariate B-Splines

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Griessmair, Josef

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Purgathofer, Werner

Non-Planar Polygons and Photographic Components for Naturalism in Computer Graphics

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Hofmann, Georg Rainer

Forest of Quadtrees: An Object Representation for 3D Graphics

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Kaufman, Arie

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Bandopadhay, Amit

Adding Parallelism in Object Space to the Rendering Pipeline

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Chapman, Paul A.

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Lewis, Eric

Visualisation in Astrophysics

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Ertl, T.

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Geyer, F.

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Herold, H.

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Kraus, U.

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Niemeier, R.

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Nollert, H.- P.

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Rebetzky, A.

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Ruder, H.

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Zeller, G.

Hierarchical Texture Synthesis on 3-D Surfaces

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Bennis, Chakib

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Gagalowicz, Andre

A Topological Map-Based Kernel for Polyhedron Modelers: Algebraic Specification and Logic Prototyping

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Dufourd, Jean-Francois

Highlight Shading: Lighting and Shading in a PHIGS+/PEX-Environment

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Poepsel, J.

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Hornung, C.

A Model for Description and Synthesis of Heterogeneous Textures

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Englert, Gabriele

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Sakas, Georgios

Toward Realistic Formal Specifications for Non-Trivial Graphical Objects

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Fiume, Eugene

Anti-Aliasing by Successive Steps with a Z-Buffer

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Ghazanfarpour, D.

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Peroche, B.

A Reference Model for the Visualisation of Multi-Dimensional Data

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Bergeron, R. Daniel

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Grinstein, Georges G.

Representing Tolerance Information in Feature-Based Solid Modelling

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Falcidieno, Bianca

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Fossati, Bruno

The Use of Finite Element Theory for Simulating Object and Human Body Deformations and Contacts

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Gourret, Jean-Paul

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Magnenat-Thalmann, Nadia

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Thalmann, Daniel

Graph Grammars, A New Paradigm for Implementing Visual Languages

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Goettler, Herbert

When is a Line a Line?

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Brodlie, Ken W.

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Göbel, Martin

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Roberts, Ann

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Ziegler, Rolf

Message-Based Object-Oriented Interaction Modeling

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Breen, David E.

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Kühn, Volker

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Item Accelerated Radiosity Method for Complex Environments(Eurographics Association, 1989) Xu, Hau; Peng, Qun-Sheng; Liang, You-DongShow more As form-factor calculation costs about 90% of the computing time when applying radiosity approach for realistic image synthesis, it is of great significance to reduce the required computation, An accelerated radiosity algorithm for general complex environments, based on environment localization and the directional form-factor concept, is presented in this paper. First we subdivide the object space into many regions. Objects contained in each region are adjacent to each other and pose more illumination effects to their neighbours. Then form-factors are calculated in each local environment,. The radiant light energy transfer between different regions is evaluated at their common boundaries. Directional form-factors are introduced to simulate the interaction of light between local environments and between non-diffuse surfaces. Comparison is made to existing algorithms. Statistic results and theoretical analysis show that the new algorithm is much faster than previous ones. The technique is especially fit for interactive design and animation sequence since modification to the shape or location of objects usually happens in local environments.Show more Item Pixel Selected Ray Tracing(Eurographics Association, 1989) Akimoto, Taka-aki; Mase, Kenji; Hashimoto, Akihiko; Suenaga, YasuhitoShow more This paper presents a new ray-tracing acceleration technique called Pixel Selected Ray-Tracing (PSRT). PSRT uses undersampling based on Iterative Central Point Selection(ICPS) along with checking for similarities among trees in neighboring pixels. By using ICPS and trees, the largest danger of missing object borders can be drastically reduced. Although the speed increase attributable to PSRT varies with the image generation environment, according to experiments comparing PSRT with standard ray-tracing, PSRT is 2.6 to 8.2 times faster than standard ray-tracing for 512 by 512 pixel images, maintaining the same visual image quality. It is true that images generated by this method may contain very small errors. However, such errors can be reduced and may be made visually negligible by using ICPS and the trees of ray-object intersection to check for similarities.Show more Item The Macro-Regions: An Efficient Space Subdivision Structure for Ray Tracing(Eurographics Association, 1989) Devillers, OlivierShow more Ray tracing is the usual image synthesis technique which allows rendering of specular effects. The use of space subdivision for ray tracing optimization is studied. A new method of subdivision is proposed : the macro-regions. This structure allows a different treatement of the regions with a low density of information, and the regions with a high density of information. A theoretical and practical study of space subdivision methods -grid, octree- and the macro-regions structure is presented.Show more Item MICRO-UIDT: A User Interface Development Tool(Eurographics Association, 1989) Mao, QijingShow more A user interlace development tool called Micro-UIDT is described. Micro-UIDT provides an interactive design environment fur the user interface designers. The designing language for defining user interfaces are visual and nonprocedural. State transition diagrams are used as the notation for specifying man-machine dialogue control. Some extensions are added into the notation, so that the user interfaces with semantic feedback can be defined. The approach of specifying the presentation of application data is bottom-up and direct operation. The designing language for this has two major description facilities, one for describing graphics and another for describing the relationships between the graphics and the application variables. A concept of graphic object is used in the language, which can make the design result be abstracted and reused. The user interfaces developed with Micro-UIDT are small in size and fast in speed.Show more Item The Structure of Tube - A Tool for Implementing Advanced User Interfaces(Eurographics Association, 1989) Hill, Ralph D.; Herrmann, MarcShow more Good user interfaces are very costly to implement and maintain. As user interfaces become more advanced, moving to various forms of direct manipulation, they become even more expensive and difficult to implement. In the recent past, many user interface management systems and related tools for the rapid development of user interfaces have been developed. Some have been successful at reducing interface development costs for some styles of interface, but none fully address the requirements of advanced direct manipulation interfaces. We claim this is because they are founded on basic models and components that work only for simpler interaction styles. We present Tube, a tool for the rapid development of advanced direct manipulation user interfaces, describe its structure, and show how it differs from, and is better than, traditional structures.Show more Item Ray Tracing Polynomial Tensor Product Surfaces(Eurographics Association, 1989) Giger, ChristineShow more With regard to ray tracing algorithms for polynomial tensor product surfaces, the most timecritical step is to find an intersection point of a ray and a surface. In this case it proves to be very difficult to decide whether numerical methods will converge to the correct solution. In this paper we present a new method based on numerical algorithms which is suitable to solve the intersection problem. We mention how to force correct convergence and give some information about techniques to speed up the algorithm.Show more Item A VLSI Chip for Ray Tracing Bicubic Patches(Eurographics Association, 1989) Bouatouch, Kadi; Saouter, Yannick; Candela, Jean CharlesShow more This paper deals with the integration of a VLSI chip dedicated to ray tracing bicubic patches. A recursive subdivision algorithm is embedded in this chip. The recursion stops when the termination conditions are met. A software implementation allowed for the determination of key parameters which influenced the choice of the proposed chip' architecture. Only some modules of the chip are, at the present time, simulated and laid out, the rest is being implemented. A detailed description of the chip' modules is given.Show more Item Components, Frameworks and GKS Input(Eurographics Association, 1989) Duce, D. A.; Ten Hagen, P.J.W.; Van Liere, R.Show more This paper was inspired by the Components/ Frameworks approach to a Reference Model for computer graphics, currently under discussion in the ISO computer graphics subject committee. The paper shows how a formal description of the GKS input model may be given in Hoare’s CSP notation and explores some extensions in which some of the components in the GKS model are replaced by more interesting ones. The paper thus demonstrates some of the power and flexibility inherent in the Component/ Frameworks idea. The use of a formal notation led to a deepening of the authors’ understanding of the input model and suggested some different ways of looking at the input model.Show more Item Two Object-Oriented Models to Design Graphical User Interfaces(Eurographics Association, 1989) Hübner, Wolfgang; Gomes, Mario RuiShow more Object-oriented concepts are well-suited to deal with the characteristics of user interfaces. Up to now several attempts to integrate the object-oriented paradigm in user interface models were evolved and led to distinctive resulting models due to different requirements of the target application area. Within this paper two independently developed object-oriented interaction models are presented which emphasize the graphical requirements to user interfaces. These are among others its hierarchical nature, dynamical topology of the user interface, strong connection between input, output and the semantics of the application and the diversity of the graphics input devices and interaction techniques. Both approaches converge in the following aspects: Instead of having separated user interface layers the components of an interactive graphics application's user interface are embedded locally within interaction objects. Therefore dialogue control, input, output and the dynamical behavior are organized as a micro-cosmos within each object. Compound interaction objects can be designed. Temporal logical operators are used to specify the dialogue. Tools to support the implementation of each model are described. By describing both approaches this paper could be a contribution toward establishing a uniform object-oriented framework for the design of graphical user interfaces.Show more Item On the Software Structure of User Interface Management Systems(Eurographics Association, 1989) Burgstaller, Johann; Grollmann, Joachim; Kapsner, FranzShow more Specific systems for the development of user interfaces (Uls) are used today for coping with the increasing problems of human-computer communication. Some of those systems are based on well-defined models for humancomputer interaction. Important requirements of such systems are: consideration of standards, most notably graphics functionality and windowing functionality, openness to all interaction styles, and provision of comfortable design tools that allow UI prototyping. An evaluation of the existing systems reveals that they fulfill only some of those requirements. We present a layered model for the interface between an application's functionality and its UI, which explicitly takes care of standards. Based on this model we implement a system for efficient design and administration of Uls. An internal interface among all tools, namely, a PROLOG-like formalism used for the description of UI objects, is of central importance. This formalism makes all tools independent from the dialog objects, hence our system is truly open. The core of our system consists of a comfortable graphically interactive editor for UI design and an interpreter. The interpreter is mainly responsible for the presentation of Uls which are described according to this formalism. The output of the editor will be a description of Uls according to the formalism. Our oal is the development of a functionally complete object-oriented set of formalism-based tools; these tools will also use artificial intelligence techniques for an adaptation of Uls to user needs.Show more Item Visualisation of Digital Terrain Data(Eurographics Association, 1989) Thiemann, Rolf; Fischer, Joachim; Haschek, Guido; Kneidl, GeraldShow more Visualisation technology has found practical application in the field of terrain data processing. A raster data base (RDB-) concept will be introduced, i.e. a multi-dimensional concept of terrain data using elevation data, description data and/or aerial image or satellite data. Other data sources in raster or vector form may also be considered. Methods of 2- and 3-D-imaging of terrain data are pre- sented. Two-dimensional presentation will include grey- and colorcoding of different RDB layers. Techniques for superimposing two datasets are shown using relief data as one source. Color-coding, color-space transformation or a slide-effect process will be used for superimposition. The mapping of aerial image or satellite data onto the relief data will be achieved by known texture-map algorithms. The overlay technique is used for superimposing raster with vector data from geographic data bases. For superimposition, the geometry of the two datasets must not be different. Many applications need the generation of perspective views of the terrain data. For the generation a terrainraytracer will be introduced. Color impression again will be achieved by texture-mapping. Fore- and background can be handled separately. All algorithms presented are implemented in the GELA software.Show more Item A Parallel Image Computer with a Distributed Frame Buffer: System Architecture and Programming(Eurographics Association, 1989) Potmesil, Michael; McMillan, Leonard; Hoffert, Eric M.; Inman, Jennifer F.; Farah, Robert L.; Howard, MarcShow more We describe the system architecture and the programming environment of the Pixel Machine - a parallel image computer for 2D and 3D image synthesis and analysis. The architecture of the computer is based on an array of asynchronous MIMD nodes with a parallel access to a large frame buffer. The system consists of a pipeline of pipe nodes which execute sequential algorithms and an array of m x n pixel nodes which execute parallel algorithms. A pixel node accesses every m-th pixel on every n-th scan line of a distributed frame buffer. Each processing node is based on a high-speed, floating-point programmable processor. The programmability of the computer allows all algorithms to be implemented in software. A set of mapping functions transfers image algorithms written for conventional single-processor computers to algorithms which execute in the pixel nodes and access the distributed frame buffer. The ability to use floating-point computations in pixel operations, such as antialiasing, ray tracing, and filtering, allows high-quality image generation and processing. The image computer provides up to 820 megaflops of peak processing power and 48 megabytes of memory for data-visualization applications.Show more Item Deformation of Solids with Trivariate B-Splines(Eurographics Association, 1989) Griessmair, Josef; Purgathofer, WernerShow more Solid geometric models can be deformed to free-form solids by the use of trivariate B-splines. This paper describes the problems of implementing such transformations for shaded rendering. The surfaces are subdivided into triangles adaptively so that the error in image space is limited. This adaptive triangulation ensures a smooth appearance of the resulting pictures.Show more Item Non-Planar Polygons and Photographic Components for Naturalism in Computer Graphics(Eurographics Association, 1989) Hofmann, Georg RainerShow more The measuring of natural objects like landscapes and already existing (not simply planned!) buildings produces natural data. That data of hue geometry typically consists of Non-planar Polygons. These may be triangulized, but the results are unfortunately: - a large increase of the number of polygons, - texture mapping becomes more complicated, - facetting effects in the rendered image. This paper addresses methods and algorithms of the direct rendering of Non-planar Polygons. Special "texture mapping" is presented to insert especially Photographic Components in Non-planar Polygons to obtain naturalistic images. With Photographic Components, a very simple illumination model is sufficient to obtain good results in rendering quality. Further on an application example is presented. The images of this example are outstanding both for their naturalism and the little computer CPU time spent for their rendering. Basics on naturalism and photorealism in Computer Graphics are discussed.Show more Item Forest of Quadtrees: An Object Representation for 3D Graphics(Eurographics Association, 1989) Kaufman, Arie; Bandopadhay, AmitShow more A forest of quadtrees is proposed as an alternative data structure for representing and manipulating 3D and 2.5D graphics. A data representation of a forest offers space savings over common quadtrees by concentrating the vital information and discarding unused pointers. Several properties of the forest of quadtrees and the basic operations for display and elementary transformations like rotation, reflection, enlargement, reduction, and translation are investigated. Specifically, the temporary memory requirements and duplication time of the algorithms are analyzed.Show more Item Adding Parallelism in Object Space to the Rendering Pipeline(Eurographics Association, 1989) Chapman, Paul A.; Lewis, EricShow more This paper analyses the problem of adding parallelism to the rendering pipeline and discusses the reasons for advocating an object-space partition. Consideration of the methods of work distribution and the rendering techniques which are desired, leads to the proposition of two algorithms for performing the partition. An architecture for their implementation is considered and evaluated.Show more Item Visualisation in Astrophysics(Eurographics Association, 1989) Ertl, T.; Geyer, F.; Herold, H.; Kraus, U.; Niemeier, R.; Nollert, H.- P.; Rebetzky, A.; Ruder, H.; Zeller, G.Show more This paper reports on progress we have made in modelling cosmic X-ray sources on supercomputers. The results we present are meant to serve as an example for the fact that sophisticated visualization techniques play a crucial role in scientific computing. Among the graphical methods we demonstrate, raytracing in curved space-time and a physically motivated 3D-volume rendering algorithm might be of interest to the graphics community in general.Show more Item Delauney Triangulations and the Radiosity Approach(Eurographics Association, 1989) Schuierer, SvenShow more The radiosity approach requires the subdivision of complex surfaces into simple components called patches. Since we assume to have constant intensity over a patch, the generation of regular patches is a desirable property of the subdivision algorithm. We show that constrained Delaunay triangulations produce patches that are as close to equilateral triangles as possible and thus are well suited for the partitioning of surfaces into patches. Since a number of optimal algorithms to generate constrained Delaunay triangulations have been published, the implementation presented here made use of the earlier work. The implementation consists of a rather simple modeling tool called POLY, a fast triangulation algorithm for arbitrary polygons and the form factor computation combined with a z-buffer output module.Show more Item Hierarchical Texture Synthesis on 3-D Surfaces(Eurographics Association, 1989) Bennis, Chakib; Gagalowicz, AndreShow more This paper presents a new method for synthesizing hierarchical textures on 3-D surfaces. This method utilizes both a mapping technique for rendering the macroscopic structure on the surface and a generalization of the direct 3-D microscopic synthesis algorithms (presented in earlier publications) for generating a homogeneous texture inside each pattern. To produce the macroscopic structure on the 3-D shape a new mapping technique is proposed. With this technique patterns distortion is minimized locally. Finally a solution to the aliasing problem adapted to our mapping is given.Show more Item A Topological Map-Based Kernel for Polyhedron Modelers: Algebraic Specification and Logic Prototyping(Eurographics Association, 1989) Dufourd, Jean-FrancoisShow more This paper deals with the topology of surfaces, in the boundary representation of three dimensional objects. Orientable, not orientable, closed or open surfaces are efficiently described and handled when considered as combinatorial generalized maps. An algebra of such maps is first described. Using this algebra, operations to build polyhedra step by step are next defined. That is the basis of a graphical modeler presently under consideration. The presentation uses algebraic software specification techniques in an abstract way. Finally, a systematical validation of the specification by logic prototyping is described.Show more Item Highlight Shading: Lighting and Shading in a PHIGS+/PEX-Environment(Eurographics Association, 1989) Poepsel, J.; Hornung, C.Show more Todays graphics standard for the rendering of scenes with illumination and reflection is defined by PHIGS+ . PEX is a proposal to integrate that functionality into the window environment of X. This paper first describes the lighting and shading models of PHIGS+/- PEX . Then a comparison of the different shading methods follows. At last, a new shading method, the Highlight Shading, is developed. The Highlight Shading combines both speed and image quality and therefore is an attractive alternative to existing shading algorithms.Show more Item A Model for Description and Synthesis of Heterogeneous Textures(Eurographics Association, 1989) Englert, Gabriele; Sakas, GeorgiosShow more Existing texture models either describe textures as a non-hierarchical surface property (by means of Markov chains, time series and other stochastic methods) or distinguish only between micro and macro textures. Besides this, textures are used in general only for mapping colour-information (usually derived from digitized photographs) on the object surface or for varying the normal vector of a given surface (bumps mapping). In addition, the different models are strongly combined with special generation algorithms and the produced textures are exclusively raster images. As a consequence, the above models are not able to describe more than a few types of textures. In this paper a definition of the term texture is first presented and a hierarchical texture model in accordance with the above definition is then proposed. We provide complete textures, consisting of several slices, to be mapped on geometrical objects. Each slice represents an optical surface property. These properties are. approximated by the different parameters of an illumination model. The slices themselves are hierarchical compositions of several levels. Each "intermediate texture" is derived by operations (transformations and combinations) performed on the textures of the next lower level. A texture is not limited in space and is described by means of a complete texture function which affects all texture slices. Such functions can be either usual algebraical functions, or they can determine the placement of elements on the texture plane.Show more Item GKS, Structures and Formal Specification(Eurographics Association, 1989) Duce, D. A.Show more There are now three International Standards for application program interfaces for computer graphics programming, GKS, GKS-3D and PHIGS. In this paper a simplified model GKS-like system is described and a 2D PHIGS-like system is then described in terms of this and a centralized structure store. Formal specifications of the systems are given illustrating how the specification of a system can be built up from a hierarchy of simple components. The purpose of the paper is to illustrate one approach to the description of a compatible family of graphics standards and the use of formal specification techniques in this process.Show more Item Toward Realistic Formal Specifications for Non-Trivial Graphical Objects(Eurographics Association, 1989) Fiume, EugeneShow more Formal specification has long been advocated in programming methodology, and is becoming increasingly popular in computer graphics to characterise the semantics of components of graphics systems. Unfortunately, formal specifications tend to sacrifice realism for abstraction. The result is often a specification that is not as relevant to real graphics systems as it could be. This paper suggests that the use of sharper mathematical tools, together with the use of object orientation (i.e., data abstraction with inheritance) provides a way of resolving this problem. As an example, we attempt to specify formally classes of bitmaps and images. These are particularly interesting choices, for bitmaps and images are mutable, bitmaps can have a perceived effect on images, and their semantics depends on context.Show more Item On Reducing the Phong Shading Method(Eurographics Association, 1989) Claussen, UteShow more Today, the shading method of Phong plays an important role in the design of realtime image generation systems. Often, the model has been used in combination with a color interpolation, suppressing a main property of this model, namely the visually acceptable rendering of highlights. Unfortunately, Phong’s algorithm demands a normalization, which is expensive to implement in hardware. We will present several shading methods which are reductions of the Phong algorithm. They will be compared both visually and theoretically. The alternatives are judged concerning their costs for a hardware implementation. The result is a hierarchy of shading methods that can be used to select the required cost-performance ratio for a given visualization task.Show more Item Anti-Aliasing by Successive Steps with a Z-Buffer(Eurographics Association, 1989) Ghazanfarpour, D.; Peroche, B.Show more We present a method allowing to solve the three problems arising when a scene is displayed with the z-buffer algorithm. The proposed algorithm only requires one extra memory bit per pixel and delivers good quality images. It is fast because, in particular, the most expensive calculations such as antialiasing or texture mapping are made only for visible pixels of the scene.Show more Item Algorithms for 2D Line Clipping(Eurographics Association, 1989) Skala, VaclavShow more New algorithms for 2D line clipping against convex, non-convex windows and windows that consist of linear edges and arcs are being presented. Algorithms were derived from the Cohen-Sutherland 's and Liang-Barsky s algorithms. The general algorithm with linear edges and arcs can be used especially for engineering drafting systems. Algorithms are easy to modify in order to deal with holes too. The presented algorithms have been verified in TURBO-PASCAL. Because of the unifying approach to the clipping problem solution all algorithms are simple, easy to understand and implement.Show more Item Colour Section(Eurographics Association, 1989) -Show more Item GEO++ - A System for Both Modelling and Display(Eurographics Association, 1989) Wisskirchen, PeterShow more We present a new concept for a graphics system which we call GEO++ . Apart from the manipulation of groups (structures in PHIGS-terminology), GEO++ permits a direct access to the tree structure required for display. With this concept we believe to have achieved a synthesis between the requirements of modelling in the sense of manipulation of building patterns and of display in the sense of editing individual objects (parts) on the screen.Show more Item Subdivisions of Surfaces and Generalized Maps(Eurographics Association, 1989) Lienhardt, PascalShow more The modeling of subdivisions of surfaces is of greatest interest in Geometric Modeling (in particular for Boundary Representation) , and many works deal with the definition of models, which enable the representation of closed, orientable subdivisions of surfaces, and with the definition of elementary operations, which can be applied to these models (Euler operators) . We study in this paper the notion of 2-dimensional generalized map (or 2-G-map), which make possible the definition of the topology of any subdivision of surface, orientable or not orientable, opened or closed ; reciprocally, the topology of any subdivision of any surface may be defined by a 2-G-map . Three characteristics are associated to any 2-G-map G (the most elementary being the number of boundaries, the most known being the genus ...), and can be directly computed on G . These characteristics define the subdivision of surface modelled by G (static classification of the subdivision) . We define also operations which can be applied to 2-G-maps . Any 2-G-map (and then any subdivision of surface) can be constructed by a sequence of operations . To these operations correspond variations of the characteristics associated to the 2-G-maps . These variations enable the control of the effect of an operation on the modelled subdivision (dynamic classification of the subdivision) . The notion of 2-G-map defines the different elements of a subdivision (vertex, edge, face, bound ary...) by using one unique kind of elements, in a rigorous and unambiguous manner. Data structures may be deduced from the notion of 2-G-map . These data structures make possible the representation of any subdivision of surface , in a way near to the well-known "windged-edge" data structure defined by B. Baumgart in [BA75] . The constraints of consistency about these data structures can be directly deduced from the definition of 2-G-maps . The set of the properties of 2-G-maps (rigour, consistency, possibility of static or dynamic classification) makes the greatest interest of the 2-G-maps, with respect to other models of subdivisions of surfaces used in Geometric Modeling .Show more Item 2.5 Dimensional Graphics Systems(Eurographics Association, 1989) Herman, IvanShow more The outline of an extension of traditional 2D graphics systems is given. This extension is aimed at supporting a three dimensional application program, without incorporating full viewing into the general graphics system itself. The resulting system might be very advantageous for large application programs which have their own three dimensional facilities.Show more Item Blending Rational B-Spline Surfaces(Eurographics Association, 1989) Bardis, L.; Patrikalakis, N.M.Show more A method for blendin non uniform rational B-spline surface patches, either open or periodic, is developed. he blending surface is expressed in terms of an integral, bicubic B-spline patch. The blend ensures position and normal vector continuity along linkage curves to within a specified accuracy. The linkage curves are either user-defined or are obtained by offsetting the intersection of the two patches using geodesics on each patch. An example illustrates the applicability of our method.Show more Item A Reference Model for the Visualisation of Multi-Dimensional Data(Eurographics Association, 1989) Bergeron, R. Daniel; Grinstein, Georges G.Show more This paper presents a reference model for the development of systems for the visualization of multidimensional data. The purpose of the reference model is to build a conceptual basis for thinking about multi-dimensional visualization and for use in developing visualization environments. We describe the reference model in terms of the fundamental concepts of PHIGS (Programmer’s Hierarchical Interactive Graphics System), but extend those concepts to the representation of objects of arbitrary dimensionality.Show more Item Visualizing Curvature Discontinuities of Free-Form Surfaces(Eurographics Association, 1989) Pottmann, HelmutShow more A new method for the visualization of curvature discontinuities of free-form surfaces is presented. It is based upon an improvement and refinement of the well-known technique of displaying isophotes.Show more Item An Analysis of Modeling Clip(Eurographics Association, 1989) O Bara, Robert M.; Abi-Ezzi, SalimShow more Modeling clip gives an application the ability to remove sections of an object in order to view internal detail. The clipping volume defied by modeling clip can be concave and disjoint, and is composed of a set of volumes that are specified in modeling coordinates. The modeling clip functionality has been included in the PHIGS specification [4], Some interesting peculiarities arise from the fact that most graphics pipelines (such as PHIGS) are algebraically based and that modeling clip regions are specified in modeling coordinates. One such peculiarity occurs when the transformation relating the coordinate system of the clip region to world coordinates is singular. A study on the algorithmic and architectural issues of implementing modeling clip is presented. The resulting algorithm to implement the modeling clip mechanism represents the clip volume as a pipeline of filters with each filter representing one of the sub-volumes. The method handles all of the sixteen possible set combinations between two regions in space. The effects of transformations on modeling clip have been examined, and has resulted in identifying when modeling clip can be efficiently performed in device coordinates as well as the cases when it can not. When handling singular modeling transformations, it is shown that it iShow more Item Representing Tolerance Information in Feature-Based Solid Modelling(Eurographics Association, 1989) Falcidieno, Bianca; Fossati, BrunoShow more In this paper a system for defining dimensions and tolerances is presented which deals with the geometric representation of the objects in a coherent and compact way. This model is a combination of a hierarchical boundary model to represent geometry of the object with features and a relational graph model to encode dimensions and tolerances. In this way, the proposed model can be considered a ”product model” that, besides geometric and topological information about the feature components of a solid object, also codifies information about dimensions represented by relative positron operators connected to faces which are the primitive geometric entities of the object model. The method can automatically control the validity of the geometric and topological model of the object each tame that a new tolerance node is added to the structure or a tolerance constraint already existing is modified. In this case, it also translates changes in dimensional values into corresponding changes an geometry and topology.Show more Item The Use of Finite Element Theory for Simulating Object and Human Body Deformations and Contacts(Eurographics Association, 1989) Gourret, Jean-Paul; Magnenat-Thalmann, Nadia; Thalmann, DanielShow more This paper presents a method for combining image synthesis and modeling based on a finite element method (FEM) to get realistic intelligent images. FEM is used for modeling both elastically and plastically deformations of objects, and impacts with or without penetration between deformable objects. The concept of deformable objects is applied to human flesh to improve the behavior of synthetic human grasping and walking. The paper also discusses the introduction of this method in an animation system based on the concept of "intelligent" synthetic actors with automatic motion control performed using A.I. and robotics techniques. In particular, motion is planned at a task level and computed using physical laws.Show more Item Graph Grammars, A New Paradigm for Implementing Visual Languages(Eurographics Association, 1989) Goettler, HerbertShow more This paper is a report on an ongoing work which started in 1981 and is aiming at a general method which would help to considerably reduce the time necessary to develop a syntax-directed editor for any given diagram technique. The main idea behind the approach is to represent diagrams by (formal) graphs whose nodes are enriched with attributes. Then, any manipulation of a diagram (typically the insertion of an arrow, a box, text, coloring, etc.) can be expressed in terms of the manipulation of its underlying attributed representation graph. The formal description of the manipulation is done by programmed attributed graph grammars.Show more Item Supporting Graphical Languages with Structure Editors(Eurographics Association, 1989) Szwillus, GerdShow more Graphical editors are used in numerous application fields for purposes like specification, design, modelling, or description of structures of various kinds. These editors handle the graphical representations based on objects that are relevant to the application, rather than editing basic picture elements like line segments or rectangles. The GEGS project is concerned with the generation of object-oriented graphical editors like these from an appropriate specification. The advantage of this is that editing a specification and generating a new editor is much quicker and less errorprone than implementing a new graphical editor. An editor generator also allows adaption to technology changes, generation of application-dependent graphics, individualization to group needs, and experimentation with new graphical languages.Show more Item When is a Line a Line?(Eurographics Association, 1989) Brodlie, Ken W.; Göbel, Martin; Roberts, Ann; Ziegler, RolfShow more Conformance testing of graphics systems is a very complex and exhausting task. Years of practice with the GKS testing tools have shown a need for the automatic testing of visual output. Indeed, with regard to graphics systems which are more precisely specified than GKS like the Computer Graphics Interface (CGI), conformance testing is not manageable at all unless a major part can be automated. This paper discusses different strategies for the automatic testing of pictorial effect. It concentrates on the definition of lines and describes a strategy to answer the question put in the title by the testing system. Finally, automatic testing of simple graphical operations such as segment highlighting and visibility is discussed.Show more Item Variations on a Dither Algorithm(Eurographics Association, 1989) Pins, Markus; Hild, HermannShow more Mapping continuous-tone pictures into digital halftone pictures, i.e. 0/1-pictures, for printing purposes is a well explored technique. In this paper, one of these algorithms, the two-dimensional error-diffusion algorithm is extended to color pictures and animated pictures. The color picture algorithm is superior to existing algorithms by considering extreme color values as well as adjacent color values. The animation algorithm eliminates the noise created by the correct but varying pixel patterns generated by applying a single picture dithering algorithm on every frame. The power of the algorithms is demonstrated by experiments carried out on synthetic images generated by ray tracing.Show more Item Message-Based Object-Oriented Interaction Modeling(Eurographics Association, 1989) Breen, David E.; Kühn, VolkerShow more This paper describes a message-based object-oriented tool for exploring mathematically-based interactions which produce complex motions for computer animation. The tool has been implemented as an object in the object-oriented computer animation system The Clockworks. It supports the definition of complex interactions between geometric objects through the specification of messages to the interacting objects. Our approach is general, flexible and powerful. The tool itself is not hardcoded to a particular application. It simply sends the messages specified by the user. Messages are specified as strings which may be stored, modified and interpreted. Since the tool is part of The Clockworks it may utilize many of the powerful features of the system, including data structuring, mathematical, geometric modeling, and rendering objects. The tool has been used to explore a general spring and mass model, and the response of objects in a vector field.Show more