EG1989 Proceedings (Technical Papers)

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Visualizing Curvature Discontinuities of Free-Form Surfaces
(Eurographics Association, 1989) Pottmann, Helmut
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.
Graph Grammars, A New Paradigm for Implementing Visual Languages
(Eurographics Association, 1989) Goettler, Herbert
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.
Hierarchical Texture Synthesis on 3-D Surfaces
(Eurographics Association, 1989) Bennis, Chakib; Gagalowicz, Andre
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.
A VLSI Chip for Ray Tracing Bicubic Patches
(Eurographics Association, 1989) Bouatouch, Kadi; Saouter, Yannick; Candela, Jean Charles
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.
Variations on a Dither Algorithm
(Eurographics Association, 1989) Pins, Markus; Hild, Hermann
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.
Blending Rational B-Spline Surfaces
(Eurographics Association, 1989) Bardis, L.; Patrikalakis, N.M.
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.
Highlight Shading: Lighting and Shading in a PHIGS+/PEX-Environment
(Eurographics Association, 1989) Poepsel, J.; Hornung, C.
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.
A Model for Description and Synthesis of Heterogeneous Textures
(Eurographics Association, 1989) Englert, Gabriele; Sakas, Georgios
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.
Accelerated Radiosity Method for Complex Environments
(Eurographics Association, 1989) Xu, Hau; Peng, Qun-Sheng; Liang, You-Dong
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.
Visualisation of Digital Terrain Data
(Eurographics Association, 1989) Thiemann, Rolf; Fischer, Joachim; Haschek, Guido; Kneidl, Gerald
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.
Delauney Triangulations and the Radiosity Approach
(Eurographics Association, 1989) Schuierer, Sven
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.
A Reference Model for the Visualisation of Multi-Dimensional Data
(Eurographics Association, 1989) Bergeron, R. Daniel; Grinstein, Georges G.
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.
Colour Section
(Eurographics Association, 1989) -
Supporting Graphical Languages with Structure Editors
(Eurographics Association, 1989) Szwillus, Gerd
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.
An Analysis of Modeling Clip
(Eurographics Association, 1989) O Bara, Robert M.; Abi-Ezzi, Salim
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 i
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, Daniel
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.
Non-Planar Polygons and Photographic Components for Naturalism in Computer Graphics
(Eurographics Association, 1989) Hofmann, Georg Rainer
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.
On Reducing the Phong Shading Method
(Eurographics Association, 1989) Claussen, Ute
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.
Anti-Aliasing by Successive Steps with a Z-Buffer
(Eurographics Association, 1989) Ghazanfarpour, D.; Peroche, B.
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.
On the Software Structure of User Interface Management Systems
(Eurographics Association, 1989) Burgstaller, Johann; Grollmann, Joachim; Kapsner, Franz
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.

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