EG1989

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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.
Colour Section
(Eurographics Association, 1989) -
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.
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 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, Marc
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.
GEO++ - A System for Both Modelling and Display
(Eurographics Association, 1989) Wisskirchen, Peter
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.
Subdivisions of Surfaces and Generalized Maps
(Eurographics Association, 1989) Lienhardt, Pascal
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 .
2.5 Dimensional Graphics Systems
(Eurographics Association, 1989) Herman, Ivan
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.
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.
Ray Tracing Polynomial Tensor Product Surfaces
(Eurographics Association, 1989) Giger, Christine
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.
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.
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.
Deformation of Solids with Trivariate B-Splines
(Eurographics Association, 1989) Griessmair, Josef; Purgathofer, Werner
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.
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.
Components, Frameworks and GKS Input
(Eurographics Association, 1989) Duce, D. A.; Ten Hagen, P.J.W.; Van Liere, R.
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.
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
Representing Tolerance Information in Feature-Based Solid Modelling
(Eurographics Association, 1989) Falcidieno, Bianca; Fossati, Bruno
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.
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.

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