Volume 09 (1990)

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    Factoring a Homogeneous Transformation for a more Efficient Graphics Pipeline
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Abi-Ezzi, Salim S.; Wozny, Michael J.
    We identify an intermediate coordinate system situated between world coordinates and display coordinates, which exhibits unique features for lighting calculations and for clipping in homogeneous coordinates. Our key contribution is an algorithm for extracting such a coordinate system from a homogeneous viewing transformation that relates WC to DC. The algorithm is based on factoring the transformation into a product of a Euclidean factor and a sparse (computationally cheap) but non-Euclidean factor.A particularly strong application of the proposed technique is the graphical processing of curved surface primitives, such as what is needed in the PHIGS PLUS viewing pipeline. Furthermore, in PHIGS PLUS the graphical data is retained by the graphics system, therefore, it is possible to perform the factoring of the viewing transformation at creation time, and to take advantage of this factored form at traversal time.
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    Some Possible Applications of CORDIC Processors in Computer Graphics
    (Eurographics Association, 1990) Kocsis, F.; Böhme, J.F.
    Some application possibilities of an ASIC-type processing element, the CORDIC processor, in computer graphics are discussed. CORDIC-based solutions are derived for some basic computer geometry computations: conversion between coordinate systems, rotations, point-line and pointplane distance calculations, ray-patch intersection computations, intensity and scalar product calculations. The main results are the following. Some basic computational tasks of computer graphics can be advantageously implemented using CORDIC arithmetic. The CORDIC processing element can serve as a building block even in high performance parallel graphics systems. A short example compares the possibilities of the CORDIC-based solution to the performance of the well-known polygon rendering with Pixel-planes.
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    DaScript Plus A PostScript Extension supporting 3D Graphics with 2D Functionality
    (Eurographics Association, 1990) Samara, Veronika; Schaub, Jutta; Noll, Stefan
    In the world of electronic publishing page description languages describe a very powerful interface between document creation software and raster output devices. 3D graphics systems offer the possibility to give a more or less realistic description of the 3D world. The current page description languages support 2D graphics only. However, documents also need graphics descriptions that contain 3D information. DaScript Plus provides a sufficient mapping of the PHIGS PLUS functionality. It allows the device independent incorporation of realistic 3D pictures within documents, and their high quality output on laser printers and type setters.
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    COMPUTER GRAPHICS PROFESSIONALS
    (Blackwell Publishing Ltd and the Eurographics Association, 1990)
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    Joint Editing with DAPHNE A System integrating CGMs into SGML Documents
    (Eurographics Association, 1990) Scheller, Angela; Fuhrhop, Christian
    This paper presents DAPHNE, a document processing system for joint editing within the German Research Network DFN. DAPHNE is based on two international standards in the area of document and graphics processing, the Standard Generalized Markup Language SGML and the Computer Graphics Metafile CGM. The functionality of DAPHNE is described with special emphasis on integrating graphics in documents, as well as the experience with the system in a pilot phase and future plans for extensions.
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    COMPUTER GRAPHICS PROFESSIONALS
    (Blackwell Publishing Ltd and the Eurographics Association, 1990)
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    Fifth Eurographics Workshop on Graphics Hardware
    (Blackwell Publishing Ltd and the Eurographics Association, 1990)
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    Combining Graphics and Windowing Standards in the XGKS System
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Rogers, Greg; Sung, Kelvin; Kubitz, William
    In the past few years we have seen the acceptance of standards for both two and three dimensional computer graphics. Also during this time, the workstation community has converged on a common windowing system. This paper discusses the problems encountered in implementing graphics standards such as GKS and PHIGS PLUS within the X Window System environment.
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    EDITORIAL
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Arnold, David
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    RECONSTRUCTION OF A BOUNDARY REPRESENTATION MODEL FROM THREE ORTHOGRAPHIC PROJECTIONS: A GEOMETRICAL APPROACH
    (Eurographics Association, 1990) Müller, A.; Richter, D.
    A method is presented for creating a boundary representation model from engineering projections. Although the topic of this reconstruction method has been studied for a few years the fundamentals of reconstruction are rather scanty. In this paper we provide a combined geometrical and topological approach to reconstruction. All considerations are restricted to polyhedral objects that consist of only one shell and edges belonging to exactly two faces. The reconstruction problem is mathematically described by introducing dome definitions, and criteria are derived that allow to solve the reconstruction problem for the restricted class of objects provided that the three given projections define a three-dimensional object unambiguously.
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    Book Reviews
    (Blackwell Publishing Ltd and the Eurographics Association, 1990)
    Book reviewed in this article:Reviewer: Ralph Martin. University of Wales College of Cardiff
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    HYPERIMAGES - AN ALTERNATIVE TO THE CONVENTIONAL DIGITAL IMAGES
    (Eurographics Association, 1990) Bieri, Hanspeter
    Hyperimages represent a variation of the conventional digital images which implies pixels of different dimensions within the same image. The extent of a hyperimage is the disjoint union of all pixel extents it contains, which are relatively open unit cubes with respect to the euclidean topology of the underlying space. This approach is independent of any specific dimension of image and space, respectively, and allows strict partitioning of images into subimages, not just subdividing. The applicability of hyperimages is illustrated by a number of algorithms useful in image analysis.
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    General Assembly of the EUROGRAPHICS Association
    (Blackwell Publishing Ltd and the Eurographics Association, 1990)
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    Eurographics 90 Tutorials Montreux - Switzerland - September 3-4, 1990
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Herman, Ivan
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    EDITORIAL
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Arnold, David
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    A RASTER GRAPHICS APPROACH TO FLOW VISUALIZATION
    (Eurographics Association, 1990) van Wijk, Jarke J.
    Most techniques for the visualization of fluid dynamics are based on vector graphics. Streamlines or arrows are calculated as vectors, which are converted to pixels for display on raster devices. The techniques described here show that it can be advantageous to use a raster graphics approach to the visualization of fluid dynamics. The properties of raster devices can be exploited better, while also anti-aliasing can be realized in a simple way. Three techniques for visualization of two-dimensional flow are described: for the calculation and display of streamlines; an alternative technique based on particle systems for capturing flow in a still image; and for the creation of animations using particles.
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    Language for Description of Geometric Configurations
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Barbic, Janez; Spegel, Marjan
    This contribution is an informal presentation of some concepts, facts, and definitions about general configurations, as well as a description of our proposed GL/0 language for symbolic description of geometric configurations. Emphasis is placed on the demand of invariance of geometric descriptions in the spirit of the Erlangen program of Felix Klein, and on the need for separation between the notions of configuration and of segments. Some possibilities for use of the same ideas in other, not necessarily geometric domains are described.
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    SIGGRAPH/EUROGRAPHICS Curriculum Review Call for Reviewers
    (Blackwell Publishing Ltd and the Eurographics Association, 1990)
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    Shading and Shadowing with Linear Light Sources
    (Eurographics Association, 1990) Poulin, Pierre; Amanatides, John
    In virtually all rendering systems, linear light sources are modeled with a series of point light sources that require considerable computing resources to produce realistic looking results. A general solution for shading surfaces illuminated by a linear light source is proposed. A formulation allowing for faster computation of the diffuse component of light reflection is derived. By assuming Phong's specular component, simple, inexpensive and convincing results are produced with the use of a Chebyshev approximation. A shadowing algorithm is also presented. As shadowing from linear light sources is expensive, two acceleration schemes, extended from ray tracing, are evaluated.
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    Tightly-Coupled Multiprocessing for a Global Illumination Algorithm
    (Eurographics Association, 1990) Drettakis, George; Fiume, Eugene; Fournier, Alain
    A prevailing trend in computer graphics is the demand for increasingly realistic global illumination models and algorithms. Despite the fact that the computational power of uniprocessors is increasing, it is clear that much greater computational power is required to achieve satisfactory throughput. The obvious next step is to employ parallel processing. The advent of affordable, tightly-coupled multiprocessors makes such an approach widely available for the first time. We propose a tightly-coupled parallel decomposition of FIAT, a global illumination algorithm, based on space subdivision and power balancing, that we have recently developed. This algorithm is somewhat ambitious, and severely strains existing uniprocessor environments. We discuss techniques for reducing memory contention and maximising parallelism. We also present empirical data on the actual performance of our parallel solution. Since the model of parallel computation that we have employed is likely to persist for quite some time, our techniques are applicable to other algorithms based on space subdivision.