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Now showing 1 - 10 of 82
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    A Prolog Rule-Based System for cartographic Name Placement
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Cook, Anthony C.; Jones, Christopher B.
    Manual name placement is an extremely time consuming task and has been one of the most difficult aspects of the map production process to automate. It is complicated by the large number of rules required for the selection and placement of names. A hybrid Prolog/Fortrau rule-based system is described for placing names on a variety of map types. It uses a set of Prolog primitives for spatial search and name placement operations. The Ordnance Surveyâ s 1:625000 scale digital dataset has been used to illustrate the application of rules for the selection of labels as well as for controlling their size and orientation. The application to other types of maps and diagrams is also briefly described.
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    An Approach to Hierarchical Input Devices
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Duce, D. A.; Liere, R van; Hagen, P.J.W. ten
    This paper shows how a formal description of the GKS input model can be extended to include hierarchically structured input devices
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    A Stochastic Functional Approach for Terrain Modeling
    (Eurographics Association, 1990) Dong, Jun-Cai; Peng, Qun-Sheng; Liang, You-Dong
    A new functional modeling approach - -functional modeling, is presented to depict various classes of natural terrain. While this approach possesses the functions of several previous methods, it does not suffer the drawbacks of creases or periodity. By choosing the control parameters properly, our approach can easily generate different terrains related to various smoothness, such as cliffs,fractal mountains and smooth terrains. It can also simulate the natural weathering processes as from the cliff to the fractal mountain and to the smooth terrain not only in the appearance but also in quantity. And it is capable of modeling the terrain whose "rock bed” and "rock quilt" are associated with different smoothness.
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    IFSs and Interactive Image Synthesis
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Horn, Alastair N.
    Deterministic Fractal geometry provides a framework for describing both the geometry of man-made structures and the geometry of nature.Certain deterministic Fractals which exist in the plane may be"partitioned" into a number of"tiles" equivalent to the whole under some geometric mapping. We term such Fractals self-tiling images.We describe a scheme called Iterated Function Systems (IFSs) which an represent self-tiling images. IFSs make explicit the mappings which take a self-tiling image into its tiles.We show how a self-tiling image exists as the limit of both random and deterministic processes based upon its associated IFS, and exploit massive SIMD parallelism in image generation on the AMT DAP.We also attempt to answer the question:"Can one synthesise images by the interactive graphical manipulation of a representation of IFSs?", and present our interactive system for image synthesis (ISIS).
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    Durer, Gaskets and Barnsley s Chaos Game
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Jones, Huw
    Michael Barnsley has generated the Sierpinski triangle or gasket using his"Chaos Game", a technique for generating random points within a fractal object. Extensions of the method are discussed to generate fractal"gaskets" based on other regular polygons. One such figure resembles a tiling pattern based on pentagons known to Albrecht Durer almost 500 years ago.
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    A New Space Partitioning for Mapping Computations of the Radiosity Method onto a Highly Pipelined Parallel Architecture
    (The Eurographics Association, 1990) Shen, Li-Sheng; Deprettere, E.; Dewilde, P.; Richard Grimsdale and Arie Kaufman
    Despite the fact that realistic images can be generated by ray-tracing and radiosity shading, these techniques are impractical for scenes of high complexity because of the extremely high time cost. Several attempts have been made to reduce image synthesis time by using parallel architectures, but they still suffer from communication problems. In this paper, we present a new space partitioning which is adaptive to the local environment seen by a bundle of rays. Two tracking mechanisms are embedded to guarantee adaptation. When using a shared memory parallel architecture, the communication load between the host and the PEs can be alleviated with this approach. Furthermore, the partitioning provides a better balancing between processing throughput and I/O bandwidth which will enhance the pipelinability of computations, especially when a high speed cache memory is allowed for each PE. Combining those factors, a highly pipelined parallel architecture can be used to accelerate computations in ray-tracing and radiosity methods. The technique has been tested on different scenes with randomly generated patches in a 2D setting. When compared with the conventional technique, promising results have been observed. This technique can be easily extended to 3D.
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    EDEN - AN EDITOR ENVIRONMENT FOR OBJECT- ORIENTED GRAPHICS EDITING
    (Eurographics Association, 1990) Fellner, Dieter W.; Kappe, F.
    Systems allowing the creation and manipulation of graphical information (so-called Graphic Editors) have become essential in various fields of applications. At the same time the typical user of such a system has changed. Not computer experts, but designers, secretaries, technicians, teachers etc. are today's typical users of computer graphics, mostly on microcomputers. Obviously it would be desirable to have a common concept of graphics editing covering many applications. The purpose of this paper is a brief survey of the EDEN project started at the IIGb in 1987: the motivation for the project, the major steps, results, current status and future work is presented here. EDEN (short for EDitor ENvironnient) is a generic concept for object-oriented graphics editing, providing device independence at the workstation and graphics output level as well as an application independent file-format for the storage and exchange between different graphics applications.
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    OPTIMIZATION OF THE BINARY SPACE PARTITION ALGORITHM (BSP) FOR THE VISUALIZATION OF DYNAMIC SCENES
    (Eurographics Association, 1990) Torres, Enric
    This paper describes an improvement of the generation of BSP trees and its utilization in the visualization of dynamic polyhedral scenes. Dynamic BSP trees, a new six-level structure, are presented. Dynamic BSP trees are based on the inclusion of five different kinds of auxiliary planes in the generation of BSP trees. These planes are included in the structure before the polygons of the scene. In most cases the inclusion of polygons is performed in zero time by making use of precomputed BSP trees of the single objects of the scene. Dynamic BSP trees lead to a very significant reduction in the computation time of the BSP tree building and the posibility of its utilization at interactive speeds for complex scenes where both viewpoint and objects are dynamic. Description and pseudocode of the generation and dynamic modification management algorithms are included, along with a set of examples from a real implementation.
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    A shadow algorithm for CSG
    (Eurographics Association, 1990) Jansen, Frederik W.; van der Zalm, Arno N. T.
    An algorithm is presented for constructing shadow volumes for CSG objects. For each primitive solid, the algorithm calculates a tree of shadow volumes to model the shadows generated by the shadow-generating parts of the boundary of the primitive. The shadow of the complete CSG object is the union of these shadow trees. An implementation of the algorithm is described for a scan-line display algorithm for CSG objects with polygonal primitives.
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    THREE-DIMENSIONAL TEXTURING USING LATTICES
    (Eurographics Association, 1990) Lewis, Robert R.
    This paper describes a way to perform realistic three-dimensional texturing of ray-traced objects with irregular surfaces. Such texturing has teen done in the past with texture mapping, particle systems, or volumetric methods. We propose an alternative to these called a lattice. Lattices work as fast but inexact ray tracers. As long as lattices are used for small objects, though, the inexactness doesn't show on the scale of the display, and the result is acceptable. The paper shows how lattices can be integrated with a more traditional ray tracer, with several examples. Time and memory space considerations are major constraints on lattices, preventing widespread practical application at the present time. The paper discusses these limitations and how they might be reduced.