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Item Constructive Page Description Opening Up the Prepress World(Eurographics Association, 1991) Samara, Veronika; Wiedling, Hans-PeterConstructive Page Description (CPD) is an overall approach allowing different kinds of data to be exchanged between a variety of systems and manipulated in arbitrary system environments. Fully changeable pages, which keep information for modification as long as necessary, as well as fully assembled pages, ready for the printing process, can be constructed by the use of CPD. Moreover, descriptions of data as well as operations can be distributed, and so allow the use of networking facilities. CPD is thereby very flexible in handling, combining, and exchanging data and operations used in the construction of pages. In sum, CPD helps bridge the gap between the printing and the computer graphics world; it is an approach to lead prepress towards an open system architecture.Item A Stochastic Functional Approach for Terrain Modeling(Eurographics Association, 1990) Dong, Jun-Cai; Peng, Qun-Sheng; Liang, You-DongA 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.Item Refinement criteria for adaptive stochastic ray tracing of textures(Eurographics Association, 1991) van Walsum, Theo; van Nieuwenhuizen, Peter R.; Jansen, Frederik W.Adaptive stochastic ray tracing is a rendering technique that generates high-quality anti-aliased images by sampling the image in a non-regular pattern that is adaptively refined. Image refinement can be guided by image space or object space criteria. For display of textures, additional criteria that operate in texture space can be added to further improve image quality. In this paper three texture space refinement criteria are introduced. The methods minimize the chance of sampling errors at the cost of only a small amount of preprocessing and are comparable in efficiency with existing texture prefiltering methods.Item Several approaches to implement the merging step of the split and merge region segmentation(Eurographics Association, 1991) Popovic, M.; Chantemargue, F.; Canals, R.; Bonton, P.The purpose of this paper is to propose several approaches for the implementation of the merging step of split and merge region segmentation. The splitting step has already been studied and its parallelization has subsequently been implemented on a transputer network. First, the most widely known merging step is described. Then, two approaches which are better suited to a parallelization are presented. Next we discuss the principle behind these approaches. Finally region segmentation according to motionbased criteria has been chosen in order to provide results to evaluate the performance of each approach. We emphasize that the description is general and can be applied to all split and merge algorithms. Therefore this work is a contributory factor in the evolution of region segmentation towards its parallelization.Item Variable-Radius Blending by Using Gregory Patches in Geo- metric Modeling(Eurographics Association, 1991) Harada, T.; Konnoa, K.; Chiyokura, H.Blending surfaces, which connect two curved surfaces smoothly, often appear in geometric modeling. Many of the blending surfaces are variable-radius blends. Variableradius blending surfaces are very important in the design process, but it is difficult to generate such surfaces with existing geometric modelers. This paper proposes a new method to generate variable-radius blends. Instead of the popular rolling-ball method, we adopt “sliding-circle” blending. A circle slides on two curved surfaces so that the circle is perpendicular to a specified control curve, and its trajectory defines a blending surface. A variable-radius blend can be generated if the radius of the circle changes smoothly. In our method, the shape of the variable-radius blend is represented by Gregory patches. The Gregory patch is an extension of a Bezier patch and two Gregory patches can be connected together with tangential continuity. The characteristics of the Gregory patch are suitable for representing blending surfaces with geometric modelers.Item 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.Item Integrating Inheritance and Composition in an Objective Presentation Model for Multiple Media(Eurographics Association, 1991) Took, RogerA formal model is presented which combines, in a single structure called a tangle, the power to express both the composition of aggregate objects, and the selective inheritance of object properties over a number of instances or manifestations. The model allows an objective implementation, that is, one in which objects can be created and updated randomly, incrementally, and dynamically. Such a model is ideal as the basis for interactive presentation. The tangle is defined as generic in its node type, and so can model the structure of multiple presentation media.Item Using temporal and spatial coherence for accelerating the calculation of animation sequences(Eurographics Association, 1991) Gröller, Eduard; Purgathofer, WernerRay tracing is a well known technique for generating realistic images. One of the major drawbacks of this approach are the extensive computational requirements for image calculation. When generating animation sequences frame by frame the computational cost might easily become intolerable. In the last years several methods have been devised for accelerating the computational speed by using spatial and temporal coherence. While these techniques work only under certain restrictions, a new approach is presented in this paper which leads to a considerable speed-up of the calculation process without putting any limitations on camera or object movement. In principle, the method is an extension of /ArKi87/, where rays are considered points in 5D space, by the time dimension. CSG is used for object description and has been modified correspondingly to allow easy use of coherence properties. The paper describes the theoretical background and the main concepts of a practical implementation.Item OPTIMIZATION OF THE BINARY SPACE PARTITION ALGORITHM (BSP) FOR THE VISUALIZATION OF DYNAMIC SCENES(Eurographics Association, 1990) Torres, EnricThis 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.Item A DDA Octree Traversal Algorithm for Ray Tracing(Eurographics Association, 1991) Sung, KelvinA spatial traversal algorithm for ray tracing that combines the memory efficiency of an octree and the traversal speed of a uniform voxel space is described. A new octree representation is proposed and an implementation of the algorithm based on that representation is presented. Performance of the implementation and other spatial structure traversal algorithms are examined.