Volume 07 (1988)
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Item Free-Form Surfaces Modeling by Evolution Simulation(Eurographics Association, 1988) Lienhardt, PascalWe present in this paper a procedural method for modeling free-form, planar surfaces subdivisions, which allows simulating evolutions of such subdivisions. This method is founded on the common principles deduced from corpuscular phenomena modeling method (particle systems), and method for vegetal trees modeling by simulation of evolution. These principles are : - use of a discrete model, which is a set of basic elements, from which time discretization is deduced, -proper activity of basic elements; these methods consists in simulating the behaviour of these elements; - characterization of modelled object evolution, which is achieved by "functions" associated to basic elements; - priority of topology over geometry. A surface is defined as a set of surface elements, supported by a rooted, planar tree. A surface is initially reduced to a point. Surface evolution characterization and control are exclusively exerted through this tree. This method is applied to image synthesis and animation of natural shapes, especially vegetal shapes.Item Computer Generation of Penrose Tilings(Blackwell Publishing Ltd and the Eurographics Association, 1988) Rangel-Mondragon, J.; Abas, S.J.Item Editorial(Blackwell Publishing Ltd and the Eurographics Association, 1988)Item Architectures for Mass Market 3D Displays(Eurographics Association, 1988) Winser, Paul; Bonnet, Thierry; Dumont, Dominique; Mathieu, YvesWe discuss the specific architecture requirements of real time 3D display systems intended for low cost mass market products of the near future. Vertex transformation and polygon rendering are two processing aspects where hardware acceleration must be used to achieve the performance target. The use of one or more DSP chips as vertex processors is discussed, and two efficient z-buffer implementations described. Antialiasing and texture mapping greatly improve the visual impression at some processing cost.Item Third Alvey Vision Conference University of Cambridge 15-17 September 1987(Blackwell Publishing Ltd and the Eurographics Association, 1988) CrennelF, K. M.Item A Proposal for a Distributed Model of GKS Based on Prolog(Blackwell Publishing Ltd and the Eurographics Association, 1988) Milanese, V.The Graphical Kernel System GKS is so well established as a standard for graphics programming that quite a number of models for multiprocessor and distributed environments have already been suggested. It is therefore necessary to consider new languages and methodologies capable of supporting its distributed implementation. In this context, clausal logic languages provide suitable means for describing the system in a declarative form and, moreover, ensure the applicability of meta-programming techniques for specifying the semantics of implementation. The Prolog language, extended with communication and modularization structures required by the distributed programming, is thus here considered as a feasible means for establishing a model of GKS organized in functional modules which could be supported by different processors. For such a model a two-level implementation scheme is outlined and a reconfiguration and personalization methodology is suggested.Item An Evaluation of CSG Trees Based on Polyhedral Solids(Eurographics Association, 1988) Badouel, Didier; Hegron, GerardSet operation on polyhedra is an important component of Geometric Modeling System (GMS) when a Constructive Solid Geometry (CSG) representation with polyhedral solid primitives is used. Output data will be the unique resulting polyhedron which provides an efficient data structure for displaying objects. With no use of spatial coherency, computational complexity of a set operation is quadratic. The new evaluation scheme called Boolean Octree limits set operation evaluation in a ‘minimal space of calculation’ where primitive boundaries intersect each other and where resulting evaluation participates in the construction of the final resulting object. Boolean Octree computes set operations in a local level providing a linear complexity for geometric calculations. During space subdivision, Boolean Octree has a global view on local CSG tree (projection of the CSG tree in local space) taking into account simplifications of the boolean expression. Set evaluation is done in the local volumes containing only two operands the configurations of which are ‘simple’, that is to say for a local description of an object there is only one vertex with any face number, one edge, or one face.Item The Second Eurographics Workshop on Graphics Hardware(Blackwell Publishing Ltd and the Eurographics Association, 1988) Claussen, U.Item A Note on Random Thresholding for Colour Synthesis(Blackwell Publishing Ltd and the Eurographics Association, 1988) Lastra, G.L.; Rudinger, E.N.A simple algorithm that improves colour shaded images is presented. The algorithm does not trade spatial resolution for intensity resolution. The basic technique, based on random thresholding modulated by a pseudo-random number generator of uniform distribution, is introduced to render halftone images on bi-level displays. A generalization of the technique is done for displays with multiple bi-per-colour components. An obvious advantage of the algorithm presented over other reported methods is its simplicity. Pictures are included to show results of the algorithm.Item G1 Smoothing Solid Objects by Bicubic Bezier Patches(Eurographics Association, 1988) Liang, Youdong; Ye, Xiuzi; Fang, ShiaofenA general and unified method is presented for generating a wide range of 3D objects by smoothing the vertices and edges of a given polyhedron with arbitrary topology using bicubic Bezier patches. The common solution to the compatibility equations of geometric continuity between two Bezier patches is obtained and employed as the foundation of this new method such that this new solid and surface model is reliable and compatible with the solid modeling and surface modeling system in the most common use. The new method has been embeded in an algorithm supported by our newly developed solid modeling system MESSAGE. The performance and implementation of this new algorithm show that it is efficient, flexible and easy to manipulate.Item A Procedural System for the Definition and Storage of Technical Drawings in Parametric Form(Eurographics Association, 1988) Cugini, U.; Folini, F.; Vicini, I.The construction of a truly USER-FRIENDLY CAD system requires the acquisition and management of a tremendous amount of information which cannot be. and must not be. directly requested from the user, but which has to be obtained by intelligently interpreting the sequence of operations performed by him. The system described here is out forward as a USERFRIENDLY tool for the definition. storage and modification of technical drawings in parametric form. The system that has been implemented (GIPS Graphic Interactive Parametric System) assists the user during the steps of definition and modification. taking advantage of the abiIity to interpret the procedure the user follows in describing the object he wants to design.Item A System for Graphical Interaction on Parametrized Models(Eurographics Association, 1988) Van Emmerik , Maarten J.G.M.A system that enables the definition of parametrized solid models by means of graphical interaction is presented. The position, orientation and dimensions of primitive volumes for Constructive Solid Geometry (CSG) are determined by a number of control points. All control points are linked to nodes in a tree of local coordinate systems. The relations between control points is therefore determined by the relations of the nodes in this geometric tree. The user can create nodes and define geometric relations between them by graphical interaction on the geometric tree. With the system described in this paper, it is possible to define relationsItem Report on the"CGM in the Real World" Workshop (NBS, Wasington)(Blackwell Publishing Ltd and the Eurographics Association, 1988) Carr, R.; Pink, J.Item Boundary to Constructive Solid Geometry: A Step Towards 3D Conversion(Eurographics Association, 1988) Juan, R.Several solid representation schemes exist today in solid modeling. As none of them has properties that are uniformly better than any other, the need for modeling systems working on two or more different schemes which perform every operation in the most suitable scheme, became evident. Then it is necessary to provide geometric modeling systems with the ability of converting from one scheme into another scheme. As most solid modellers use either, a boundary representation (BR) or a constructive solid geometry representation (CSG), conversion from one into the other appears to be of capital importance. Conversion from CSG into BR has been carefully studied but a few attention has been deserved to the conversion from BR to CSG. This paper presents an algorithm which generates CSG binary trees from BR representations over a restricted class of polyhedra. The tree is optimal in the output size. Unfortunately, the algorithm does not in general warrant a correct conversion and, consequently some open questions and ideas for further research are presented.Item Calendar of Events(Blackwell Publishing Ltd and the Eurographics Association, 1988)Item Optimal Texture Mapping(Eurographics Association, 1988) De Ma, Song; Lin, HongTexture mapping is one of the most important techniques for highquality image synthesis. It can enhance immensely the visual richness of raster-scan images. We address in this paper the problem of mapping planar texture pattern onto arbitrarily curved surfaces. It is well known that such a mapping will inevitably produce distortion for any undevelopable surface. Although many techniques for texture mapping have been presented in the literature [1], to our knowledge, no general method existed which could control or minimize this distortion. We present in this paper a new method for texture mapping. The main idea is to develop the given curved surface approximately on a two-dimensional plane using an approximate locally isometric mapping while minimizing the distortion by an optimization technique. Our experience has shown that by using this technique, one can reduce considerably the distortion and thus improve the quality of the generated images.Item Eurographics Workshops and Book Board Future Directions for Computer Graphics Teaching(Blackwell Publishing Ltd and the Eurographics Association, 1988)Item CALL FOR PAPERS AND EARLY REGISTRATION(Blackwell Publishing Ltd and the Eurographics Association, 1988)Item A Evalution of Some Three-Color Tiling Patterns(Eurographics Association, 1988) Alt, Paul; Cordonnier, VincentSome new technologies for information display use discrete arrays of cells or picture elements. Each cell displays a single color and the colors do not overlap as they do on a CRT screen. Colored cells are distributed on the two dimension display surface by repeating a basic model called a pattern. Patterns can be evaluated by observing images displayed using them. However, such approaches usually do not give numerical results and depend strongly on the selected images and the observers. In this paper, we suggest and examine some pattern evaluation criteria which relate only to the pattern and its geometrical aspect: Fidelity of color location, the quality of white area and the fidelity of shapes used for lines drawing or characters. Numerical and geometrical approaches are proposed to evaluate the quality of several patterns. The result is a classification of the test patterns. Some of them seem to be better than frequently used patterns. In addition, comments are offered on future pattern design.Item P.A. Firby and D.J. Stone"Interference in Computer Graphics"(Blackwell Publishing Ltd and the Eurographics Association, 1988)