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Has files: true × Start date: 1988 × End date: 1989 ×

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Now showing 1 - 10 of 83
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    Free-Form Surfaces Modeling by Evolution Simulation
    (Eurographics Association, 1988) Lienhardt, Pascal
    We 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.
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    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.
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    Architectures for Mass Market 3D Displays
    (Eurographics Association, 1988) Winser, Paul; Bonnet, Thierry; Dumont, Dominique; Mathieu, Yves
    We 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.
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    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.
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    An Evaluation of CSG Trees Based on Polyhedral Solids
    (Eurographics Association, 1988) Badouel, Didier; Hegron, Gerard
    Set 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.
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    Two Object-Oriented Models to Design Graphical User Interfaces
    (Eurographics Association, 1989) Hübner, Wolfgang; Gomes, Mario Rui
    Object-oriented concepts are well-suited to deal with the characteristics of user interfaces. Up to now several attempts to integrate the object-oriented paradigm in user interface models were evolved and led to distinctive resulting models due to different requirements of the target application area. Within this paper two independently developed object-oriented interaction models are presented which emphasize the graphical requirements to user interfaces. These are among others its hierarchical nature, dynamical topology of the user interface, strong connection between input, output and the semantics of the application and the diversity of the graphics input devices and interaction techniques. Both approaches converge in the following aspects: Instead of having separated user interface layers the components of an interactive graphics application's user interface are embedded locally within interaction objects. Therefore dialogue control, input, output and the dynamical behavior are organized as a micro-cosmos within each object. Compound interaction objects can be designed. Temporal logical operators are used to specify the dialogue. Tools to support the implementation of each model are described. By describing both approaches this paper could be a contribution toward establishing a uniform object-oriented framework for the design of graphical user interfaces.
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    A Topological Map-Based Kernel for Polyhedron Modelers: Algebraic Specification and Logic Prototyping
    (Eurographics Association, 1989) Dufourd, Jean-Francois
    This paper deals with the topology of surfaces, in the boundary representation of three dimensional objects. Orientable, not orientable, closed or open surfaces are efficiently described and handled when considered as combinatorial generalized maps. An algebra of such maps is first described. Using this algebra, operations to build polyhedra step by step are next defined. That is the basis of a graphical modeler presently under consideration. The presentation uses algebraic software specification techniques in an abstract way. Finally, a systematical validation of the specification by logic prototyping is described.
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    Non-Planar Polygons and Photographic Components for Naturalism in Computer Graphics
    (Eurographics Association, 1989) Hofmann, Georg Rainer
    The measuring of natural objects like landscapes and already existing (not simply planned!) buildings produces natural data. That data of hue geometry typically consists of Non-planar Polygons. These may be triangulized, but the results are unfortunately: - a large increase of the number of polygons, - texture mapping becomes more complicated, - facetting effects in the rendered image. This paper addresses methods and algorithms of the direct rendering of Non-planar Polygons. Special "texture mapping" is presented to insert especially Photographic Components in Non-planar Polygons to obtain naturalistic images. With Photographic Components, a very simple illumination model is sufficient to obtain good results in rendering quality. Further on an application example is presented. The images of this example are outstanding both for their naturalism and the little computer CPU time spent for their rendering. Basics on naturalism and photorealism in Computer Graphics are discussed.
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    Highlight Shading: Lighting and Shading in a PHIGS+/PEX-Environment
    (Eurographics Association, 1989) Poepsel, J.; Hornung, C.
    Todays graphics standard for the rendering of scenes with illumination and reflection is defined by PHIGS+ . PEX is a proposal to integrate that functionality into the window environment of X. This paper first describes the lighting and shading models of PHIGS+/- PEX . Then a comparison of the different shading methods follows. At last, a new shading method, the Highlight Shading, is developed. The Highlight Shading combines both speed and image quality and therefore is an attractive alternative to existing shading algorithms.
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    G1 Smoothing Solid Objects by Bicubic Bezier Patches
    (Eurographics Association, 1988) Liang, Youdong; Ye, Xiuzi; Fang, Shiaofen
    A 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.