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Now showing 1 - 10 of 42
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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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    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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    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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    Graph Grammars, A New Paradigm for Implementing Visual Languages
    (Eurographics Association, 1989) Goettler, Herbert
    This paper is a report on an ongoing work which started in 1981 and is aiming at a general method which would help to considerably reduce the time necessary to develop a syntax-directed editor for any given diagram technique. The main idea behind the approach is to represent diagrams by (formal) graphs whose nodes are enriched with attributes. Then, any manipulation of a diagram (typically the insertion of an arrow, a box, text, coloring, etc.) can be expressed in terms of the manipulation of its underlying attributed representation graph. The formal description of the manipulation is done by programmed attributed graph grammars.
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    The Use of Finite Element Theory for Simulating Object and Human Body Deformations and Contacts
    (Eurographics Association, 1989) Gourret, Jean-Paul; Magnenat-Thalmann, Nadia; Thalmann, Daniel
    This paper presents a method for combining image synthesis and modeling based on a finite element method (FEM) to get realistic intelligent images. FEM is used for modeling both elastically and plastically deformations of objects, and impacts with or without penetration between deformable objects. The concept of deformable objects is applied to human flesh to improve the behavior of synthetic human grasping and walking. The paper also discusses the introduction of this method in an animation system based on the concept of "intelligent" synthetic actors with automatic motion control performed using A.I. and robotics techniques. In particular, motion is planned at a task level and computed using physical laws.
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    Subdivisions of Surfaces and Generalized Maps
    (Eurographics Association, 1989) Lienhardt, Pascal
    The modeling of subdivisions of surfaces is of greatest interest in Geometric Modeling (in particular for Boundary Representation) , and many works deal with the definition of models, which enable the representation of closed, orientable subdivisions of surfaces, and with the definition of elementary operations, which can be applied to these models (Euler operators) . We study in this paper the notion of 2-dimensional generalized map (or 2-G-map), which make possible the definition of the topology of any subdivision of surface, orientable or not orientable, opened or closed ; reciprocally, the topology of any subdivision of any surface may be defined by a 2-G-map . Three characteristics are associated to any 2-G-map G (the most elementary being the number of boundaries, the most known being the genus ...), and can be directly computed on G . These characteristics define the subdivision of surface modelled by G (static classification of the subdivision) . We define also operations which can be applied to 2-G-maps . Any 2-G-map (and then any subdivision of surface) can be constructed by a sequence of operations . To these operations correspond variations of the characteristics associated to the 2-G-maps . These variations enable the control of the effect of an operation on the modelled subdivision (dynamic classification of the subdivision) . The notion of 2-G-map defines the different elements of a subdivision (vertex, edge, face, bound ary...) by using one unique kind of elements, in a rigorous and unambiguous manner. Data structures may be deduced from the notion of 2-G-map . These data structures make possible the representation of any subdivision of surface , in a way near to the well-known "windged-edge" data structure defined by B. Baumgart in [BA75] . The constraints of consistency about these data structures can be directly deduced from the definition of 2-G-maps . The set of the properties of 2-G-maps (rigour, consistency, possibility of static or dynamic classification) makes the greatest interest of the 2-G-maps, with respect to other models of subdivisions of surfaces used in Geometric Modeling .
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    A Parallel Image Computer with a Distributed Frame Buffer: System Architecture and Programming
    (Eurographics Association, 1989) Potmesil, Michael; McMillan, Leonard; Hoffert, Eric M.; Inman, Jennifer F.; Farah, Robert L.; Howard, Marc
    We describe the system architecture and the programming environment of the Pixel Machine - a parallel image computer for 2D and 3D image synthesis and analysis. The architecture of the computer is based on an array of asynchronous MIMD nodes with a parallel access to a large frame buffer. The system consists of a pipeline of pipe nodes which execute sequential algorithms and an array of m x n pixel nodes which execute parallel algorithms. A pixel node accesses every m-th pixel on every n-th scan line of a distributed frame buffer. Each processing node is based on a high-speed, floating-point programmable processor. The programmability of the computer allows all algorithms to be implemented in software. A set of mapping functions transfers image algorithms written for conventional single-processor computers to algorithms which execute in the pixel nodes and access the distributed frame buffer. The ability to use floating-point computations in pixel operations, such as antialiasing, ray tracing, and filtering, allows high-quality image generation and processing. The image computer provides up to 820 megaflops of peak processing power and 48 megabytes of memory for data-visualization applications.