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Now showing 1 - 10 of 59
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    A Graph-Based Approach to Surface Reconstruction
    (Blackwell Science Ltd and the Eurographics Association, 1995) Mencl, Robert
    A new approach to the reconstruction of a surface from an unorganized set of points in space is presented. The point set may for example be obtained with a laser scanner or a manual digitizing tool, and is the only source of information about the shape of the acquired object. The basic idea is to calculate the Euclidean minimum spanning tree (EMST) of the given points. The EMST is then augmented to the so-called surface description graph (SDG). Finally the wire frame defined by the SDG are filled with triangles. The advantage of our approach is that also highly non-convex and even disconnected surfaces are reconstructed quite reliably. This is demonstrated for a variety of data sets.
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    Multiresolution B-spline Radiosity
    (Blackwell Science Ltd and the Eurographics Association, 1995) Yu, Yizhou; Peng, Qunsheng
    This paper introduces a kind of new wavelet radiosity method called multiresolution B-spline radiosity, which uses B-splines of different scales to represent radiosity distribution functions. A set of techniques and algorithms, such as function extrapolation, adaptive quadrature, scale adjustment and octree, are proposed to implement it. This method sets up hierarchical structures on surfaces, keeps radiosity distribution continuous at element boundaries, does not need postprocessing, and does not prevent the use of any surface whose parameter domain is rectilinear.
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    Isometric Piecewise Polynomial Curves
    (Blackwell Science Ltd and the Eurographics Association, 1995) Fiume, Eugene
    The main preoccupations of research in computer-aided geometric design have been on shape-specification techniques for polynomial curves and surfaces, and on the continuity between segments or patches. When modelling with such techniques, curves and surfaces can be compressed or expanded arbitrarily. There has been relatively little work on interacting with direct spatial properties of curves and surfaces, such as their arc length or surface area. As a first step, we derive families of parametric piecewise polynomial curves that satisfy various positional and tangential constraints together with arc-length constraints. We call these curves isometric curves. A space curve is defined as a sequence of polynomial curve segments, each of which is defined by the familiar Hermite or Bezier constraints for cubic polynomials- as well, each segment is constrained to have a specified arc length. We demonstrate that this class of curves is attractive and stable. We also describe the numerical techniques used that are sufficient for achieving real time interaction with these curves on low-end workstations.
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    Automatic Reconstruction of Unstructured 3D Data: Combining a Medial Axis and Implicit Surfaces
    (Blackwell Science Ltd and the Eurographics Association, 1995) Bittar, Eric; Tsingos, Nicolas; Gascuel, Marie-Paule
    This paper presents a new method that combines a medial axis and implicit surfaces in order to reconstruct a 3D solid from an unstructured set of points scattered on the object s surface. The representation produced is based on iso-surfaces generated by skeletons, and is a particularly compact way of defining a smooth free-form solid. The method is based on the minimisation of an energy representing a"distance" between the set of data points and the iso-surface, resembling previous reserach19. Initialisation, however, is more robust and efficient since there is computation of the medial axis of the set of points. Instead of subdividing existing skeletons in order to refine the object s surface, a new reconstruction algorithm progressively selects skeleton-points from the pre- computed medial axis using an heuristic principle based on a"local energy" criterion. This drastically speeds up the reconstruction process. Moreover, using the medial axis allows reconstruction of objects with complex topology and geometry, like objects that have holes and branches or that are composed of several connected components. This process is fully automatic. The method has been successfully applied to both synthetic and real data.
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    Algorithms for Extracting Correct Critical Points and Constructing Topological Graphs from Discrete Geographical Elevation Data
    (Blackwell Science Ltd and the Eurographics Association, 1995) Takahashi, Shigeo; Ikeda, Tetsuya; Shinagawa, Yoshihisa; Kunii, Tosiyasu L.; Ueda, Minoru
    Researchers in the fields of computer graphics and geographical information systems (GISs) have extensively studied the methods of extracting terrain features such as peaks, pits, passes, ridges, and ravines from discrete elevation data. The existing techniques, however, do not guarantee the topological integrity of the extracted features because of their heuristic operations, which results in spurious features. Furthermore, there have been no algorithms for constructing topological graphs such as the surface network and the Reeb graph from the extracted peaks, pits, and passes. This paper presents new algorithms for extracting features and constructing the topological graphs using the features. Our algorithms enable us to extract correct terrain features; i.e., our method extracts the critical points that satisfy the Euler formula, which represents the topological invariant of smooth surfaces. This paper also provides an algorithm that converts the surface network to the Reeb graph for representing contour changes with respect to the height. The discrete elevation data used in this paper is a set of sample points on a terrain surface. Examples are presented to show that the algorithms also appeal to our visual cognition.
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    A Multimedia Constraint System1
    (Blackwell Science Ltd and the Eurographics Association, 1995) van Hintum, J.E.A.; Reynolds, G.J.
    The MADE constraint system provides excellent opportunities to introduce constraints in a multimedia application. Multimedia applications are not only a good place to experiment with constraint systems- constraints in a multimedia environment are almost indispensable. Due to the overwhelming amount of data and the number of relations between several parts of this data, multimedia applications almost demand the support of a constraint management system.The MADE constraint system combines the object oriented programming paradigm, inherited from the mC++ language, the declarative constraint programming paradigm and the special requirements imposed upon the constraint system by the multimedia environment. Among other things, the MADE constraint system provides parallel satisfaction techniques- several constraints may be solved simultaneously and this satisfaction process is performed in parallel with the application. This not only reduces the time needed to solve the constraints, it also allows the multimedia application to proceed with its presentation while (beneath the surface) the constraints are maintained. This not only holds for the parts of the presentation that are not constrained at all, but also for those parts that are. Furthermore, the constraint system is transparent to the multimedia application- no special coding or preparation of the objects in the application is necessary. Constraints can be added later to the application without much work. Besides that, it is also possible to add and remove constraints at runtime- objects may be constrained for only a period of the time the application is running.
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    The MADE Help System
    (Blackwell Science Ltd and the Eurographics Association, 1995) Haindl, Michal; de Ruiter, Behr
    MADE is the acronym for the ESPRIT project 6307, whose aim is to develop an object oriented multimedia application development environment. As part of this project the MADE help system is designed to be a distributed hypermedia system with additional support for run-time object monitoring and contextual help.
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    A Real-time Continuous Alphabetic Sign Language to Speech Conversion VR System
    (Blackwell Science Ltd and the Eurographics Association, 1995) Liang, Rung-Huei; Ouhyoung, Ming
    Many ways of communications are used between human and computer, while using gesture is considered to be one of the most natural way in a virtual reality system. Because of its intuitiveness and its capability of helping the hearing impaired or speaking impaired, we develop a gesture recognition system. Considering the world-wide use of ASL (American Sign Language), this system focuses on the recognition of a continuous flow of alphabets in ASL to spell a word followed by the speech synthesis, and adopts a simple and efficient windowed template matching recognition strategy to achieve the goal of a real-time and continuous recognition. In addition to the abduction and the flex information in a gesture, we introduce a concept of contact-point into our system to solve the intrinsic ambiguities of some gestures in ASL. Five tact switches, served as contact-points and sensed by an analogue to digital board, are sewn on a glove cover to enhance the functions of a traditional data glove.
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    Using Procedural RenderMan Shaders for Global Illurnination
    (Blackwell Science Ltd and the Eurographics Association, 1995) Slusallek, Philipp; Pflaum, Thomas; Seidel, Hans-Peter
    Global illumination techniques like radiosity or Monte-Carlo ray-tracing are becoming standard features of rendering systems. However, there is currently no accepted interface format which supports an appropriate physically-based scene description. In this paper we present extensions to the well-known RenderMan interface, which allow for a physically based scene description and support advanced global illumination techniques. Special emphasis has been laid on the support for procedural descriptions of reflection and emission by RenderMan surface shaders. So far, they could not be used with most global illumination algorithms. The extensions have been implemented in a physically-based rendering system and are illustrated with examples.
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    A rational model of the surface swept by a curve*
    (Blackwell Science Ltd and the Eurographics Association, 1995) Johnstone, John K.; Williams, James P.
    This paper shows how to construct a rational Bezier model of a swept surface that interpolates N frames (i.e., N position/orientation pairs) of a fixed rational space curve c(s) and maintains the shape of the curve at all intermediate points of the sweep. Thus, the surface models an exact sweep of the curve, consistent with the given data. The primary novelty of the method is that this exact modeling of the sweep is achieved without sacrificing a rational representation for the surface. Through a simple extension, we also allow the sweeping curve to change its size through the sweep. The position, orientation, and size of the sweeping curve can change with arbitrary continuity (we use C2 continuity in this paper). Our interpolation between frames has the classical properties of Bezier interpolation, such as the convex hull property and linear precision.This swept surface is a useful primitive for geometric design. It encompasses the surface of revolution and extruded surface, but extends them to arbitrary sweeps. It is a useful modeling primitive for robotics and CAD/CAM, using frames generated automatically by a moving robot or tool.