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Computer Graphics International, 1998. Proceedings

Date 26-26 June 1998

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Displaying Results 1 - 25 of 96
  • Proceedings. Computer Graphics International (Cat. No.98EX149)

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    Freely Available from IEEE
  • An anti-aliasing method for parallel rendering

    Page(s): 228 - 235
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    We describe a parallel rendering method based on the adaptive supersampling technique to produce anti-aliased images with minimal memory consumption. Unlike traditional supersampling methods, this one does not supersample every pixel, but only those edge pixels. We consider various strategies to reduce the memory consumption in order for the method to be applicable in situations where limited or fixed amount of pre-allocated memory is available. This is a very important issue, especially in parallel rendering. We have implemented our algorithm on a parallel machine based on the message passing model. Towards the end of the paper, we present some experimental results on the memory usage and the performance of the method. View full abstract»

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  • Author index

    Page(s): 798 - 800
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    Freely Available from IEEE
  • Random walk radiosity with generalized absorption probabilities

    Page(s): 658 - 665
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    The author studies random walk estimators for radiosity with generalized absorption probabilities. That is, a path will either die or survive on a patch according to an arbitrary probability. The estimators studied so far, the infinite path length estimator and finite path length one, can be considered as particular cases. Practical applications of the random walks with generalized probabilities are given. A necessary and sufficient condition for the existence of the variance is given, together with heuristics to be used in practical cases. The optimal probabilities are also found for the case when one is interested in the whole scene, and are equal to the reflectivities View full abstract»

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  • A new type of free-form curve given by an integral form

    Page(s): 722 - 725
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    The paper proposes a new type of free-form curve for fairness. A unit quaternion curve is used to specify the tangent of the curve in order to more directly manipulate its curvature and variation of curvature than is possible for the traditional parametric representations like Bezier and NURBS curves. Since the new curve is represented by can integral form of a unit quaternion curve, it is named unit quaternion integral curve or QI curve for brevity. It is a generalization and an extension of the clothoid into three dimensional space and the norm of its tangent is always equal to 1. Its curvature and variation of curvature are given by rather simple expressions View full abstract»

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  • Modelling by a rational spline with interval shape control

    Page(s): 730 - 737
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    Various models have been developed for the design of distinct objects and for applications such as font design, computer aided design (CAD), computer aided engineering (CAE), etc. Some methods are better suited for controlling the shape of the curve on an interval, while others are better suited for controlling the shape at individual control points. The work reviews C2 rational splines with interval tension and extends this work for the modelling of interpolatory curves and surfaces through B-spline formulation View full abstract»

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  • Scaling VR in VRML: integrating different VR methodologies in a VRML browsing system

    Page(s): 564 - 567
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    In this paper we examine the potential of the virtual reality modeling language (VRML) to support different methodologies used in virtual reality (VR), like head tracking or special VR input and output devices. A realization concept is presented and its implementation in the VRML browser CASUS Presenter is described View full abstract»

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  • Image retrieval in digital library based on symmetry detection

    Page(s): 366 - 372
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    We present a technique of content-based image retrieval based on the symmetric property of an image and its generalized complex moments. We propose a novel symmetry detection algorithm that is both fast and general compared with existing symmetry detection algorithms. Given the sensitivity of human perception to symmetry, the use of symmetry class helps to ensure that the retrieved images are visually similar. Experimental results show that these features are effective in retrieving binary images and our similarity function is able to rank them first place for nearly all the sample queries used in our experiment View full abstract»

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  • Hierarchical meshes for volume data

    Page(s): 761 - 769
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    An algorithm for adaptive refinement of 3D meshes is presented. This algorithm can be applied for the generation of mesh hierarchies used for efficient volume visualization algorithms, e.g. iso-surface extraction or direct volume rendering, as well as for multilevel finite element computations. The aim was to construct an algorithm which generates as few congruence classes as possible. The main idea is to work with consistent partitions of the domain into tetrahedra and octahedra. The refinement consists of regular refinement rules which produce per element type one congruence class. In the case of local mesh refinement, for generating consistent subdivisions a temporary (virtual) closure is done based on suitable irregular refinement rules View full abstract»

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  • Virtual 3D sculpturing with a parametric hand surface

    Page(s): 178 - 186
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    Many techniques have been developed for 3D object deformation. These techniques have been widely used in most CAD/CAM systems. Intuitive while efficient methods for interactive 3D object deformation in a VR environment, however, are rare. One of our current research projects is to develop such a technique based on the use of a sensor glove. The idea is to create a hand surface interpolating through all the data points of the sensor glove. Through mapping the vertices of an object model to the hand surface, the object model may be deformed simply by changing the hand gesture. An initial method for implementing this idea was presented in our recent paper. In this paper, we discuss some of the limitations of the earlier method and present a refined method that overcomes most of the limitations. The resulting method is both efficient and intuitive as demonstrated by the results of our experiments View full abstract»

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  • “Thin” vs. “fat” visualization client

    Page(s): 772 - 788
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    The paper explains the advantage of using low-cost, configurable, data visualization components, which can be embedded and distributed in electronic documents and reports. With the increasing use of electronic documents, distributed by intranets and the Internet, the opportunity to provide interactive visualization techniques within scientific and engineering reports has become practicable. This new technology of components allows authors of a report to distribute with a specific “data viewer”, for example, allowing the recipients to interactively examine the data in the same way as the original analyst. A “thin” client, by definition, has minimal software requirements necessary to function as a user interface front-end for a Web enabled application and raises the issue of client vs. Server data visualization rendering. Real-time visual data manipulation doesn't translate well into a “thin” client. While the VRML file format allows distribution of 3D visualization scenes to the Web, the user has no direct access to the underlying data sources. The “mapping” of numerical data into geometry format (VRML) takes place at the server side. In the “thin” client model, nearly all functionality is delivered from the server side of the visualization engine while the client perform very simple display and querying functions View full abstract»

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  • The Styria Flyover-LOD management for huge textured terrain models

    Page(s): 444 - 454
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    With the Styria Flyover one can virtually fly over Styria, a province of Austria. The countryside is characterized by a mixture of rather flat regions in the south east and mountains up to 3000 m in the north west. The digital model covers Styria and parts of its adjoining provinces (30,000 km2); it is based on a DTM consisting of more than 23 million triangles and on 50 Mbyte texture data (satellite images). The framework combines an R-tree data structure with efficient LOD management (automatic mesh refinement), progressive rendering and dynamic performance adjustment. On a SGI O2 it delivers more than 8 frames per second. The authors' approach demonstrates that efficient algorithms make a fast 3D GIS user interface possible without spending a fortune on hardware. The paper focuses on techniques and data structures to maximize the performance of visualization View full abstract»

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  • Adaptive subdivision curves and surfaces

    Page(s): 48 - 58
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    Well-known schemes of subdivision curves and surfaces are modified so that they allow an adaptive refinement. Adaptation is controlled by an error measure which indicates for the vertices of a mesh whether the approximation is sufficient. The adaptive constructions are based on local operations of refining or coarsening. They allow to reach all other subdivisions, in particular the non-adaptive ones, from any given subdivision. The local operations also make possible, besides static top-down and bottom-up calculations, the fully dynamic adaptation of a given mesh to varying error conditions, for instance caused by changes of view during visualization of the curve or surface. The adaptive constructions reduce the computational requirements View full abstract»

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  • Robust tessellation of trimmed rational B-spline surface patches

    Page(s): 543 - 555
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    We present an unstructured triangular mesh generation algorithm that approximates a set of mutually non-intersecting simple trimmed rational B-spline surface patches within a user specified geometric tolerance. The proposed method uses numerically robust interval geometric representations/computations and also addresses the problem of topological consistency (homeomorphism) between the exact geometry and its approximation. Those are among the most important outstanding issues in geometry approximation problems. Our surface tessellation algorithm is based on the unstructured Delaunay mesh approach which leads to an efficient adaptive triangulation. A robust decision criterion is utilized to prevent possible failures in the conventional Delaunay triangulation. To satisfy the prescribed geometric tolerance, an adaptive node insertion algorithm is employed. Unstructured triangular meshes for free-form surfaces frequently involve triangles with high aspect ratio and accordingly, result in ill-conditioned meshing. Our proposed algorithm constructs 2D triangulation domains which sufficiently preserve the shape of triangles when mapped into 2D space and furthermore, the algorithm provides an efficient method that explicitly controls the aspect ratio of the triangular elements View full abstract»

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  • Automatic creation of flexible antropomorphic models for 3D videoconferencing

    Page(s): 520 - 527
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    The contribution describes the automatic creation of highly realistic flexible 3D models of participants for distributed 3D videoconferencing systems. The proposed technique uses a flexible mesh template surrounding an interior skeleton structure, which is based on a simplified human skeleton. The vertices of this template are arranged in rigid rings along the bones of the skeleton. Using 3D data obtained by a shape from silhouette approach the size and shape of the mesh template is adapted to the real person. Texture mapping of the adapted mesh using real camera images leads to a natural impression. The mesh organization in rigid rings allows an efficient surface deformation according to the skeleton movements. Once the resulting model is transmitted, it can be animated subsequently using the simple parameter set of the interior skeleton structure. Results obtained with real image data confirm the eligibility of the animated person models in terms of realism and efficiency for 3D videoconferencing applications View full abstract»

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  • Interactive exploration of distributed 3D databases over the Internet

    Page(s): 324 - 335
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    Interactive 3D visualization and Internet-based access to information are already common. Their combination is-or soon will be-the primary vehicle for accessing remote databases in fundamental areas of manufacturing, architecture, petroleum, urban planning, tourism, defense, medicine, electronic commerce, and entertainment. Unfortunately, whether based on precise 3D geometry or involving combinations of shapes and images, the complexity of 3D graphic models of airplanes, cities, or virtual stores significantly exceeds the limits of what can be quickly downloaded over popular connections and what can be rendered on personal workstations during interactive exploration. The author reviews recent progress in the compression and simplification of 3D models and in the progressive transmission of these models for interactive graphic exploration, which may combine traditional 3D graphics with image-based rendering. The author proposes an architecture for a 3D server capable of supporting a large number of independent client-users accessing interactively various subsets of a possibly distributed database of complex 3D models View full abstract»

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  • Using GIS to visualise environmental information a case study based on digital terrain models

    Page(s): 123 - 127
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    We present an experience of use of geographic information system (GIS) to visualise environmental information. Our experience suggests that digital terrain models may represent a common base to provide consistent information derived combining different data. Some considerations about the use of realistic visualisation (rendering) versus semantic representation based on geometric reasoning are provided View full abstract»

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  • Virtual humans in CyberDance

    Page(s): 142 - 153
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    This paper presents an account of a Cyberdance performance involving both real and virtual dancers. Preparing for this performance required the integration of a number of virtual human modules into a single system framework capable of handling all aspects of the show. We describe the modules that deal with creation, modeling and texturing the virtual humans, as well as those that manage the animation of bodies within real-time applications, and control several bodies simultaneously, as choreographed. Real-time hand deformation and facial animation modules increase the realism of the virtual dancers. Two techniques are described for improving the quality of the rendering in the virtual component of the scenario. We describe the VR devices for merging the interactive dancers into the virtual environment. In conclusion, we report on experiences during the actual presentation of the show and suggest topics for future research into improvements of various parts of our system View full abstract»

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  • On optimality of OBBs for visibility tests for frustum culling, ray shooting and collision detection

    Page(s): 256 - 263
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    Bounding volume hierarchies are widely employed in many areas of computer graphics. Usually they are used as crude approximations of the scene geometry to speed up some time-consuming computations, such as visibility tests for frustum culling, ray shooting, collision detection, etc. A number of bounding volume types have been discussed by various researchers. They include bounding spheres, axis-aligned and oriented bounding boxes, and others. Although it is practically possible to use any of these bounding volumes, some types prove to be particularly useful in certain applications, e.g. Gortschalk et al. (1996) used oriented bounding boxes to implement a very effective exact collision detection scheme. The authors address the problem of efficient bounding volume selection, the solution of which allows one to significantly accelerate such operations as visibility tests for frustum culling, collision detection and ray shooting. They prove that minimal surface area (perimeter in 2D) oriented bounding box is optimal among all the oriented bounding boxes with respect to the three operations stated above. Then, they develop a number of algorithms to create optimal oriented bounding boxes and their approximations and finally discuss the results of the practical implementation View full abstract»

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  • Design of anisotropic functions within spatial analysis of data

    Page(s): 726 - 729
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    The calculation of the minimum cost path is one of the newest tools in the spatial analysis of data. The problem acquires an added complexity when the cost associated to a phenomenon not only depends on its intensity but also on the direction in which it is revealed in the space. In this case, the authors run into an anisotropic phenomenon where the friction associated with it is also anisotropic. The article describes a methodology for the design of cost functions as well as anisotropic friction functions, which are based on semispatial statistical items as they are the circular variables View full abstract»

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  • VEplatform: a base system for distributed virtual reality

    Page(s): 568 - 569
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    The VEplatform project aims at the development of a highly scalable system which allows distributed virtual reality applications to be built. The system is decentralised i.e. there is no central component which controls it and which can become a bottleneck. At this moment VEplatform is already a working system allowing many participants to join a virtual world. In this article the software architecture of VEplatform is explained and some hints to the future are given View full abstract»

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  • Rational quadratic Bezier triangles on quadrics

    Page(s): 34 - 40
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    First, different ways of solving the problem, if a given rational triangular Bezier patch of degree 2 lies on a quadric surface, are presented. Although these approaches are theoretically equivalent, their difference from the practical point of view is illustrated by analysing and comparing the numerical condition of the respective problems. Second, given a rational triangular Bezier patch of degree 2 in standard form with five fixed control points, geometrical conditions on the locus of the sixth control point are derived and the remaining inner weights are determined. The locus of this remaining control point results to be part of a quadric surface. The obtained results are illustrated for a representative example View full abstract»

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  • Uncertainty coding and controlled data reduction using fuzzy-B-splines

    Page(s): 536 - 542
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    In this paper, a method is described for the representation and reconstruction of single-valued surfaces given as sets of measured data, which may be uncertain as well as crisp. In the case of imprecise data, the fuzzy B-spline representation is able to keep track of uncertainty and provide tools for interrogating the model at prescribed presumption levels. In both cases, a very high degree of compression can be achieved through a procedure which defines, among spatially-clustered points, the most significant representative of the local neighbourhood. Experimental results are shown to prove the effectiveness of the proposed approach View full abstract»

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  • Determining visibility between extended objects

    Page(s): 23 - 31
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    Two query problems for visibility are considered. The first one is to find the visibility set of two query objects A and B of the same type as the objects of the given scene. The visibility set is characterized by those line segments connecting points on A and B which do not intersect scene objects between A and B. We show that scenes consisting of disjoint line segments in the plane can be processed into a data structure of about linear size so that the visibility set can be found in sublinear time per component of the representation chosen for the visibility set. The construction can also be applied to scenes of disjoint triangles in space. The disadvantage of possibly many components can be diminished by pre-clipping against the viewing hull of A and B. The query version of the clipping problem can also be solved in about linear space and sublinear query time. The result of the first problem is used for an efficient solution of the second problem which is to calculate the visibility sets between query object A and all scene objects visible from A View full abstract»

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  • An array processor architecture with parallel data cache for image rendering and compositing

    Page(s): 411 - 414
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    This paper proposes a new array architecture for MPEG-4 image compositing and 3D rendering. The emerging MPEG-4 standard for multimedia applications allows VRML-like script-based compositing of audio-visual scenes from multiple audio and visual objects. MPEG-4 supports both natural (video) and synthetic (3D) visual objects or a combination of both. Objects can be manipulated e.g. positioned, rotated, warped or duplicated by user interaction. A coprocessor architecture is presented, that works in parallel to an MPEG-4 video and audio-decoder and a floating-point geometry-processor. It performs computation and bandwidth intensive low-level tasks for image compositing and rasterization. The processor consists of a SIMD array of 16 identical DSPs to reach the required processing power for real-time image warping, alpha-blending, z-buffering and phong-shading. The processor has an object-oriented parallel cache architecture with 2D virtual address space (e.g. textures) that allows concurrent and conflict-free access to shared image data objects for all 16 DSPs View full abstract»

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