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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
  • Object and ray coherence in the optimization of the ray tracing algorithm

    Page(s): 264 - 267
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    The authors' proposal for ray tracing optimization is based on the combined use of object and ray coherence when tracing beams in scenes subdivided by octrees. With this algorithm they take advantage of the benefits of space subdivision structures (octrees), facilitating that a ray only has to calculate its intersection with a reduced number of objects (those located in the node to which the ray has arrived). On the other hand, the simultaneous tracing of rays integrated in a beam reduces the necessary time to obtain the final image 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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  • Varying neighbourhood parameters for the computation of normals on surfaces in discrete space

    Page(s): 616 - 625
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    A method is examined which computes normal vectors on binary discrete surfaces by making use of the local separation criterion of surfaces. The method considers points in the neighbourhood of a surface point in object space to recover information about the local surface inclination. The article examines and evaluates the different parameters used in the computation of the normals, such as neighbourhood size and weighting factors, both from a numerical and from a visual point of view. Moreover far the discrete space the use of spherical neighbourhoods is introduced for the computation, and the vectors computed from the two different sides of a surface are compared View full abstract»

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  • The analysis and reconstruction of repetitive textures

    Page(s): 273 - 276
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    Many interesting textures, whether natural, such as reptile skin, or synthetic, such as knitting, are made up of repeating elements. For these textures it can be shown that a suitably painted parallelogram tile can recreate the original image. This tile can be characterised by the vectors that define adjacent sides. Several methods have been proposed to extract these vectors. The paper examines and extends these and introduces new ones. These methods have been applied to a wide variety of images, and interesting and novel ways of modifying the synthesis process to introduce local deformations are explored View full abstract»

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  • 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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  • Memory management schemes for radiosity computation in complex environments

    Page(s): 706 - 714
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    Hierarchical radiosity is a very demanding process in terms of computation time and memory resources even for scenes of moderate complexity. To handle complex environments which don't fit in the memory, new solutions have to be devised. One solution is to partition the scene into subsets of polygons (3D cells or clusters) and to maintain in memory only some of them. The radiosity computation is performed only for this resident subset which changes during the resolution process. This change entails many read and write operations from or onto the disk. These disk transfers must be ordered to make the radiosity algorithms tractable. The authors propose different ordering strategies which can be seen as complementary to those devised by Teller (1994) View full abstract»

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  • Automatic exposure in computer graphics based on the minimum information loss principle

    Page(s): 666 - 677
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    The available contrast of common display devices is much lower than image data often demand. Usually a variant of an average of the field of view is used to normalize the image. An alternative approach is introduced to define the mapping of rendered values to the displayable intensity range. The luminance range is chosen such that a minimum amount of information is lost thereby preserving the contrast ratio of all correctly displayed parts. The loss of information can be regulated by different error functions. If the loss is too large, the luminance range can be increased, but the original contrast is not presented any more. In this case the method represents an improvement of Schlick's (1994) mapping technique. The newly introduced method can be applied on color and gray scale images, rendered in absolute or fictitious units View full abstract»

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  • An adaptable modular software architecture for distant control of virtual actors

    Page(s): 245 - 247
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    This paper presents an adaptable software architecture for distributed real-time animation of 3D virtual actors. The animation system is divided into several modules that are running either on the server or on the client. This approach enables an individual configuration of the system according to the demands of the connection and the software and hardware performance of the involved computers View full abstract»

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  • Towards an understanding of surfaces through polygonization

    Page(s): 416 - 425
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    We identify some of the major problems in polygonizing parametric surfaces. We are interested in associating an error with a polygonization which tells us how well we have done, rather than judging a surface by its looks alone. We introduce an error measurement which is more intuitive and helps to understand the surface View full abstract»

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  • Floating ring: a new tool for visualizing distortion in map projections

    Page(s): 466 - 480
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    The authors present a new method for interactive visualization of distortion in map projections. The central idea is a floating ring on a sphere (globe) that can be interactively positioned and scaled. As the ring is manipulated on the globe, the corresponding projection of the ring is distorted using the same map projection parameters. They apply this method to study a real and angular distortion. This method is particularly useful when analyzing large geographical extents (such as in global climate studies) where distortions are significant, as well as visualizations for which information is geo-referenced and perhaps scaled to the underlying map. It serves as a reminder that distortion exists in maps and provides information about the degree, location, and type of distortion View full abstract»

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  • A method for filling n-sided holes in a surface

    Page(s): 578 - 582
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    While parametric surfaces are most conveniently described by rectangular patches, most complex objects require the use of patches with other than four sides. Methods to generate such patches are widely used but all have drawbacks. This paper describes the creation of a surface which covers the original surface and the non-rectangular “hole” with a new, smooth surface. The method employs recursive splines and can be used with a control mesh of arbitrary topology. Control of the shape of the patch covering the “hole” can be achieved by user manipulation of a “controller” point on the patch View full abstract»

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  • Deforming virtual objects with an instrumented glove

    Page(s): 393 - 395
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    A virtual hand controlled with an instrumented glove is used for visualizing the interaction between the hand and a virtually deformable object. Using a sphere-tree representation, collision between the fingers and the object is detected. Contacts between the virtual hand and the object are used for establishing constraints for the evaluation of deformation based on the finite element technique. Experiments showed that the critical process for attaining interactive response is the inversion of the stiffness matrix in finite element analysis. By using a parallel processing technique for the matrix inversion process, interactive response is attained for objects with a mesh composed of 300 nodes View full abstract»

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  • Interactive, animated 3D widgets

    Page(s): 278 - 286
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    If 3D applications become large, hierarchical networks of geometric objects lead to messy specifications. Furthermore, if time- and event-dependencies are merged with geometric modeling, complex animations and interactions cannot be modeled independently and hierarchically since their specifications are dispersed throughout the static scene description. The authors present an object-oriented architecture for interactive, animated 3D widgets which reduces the complexity of building 3D applications. 3D widgets encapsulate geometry and behavior into high-level building blocks based on two types of directed acyclic graphs, geometry graphs and behavior graphs. 3D widgets construct internal geometry graphs and behavior graphs, and perform operations on these graphs through high-level interfaces which hide details and raise the level of abstraction. 3D widgets define object ports which are used to link together different 3D widgets. A visual language for 3D widgets allows the developer the interactive construction of 3D applications View full abstract»

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  • Visualizing 3-D geographical data with VRML

    Page(s): 108 - 110
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    The article discusses visualizing and interacting with 3D geographical data via VRML in the Web environment. For this purpose, the Web based desktop VR for geographical information is conceptualized. After VRML is briefly introduced, issues in modeling geographical data such as modeling geometry, topology and appearance are addressed. Sample visualization results for terrain and buildings are given, followed by discussions on the application of VRML. Cooperation within computer graphics and GIS is prospected in automatic model reconstruction and in exploring VRML application potential in visualizing geographical information 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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  • 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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  • Deformable surfaces for feature based indirect volume rendering

    Page(s): 752 - 760
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    The authors present an indirect volume visualization method, based on the deformable surface model, which is a three dimensional extension of the snake segmentation method. In contrast to classical indirect volume visualization methods, this model is not based on iso-values but on boundary information. Physically speaking it simulates a combination of a thin plate and a rubber skin, that is influenced by forces implied by feature information extracted from the given data set. The approach proves to be appropriate for data sets that represent a collection of objects separated by distinct boundaries. These kind of data sets often occur in medical and technical tomography, as they demonstrate by a few examples. They propose a multilevel adaptive finite difference solver which generates a target surface minimizing an energy functional based on an internal energy of the surface and an outer energy induced by the gradient of the volume. This functional tends to produce very regular triangular meshes compared to results of the marching cubes algorithm. It makes this method attractive for meshing in numerical simulation or texture mapping. Red-green triangulation allows an adaptive refinement of the mesh. Special considerations have been made to prevent self inter-penetration of the surfaces View full abstract»

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  • Rendering objects with small elements based on their micro and macro structures

    Page(s): 268 - 272
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    The paper presents a method to render objects which consist of numerous small elements such as fur and leaves. The method visualizes both an effect under the pixel size such as the dark shade of fur toward viewers and an effect over the pixel size such as the shape of fur at contours. As for the effect under the pixel size, the intensity is computed based on the microstructure such as shadows by adjacent fur. After the intensity is computed, the shape of each element is generated by sweeping a two dimensional color element and applying transparency filters. Since shape generation is a post process, parameters such as length, width, curvature and color of small elements can be modified without repeating the intensity computation. It is useful for interactive design. The method is especially suitable to create still images because it is intrinsically two dimensional and screen resolution dependent. However techniques to keep three dimensional consistency and avoid problems of discreteness are taken into account for animation 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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  • Stability conditions for free form surfaces

    Page(s): 41 - 47
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    In CAD/CAM technology, the design of free form surfaces is the beginning of a chain of operations, which ends with the numerically controlled (NC) production of the designed object. An important part of this chain is shape analysis. We present a stability concept for surfaces based on infinitesimal bendings. The infinitesimal rigidity is enforced by certain boundary conditions View full abstract»

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  • Synthesis of facial expressions for semantic coding of videophone sequences

    Page(s): 512 - 519
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    A method for the synthesis of facial expressions for semantic coding of videophone sequences is presented. Firstly, a generic 3D face model is automatically adapted to the eyes, mouth, eyebrows, nose and chin and cheek contours of the individual face in the sequence. Secondly, a synthesis of facial expressions of this individual face is carried out using a model of the human facial muscles. Applying the described algorithms to the videophone sequences Akiyo and Miss America (CIF 10 Hz), the face model is successfully adapted at the beginning of the videophone sequence and facial expressions of the individual faces are synthesized 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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