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Computer Graphics International, 2000. Proceedings

Date 19-24 June 2000

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Displaying Results 1 - 25 of 40
  • Proceedings Computer Graphics International 2000

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    Freely Available from IEEE
  • Author index

    Page(s): 353
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    Freely Available from IEEE
  • Implementing fast cloth simulation with collision response

    Page(s): 257 - 266
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    The article details and implements efficient techniques for cloth simulation, both in the area of numerical simulation and the area of collision detection and response. Emphasis is put on the efficient implementation of implicit numerical methods with many improvements toward better realism, as well as computation simplicity. A constraint based collision response scheme is adapted to this scheme in order to provide an accurate and stable collision response View full abstract»

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  • An animation toolkit based on motion mapping

    Page(s): 11 - 17
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    We present a character animation toolkit for generating animation sequences interactively. It is based on a motion mapping technique that an object's motion can be applied to another object interactively. The toolkit generates the mesh for an object from several feature points on photo images automatically. An object's motion is defined and manipulated independently of modeling data. The motion generated once is applied to any object by the mapping technique according to an animation hierarchical data structure. The animation toolkit is appropriate for generating character animation that needs interactive motion modification and reuse rather than accurate modeling View full abstract»

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  • SQUEEZE: fast and progressive decompression of triangle meshes

    Page(s): 173 - 182
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    An ideal triangle mesh compression technology would simultaneously support the following objectives: (1) progressive refinements of the received mesh during decompression, (2) nearly optimal compression ratios for both geometry and connectivity, and (3) in-line, real-time decompression algorithms for hardware or software implementations. Because these three objectives impose contradictory constraints, previously reported efforts have focused primarily on one (sometimes two) of these objectives. The SQUEEZE technique introduced in this paper addresses all three constraints simultaneously, and attempts to provide the best possible compromise. For a mesh of T triangles, SQUEEZE compresses the connectivity to 3.7T bits, which is competitive with the best progressive compression techniques reported so far. The geometric prediction error encoding technique introduced in this paper leads to a geometry compression that is improved by 20% over that of previous schemes. Our initial implementation on a 300-MHz CPU achieved a decompression rate of up to 46,000 triangles per second. SQUEEZE downloads a model through a number of successive refinement stages, providing the benefit of progressivity View full abstract»

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  • Modeling Murex cabritii sea shell with a structured implicit surface modeler

    Page(s): 55 - 64
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    Implicit surface modeling systems have been used since the mid-1980's for the generation of cartoon like characters. Recently implicit models combined with constructive solid geometry (CSG) have been used to build engineering models with automatic blending. This work is built on a structured implicit modeling system which includes CSG, warping, 2D texture mapping and operations based on the BlobTree, and its application to the generation of a complex and visually accurate biological model of the sea shell Murex cabritii. Since the model is purely procedurally defined and does not rely on polygon mesh operations, it is resolution independent and can be rendered directly using ray tracing. An interface has been built to the BlobTree using an interpreted programming language (Python). The language interface readily allows a user to procedurally describe the shell based on numeric data taken from the actual object View full abstract»

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  • Crack pattern simulation based on 3D surface cellular automaton

    Page(s): 153 - 162
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    Describes a method for modeling the propagation of cracks on any 3D surface. Taking a previous cellular automata model of the authors (1999) as the basis, this method allows just about any type of cracks on any type of triangulated 3D object. Our model's main advantage is that it proposes a semi-physical solution, making it at the same time user-controllable and easily extendable. After summarizing works in the literature, we make a brief and simple description of what cracks are physically, and how they are generated. Based on this idea, we detail our model of crack propagation. We first introduce the general development of cracks. We then propose an original model of spectrum stress. This is followed by a description of the mutual interaction between cracks and stresses. Finally, a set of graphical examples, together with their respective parameters, concludes this paper View full abstract»

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  • Orientation lightmaps for photon tracing in complex environments

    Page(s): 279 - 286
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    We present a method that makes the use of photon tracing methods feasible for complex scenes when a totally accurate solution is not essential. This is accomplished by using orientation lightmaps, which average the illumination of complex objects depending on the surface normal. Through this averaging, they considerably reduce the variance of the stochastic solution. In order to use these specialised lightmaps, which consume comparatively small amounts of memory, no changes have to be made to the basic photon tracing algorithm. Also, they can be freely mixed with normal lightmaps. This gives the user good control over the amount of inaccuracy he introduces by their application. The area computations necessary for their insertion are performed using a stochastic sampling method that performs well for highly complex objects View full abstract»

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  • VPARK - a Windows NT software platform for a virtual networked amusement park

    Page(s): 309 - 315
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    Presents the VPARK (Virtual Park) system, which includes a networked virtual environment (NVE) system called W-VLNET and an “attraction building system” that is able to create and modify the attractions used in the NVE. Both systems have been developed in the Windows NT environment. The paper outlines the techniques for communication, scene management, facial and body animation, and general user interaction modules. The use of VRML97 and MPEG-4 SHNC is overviewed for the purpose of outlining the compatability of the system with other similar virtual reality systems. The software provides realistic virtual actors as well as sets of high-level actions that are applicable to them in real-time. Related issues on obtaining actor models and animating them in real time are presented. The creation process of an attraction incorporates assembling animation units through a timeline. Using this software, the users are able to bring their own scenario-based applications into a shared virtual environment View full abstract»

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  • Fast and stable animation of cloth with an approximated implicit method

    Page(s): 247 - 255
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    Realistic animation of soft objects such as cloth is essential for plausible character animation. Many techniques have been proposed for the simulation of soft objects, and most of them are based on numerical integration. Among the techniques, the implicit integration method is the most likely technique for real time environments, since it allows large time steps for cloth simulation by ensuring the stability of systems. However the most critical flaw of the implicit method is that it involves a large linear system. The paper presents a fast animation technique for animating soft objects based on a mass-spring model with an approximated implicit method which does not involve linear system solving. The proposed technique stably updates the state of n mass-points in O(n) time when the number of total springs are O(n). Because the mass-spring model shows a superelastic effect, the excessively deformed springs (i.e., super-elongated springs) should be adjusted for reality. The paper presents an efficient inverse dynamics process to adjust the super-elongated springs View full abstract»

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  • Simulated patient for orthognathic surgery

    Page(s): 239 - 245
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    Orthognathic surgery corrects a wide range of minor and major facial and jaw irregularities. This surgery will improve the patients' ability to chew, speak and breathe. In many cases, a better appearance will also result. With the recent advances in virtual reality (VR) and three-dimensional (3D) medical imaging technology, orthognathic surgery simulations typically requires costly volumetric data acquisition modalities such CT or MRI imaging for patient modeling. The authors present an approach for constructing 3D hard and soft tissue models of a patient based on colour portraits and conventional radiographs. This allows patient modeling to be done efficiently on low-cost platforms. Specifically, we extend the techniques developed by the author (H.S.H Ip and Lijin Yin, 1996) to hard tissue modeling. The extended technique employs a user-assisted approach to obtain the 3D coordinates of the feature points of the human face and jaw respectively from conventional photographs and radiographs. Then the displacement vectors of the feature points are computed by correspondence matching and interpolation against a generic head model and jaw bone model. The resulting combined hard and soft tissue models can be used for orthognathic surgical planning on a low-cost, PC based platform View full abstract»

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  • Ocean waves synthesis using a spectrum-based turbulence function

    Page(s): 65 - 72
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    The representation of ocean waves is not a resolved problem in computer graphics yet. There is still no existing method that allows one to simply describe an agitated surface of any size that is visually sufficiently realistic, without using entirely physical models that are usually very complex. We present a simple method to represent and animate an ocean surface in deep water by considering it as a procedural texture. This texture is defined by a combination of two levels of detail. The first one is a superposition of 2D trochoids whose parameters are determined by ocean wave characteristics infrequency domain. In order to increase the visual complexity of this model and to reduce computation, we incorporate a 3D turbulence function to provide a second level of detail. This turbulence function is also determined by frequency characteristics of ocean waves. Since our synthesized ocean waves spectrum approaches a real ocean waves spectrum, we obtain realistic water waves in the spatial domain. The animation of our model is performed by shifting the phase of the trochoids and by moving into the 3D turbulence function. Since our definition is procedural and continuous, it permits us to obtain any size of water surface with any level of detail as well as a simple, direct, antialiasing method. Our model can be used to generate ocean waves using 2D textures or bump maps as well as 3D textures View full abstract»

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  • Reconstruction of B-spline surfaces from scattered data points

    Page(s): 163 - 170
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    We present a new approach for reconstructing a smooth surface from a set of scattered points in 3D space. Our algorithm first decomposes a given point set into a quadtree-like data structure known as a strip tree. The strip tree is used to fit a set of least squares quadratic surfaces to the data points. These quadratic surfaces are then degree-elevated to bi-cubic surfaces and blended together to form a set of B-spline surfaces that approximates the given point set View full abstract»

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  • Augmented reality for real and virtual humans

    Page(s): 303 - 307
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    Current virtual reality technologies provide many ways to interact with virtual humans. Most of those techniques, however, are limited to synthetic elements and require cumbersome sensors. We have combined a real-time simulation and rendering platform with a real-time, non-invasive vision-based recognition system to investigate interactions in a mixed environment with real and synthetic elements. In this paper, we present the resulting system, the example of a checkers game between a real person and an autonomous virtual human to demonstrate its performance View full abstract»

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  • Visualization of biomedical processes: local quantitative physiological functions in living human body

    Page(s): 319 - 323
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    Functional imaging with dynamic positron emission tomography (PET) has been playing a crucial and expanding role in biomedical research and clinical diagnosis, providing image-wide quantitative and qualitative physiological functions in the human body, and supporting visualization of the distribution of these functions corresponding to anatomical structures. A number of parametric imaging algorithms have been developed. We give a brief study on some existing and our recently, developed techniques for generating parametric images. An integrated system for functional image data processing and visualization, and a Web-based application are presented View full abstract»

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  • A homotopy model for cup lifting

    Page(s): 117 - 125
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    Introduces two new theoretical tools - homotopy and cellular structured spaces - for visualization. Any object is represented by a filtration space, which is a sequence of skeletons that are topological spaces. Using an attaching function that attaches n-1 dimensional balls to the boundaries of n-dimensional balls, a filtration space is composed inductively and step-by-step, by increasing the dimensions. The space obtained by this process is called a cellular structured space, which is composed of cells. The cellular structured space preserves invariant properties of entities. On the other hand, traditional polygonalization has difficulty in preserving invariant properties. A change from one situation represented by a cellular structured space to another situation of a cellular structured space is represented by a homotopy if the change is continuous. Using homotopy and cellular structured spaces, invariant properties are preserved while very large data compression is achieved View full abstract»

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  • Homological invariants and holorgraphic representations of topological structures in cellular spaces

    Page(s): 89 - 97
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    Geometric modeling and computational representations of shapes have been subject to intense research for more than three decades. Interestingly, these subjects are still at the heart of a continuous activity of research and development in computer graphics, virtual environments, image-based rendering, computer-aided geometric design and physical simulations. Currently, geometric and physically-based modeling still face two main challenges: (1) the identification of topological features, and (2) the representation of the modes of interaction between them, both in static and dynamic environments. Current methods have offered many different forms of associating abstract structures with analytical expressions. The variety of modeling tools, from combinational methods to analytic algebraic geometry, not only reflects the richness of ideas in this domain of study but also the desire to improve, enhance and simplify. It is within this realm that we introduce a new framework, called holorgraphic geometric modeling (HGM). This framework combines the advantages of the graph-theoretic representation of combinatorial structures with the analytical flexibility, expressional power and scalability of higher-order, multi-dimensional variables and operators in the form of holors. HGM not only complements the combinatorial structures in geometric modeling but also enhances and reveals new concepts and ideas in the process of developing robust, flexible and scalable domains of formulation for simplicial complexes, cellular spaces, and homotopy in general View full abstract»

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  • Head detection and tracking by 2-D and 3-D ellipsoid fitting

    Page(s): 221 - 226
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    A novel procedure for segmenting a set of scattered 3D data obtained from a head and shoulders multiview sequence is presented. The procedure consists of two steps. In the first step, two ellipses corresponding to the head and the body of the person are identified based on ellipse fitting of the outline of the person in each image. The fitting is based on a fast direct least squares method using the constraint that forces a general conic to be an ellipse. In order to achieve head/body segmentation, a K-means algorithm is used to minimise the fitting error between the points and the two ellipsoids. In the second step, a 3D ellipsoid model corresponding to the head of the person is identified using an extension of the above method. Robustness and outlier removal can be achieved if a 3D ellipsoid model estimation technique is used in conjunction with the Median of Least Squares (MedLS) technique, which minimises the median of the errors corresponding to each 3D point. An interesting application of the proposed method is the combination of the 3D ellipsoid model with a generic face model which is adapted to the face images to provide information only for the high-detail front part of the head while the 3D ellipsoid is used for the back of the head, which is usually not visible View full abstract»

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  • Hand gesture animation from static postures using an anatomy-based model

    Page(s): 29 - 36
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    Automatic interpretation and animation of human motion has become an important research topic among researchers in virtual reality and computer animation. One major problem encountered during hand motion analysis is the large amount of data that need to be captured and analyzed. Even for a human hand, although only a small part of the body is involved, there are about 30 motion parameters for each hand posture. The authors present an approach to hand motion animation using only static images of the set of target gestures. We achieve naturalistic hand motion animation by the use of an anatomy based hand model and a hand gesture coding system, which we called Hand Action Coding System (HACS). This allows complex sequences of hand gestures to be animated based only on the static image of the hand gestures to be animated. This approach greatly simplifies motion data acquisition and the process of motion analysis and synthesis View full abstract»

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  • VISJET-a computer ocean outfall modelling system

    Page(s): 75 - 80
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    Sewage and industrial effluents from coastal cities are often discharged into the adjacent sea after some land-based treatment. In modern design, the wastewater is often discharged in buoyant jet groups from risers mounted on a submarine outfall on the seabed to achieve rapid mixing of effluents with tidal flow. A mathematical model for buoyant jets in currents based on the Lagrangian models, called JETLAG, was developed. The paper presents a system called VISJET, for visualizing the ocean sewage discharge system based on the JETLAG model. We discuss the features of VISJET system and show how computer visualization can be used to help with the design of an ocean sewage discharge system View full abstract»

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  • Real-time collision detection and response for complex environments

    Page(s): 105 - 113
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    Presents a method for collision detection that is well suited to complex environments, such as those obtained from medical imaging and for objects that are in permanent contact. The method is based on a point-in-tetrahedral-mesh query. Spatial and temporal coherence are used to achieve interactive speed. In addition to collision detection, the system calculates a force and torque that can be used for collision response. Experimental results show that it performs well compared to the RAPID (Robust and Accurate Polygon Interference Detection) collision detection library, which is a standard in the field View full abstract»

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  • Haptics issues in virtual environments

    Page(s): 295 - 302
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    Haptics is a recent enhancement to virtual environments, allowing users to “touch” and feel the simulated objects they interact with. Current commercial products allow tactile feedback through desktop interfaces (such as the FEELItTM mouse or the PHANToMTM arm) and dextrous tactile and force feedback at the fingertips through haptic gloves (such as the CyberTouchTM and the CyberGraspTM). Virtual reality haptic programming requires good physical modeling of user interactions, primarily through collision detection, and of object responses, such as surface deformation, hard-contact simulation, slippage, etc. It is at present difficult to simulate complex virtual environments that have a realistic behavior. This task is added to by the recent introduction of haptic toolkits (such as GhostTM or VPS). Current technology suffers from a number of limitations, which go beyond the higher production cost of haptic interfaces. These technical drawbacks include the limited workspace of desktop interfaces, the large weight of force-feedback gloves, the lack of force feedback to the body, safety concerns, etc. Not to be neglected is the high bandwidth requirement of haptics, which is not met by current Internet technology. As a result, it is not possible at present to have a large number of remote participants interacting haptically in a shared virtual space View full abstract»

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  • To gesture or not to gesture: what is the question?

    Page(s): 3 - 9
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    Computer synthesized characters are expected to make appropriate face, limb, and body gestures during communicative acts. We focus on non-facial movements and try to elucidate what is intended with the notions of “gesture” and “naturalness”. We argue that looking only at the psychological notion of gesture and gesture type is insufficient to capture movement qualities needed by an animated character. Movement observation science, specifically Laban Movement Analysis and its Effort and Shape components with motion phrasing provide essential gesture components (I. Bartenieff and D. Lewis, 1980). We assert that the expression of movement qualities from the Effort dimensions are needed to make a gesture naturally crystallize out of abstract movements. Finally, we point out that nonfacial gestures must involve the rest of the body to appear natural and convincing. A system called EMOTE has been implemented which applies parameterized Effort and Shape qualities to movements and thereby forms improved synthetic gestures View full abstract»

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  • Local and global geometric methods for analysis, interrogation, reconstruction, modification and design of shape

    Page(s): 137 - 151
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    Gives an overview of some recent methods useful for local and global shape analysis and for the design of solids. These methods include, as new tools for global and local shape analysis, the spectra of the Laplace and Laplace-Beltrami operators and the concept of stable umbilical points, i.e. stable singularities of the “principal curvature line” wire-frame model of the solid's boundary surface. Most of the material in this paper deals with the medial axis transform as a tool for shape interrogation, reconstruction, modification and design. We show that it appears to be possible to construct an intuitive user interface that allows one to mould shapes by employing the medial axis transform. We also explain that the medial axis and Voronoi diagram can also be defined and computed on free surfaces in a setting where the geodesic distance between two points p and q on a surface S is defined by the shortest surface path on S joining the two points p, q. This leads to the natural and computable generalized concepts of the geodesic medial axis and geodesic Voronoi diagram on free-form surfaces. Both can be computed with a reasonable speed and with high accuracy (of about 12 digits when double floating-point arithmetic is used for the computations) View full abstract»

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  • Dynamic 3D maps and their texture-based design

    Page(s): 325 - 334
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    Three-dimensional maps are fundamental tools for presenting, exploring, and manipulating geo data. This paper describes multiresolution concepts for 3D maps and their texture-based design. In our approach, 3D maps are based on a hybrid, multiresolution terrain model composed of data sets having different topological structure, for example a coarse regular grid combined with by triangulated microstructure. Any number of texture layers can be associated with the terrain model. For each texture layer, the multiresolution structure builds a texture tree which is linked to geometry patches of the multiresolution terrain model. The terrain model together with multiple texture layers can be rendered in real-time, in particular if multitexturing is available. Texture layers can be combined by high-level operations such us blending and masking and can be rebuilt at run-time. This mechanism simplifies the implementation of visual exploration tools and of procedural, automated map designs. 3D maps facilitate the visual simulation of environmental issues in spatial support systems, virtual reality applications, real-time GIS, and interactive cartography View full abstract»

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