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Computer Graphics International, 2004. Proceedings

Date 19-19 June 2004

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Displaying Results 1 - 25 of 104
  • Proceedings. Computer Graphics International

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  • Proceedings of the Computer Graphics International Conference 2004

    Page(s): ii
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  • Proceedings of the Computer Graphics International Conference 2004

    Page(s): iii
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  • Copyright page

    Page(s): iv
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  • Proceedings of the Computer Graphics International Conference 2004 Table of contents

    Page(s): v - xii
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  • Preface

    Page(s): xiii
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  • Conference committee

    Page(s): xiv - xv
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  • Multi-path algorithm for triangle strips

    Page(s): 2 - 9
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (633 KB) |  | HTML iconHTML  

    Triangle surface models belong to the most popular type of geometric objects description in computer graphics. Therefore, the problem of fast visualization of this type of data is often solved. One of popular approaches is stripification, i.e., a conversion of triangle surface into strips of triangles. This enables to reduce the rendering time by reduction data size and by avoiding of redundant lighting and transformations computations. In this paper we present a new stripification algorithm for static fully triangulated meshes. Our new algorithm is based on the dual graph of triangulation. The experimental results show that our stripification produces much lower number of triangle strips than other stripification algorithms (except one) View full abstract»

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  • Curvature tensor based triangle mesh segmentation with boundary rectification

    Page(s): 10 - 25
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (842 KB) |  | HTML iconHTML  

    This paper presents a new and efficient algorithm for the decomposition of 3D arbitrary triangle meshes into surface patches. The algorithm is based on the curvature tensor field analysis and presents two distinct complementary steps: a region based segmentation, which is an improvement of that presented by [G. Lavoue et al., (2004)] and which decomposes the object into known and near constant curvature patches, and a boundary rectification based on curvature tensor directions, which corrects boundaries by suppressing their artifacts or discontinuities. Experiments were conducted on various models including both CAD and natural objects, results are satisfactory. Resulting segmented patches, by virtue of their properties (known curvature, clean boundaries) are particularly adapted to computer graphics tasks like parametric or subdivision surface fitting in an adaptive compression objective View full abstract»

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  • Consistent normal orientation for polygonal meshes

    Page(s): 18 - 25
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1138 KB) |  | HTML iconHTML  

    In this paper, we propose a new method that can consistently orient all normals of any mesh (if at all possible), while ensuring that most polygons are seen with their front-faces from most viewpoints. Our algorithm combines the proximity-based with a new visibility-based approach. Thus, it virtually eliminates the problems of proximity-based approaches, while avoiding the limitations of previous solid-based approaches. Our new method builds a connectivity graph of the patches of the model, which encodes the "proximity" of neighboring patches. In addition, it augments this graph with two visibility coefficients for each patch. Based on this graph, a global consistent orientation of all patches is quickly found by a greedy optimization. We have tested our new method with a large suite of models, many of which from the automotive industry. The results show that almost all models can be oriented consistently and sensibly using our new algorithm View full abstract»

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  • Physically-based simulation of objects represented by surface meshes

    Page(s): 26 - 33
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1302 KB) |  | HTML iconHTML  

    Objects and scenes in virtual worlds such as 3D computer games are typically represented by polygonal surface meshes. On the other hand, physically-based simulations of deformations or fracture effects require volumetric representations such as tetrahedral meshes. In this paper we propose techniques to generate volumetric meshes dynamically for objects represented by surface meshes allowing the simulation of physical effects such as motion, deformation and fracture. We use the finite element method based on cubical elements of uniform size. Regular cube meshes have several advantages over geometrically more complex representations. Because of their simplicity, cube meshes can be generated quickly by voxelizing objects while neither geometry nor stiffness information needs to be stored explicitly. The low memory consumption makes physically-based animation possible for large scenes even on game consoles. We animate the original high resolution surface mesh by coupling it to the underlying volumetric mesh. This way, the regular structure of the volumetric mesh is hidden from the user. We also propose a technique to fracture the surface mesh along with the cube mesh which keeps the surface watertight and results in realistic fracture patterns View full abstract»

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  • Adaptive edge spinning algorithm for polygonization of implicit surfaces

    Page(s): 36 - 43
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1558 KB) |  | HTML iconHTML  

    This paper presents an adaptive method for polygonization of implicit surfaces. The method insists on the shape of triangles and the accuracy of resulting approximation as well. The main advantages of the triangulation presented are simplicity and the stable features that can be used for next expanding. The implementation is not complicated and only the standard data structures are used. The presented algorithm is based on the surface tracking scheme and it is compared with the other algorithms based on the similar principle, such as the Marching cubes and the Marching triangles algorithms View full abstract»

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  • A hybrid physics-based subdivision technique using coupled dynamic and subdivision parameters

    Page(s): 44 - 51
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (493 KB) |  | HTML iconHTML  

    The last few decades have seen enormous progress in both geometric subdivision, and physics-based simulation techniques. Mesh-based dynamic systems often require both subdivision and physical simulation for realistic and accurate results. However, the simulation parameters have been independent of the subdivision parameters, and vice-versa. This paper attempts to bridge this gap. We propose a hybrid approach that combines the physics-based simulation techniques and geometric subdivision algorithms, and demonstrate a mass-spring based system with physics-based butterfly subdivision. The initial subdivision coefficients are extracted using the physical properties of the base (L 0) mesh. Latter subdivision steps generate both the geometric and physical properties of the subdivided (Lk) mesh. This approach conserves mass, center of gravity, linear momentum and external force, and minimizes the distance between the Lk and Lk+1 meshes, at any time step. Our approach is general, efficient, and serve as a foundation for many applications in many fields View full abstract»

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  • Point set surface editing techniques based on level-sets

    Page(s): 52 - 59
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (585 KB) |  | HTML iconHTML  

    In this paper we articulate a new modeling paradigm for both local and global editing on complicated point set surfaces of arbitrary topology. In essence, the proposed technique leads to a novel point-set methodology that can unify the topological advantage of the level-set methods and the simplicity of point-sampled surfaces. Any user-specified region of a point set surface in our system can be embedded into a grid-based level-set framework. The super-imposed grid structure enables both powerful local surface editing and global scalar-field free-form deformation anywhere across the point-sampled geometry. Furthermore, the underlying level-set representation, coupled with the concept of digital topology, greatly facilitates the topological modification of the sculpted point-set geometry whenever necessary during shape deformation. We have developed a variety of editing toolkits that can allow users to directly manipulate the point-set surface through interactive sketching, smoothing, embossing, and global free-form deformations with ease. We demonstrate the usefulness and efficacy of our prototype system for the point-sampled geometry via many examples View full abstract»

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  • Modelling and animating cartoon hair with NURBS surfaces

    Page(s): 60 - 67
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (709 KB) |  | HTML iconHTML  

    In this paper we present a technique for the modelling and animation of cartoon hair. In our approach the primary shape and motion of the hair is defined by an animated NURBS volume, along whose surface are generated clumps of hair geometry. The basis of these hair clumps is formed by key hair curves that are grown along the isocurves of the originating surface and which follow its motion. Particle dynamics are applied to each key hair and blended with initial animation using springs. Profile curves are then extruded along the length of the hey hairs to create the geometry details of the hairdo. The finished animated hairdo is rendered nonphotorealistically in cartoon style shading View full abstract»

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  • Surface models of tube trees

    Page(s): 70 - 77
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (545 KB) |  | HTML iconHTML  

    This paper describes a new method for generating surfaces of branching tubular structures with given center-lines and radii. As the centerlines are not straight lines, the cross-sections are not parallel and well-known algorithms for surface tiling from parallel cross-sections cannot be used. Nonparallel cross-sections can be tiled by means of the maximal-disc interpolation method; special methods for branching-structures modeling by means of convolution surfaces produce excellent results, but these methods are more complex than our approach. The proposed method tiles nonparallel circular cross-sections and constructs a topologically-correct surface mesh. The method is not artifact-free, but it is fast and simple. The surface mesh serves as a data representation of a vessel tree suitable for real-time virtual reality operation planning and operation support within a medical application. Proposed method extracts a "classical" polygonal representation, which can be used in common surface-oriented graphic accelerators View full abstract»

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  • BlobTree trees

    Page(s): 78 - 85
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1174 KB) |  | HTML iconHTML  

    In recent years several methods for modeling botanical trees have been proposed. The geometry and topology of tree skeletons can be well described by L-systems; however, there are several approaches to modeling smooth surfaces to represent branches, and not all of the observed phenomena can be represented by current methods. Many tree types exhibit nonsmooth features such as branch bark ridges and collars. In this research a hierarchical implicit modeling system is used to produce models of branching structures that capture smooth branching, branch collars and branch bark ridges. The BlobTree provides several techniques to control the combination of primitives, allowing both smooth and nonsmooth effects to be intuitively combined in a single blend volume. Irregular effects are implemented using precise contact modeling, constructive solid geometry and space warping. We show that smooth blends can be obtained, without noticeable bulging, using summation of distance based implicit surfaces. L-systems are used to create the branching structure allowing botanically based simulations to be used as input View full abstract»

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  • Computing polygonal surfaces from unions of balls

    Page(s): 86 - 92
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1072 KB) |  | HTML iconHTML  

    We present a new algorithm for computing a polygonal surface from a union of balls. The method computes and connects the singular points of a given union of balls in an efficient manner to approximate the boundary. The algorithm uses the dual shape of the balls to give the resulting surface the correct topology. Our method is simple and demonstrated to be robust View full abstract»

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  • Computer aided design for Origamic Architecture models with polygonal representation

    Page(s): 93 - 99
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (588 KB) |  | HTML iconHTML  

    An Origamic Architecture (OA) is a folded sheet of perforated paper from which a three-dimensional structure "pops up" when it is opened. It is similar to a "pop-up story book", but its unique feature is that it is made purely by cutting a single piece of paper. Because of this limitation, designing an OA requires considerable experience. We propose a computerised method which assists design of OAs. An OA is modelled using a set of planar polygons. This model must satisfy the conditions required of a valid, realisable OA. A unique point of our method is the application of Boolean set operations to the polygons on the unfolded pattern to guarantee that the model can be made from a single sheet of paper. We also present a procedure for checking the model's validity. Additionally, we propose methods for creating openings, for generating unfolded patterns, and for displaying folding animation. We have implemented a system based on these methods and demonstrated its usefulness for creating OA. Our system allows designers to intuitively design OA models and to easily generate the unfolded patterns View full abstract»

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  • A virtual light field approach to global illumination

    Page(s): 102 - 109
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (389 KB) |  | HTML iconHTML  

    This paper describes an algorithm that provides real-time walkthrough for globally illuminated scenes that contain mixtures of ideal diffuse and specular surfaces. A type of light field data structure is used for propagating radiance outward from light emitters through the scene, accounting for any kind of L(SD)* light path. The light field employed is constructed by choosing a regular point subdivision over a hemisphere, to give a set of directions, and then corresponding to each direction there is a rectangular grid of parallel rays. Each rectangular grid of rays is further subdivided into rectangular tiles, such that each tile references a sequence of 2D images containing colour values corresponding to the outgoing radiances of surfaces intersected by the rays in that tile. This structure is then used for final image rendering. Propagation times can be very long and the memory requirements very high. This algorithm, however, offers a global illumination solution for real-time walkthrough even on a single processor View full abstract»

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  • Exploiting temporal coherence in final gathering for dynamic scenes

    Page(s): 110 - 119
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB) |  | HTML iconHTML  

    Efficient global illumination computation in dynamically changing environments is an important practical problem. In high-quality animation rendering costly "final gathering" technique is commonly used. We extend this technique into temporal domain by exploiting coherence between the subsequent frames. For this purpose we store previously computed incoming radiance samples and refresh them evenly in space and time using some aging criteria. The approach is based upon a two-pass photon mapping algorithm with irradiance cache, but it can be applied also in other gathering methods. The algorithm significantly reduces the cost of expensive indirect lighting computation and suppresses temporal aliasing with respect to the state of the art frame-by-frame rendering techniques View full abstract»

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  • Spatio-temporal photon density estimation using bilateral filtering

    Page(s): 120 - 127
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (454 KB) |  | HTML iconHTML  

    Photon tracing and density estimation are well established techniques in global illumination computation and rendering of high-quality animation sequences. Using traditional density estimation techniques it is difficult to remove stochastic noise inherent for photon-based methods while avoiding overblurring lighting details. In this paper we investigate the use of bilateral filtering for lighting reconstruction based on the local density of photon hit points. Bilateral filtering is applied in spatio-temporal domain and provides control over the level-of-details in reconstructed lighting. All changes of lighting below this level are treated as stochastic noise and are suppressed. Bilateral filtering proves to be efficient in preserving sharp features in lighting which is in particular important for high-quality caustic reconstruction. Also, flickering between subsequent animation frames is substantially reduced due to extending bilateral filtering into temporal domain View full abstract»

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  • Interactive global illumination for quasi-static scenes

    Page(s): 128 - 131
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (236 KB) |  | HTML iconHTML  

    This paper describes an approach to obtain interactive recalculation of global illumination for scenes with small moving objects (with respect to the complete geometry), on a standard PC, using density estimation techniques View full abstract»

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  • Bounding volumes for linearly interpolated shapes

    Page(s): 134 - 139
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB) |  | HTML iconHTML  

    Bounding volumes are crucial for culling in interactive graphics applications. For dynamic shapes, computing a bounding volume for each frame could be very expensive. We analyze the situation for a particular class of dynamic geometry, namely, shapes resulting from the linear interpolation of several base shapes. The space of weights for the linear combination can be decomposed into cells so that in each cell a particular vertex is maximal (resp. minimal) in a given direction. This cell decomposition of the weight space allows deriving bounding volumes from the weight vectors rather than the generated geometry. We present algorithms to generate the cell decomposition, to map from weights to cells, and to efficiently compute the necessary data structures. This approach to computing bounding volumes for dynamic shapes proves to be beneficial if the geometry representation is large compared to the number of base shapes View full abstract»

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  • Determining collisions between moving spheres for distributed virtual environments

    Page(s): 140 - 147
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (341 KB) |  | HTML iconHTML  

    We present an approach to collision detection that is appropriate for satisfying the requirements of interest management schemes used in distributed virtual environments. Such environments are characterized by their distributed deployment over a number of nodes connected via a computer network. The aim of an interest management scheme is to identify when objects that populate a simulation supported by a distributed virtual environment (objects could be hosted on different nodes) should be interacting via message exchange while preventing objects that should not be interacting from exchanging messages. The approach to collision detection presented in this paper produces accurate results when determining object interactions. Furthermore, we present variations on our approach that exploit any coherence that may exist in a simulation to provide a solution that may scale for large numbers of objects View full abstract»

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