@article{Wooten:1996:AOH, author = {Wayne L. Wooten and Jessica K. Hodgins}, title = {Animation of Human Diving}, volume = {15}, number = {1}, journal = {Computer Graphics Forum}, year = {1996}, pages = {3-14}, note = {{ISSN} 0167-7055}, annote = {The motion of a human platform diver was simulated using a dynamic model and a control system. The dynamic model has 32 actuated degrees of freedom and dynamic parameters within the range of those reported in the literature for humans. The control system uses algorithms for balance, jumping, and twisting to initiate the dive, sequences of desired values for proportional-deritvative servos to perform the aerial portion of the dive, and a state machine to sequence the actions throughout the dive. The motion of the simulated diver closely resembles video footage of dives performed by human athletes. The control and simulation techniques presented in this paper are useful for providing realistic motion for synthetic actors in computer animations and virtual environments and may someday be useful for analysis of sports performance. }, } @article{Pfeifle:1996:FTB, author = {Ron Pfeifle and Hans-Peter Seidel}, title = {Fitting Triangular B-Splines to Functional Scattered Data}, volume = {15}, number = {1}, journal = {Computer Graphics Forum}, year = {1996}, pages = {15-24}, note = {{ISSN} 0167-7055}, keywords = {scattered data approximation, triangular B-Splines, {DMS} splines, simplex splines, quadtrees}, annote = {Scattered data is, by definition, irregularly spaced. Uniform surface schemes are not well adapted to the locally varying nature of such data. Conversely, Triangular B-Spline surfaces are more flexible in that they can be built over arbitrary triangulations and thus can be adapted to the scattered data. This paper discusses the use of {DMS} spline surfaces for approximation of scattered data. A method is provided for automatically triangulating the domain containing the points and generating basis functions over this triangulation. A surface approximating the data is then found by a combination of least squares and bending energy minimization. This combination serves both to generate a smooth surface and to accommodate for gaps in the data. Examples are presented which demonstrate the effectiveness of the technique for mathematical, geographical and other data sets. }, } @article{Lamouret:1996:SIP, author = {Alexis Lamouret and Marie-Paule Gascuel}, title = {Scripting Interactive Physically-Based Motions with Relative Paths and Synchronization}, volume = {15}, number = {1}, journal = {Computer Graphics Forum}, year = {1996}, pages = {25-34}, note = {{ISSN} 0167-7055}, keywords = {animation, simulation, motion control, collisions}, annote = {This paper presents a novel approach for facilitating the use of physically based models by animators. The idea is to let the user guide motion at a high level of control by giving approximate desired trajectories and synchronization constraints between the objects over time, while a simulation module computes the final motion, dealing with collision detection and response, and enhancing realism. The objects, which are either isolated or components of an articulated structure, are guided through the specification of key-positions and orientations, defined by coordinates that can be fixed or relative to another object. The animation sequence is scripted by specifying a graph of synchronization constraints between objects over time. During the animation, objects automatically regulate their speed in order to meet these constraints. }, } @article{McCool:1996:AEO, author = {Michael D. McCool}, title = {Accelerated Evaluation of Box Splines via a Parallel Inverse {FFT}}, volume = {15}, number = {1}, journal = {Computer Graphics Forum}, year = {1996}, pages = {35-46}, note = {{ISSN} 0167-7055}, keywords = {box spline evaluation, volume rendering, Fast Fourier Transform, {FFT}, parallelism}, annote = {Box splines are a multivariate extension of uniform univariate B-splines. Direct evaluation of a box spline basis function can be difficult, but they have a relatively simple Fourier transform and can therefore be evaluated with an inverse FFT. Symmetry, recursive evaluation of the coefficients, and parallelization can be used to improve absolute performance. A windowing function can also be used to reduce truncation artifacts. We explore all these options in the context of a high-performance parallel implementation. Our goal is the provision of an empirical touchstone for the inverse {FFT} evaluation of box spline basis functions,for eventual application to forward projection (splat-based) volume rendering. }, } @article{Algorri:1996:SRF, author = {Maria-Elena Algorri and Francis Schmitt}, title = {Surface Reconstruction from Unstructured {3D} Data}, volume = {15}, number = {1}, journal = {Computer Graphics Forum}, year = {1996}, pages = {47-60}, note = {{ISSN} 0167-7055}, keywords = {surface reconstruction, triangulation, deformable models, visualization}, annote = {Building {3D} models from unstructured data is a problem that arises increasingly as new {3D} scanning technology is able to produce large and complex databases of full {3D} information. Huge efforts put into segmenting entire sets of {2D} images demand robust tools that are then able to reconstruct any arbitrary {3D} surface segmented from the images. In this paper we propose an algorithmic methodology that automatically produces a surface from a set of points in R3 about which we have no topological knowledge. Our method uses a spatial decomposition and a surface tracking algorithm to produce a rough approximation S' of the unknown manifold S. The produced surface \bfS' serves as a robust initialisation for a physically based modeling technique that yields the fine details of S and so improves the quality of the reconstruction. }, } @article{Skala:1996:AEA, author = {V{\'{a}}clav Skala}, title = {An Efficient Algorithm for Line Clipping by Convex and Non-convex Polyhedra in E3}, volume = {15}, number = {1}, journal = {Computer Graphics Forum}, year = {1996}, pages = {61-68}, note = {{ISSN} 0167-7055}, keywords = {line clipping, convex polyhedron, non-convex polyhedron, computer graphics, algorithm complexity, geometric algorithms, algorithm analysis}, annote = {A new algorithm for clipping lines against convex polyhedron with O(N) complexity is given with modification for non-convex polyhedron. The suggested algorithm is faster for higher number of facets of the given polyhedron than the traditional Cyrus-Beck's algorithm. Some principal results of comparison of all algorithms are shown and give some ideas how the proposed algorithm could be used effectively. }, } @article{Grimsdale:1996:TLD, author = {R. L. Grimsdale and C. W. Chang}, title = {The Layout Design Language: A Technique for Generating Layout Plans}, volume = {15}, number = {2}, journal = {Computer Graphics Forum}, year = {1996}, pages = {97-106}, note = {{ISSN} 0167-7055}, keywords = {{3D} model databases, urban layout plan, spatial representation, shape grammar, knowledge based design system}, annote = {The work described in this paper arose from a requirement for a system to support the production of models for training simulator visual systems and other vislialisation applications. To reduce the labour involved in generating such models, it was decided to develop a technique whereby models could be generated by a high-level language. For these models there is a requirement to generate 2-D plans showing, for example, the locations of roads and buildings, subsequently 3-D models of the buildings are placed at the defined locations. The 2-D plans can be created through the use of the Layout Design Language (LD-Language). LD-Language has been formulated particularly for designing urban area street plans. The primitive elements of the LD-Language, plots, are assembled into patterns which can be.further combined into a layout plan, with some support provided by the system. The work reported has successfully demonstrated that a complex layout plan can he developed using this language. }, } @article{Turner:1996:ELI, author = {Martin J. Turner and Neil E. Wiseman}, title = {Efficient Lossless Image Contour Coding}, volume = {15}, number = {2}, journal = {Computer Graphics Forum}, year = {1996}, pages = {107-118}, note = {{ISSN} 0167-7055}, annote = {A process is presented for converting a raster image into a discrete set of plateaus or contours. A contour coder has been developed which fully describes these contours via their boundary descriptions in a compact and computationally efficient manner, and is the basis for an image compression method. An analysis of some of the possible edge coding schemes is presented with both theoretical and practical conclusions. Described is a detailed study of the problems encountered and solutions chosen. }, } @article{Callet:1996:PDF, author = {Patrick Callet}, title = {Pertinent Data for Modelling Pigmented Materials in Realistic Rendering}, volume = {15}, number = {2}, journal = {Computer Graphics Forum}, year = {1996}, pages = {119-128}, note = {{ISSN} 0167-7055}, keywords = {rendering, physically-based modelling, photorealism, image synthesis, metamerism, Melamed model, Kubelka-Munk model, radiative transfer, scattering, powders, paints, plastics, pigmented media}, annote = {This article discusses the important problem of determining pertinent data to describe a pigmented medium. The first part deals with optical characteristics of pigments and the general properties of binders and fillers. It also exposes the limits and conditions of applicability of single scattering. In the second part the connection between individual optical properties, size, and form of particles is made with phenomenological theories of multiple scattering in absorbing media. Progressively, it appears that pertinent data in realistic modelling are always in relation with true or effective complex refractive indices and size parameters. }, } @article{Rumpf:1996:FDA, author = {Martin Rumpf and Alfred Schmidt and Kunibert G. Siebert}, title = {Functions Defining Arbitrary Meshes - A Flexible Interface between Numerical Data and Visualization}, volume = {15}, number = {2}, journal = {Computer Graphics Forum}, year = {1996}, pages = {129-142}, note = {{ISSN} 0167-7055}, keywords = {arbitrary meshes, mixed elements, procedural access}, annote = {Most of the rendering tools in scientific visualization are restricted to special data structures which differ substantially from the data formats used in numerical applications. Trying to close this gap, we present an interface between data from numerical methods on general types of grids - like cuboidal, prismatic, simplicial, parametric, mixed, or hierarchical meshes - and general visualization routines. It is based on a procedural approach managing a collection of arbitrary elements and a set of functions describing each element type. No mapping of (an in general enormous amount of) numerical data onto new data structures is necessary; a user may use his own data structures and only has to provide this small set of procedures and functions. The visualization tools will then use these routines to access (temporarily and locally) data of interest, like information about a single element. Compared with display routines on a specialized data structure, this general interface does not produce much cpu overhead. }, } @article{Bercovier:1996:EDM, author = {M. Bercovier and O. Volpin}, title = {Energy Duality Methods for Piecewise B{\'{e}}zier Curve Construction}, volume = {15}, number = {2}, journal = {Computer Graphics Forum}, year = {1996}, pages = {143-154}, note = {{ISSN} 0167-7055}, keywords = {finite-element method, {FEM}, stiffness matrix, piecewise B{\'{e}}zier curve, local refinement, computer-aided geometric design, Lagrange multiplier, duality, minimization under constraints}, annote = {Piecewise B{\'{e}}zier Curves are constructed using a minimization principle. Ck and GCk continuity is imposed by linear constraints. The corresponding quadratic programming with linear constraints problem is introduced and solved by duality methods. Bordering matrices methods are implemented to deal with local refinement (subdivision). The result is a versatile tool for defining / editing contours made of piecewise B{\'{e}}zier curves. }, } @article{Grimstead:1996:ILL, author = {I. J. Grimstead and R. R. Martin}, title = {Incremental Line Labelling for Sketch Input of Solid Models}, volume = {15}, number = {2}, journal = {Computer Graphics Forum}, year = {1996}, pages = {155-166}, note = {{ISSN} 0167-7055}, keywords = {sketch input, line labelling, reconstruction, solid modelling}, annote = {Designers need to transfer three-dimensional objects from their minds via a two-dimensional interface into the a solid modelling system. We propose a system where objects are sketched interactively in two-dimensions and incrementally line-labelled as the drawing progresses, as the preliminary stage in constructing a solid model. Once the sketch is complete, the line-labels are coupled with various inferred constraints to enable us to generate a solid model. In this paper we describe and evaluate a modification to existing line labelling methods to allow them to work incrementally. In this way, the labelling and region information can be built up as the user sketches, rather than all at once at the end of the sketching process, which reduces the delay before the final solid model is built. }, } @article{Zakai:1996:TMA, author = {Yaron Zakai and Ari Rappoport}, title = {Three-Dimensional Modeling and Effects on Still Images}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {3-10}, note = {{ISSN} 1067-7055}, keywords = {image manipulation, {3D} modeling from images, special effects}, annote = {Designers and creative artists use computer graphics and image processing effects on still photographs in application areas such as advertising, entertainment, broadcasting and the arts. Most of the effects available in reserach and commercial work are two-dimensional in nature, for example image processing filters (blur, edge enhancement) and creative effects (tiling, reflections). There is almost no usage of information taken from the {3D} world in which the objects appearing in the image are located. In this paper we present a novel method for creating {3D} effets on photographs, or in general on any image created by rendering a {3D} workd. The artist interacts with the image using a set of intuitive direct manipulation interface objects. These objects let the user define a {3D} model, display it, and manipulate it in a {3D} space which is correlated with that of the input image. The generated model can be an arbitrarily complex {3D} polyhedron. Any texture, including texture taken from the input photograph, can be mapped into any of its faces and used for special effects. We discuss and show examples for effects such as copy and paste, motion blur, model editing and deformations, lighting effects, and shadows. Proceedings of Eurographics '96. }, } @article{Breen:1996:IOA, author = {David E. Breen and Ross T. Whitaker and Eric Rose and Mihran Tuceryan}, title = {Interactive Occlusion and Automatic Object Placement for Augmented Reality}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {11-22}, note = {{ISSN} 1067-7055}, annote = {We present several techniques for producing two visual and modeling effects in augmented reality. The first effect involves interactively calculating the occlusions between real and virtual objects. The second effect utilizes a collision detection algorithm to automatically move dynamic virtual objects until they come in contact with static real objects in augmented reality, All of the techniques utilize calibrated data derived from images of a real-world environment. Proceedings of Eurographics '96. }, } @article{Berger:1996:CCA, author = {M.-O. Berger and C. Chevrier and G. Simon}, title = {Compositing Computer and Video Image Sequences: Robust Algorithms for the Reconstruction of the Camera Parameters}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {23-32}, note = {{ISSN} 1067-7055}, annote = {A augmented reality shows great promises in fields where a simulation in situ would be impossible or too expensive. When mixing synthetic and real objects in the same animated sequence, we must be sure that the geometrical coherence as well as the photometrical coherence is ensured. One major challenge is to compute the camera viewpoint with sufficient accuracy to ensure a satisfactory composition. We especially address this point in this paper using computer vision techniques and robust statistical methods. We prove that such techniques make it possible to compute almost automatically the viewpoint for long video sequences even for bad quality images in outdoor environments. Significant results on the lighting simulation of the bridges of Paris are shown. Proceedings of Eurographics '96. }, } @article{Beylot:1996:3IT, author = {P. Beylot and P. Gingins and P. Kalra and N. Thalmann and W. Maurel and D. Thalmann and J. Fasel}, title = {{3D} Interactive Topological Modeling using Visible Human Dataset}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {33-44}, note = {{ISSN} 1067-7055}, keywords = {Visible Human Dataset, Topological Modeling, Surface Reconstruction, Medical Imaging}, annote = {Availability of Visible Human Dataset (VHD) has provided numerous possibilities for its exploitation in both medical applications and {3D} animation. In this paper, we present our interactive tools which enable extraction of surfaces for different organs, including bones, muscles, fascia, and skin, from the {VHD}. The reconstructed surfaces then are used for defining the inter-relationship of organs, a process we refer to as topological modeling. A data base is constructed, which encapsulates structural, topological, mechanical and other relevant information about organs. A {3D} interactive tool enables the building and editing of this data base. Such a data base can later be used for different applications in fields such as medicine, sports, education, and entertainment. Proceedings of Eurographics '96. }, } @article{Haley:1996:IVR, author = {Michael B. Haley and Edwin H. Blake}, title = {Incremental Volume Rendering Using Hierarchical Compression}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {45-56}, note = {{ISSN} 1067-7055}, keywords = {incremental, volume rendering, octree, Shear-Warp}, annote = {We present a new algorithm here for efficient incremental rendering of volumetric datasets. The primary goal of this algorithm is to give average workstations the ability to efficiently render volume data received over relatively low bandwidth network links in such a way that rapid user feedback is maintained. Common limitations of workstation rendering of volume data include: large-memory overheads, the requirement of expensive rendering hardware, and high speed processing ability. The rendering algorithm presented here overcomes these problems by making use of the efficient Shear-Warp Factorisation method which does not require specialised graphics hardware. However the original Shear-Warp algorithm suffers from a high memory overhead and does not provide for incremental rendering which is required should rapid user feedback be maintained. Our algorithm represents the volumetric data using a hierarchical data structure which providesfor the incremental classfication and rendering of volume data. This exploits the multiscale nature of the octree data structure. The algorithm reduces the memory foot print of the original Shear-Warp Factorisation algorithm by a factor of more than two, while maintaining good rendering performance. These factors make our octree algorithm more suitable for implementation on average desktop workstations for the purposes of interactive exploration of volume models over a network. Results from tests using typical volume datasets will be presented which demonstrate the ability of the algorithm to achieve high rendering rates for both incremental rendering and standard rendering while reducing the runtime memory requirements. Proceedings of Eurographics '96. }, } @article{Bro-Nielsen:1996:RVD, author = {Morten Bro-Nielsen and Stephane Cotin}, title = {Real-time Volumetric Deformable Models for Surgery Simulation using Finite Elements and Condensation}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {57-66}, note = {{ISSN} 1067-7055}, keywords = {Virtual Surgery, Real-Time Deformation, Solid Volumetric Deformable Models, Virtual Reality, Finite Element Models}, annote = {This paper discusses the application of {3D} solid volumetric Finite Element models to surgery simulation. In particular it introduces three new ideas for solving the problem of achieving real-time performance for these models. The simulation system we have developed is described and we demonstrate real-time deformation using the methods developed in the paper. Proceedings of Eurographics '96. }, } @article{Ronfard:1996:FAO, author = {R{\'{e}}mi Ronfard and Jarek Rossignac}, title = {Full-range Approximation of Triangulated Polyhedra}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {67-76}, note = {{ISSN} 1067-7055}, keywords = {visualization, polyhedral surfaces, levels of detail, region merging}, annote = {We propose a new algorithm for automatically computing approximations of a given polyhedral object at different levels of details. The application for this algorithm is the display of very complex scenes, where many objects are seen with a range of varying levels of detail. Our approach is similar to the region-merging method used for image segmentation. We iteratively collapse edges, based on a measure of the geometric deviation from the initial shape. When edges are merged in the right order, this strategy produces a continuum of valid approximations of the original objects, which can be used for faster rendering at vastly different scales. Proceedings of Eurographics '96. }, } @article{Algorri:1996:MS, author = {Mar{\'{i}}a-Elena Algorri and Francis Schmitt}, title = {Mesh Simplification}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {77-86}, note = {{ISSN} 1067-7055}, keywords = {mesh simplification, mesh decimation,. triangulation, geometric modeling}, annote = {Mesh simplification is an important stage after surface reconstruction since the models produced can contain a large number of polygons making them difficult to manipulate. In this paper we preseat a mesh simplification algorithm to reduce the number of vertices in a dense mesh of triangles. The algorithm is based on edge operations that are performed in the inside of independent clusters distributed over the entire mesh. The clusters are well-characterized regions that can successfully accept simplification operations. The simplification operations produce only local transformations on the mesh. This region-based, distributed approach permits to easily track and control the changes in the triangulation and avoids the appearance of particular cases that would require a special handling. The algorithm uses two user-specified parameters to guide the operations. These parameters allow various simplification strategies that are illustrated on several dense triangulations. Proceedings of Eurographics '96. }, } @article{Andujar:1996:AGO, author = {C. And{\'{u}}jar and D. Ayala and P. Brunet and R. Joan-Arinyo and J. Sol{\'{e}}}, title = {Automatic Generation of Multiresolution Boundary Representations}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {87-96}, note = {{ISSN} 1067-7055}, keywords = {Geometric Modelling, multiresolution, Level of Detail, Simplification Algorithms}, annote = {The paper focuses on automatic simplification algorithms for the generation of a multiresolution family of solid models from an initial boundary representation of a polyhedral solid. An algorithm for general polyhedra based on an intermediate octree representation is proposed. Simplified elements of the multiresolution family approximate the initial solid within increasing tolerances. A discussion among different octree-based simplification methods and the standard marching cubes algorithm is presented. Proceedings of Eurographics '96. }, } @article{Buchanan:1996:SEW, author = {John W. Buchanan}, title = {Special Effects with Half-toning}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {97-108}, note = {{ISSN} 1067-7055}, keywords = {Half-toning, non-photorealistic rendering, graphic design}, annote = {Half-toning is the process by which gray-scale images are approximated with sets of black and white pixels. The process works because our eyes perceive a local average, thus half-toning seeks to approximate the local average. Ideally this approximation should be accomplished without introducing "undesirable" artifacts. In many situations the stylized display of images is desired. Often this stylized display is accomplished by the addition of semi-structured artifacts. In current applications the designer processes the image using tools provided by some image processing package. The resulting image is then half-toned and printed. Half-toning these processed images can reduce the visual impact of the special effects that have been introduced in the image. In this paper we show that the processes of controlled artifact introduction and half-toning can successfully be combined. By combining these two processes we ensure that the printed image is what the designer intended. We present a brief overview of the current error-diffusion half-toning techniques. We then propose several ways in which artifacts can be introduced to the image. This discussion is accompanied by a set of illustrative images. In particular, we discuss the introduction of false edges and the alteration of the scan pattern. We illustrate these techniques with a variety of images. We conclude the paper with a discussion on these new half-ioning methods for the generation of binary gray-scale textures. In addition to showing how to generate these binary gray-scale textures we also show how these gray-scale textures can be used to half-tone images. Proceedings of Eurographics '96. }, } @article{Dobashi:1996:MFC, author = {Yoshinori Dobashi and Kazufumi Kaneda and Hideo Yamashita and Tomoyuki Nishita}, title = {Method for Calculation of Sky Light Luminance Aiming at an Interactive Architectural Design}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {109-118}, note = {{ISSN} 1067-7055}, keywords = {realistic rendering, sky light, Fourier expansion, vector quantization, glossy specular reflection}, annote = {Recently, computer graphics are frequently used for both architectural design and visual environmental assessment. Using computer graphics, designers can easily compare the effect of the natural light on their architectural designs under various conditions, such as different times of day, seasons, atmospheric conditions (clear or overcast sky) or building wall materials. In traditional methods of calculating the luminance due to sky light, however, all calculation must be performed from scratch if such conditions undergo change. Therefore, to compare the architectural designs under different conditions, a great deal of time has to be spent on generating the images. This paper proposes a new method of quickly generating images of an outdoor scene, taking into account glossy specular reflection, even if such conditions change. In this method, luminance due to sky light is expressed by a series of basis functions, and basis luminances corresponding to each basis function are precalculated and stored in a compressed form in the preprocess. Once the basis luminances are calculated, the luminance due to sky light can be quickly calculated by the weighted sum of the basis luminances. Several examples of an architectural design demonstrate the usefulness of the proposed method. Proceedings of Eurographics '96. }, } @article{Karner:1996:AIB, author = {Konrad F. Karner and Heinz Mayer and Michael Gervautz}, title = {An Image based Measurement System for Anisotropic Reflection}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {119-128}, note = {{ISSN} 1067-7055}, keywords = {photorealism, {BRDF}, reflectance, illumination, surface properties, rendering, physically based}, annote = {This paper introduces an image based method for measuring bidirectional reflectance distribution functions (BRDF). The measurement system uses a {CCD} camera connected to a workstation to capture images from the material under investigation. The evaluation of the {BRDF} is performed in an image processing step, gathering {BRDF} values with a broad range of incident and reflected angles, followed by a fitting process, where these values are approximated by a chosen reflectance model. Absolute {BRDF} values are obtained by the usage of a diffuse reflectance standard. It is shown that the proposed measurement system produces very reasonable results compared to accurate measurements. Thus, it is an easy and cost efficient way to measure material properties needed for physically based rendering algorithms. Proceedings of Eurographics '96. }, } @article{Ranjan:1996:MAI, author = {V. Ranjan and Alain Fournier}, title = {Matching and Interpolation of Shapes using Unions of Circles}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {129-142}, note = {{ISSN} 1067-7055}, keywords = {shape interpolation, registration, morphing, unions of circles, shape distance}, annote = {While the notion of shape of an object is very intuitive, its precise definition is very elusive, and defining a useful metric for the shape distance between objects is a difficult endeavor. At the same time many successful techniques have been developed which interpolate between two objects, so in essence interpolate between shapes. We present here work which uses a representation of objects as union of circles to define a distance between two objects and to base a method to interpolate between the two. This method can be used in a totally automatic fashion (that is, without any user intervention), or users can guide a pre-registration phase as well as a segmentation phase, after which the matched segments are interpolated pair-wise. The union of circles representation of the two objects is obtained from the Delaunay triangulation of their boundary points. The circles can be simplified to obtain smaller data sets. The circles are then optimally matched according to a distance metric between circles which is a function of their position, size, and feature, that is, a local configuration of circles. The interpolation between the two objects is then obtained by interpolating between the matched pairs of circles (the interpolations can be affine or non-affine). Examples with simple and more complex objects show how the technique can give results which correspond closely to the human notion of shape interpolation. The interpolations shown include some between a calf and a cow and between a cow and a giraffe. The examples given are in two dimensions, but all the steps except the segmentation have been implemented as well for three dimensional objects. We also show the results of computation of distances between the objects used in our examples. Proceedings of Eurographics '96. }, } @article{Galin:1996:BMB, author = {E. Galin and Samir Akkouche}, title = {Blob Metamorphosis based on Minkowski Sums}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {143-154}, note = {{ISSN} 1067-7055}, keywords = {animation, blobs, implicit surfaces, Minkowski sums, metamorphosis, skeletons, soft objects}, annote = {This paper addresses the metamorphosis of soft objects built from skeletons. We propose a new approach that may be split into three steps. The first step consists in an original splitting of the initial and the final shapes with a view to creating a bijective graph of correspondence. In the second step, we assume that the skeletons are convex polygonal shapes, and thus take advantage of the properties of Minkowski sums to characterize the skeletons of Intermediate shapes. Eventually, we characterize the intermediate distance and field functions; we describe a set of interpolation methods and propose to use a restricted class of parametrized distance and field functions so as to preserve coherence and speed-up computations. We show that we can easily extend those results to achieve a B{\'{e}}zier like metamorphosis where control points are replaced by control soft objects; in this scope, we have adapted existing accelerated techniques that build a B{\'{e}}zier transformation from a set of convex polyhedra to any kind of convex polygonal shapes. Eventually, we point out that matching all components of the initial and the final shapes generates amorphous intermediate shapes based on an overwhelming number of intermediate sub-components. Thus, we propose heuristics with a view to preserving coherence during the transformation and accelerating computations. We have implemented and tested our techniques in an experimental ray-tracer. Proceedings of Eurographics '96. }, } @article{Promayon:1996:PDC, author = {Emmanuel Promayon and P. Baconnier and Claude Puech}, title = {Physically-Based Deformations Constrained in Displacements and Volume}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {155-164}, note = {{ISSN} 1067-7055}, keywords = {Dynamic simulation, constant volume, physically-based modelling, constraint, deformable models, shape memory, elasticity}, annote = {This paper presents a method of constraining physically-based deformable objects. In this method, an object can be defined locally in terms of kinetic and dynamic (mass, position, speed), and physical parameters (compressibility, elasticity, motorfunctioning) . Several problems are solved: constant volume deformation, displacement constraints (fixed or moving required positions), and real object modelling. An object is described by a set of mass points on its contour. The evolution algorithm runs in two phases dealing successively with forces and constraints (which are presented as reaction forces). The main contribution of the method is the control of object volumes during evolution. We define a function that explicitly gives the inside volume of an object in order to use it as a constraint. Thus, the volume can be kept exactly constant during deformation without using an iterative process, in opposition to lagrangian approaches. Some results are illustrated by examples at the end of the paper. Proceedings of Eurographics '96. }, } @article{Crespin:1996:ISO, author = {Beno{\^{i}}t Crespin and Carole Blanc and Christophe Schlick}, title = {Implicit Sweep Objects}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {165-174}, note = {{ISSN} 1067-7055}, annote = {Proceedings of Eurographics '96. }, } @article{Greiner:1996:DDT, author = {G{\"{u}}nther Greiner and Joachim Loos and Wieger Wesselink}, title = {Data Dependent Thin Plate Energy and its Use in Interactive Surface Modeling}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {175-186}, note = {{ISSN} 1067-7055}, keywords = {geometric modeling, spline surfaces, variational approach, optimization techniques, interactive surface modeling}, annote = {When modeling spline surfaces of complex shape, one has to deal with an overwhelming number of control points. Modeling by direct manipulation of the control points is a tedious task. In particular, it is very difficult to maintain a generally pleasant looking surface shape. It becomes therefore increasingly important to build tools that allow the designer to specify only a few geometric constraints while automatically determining the explicit representation of the surface. The basic concept of such a tool is simple. In a first step one has to somehow measure the "fairness" (=quality) of a surface. Once this is achieved, an optimization process selects the one surface with optimal fairness from all surfaces satisfying the user specified geometric constraints. To measure the fairness, thin plate energy functionals [deleted] are a good choice. However, for interactive use these functionals are far too complex. We will present appropriate approximations to these functionals that allow an optimization nearly in real time. The functionals are obtained by introducing reference surfaces thus leading to data dependent, quadratic approximations to the exact thin plate energy functionals. We apply the method to interactive surface manipulations based on energy constraints. Proceedings of Eurographics '96. }, } @article{Higashi:1996:GOS, author = {Masatake Higashi and Hideo Tsutamori and Mamoru Hosaka}, title = {Generation of Smooth Surfaces by Controlling Curvature Variation}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {187-196}, note = {{ISSN} 1067-7055}, keywords = {surface modelling, aesthetic shape, smooth surface, curvature variation, evolute}, annote = {To satisfy a designer's intention for constructing aesthetic shapes such as automotive bodies, we propose a surface generation method. In the surface design process, designers determine shapes according to their great concern for the reflected images of vehicle surroundings, shade lines and highlight lines. Since reflection and shading are affected by changes of surface normal, the curvature variation of the surface, which represents the change of the surface normal, should be smooth and distributed as designers want. The proposed method controls curvature distribution directly by determining a surface shape from an evolute, which is a locus of the curvature center of the generatrix and moves along directrices to form the surface. It first generates evolutes of boundary curves to be generatrices as rational B{\'{e}}zier curves, then interpolates their shapes with the B{\'{e}}zier polygons, and locates the interpolated shape to the corresponding position of the directrices. By applying this method we have confirmed that a smooth shape is generated from four boundary curves. Proceedings of Eurographics '96. }, } @article{Turner:1996:HSV, author = {Russell Turner and Enrico Gobbetti and Ian Soboroff}, title = {Head-Tracked Stereo Viewing with Two-Handed {3D} Interactionfor Animated Character Construction}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {197-206}, note = {{ISSN} 1067-7055}, keywords = {Interactive {3D} Graphics, Stereoscopic Display, Head-Tracking, Two Hand Input, Virtual Tools, {3D} Character Modeling, Animation Systems}, annote = {In this paper, we demonstrate how a new interactive 3D desktop metaphor based on two-handed {3D} direct manipulation registered with head-tracked stereo viewing can be applied to the task of constructing animated characters. In our configuration, a six degree-of-freedom head-tracker and CrystalEyes shutter glasses are used to produce stereo images that dynamically follow the user head motion. {3D} virtual objects can be made to appear at a fixed location in physical space which the user may view from different angles by moving his head. To construct {3D} animated characters, the user interacts with the simulated environment using both hands simultaneously: the left hand, controlling a Spaceball, is used for {3D} navigation and object movement, while the right hand, holding a 3D mouse, is used to manipulate through a virtual tool metaphor the objects appearing in front of the screen. In this way, both incremental and absolute interactive input techniques are provided by the system. Hand-eye coordination is made possible by registering virtual space exactly to physical space, allowing a variety of complex {3D} tasks necessary for constructing {3D} animated characters to be performed more easily and more rapidly than is possible using traditional interactive techniques. The system has been tested using both Polhemus Fastrak and Logitech ultrasonic input devices for tracking the head and {3D} mouse. Proceedings of Eurographics '96. }, } @article{Madritsch:1996:CBO, author = {Franz Madritsch and Michael Gervautz}, title = {CCD-Camera Based Optical Beacon Tracking for Virtual and Augmented Reality}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {207-216}, note = {{ISSN} 1067-7055}, keywords = {optical tracking, input technology, beacon tracking, virtual reality}, annote = {We introduce a scheme for optical beacon tracking using two CCD-cameras and {LED} beacons. Due to the sub-pixel accuracy of the beacon detection algorithm a very high precision can be achieved so that the tracking method is suitablefor augmented reality applications. We describe the assemblv of the equipment needed for the whole tracking system, the behavior of LED-beacons, and how three beacons can be combined to form a 6-DOF tracker. A report on our accuracy evaluation and its results are given. Furthermore we describe two application prototypes in which the tracker was incorporated and tested. Proceedings of Eurographics '96. }, } @article{Munch:1996:ICF, author = {Stefan M{\"{u}}nch and Martin Stangenberg}, title = {Intelligent Control for Haptic Displays}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {217-226}, note = {{ISSN} 1067-7055}, keywords = {Multimodal interaction, haptic output; user modelling; human-computer interaction}, annote = {Usually, a mouse is used for input activities only, whereas output from the computer is sent via the monitor and one or two loudspeakers. But why not use the mouse for output, too? For instance, if it would be possible to predict the next interaction object the user wants to click on, a mouse with a mechanical brake could stop the cursor movement at the desired position. This kind of aid is especially attractive for small targets like resize handles of windows or small buttons. In this paper, we present an approach for the integration of haptic feedback in everyday graphical user interfaces. We use a specialized mouse which is able to apply simple haptic information to the user's hand and index finger. A multi-agent system has been designed which "observes" the user in order to predict the next interaction object and launch haptic feedback, thus supporting positioning actions u@ith the mouse. Although primarily designed in order to provide "intelligent" haptic feedback, the system can be combined with other output modalities as well, due to its modular and flexible architecture. Proceedings of Eurographics '96. }, } @article{Schaufler:1996:ATD, author = {Gernot Schaufler and Wolfgang St{\"{u}}rzlinger}, title = {A Three Dimensional Image Cache for Virtual Reality}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {227-236}, note = {{ISSN} 1067-7055}, keywords = {viewing algorithms, geometric algorithms, object hierarchies, virtual reality}, annote = {Despite recent advances in rendering hardware, large and complex virtual environments cannot be displayed with a sufficiently highframe rate, because of limitations in the available rendering performance. This paper presents a new approach of software accelerated rendering which draws from the concepts of impostors, hierarchical scene subdivision and levels of detail. So far software optimization in real-time rendering has merely considered individual objects. This work is actually optimizing the rendering of the whole virtual environment by implementing a three dimensional image cache. It speeds up rendering for large portions of the scene by exploiting the coherence inherent in any smooth frame sequence. The implementation of the three dimensional image cache is discussed and the savings in rendering load achievable on a suitable hardware platform are presented. Proceedings of Eurographics '96. }, } @article{Orti:1996:RFD, author = {Rachel Orti and St{\'{e}}phane Rivi{\'{e}}re and Fr{\'{e}}do Durand and Claude Puech}, title = {Radiosity for Dynamic Scenes in Flatland with the Visibility Complex}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {237-248}, note = {{ISSN} 1067-7055}, keywords = {global illumination, radiosity, discontinuity mesh, form factor, visibility, dynamic environments}, annote = {The radiosity method is particularly suitable for global illumination calculations in static environments. Nonetheless, recent applications of image synthesis such as architectural simulation or lighting design require the ability to modify environments. Previous methods have attempted to deal with dynamic environments (environments where the geometry, the material properties, etc., can change) but still suffer some limitations in the case of moving objects. One of the main problems remaining is the efficient and accurate detection of which form factors must really be recomputed, since their calculation is the most time-consuming part of the radiosity method. To correctly understand and solve this problem, we start with a method in {2D} for polygonal scenes rising the visibility complex. It is a powerful data structure representing the visibility relationships between objects in the plane. We have developed and implemented an algorithm which uses this structure to efficiently compute the discontinuity mesh and the form factors for static scenes. We also propose an extension to our algorithm to efficiently update only the modified form factors when an object is moving. This approach enhances our understanding and will hopefully lead to efficient solutions in 3D. Proceedings of Eurographics '96. }, } @article{Sudarsky:1996:OVA, author = {Oded Sudarsky and Craig Gotsman}, title = {Output-Sensitive Visibility Algorithms for Dynamic Scenes with Applications to Virtual Reality}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {249-258}, note = {{ISSN} 1067-7055}, keywords = {visibility culling, output-sensitive hidden surface removal, virtual reality, distributed multi-user virtual environments, client-server design}, annote = {An output-sensitive visibility algorithm is one whose runtime is proportional to the number of visible graphic primitives in a scene model - not to the total number of primitives, which can be much greater. The known practical output-sensitive visibility algorithms are suitable only for static scenes, because they include a heavy preprocessing stage that constructs a spatial data structure which relies on the model objects' positions. Any changes to the scene geometry might cause significant modifications to this data structure. We show how these algorithms may be adapted to dynamic scenes. Two main ideas are used: first, update the spatial data structure to reflect the dynamic objects' current positions: make this update efficient by restricting it to a small part of the data structure. Second, use temporal bounding volumes (TBVS) to avoid having to consider every dynamic object in each frame. The combination of these techniques yields efficient, output-sensitive visibility algorithms for scenes with multiple dynamic objects. The performance of our methods is shown to be significantly better than previous output-sensitive algorithms, intendedfor static scenes. TBVs can be adapted to applications where no prior knowledge of the objects' trajectories is available, such as virtual reality (VR), simulations etc. Furthermore, they save updates of the scene model itself notjust of the auxiliary data structure used by the visibility algorithm. They can therefore be used to greatly reduce the communications overhead in client-server {VR} systems, as well as in general distributed virtual environments. Proceedings of Eurographics '96. }, } @article{Shamir:1996:EOT, author = {Ariel Shamir and Ari Rappoport}, title = {Extraction of Typographic Elements from Outline Representations of Fonts}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {259-268}, note = {{ISSN} 1067-7055}, keywords = {Digital typography, outline fonts, typographic elements, hinting, Parametric typographic representations}, annote = {Digital typefaces for computer graphics and multimedia applications should be capable of supporting operations such as font variations, transformations, deformations and blending. A powerful implementation of such operations must rely on the inherent typographic attributes of the typeface. However, even today's most advanced typeface representations support only geometric outline representations and basic font variations. In this paper we discuss high-level typeface representations which we term Parametric Typographic Representations (PTRs). We present an algorithm for automatically extracting typographic elements of typefaces from their outline representation, which is an essential initial step in converting typefaces from outline representations to PTRs. The extracted typographic elements include serifs, bars, stems, slants, bows, arcs, curve stems and curve bars. Most notable is the treatment of serifs, which are represented by finite-automata. The algorithm only needs to learn a serif type once, and is then capable of automatically recognizing it in different typefaces. We show an application of a {PTR} for automatic high-quality hinting of fonts, which is one of the most important stages in digital font production. Our system was used to generate hints for dozens of thousands of Kanji, Roman, and Hebrew Characters. Proceedings of Eurographics '96. }, } @article{Zair:1996:FMU, author = {Chems Eddine Zair and Eric Tosan}, title = {Fractal Modeling using Free Form Techniques}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {269-278}, note = {{ISSN} 1067-7055}, keywords = {Fractals, Iterative Function Systems, Subdivision matrices, B{\'{e}}zier curves, Free form techniques, Attractors, Deformations}, annote = {{IFS} models have become a powerful tool for the construction of fractal sets. They offer a straight-forward way to generate complex, self-similar figures as attractors. However, they present the fundamental disadvantage of providing little control over the global form of the attractor. In contrast, free form techniques give a high control over smooth man-made objects with the use of a set of control points. In this paper, we present a new approach of fractal modeling which is based on {IFS} theory. We shall use free form techniques to give a practical and efficient way to build controlled fracial attractors. The resulting effect consists on the ability to deform a fractal shape interactively into the desired shape, in the same way as parametric forms (B{\'{e}}zier, splines). Proceedings of Eurographics '96. }, } @article{Poulet:1996:MMS, author = {Fran{\c{c}}ois Poulet and Michel Lucas}, title = {Modelling Megalithic Sites}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {279-288}, note = {{ISSN} 1067-7055}, keywords = {Megalithic sites, Description vocabulary, Plain language, Voxels}, annote = {In this paper, we present the M{\'{e}}gaFormes project which deals with the modelling of megalithic sites. The goal is to enable virtual visits of megalithic sites and to help archaeologists in picturing the evolution of a monument.. A megalithic site is made of a set of elements that can be: fogous, dolmens, chamber tombs, stone alignments or circles. The description of such a site is done in two stages : during the first stage, a draft of the site is drawn, each stone being represented by its bounding box. The second stage allows the user to describe the content of the boxes (the stones). To describe fogous and chamber tombs, basic models of these monuments are used. These basic types are simplified representations of the monunients (walls only). The models can be modified by changing the dimensions and locations of the walls and by cutting the initial walls into individual stones. The definition of stone alignments or circles calls for the use of a one-dimensional position vocabulary (along simple geometric primitives or curves). The different elements (alignments, circles, fogous, and chamber tombs) are then combined to obtain the draft of the site. A two-dimensional vocabulary allowing to position the elements in the site is used. The paper is illustrated with examples obtained with the developed software. Proceedings of Eurographics '96. }, } @article{Smets-Solanes:1996:VFB, author = {Jean-Paul Smets-Solanes}, title = {Vector Field Based Texture Mapping ofanimated Implicit Objects}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {289-300}, note = {{ISSN} 1067-7055}, keywords = {texture, mapping, rendering, metaball, implicit surface, implicit object, animation, deformation, simulation, vector field, virtual skin, gliding, sticking}, annote = {This paper shows that an adequate use of vector fields can solve most inconsistencies related to texture mapping that appear in current animation and rendering systems based on implicit objects. The method used is based on the concept of a virtual skin. A skin with its own texture mapping is spread over an implicit object and is constrained to stick to the deformation of the implicit object. A vector field is used to compute the relationship between the motion of the skin and the deformation of the object. Visual and implementation issues are discussed with respect to typical applications of implicit objects in computer graphics. Proceedings of Eurographics '96. }, } @article{Hutchinson:1996:SGS, author = {Dave Hutchinson and F. Lin and Terry Hewitt}, title = {Surface Graph Sketching}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {301-310}, note = {{ISSN} 1067-7055}, keywords = {Geometric Modelling, {NURBS}, Patterning, Surface Graph Sketching, Texturing, Trimming}, annote = {The production of patterns and designs upon surfaces has received only limited attention, with texturing techniques being accepted as adequate. Texturing, however, can be a very unsatisfactory and clumsy method of producing complex and accurate designs upon a surface. even more so with surfaces such as {NURBS} where a texture may appear very much distorted when mapped to a surface. This paper introduces a new approach called surface graph sketching which draws upon ideas from planar graph sketching for the construction of complex curve networks across parametrically defined surfaces. Surface curves can be created by a number of methods and stored in the parameter space of the surface thereby allowing intricate and more importantly accurate surface designs to be created. Regions of the surface may be assigned a property such as colour or texture, or cut away to produce holes. Surface graph sketching has a number of applications, in the design of trimming curves, surface patterning and texture map definitions. Proceedings of Eurographics '96. }, } @article{Ghazanfarpour:1996:GO3, author = {Djamchid Ghazanfarpour and Jean-Michel Dischler}, title = {Generation of {3D} Texture Using Multiple {2D} Models Analysis}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {311-324}, note = {{ISSN} 1067-7055}, keywords = {Texturing, automatic {3D} texture generation, spectral analysis, antialiasing}, annote = {Solid (3D) texturing is commonly used in computer graphics for producing more realistic images. It is often more attractive than the conventional {2D} texture mapping but remains more complex on some points. Its major difficulty concerns the generation of {3D} texture in a general and efficient way. The well-known traditional procedural methods use generally a simplified mathematical model of a natural texture. No reliable way for the choice of the mathematical model parameters, which characterise directly the produced {3D} texture, is given. Therefore, {3D} texture generation becomes a more or less experimental process with these methods. Our recently published method for an automatic {3D} texture generation avoids this problem by the use of the spectral analysis of one {2D} model texture. The resulting {3D} texture is of good quality but one open problem remains: the aspect of the produced texture cannot be fully controlled over the entire {3D} space by only one {2D} spectral analysis. This may be considered as a serious limitation for some kinds of textures representing important variations in any direction. In this paper we present a new and more powerful analytical approach for an automatic {3D} texture generation. Contrarily to our previous method, this new approach is not exclusively based on the spectral analysis of only one {2D} model It uses two or three {2D} models corresponding to different slices of a {3D} texture block, so, the aspect of the produced {3D} texture can be controlled more efficiently over the entire {3D} space. In addition, a more efficient {3D} texture antialiasing, well adapted to this new method is presented. Proceedings of Eurographics '96. }, } @article{Bouatouch:1996:COH, author = {Kadi Bouatouch and S. N. Pattanaik and Eric Zeghers}, title = {Computation of Higher Order Illumination with a Non-Deterministic Approach}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {327-338}, note = {{ISSN} 1067-7055}, keywords = {Radiance equation, Potential equation, Adjointness, Monte Carlo quadrature, Random Walk, Particle Tracing, Weighted Function Approximation, Multiwavelet, push/pull operation}, annote = {In spite of the number of efforts made by the computer graphics researchers, till today the computation of view-independent global illumination in an environment containing non-diffusely reflecting objects is a non-resolved problem. In general, non-deterministic techniques seem to be capable of solving this problem. In this article we propose one such non-deterministic method which will permit such calculation by using a combined technique of higher order function approximation and particle tracing. We have used multi-wavelets as basis functions and have calculated the illumination function approximation coefficients by exploiting the adjointness between the radiance equation and the potential equation. Proceedings of Eurographics '96. }, } @article{Hughes:1996:SOG, author = {Merlin Hughes and Anselmo A. Lastra and Edward Saxe}, title = {Simplification of Global-Illumination Meshes}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {339-346}, note = {{ISSN} 1067-7055}, annote = {We present a method for simplifying the meshes produced as solutions to global illumination problems, reducing geometric complexity while retaining the perceived image fidelity. The method has been applied to produce meshes of linearly, quadratically and cubically colour-interpolated triangles. The goal of our work is to permit interactive rendering of more complex global illumination solutions through the application of simplification algorithms as well as the use of more powerful rendering primitives. Proceedings of Eurographics '96. }, } @article{Ouhyoung:1996:RRO, author = {Ming Ouhyoung and Yung-Yu Chuang and Rung-Huei Liang}, title = {Reusable Radiosity Objects}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {347-356}, note = {{ISSN} 1067-7055}, keywords = {Anisotropic visibility, clustering, hierarchical radiosity, visibility error}, annote = {Because of the view independence and photo realistic image generation in a diffuse environment, radiosity is suitable for an interactive walkthrough system. The drawback of radiosity is that it is time-consuming in form factor estimation, and furthermore, inserting, deleting or moving an object makes the whole costly rendering process repeat itself. To solve this problem, we encapsulate necessary information for form factor calculation and visibility estimation in each object, which is called a reusable radiosity object. An object is definied as a cluster or clusters of triangles. Whenever a scene updates, the radiosity algorithm looks tip the prestored information in each object, thus speeding itself up by two orders of magnitude. Besides, solution time based on cluster representatives is linear to the number of objects since each object is reusable, encapsulated with preprocessed data in every level of hierarchy. We also analyze the unregarded error on visibility estimation and propose a statistically optimal adaptive algorithm to maintain the same error for each link. Proceedings of Eurographics '96. }, } @article{Faure:1996:AEA, author = {Fran{\c{c}}ois Faure}, title = {An Energy-Based Approach for Contact Force Computation}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {357-366}, note = {{ISSN} 1067-7055}, keywords = {contact forces, friction, dynamics}, annote = {A new approach for computing resting contact forces between solids is presented, which handles both static and sliding friction, while avoiding the problems arising from previous approaches. Each iteration provides values for all unknowns and needs a constant computation time. The first iteration is a global dynamic solution involving inertia and external forces. The subsequent iterations consist of global redistributions of energy through the solids in order to restrict the values within correct bounds, leading to a progressive refinement of the solution. Tfiis allows the termination of the computation when a user-defined level ofprecision is reached. Convergence is proven in the frictionless case. The method is concise and is easily usable in a motion control system. It was implemented and tested on some examples involving simultaneously static and sliding friction along with motion control. Proceedings of Eurographics '96. }, } @article{Laako:1996:ICM, author = {Timo Laako and Martti M{\"{a}}ntyl{\"{a}}}, title = {Incremental Constraint Modelling in a Feature Modelling System}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {367-376}, note = {{ISSN} 1067-7055}, keywords = {Constraints, local propagation, feature modelling, geometric modelling}, annote = {The techniques of constraint propagation have recently been successfully applied to feature-based design. Because of their speed, constraint propagation methods allow incremental design and rapid local modifications of the part. However, cyclic constraints cause serious problems to current constraint propagation algorithms. Variational geometric design systems can, in principle, manage these cases. Unfortunately, this typically requires complete re-evaluation of the underlying set of constraint equations, making the method unsuitable for interactive use. The proposed system aims to localize the problem of constraint solving and maintenance. The constraint graph of the part or assembly is divided into several independent partial graphs, subsystems. Afterwards, each subsystem is handled separately using a selected constraint solving technique for the subsystem. Proceedings of Eurographics '96. }, } @article{Preston:1996:ICA, author = {Martin Preston and Terry Hewitt}, title = {Integrating Computer Animation and Multimedia}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {377-386}, note = {{ISSN} 1067-7055}, keywords = {Multimedia, Computer Animation, Keyframing}, annote = {Multimedia provides an immensely powerful tool for the dissemination of both information and entertainment. Current multimedia presentations consist of synchronised excerpts of media (such as sound, video \& text) which are coordinated by an author to ensure a clear narrative is presented to the audience. However each of the segments of the presentation consist of previously recorded footage, only the timing and synchronisation are dynamically constructed. The next logical advance for such systems is therefore to include the capability of generating material "on-the-fly" in response to the actions of the audience. This paper describes a mechanism for using computer animation to generate this interactive material. Unlike previous animation techniques the approach presented here is suitable for use in constructing a storyline which the author can control, but the user can influence. In order to allow such techniques to be used we also present a multimedia authoring \& playback system which incorporates interactive animation with existing media. Proceedings of Eurographics '96. }, } @article{Barequet:1996:BAH, author = {Gill Barequet and Bernard Chazelle and Leonidas J. Guibas and Joseph S. B. Mitchell and Ayellet Tal}, title = {{BOXTREE}: A Hierarchical Representation for Surfaces in {3D}}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {387-396}, note = {{ISSN} 1067-7055}, keywords = {collision detection, hierarchical data structures, ray shooting}, annote = {We introduce the boxtree, a versatile data structure for representing triangulated or meshed surfaces in 3D. A boxtree is a hierarchical structure of nested boxes that supports efficient ray tracing and collision detection. It is simple and robust, and requires minimal space. In situations where storage is at a premium, boxtrees (are effective alternatives to octrees and {BSP} trees. They are also more flexible and efficient than R-trees, and nearly as simple to implement. Proceedings of Eurographics '96. }, } @article{Oliva:1996:3RO, author = {J.-M. Oliva and M. Perrin and S. Coquillart}, title = {{3D} Reconstruction of Complex Polyhedral Shapes from Contours using a Simplified Generalized Voronoi Diagram}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {397-408}, note = {{ISSN} 1067-7055}, keywords = {{3D}, reconstruction, interpolation, simplified generalised Voronoi diagrams, skeleton, bisector network, cross-sectional contours}, annote = {We are interested in modelling the surface of very irregular objects known through a few planar polygonal cross-sections. This problem is considered difficult when severe topology and morphology variations appear between neighbouring cross-sections (multi-branching, holes, disconnected areas). Only few methods deal with this problem in a systematic way. The paper describes an original method allowing to build, in a fully automatic and systematic way, an external surface with a valid topology in any case. It moreover allows to adjust details of the reconstructed surface in view of the morphologies and topologies of the various initial cross-sectional contours. At first, a global correspondence is operated between each couple of adjacent cross-sections by extracting polygonal areas of difference. Next steps are based on the computation in each area of difference of the bisector network, a well-defined simplified generalised Voronoi diagram. This structure is used both for connecting initial contour points and for interpolating new intermediate portions of contours. It depends on the complexity of initial {2D} shapes. Interpolation stage is then recursively operated until a satisfactory surface has been obtained or until a maximum number of new intermediate cross-sectional contours have been built. The valid final surface is directly obtained by concatenating all the tiling areas of difference without need of any post processing step. The processing of several real data related to geological bodies or human organs has proved that the described method allows detailed modelling of irregular objects with verv performing {CPU} times. The reconstruction appears insensitive to severe variations of the object shape, including apparitions of holes or disconnections. Proceedings of Eurographics '96. }, } @article{Kobbelt:1996:ISO, author = {Leif Kobbelt}, title = {Interpolatory Subdivision on Open Quadrilateral Nets with Arbitrary Topology}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {409-420}, note = {{ISSN} 1067-7055}, keywords = {Surface modeling, interpolatory subdivision, Adaptive mesh-refinement}, annote = {A simple interpolatory subdivision scheme for quadrilateral nets with arbitrary topology is presented which generates C1 surfaces in the limit. The scheme satisfies important requirements for practical applications in (computer qraphics and engineering. These requirements include the necessity to qenerate smooth surfaces with local creases and cusps. The scheme can be applied to open nets in which case it generates boundary curves that allow a CO-join of several subdivision patches. Due to the local support of the scheme, adaptive refinement. Strategies can be applied. We present a simple device to preserve the consistency of such adoptively refined nets. Proceedings of Eurographics '96. }, } @article{Schmalstieg:1996:DGT, author = {Dieter Schmalstieg and Michael Gervautz}, title = {Demand-Driven Geometry Transmission for Distributed Virtual Environments}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {421-431}, note = {{ISSN} 1067-7055}, keywords = {virtual reality, distributed graphics, multi-user applications, levels of detail}, annote = {We present a strategy for rendering in distributed virtual environments. A geometry database is maintained by a server, while users invoke individual clients to interact with the environment. Instead of downloading a complete copy of the geometry data, the data is distributed on demand, thus gaining significant savings in network bandwidth. Our strategy combines several techniques, including levels of detail, progressive refinement and graceful degradation to deliver the data "just in time" over the network to the rendering process. The method allows operate on a tight resource budget, which important if attempting to use low cost systems for virtual reality applications. Proceedings of Eurographics '96. }, } @article{Encarnacao:1996:APF, author = {L. Miguel En{\c{c}}arnac{\~{a}}o and J{\"{u}}rgen Fechter and Thomas Grunert and Wolfgang Stra{\ss}er}, title = {A Platform for User-Tailored Interaction Development in {2D}, {3D}, and {VR}}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {432-441}, note = {{ISSN} 1067-7055}, keywords = {Development environment, user-tailored interaction development, {2D} interface, {3D} interface, {VR} interface, user-interface adaptation, hypermedia help, interaction objects, object communication, medical application system for diagnosis}, annote = {The discussion on the advantages and disadvantagesof {2D}, {3D}, and {VR} interfaces and their applicability to different types of systems, users, and information led to a series ofstand-alone implementations that lack the possibility of realizing an integrated approach. The acceptance of the different interaction techniques will depend on their success in practical applications, i.e. with systems that are used by different users for different purposes. Since this acceptance is especially hard to achieve in computer-critical environments, such as medicine, we developed a software environment that allows for the development, integration, and user-centered evaluation of existing and new interaction techniques for their use in medical applications. This environment is equipped with an innovative message-passing functionality that provides the communication to and among application objects in {2D}, {3D}, and {VR}. Furthermore, the environment contains a component for user-adapted interaction and system support at runtime. Proceedings of Eurographics '96. }, } @article{Haase:1996:SOV, author = {Helmut Haase}, title = {Symbiosis of Virtual Reality and Scientific Visualization System}, volume = {15}, number = {3}, journal = {Computer Graphics Forum}, month = {August}, year = {1996}, editor = {Jarek Rossignac and Fran{\c{c}}ois X. Sillion}, publisher = {Blackwell Publishers}, pages = {442-451}, note = {{ISSN} 1067-7055}, keywords = {Virtual Reality, Scientific Visualization, Immersive Exploration,Realtime Interaction, Inter-Process Communication, Software Architecture}, annote = {This paper describes a concept for the symbiosis of a virtual reality system and a system for scientific visualization, as well as an implementation (called ISVAS-VR) to evaluate the concept. The idea is to preserve the strengths of both systems in order to help scientists in analyzing their data by means of the joint synergy of both approaches. Motivation for this work is given along with a description of the two individual systems (ISVAS and Virtual Design). Possible communication schemes are discussed and the communication techniques which were utilized in the implementation are presented, namely shared memory and pipes. Finally, interaction of the user with the compound system is described and a number of application examples are given. Proceedings of Eurographics '96. }, } @article{Reddy:1996:SPP, author = {M. Reddy}, title = {{SCROOGE}: Perceptually-Driven Polygon Reduction}, volume = {15}, number = {4}, journal = {Computer Graphics Forum}, year = {1996}, pages = {191-203}, note = {{ISSN} 0167-7055}, keywords = {polygon reduction, level of detail, visual perception, human visual system}, annote = {Many real-time {3D} graphics renderers represent each object as a collection of simple polygons. The complexity of this polygon structure is of practical relevance because it can manifestly affect the performance of the graphics system. It is therefore commonplace to.find techniques to reduce the polygonal complexity of a model with the ultimate aim of improving the interactivity of the application. In the past, many of these schemes have not been concerned with the perceptual side-effects of this reduction and as a result a number of visual incongruities are often perceivable when these correspondingly-reduced representations are employed. As an attempt to circumvent these problems, this paper presents a methodology for reducing the polygonal complexity of a model, whilst retaining a degree of perceptual predictability. This allows the visual consequences of the degradation to be quantified and accurately modelled. }, } @article{Banerjee:1996:TEE, author = {Raja P. K. Banerjee and Jarek R. Rossignac}, title = {Topologically Exact Evaluation of Polyhedra Defined in {CSG} with Loose Primitives}, volume = {15}, number = {4}, journal = {Computer Graphics Forum}, year = {1996}, pages = {205-217}, note = {{ISSN} 0167-7055}, keywords = {constructive solid geometry, {CSG}, half-spaces, loose primitives, polyhedra, robust boundary evaluation, solid modeling}, annote = {Floating point round-off causes erroneous and inconsistent decisions in geometric modelling algorithms. These errors lead to the generation of topologically invalid boundary models for {CSG} objects and significantly reduce the reliability of {CAD} applications. Previously known methods that guarantee topological consistency by relying on arbitrary precision rational arithmetic or on symbol-manipulation techniques are too expensive for practical purposes. This paper presents a new solution which takes as input a "fixed precision" regularized Boolean combination of linear half-spaces and produces a polyhedral boundary model that has the exact topology of the corresponding solid. Each half-space is represented by four homogeneous coefficients in fixed precision format La bits for the three direction cosines and Ld bits.for the constant term, i.e. the distance from the origin). Exact answers to all topological and ordering questions are computed using a fixed length, 3 La + Ld + 2 bits, integer format. This new guaranteed tight limit on the number of bits necessary for performing intermediate calculations is achieved by expressing all of the topological decisions based on geometric computations in terms qf the signs of 4 by 4 determinants of the input coefficients. The coordinates of intersection vertices are not required for making the correct topological decisions and hence vertices and lines are represented implicitly in terms of planes. }, } @article{Daniel:1996:UAC, author = {M. Daniel}, title = {Using a Convex Pyramid to Bound Surface Normal Vectors}, volume = {15}, number = {4}, journal = {Computer Graphics Forum}, year = {1996}, pages = {219-227}, note = {{ISSN} 0167-7055}, keywords = {surface modelling, normal vectors, pyramid construction and intersection}, annote = {Determining a tight hounding volume of all the surface normal vectors is of interest in surface modelling especially for intersection problems, in order to detect closed intersection curves. It is also important to determine quickly, whether two such volumes intersect. This paper addresses both problems through the introduction qf a pyramid with a convex planar base. For intersection problems, a different method has been proposed by M. Hohmeyer. The various solutions are discussed and compared. }, } @article{Kochhar:1996:AUO, author = {Sandeep Kochhar and Jim Hall}, title = {A Unified, Object-Oriented Graphics System and Software Architecture for Visualising {CAD}/CAM Presentations}, volume = {15}, number = {4}, journal = {Computer Graphics Forum}, year = {1996}, pages = {229-248}, note = {{ISSN} 0167-7055}, keywords = {computer-aided design, object-oriented graphics, future graphics software architectures, graphical design and modelling, user interaction}, annote = {Most object-oriented graphics systems (OOGS) either support general purpose graphics capabilities (drawing editors, ray tracing, etc.), or have targeted specific areas of computer graphics, for example, interface building, animation, and visualisation. However, the key concept in {CAD}/CAM graphics systems is that of presentations - pictures that convey information about products or parts of products. {CAD}/CAM graphics systems that create and manipulate presentations have specific graphical requirements that have not been addressed by existing {OOGS}. These requirements include the support of {CAD}/CAM concepts such as drawings, views and view-specific graphics, and layers, and the ability to allow external geometric modelers to be linked into the presentation. We describe an object-oriented presentation architecture that allows the application to describe the structure of the {CAD}/CAM presentation. This architecture provides a unified interface to drawings, views, layers and entities, and allows linkage to models created with an external geometric modeler, while isolating applications from details of the underlying traditional graphics rendering systems. It is our hope that this architecture provide the foundation for the architecture of next generation {OOGS}. We also present an implementation of this architecture and compare it to other {OOGS}. }, } @article{Wiegand:1996:IRO, author = {T. F. Wiegand}, title = {Interactive Rendering of {CSG} Models}, volume = {15}, number = {4}, journal = {Computer Graphics Forum}, year = {1996}, pages = {249-261}, note = {{ISSN} 0167-7055}, annote = {We describe a {CSG} rendering algorithm that requires no evaluation of the {CSG} tree beyond normalization and pruning. It renders directly from the normalized {CSG} tree and primitives described (to the graphics system) by their.facetted boundaries. It behaves correctly in the presence of user defined, "near" and "far" clipping planes. It has been implemented on standard graphics workstations using Iris {GL} and OpenGL graphics libraries. Modestly sized models can be evaluated and rendered at interactive (less than a second per frame) speeds. We have combined the algorithm with an existing B-rep based modeller to provide interactive rendering of incremental updates to large models. }, } @article{Figueiredo:1996:AEO, author = {Luiz Henrique de Figueiredo and Jorge Stolfi}, title = {Adaptive Enumeration of Implicit Surfaces with Affine Arithmetic}, volume = {15}, number = {5}, journal = {Computer Graphics Forum}, year = {1996}, pages = {287-296}, note = {{ISSN} 0167-7055}, keywords = {cellular models, interval arithmetic, affine arithmetic, rendering, implicit surfaces}, annote = {We discuss adaptive enumeration and rendering methods for implicit surfaces, using octrees computed with affine arithmetic, a new tool for range analysis. Affine arithmetic is similar to standard interval arithmetic, but takes into account correlations between operands and sub-formulas, generally providing much tighter bounds for the computed quantities. The resulting octrees are accordingly much smaller, and the rendering faster. }, } @article{Gibson:1996:EHR, author = {S. Gibson and R. J. Hubbold}, title = {Efficient Hierarchical Refinement and Clustering for Radiosity in Complex Environments}, volume = {15}, number = {5}, journal = {Computer Graphics Forum}, year = {1996}, pages = {297-310}, note = {{ISSN} 0167-7055}, keywords = {radiosity, hierarchical radiosity, error bounds, clustering}, annote = {Generating accurate radiosity solutions of very complex environments is a time-consuming problem. We present a rapid hierarchical algorithm that enables such solutions to be computed quickly and efficiently. Firstly, a new technique for bouncing the error in the transfer of radiosity between surfaces is discussed, incorporating bounds on form factors, visibility, irradiance, and reflectance over textured surfaces. This technique is then applied to the problem of bounding radiosity transfer between clusters of surfaces, leading to a fast, practical clustering algorithm that builds on the previous work of Sillion. Volumes are used to represent clusters of small surfaces, but unlike previous algorithms, the orientations of surfaces inside each cluster are accounted for in both the error bound and radiosity transfer. This enables an accurate solution to be generated very efficiently, and results are presented demonstrating the performance of the algorithm on a variety of complex models, one containing almost a quarter of a million initial surfaces. }, } @article{Jones:1996:TPO, author = {Mark W. Jones}, title = {The Production of Volume Data from Triangular Meshes Using Voxelisation}, volume = {15}, number = {5}, journal = {Computer Graphics Forum}, year = {1996}, pages = {311-318}, note = {{ISSN} 0167-7055}, keywords = {voxelisation, volume data, polygonal meshes, volume visualisation, volume morphing, rendering, ray-tracing}, annote = {Voxelisation is the term given to the process of converting data from one source type into a three dimensional volume of data values. The techniques known collectively as volume visualisation can then be applied to the data in order to produce a graphical representation of the object. This paper gives a practical approach to the voxelisation of data in the form of triangular meshes, and demonstrates the use of the method on various datasets. Visualisation is achieved by a method also described in the paper. }, } @article{Desbrun:1996:ASO, author = {Mathieu Desbrun and Nicolas Tsingos and Marie-Paule Gascuel}, title = {Adaptive Sampling of Implicit Surfaces for Interactive Modelling and Animation}, volume = {15}, number = {5}, journal = {Computer Graphics Forum}, year = {1996}, pages = {319-325}, note = {{ISSN} 0167-7055}, keywords = {implicit surfaces, sampling, interactive visualization}, annote = {This paper presents a new adaptive sampling method for implicit surfaces that can be used in both interactive modelling and animation. The algorithm samples implicit objects composed of blending primitives and efficiently maintains this sampling over time, even when their topology changes (during fractures and fusions). It provides two complementary modes of immediate visualization: displaying "scales" lying on the surface, or a "primitive-wise" polygonization. The sampling method efficiently avoids unwanted blending between different parts of an object. Moreover, it can be used for partitioning an implicit surface into local bounding boxes that will accelerate collision detection during animation and ray intersections during final rendering. }, } @article{Velho:1996:ACO, author = {Luiz Velho and Jonas Gomes}, title = {Approximate Conversion of Parametric to Implicit Surfaces}, volume = {15}, number = {5}, journal = {Computer Graphics Forum}, year = {1996}, pages = {327-337}, note = {{ISSN} 0167-7055}, keywords = {parametric surface, implicit surface, wavelets, conversion}, annote = {In this paper we present a.framework for the approximate conversion of parametric to implicit surfaces. It takes as input a parametric description and generates a pieceivise analytic implicit representation. The conversion process consists of three steps: 1) the parametric surface is rasterized into a volumetric characteristic funciton. 2) this binary function is converted into a volume array corresponding to samples of a smooth implicit function. 3) this volumetric representation is converted into a multiscale B-spline model. This method is based on wavelet analysis and synthesis techniques and is very general. It can convert to implicit form any geometric object that is suitable for discretization into a characteristic function. }, }