@article{CGFv23i1pp001-011:2004, author = {V. Vinayagamoorthy and M. Garau and A. Steed and M. Slater}, title = {{An Eye Gaze Model for Dyadic Interaction in an Immersive Virtual Environment: Practice and Experience}}, journal = {Computer Graphics Forum}, volume = {23}, number = {1}, abstract = {This paper describes a behavioural model used to simulate realistic eye-gaze behaviour and body animations for avatars representing participants in a shared immersive virtual environment (IVE). The model was used in a study designed to explore the impact of avatar realism on the perceived quality of communication within a negotiation scenario. Our eye-gaze model was based on data and studies carried out on the behaviour of eye-gaze during face-to-face communication. The technical features of the model are reported here. Information about the motivation behind the study, experimental procedures and a full analysis of the results obtained are given in [17].}, year = {2004}, pages = {1-11}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue1/v23i1pp001-011.pdf} } @article{CGFv23i1pp013-023:2004, author = {D. Borro and A. Garci­a-Alonso and L. Matey}, title = {{Approximation of Optimal Voxel Size for Collision Detection in Maintainability Simulations within Massive Virtual Environments}}, journal = {Computer Graphics Forum}, volume = {23}, number = {1}, abstract = {This paper describes a Collision Method for massive virtual environments composed of millions of triangles. It has been applied in the aeronautics industry for maintainability simulations using virtual aircraft engine mock-ups. The method performs well and has a good interactive frame rate even when it is used for computing force feedback with haptic devices. Space sorting problems chiefly related to voxel techniques, such as memory requirements and optimal voxel size, have been solved. We use advanced memory structures and hashing techniques. To find the optimal voxel size, several analytical solutions have been proposed and compared. These solutions are based on the performance cost function of the algorithm used. Experiments have been undertaken to verify these analytical solutions.}, year = {2004}, pages = {13-23}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue1/v23i1pp013-023.pdf} } @article{CGFv23i1pp025-041:2004, author = {C. Vilbrandt and G. Pasko and A. Pasko and P.-A. Fayolle and T. Vilbrandt and J. R. Goodwin and J. M. Goodwin and T. L. Kunii}, title = {{Cultural Heritage Preservation Using Constructive Shape Modeling}}, journal = {Computer Graphics Forum}, volume = {23}, number = {1}, abstract = {Issues of digital preservation of shapes and internal structures of historical cultural objects are discussed. An overview of existing approaches to digital preservation related to shape modeling is presented and corresponding problems are considered. We propose a new digital preservation paradigm based on both constructive modeling reflecting the logical structure of the objects and open standards and procedures. Constructive Solid Geometry (CSG) and Function Representation (FRep) are examined and practically applied as mathematical representations producing compressed yet precise data structures, thus providing inter-operability between current and future computer platforms crucial to archiving. Examples of CSG reconstruction of historical temples and FRep modeling of traditional lacquer ware are given. We examine the application of fitting of a parameterized FRep model to a cloud of data points as a step towards automation of the modeling process. Virtual venues for public access to cultural heritage objects including real time interactive simulation of cultural heritage sites over the Web are discussed and illustrated.}, year = {2004}, pages = {25-41}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue1/v23i1pp025-041.pdf} } @article{CGFv23i1pp043-053:2004, author = {F. Castro and M. Sbert and L. Neumann}, title = {{Fast Multipath Radiosity using Hierarchical Subscenes}}, journal = {Computer Graphics Forum}, volume = {23}, number = {1}, abstract = {This paper presents an efficient acceleration technique for the global line radiosity Multipath method. In this approach, the scene is subdivided in a hierarchy of box bounded subscenes, the boxes subdivided in a grid of virtual patches which store angular information. A new recursive (according to the hierarchy of subscenes) function allows to execute the Multipath algorithm at different levels of the hierarchy. A speed up factor up to 3–4 has been obtained on some of the tested scenes.}, year = {2004}, pages = {43-53}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue1/v23i1pp043-053.pdf} } @article{CGFv23i1pp055-069:2004, author = {Q. Li and D. Wills and R. Phillips and W. J. Viant and J. G. Griffiths and J. Ward}, title = {{Implicit Fitting Using Radial Basis Functions with Ellipsoid Constraint}}, journal = {Computer Graphics Forum}, volume = {23}, number = {1}, abstract = {Implicit planar curve and surface fitting to a set of scattered points plays an important role in solving a wide variety of problems occurring in computer graphics modelling, computer graphics animation, and computer assisted surgery. The fitted implicit surfaces can be either algebraic or non-algebraic. The main problem with most algebraic surface fitting algorithms is that the surface fitted to a given data set is often unbounded, multiple sheeted, and disconnected when a high degree polynomial is used, whereas a low degree polynomial is too simple to represent general shapes. Recently, there has been increasing interest in non-algebraic implicit surface fitting. In these techniques, one popular way of representing an implicit surface has been the use of radial basis functions. This type of implicit surface can represent various shapes to a high level of accuracy. In this paper, we present an implicit surface fitting algorithm using radial basis functions with an ellipsoid constraint. This method does not need to build interior and exterior layers for the given data set or to use information on surface normal but still can fit the data accurately. Furthermore, the fitted shape can still capture the main features of the object when the data sets are extremely sparse. The algorithm involves solving a simple general eigen-system and a computation of the inverse or psedo-inverse of a matrix, which is straightforward to implement.}, year = {2004}, pages = {55-69}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue1/v23i1pp055-069.pdf} } @article{CGFv23i1pp071-083:2004, author = {Chiew-Lan Tai and Hongxin Zhang and Jacky Chun-Kin Fong}, title = {{Prototype Modeling from Sketched Silhouettes based on Convolution Surfaces}}, journal = {Computer Graphics Forum}, volume = {23}, number = {1}, abstract = {This paper presents a hybrid method for creating three-dimensional shapes by sketching silhouette curves. Given a silhouette curve, we approximate its medial axis as a set of line segments, and convolve a linearly weighted kernel along each segment. By summing the fields of all segments, an analytical convolution surface is obtained. The resulting generic shape has circular cross-section, but can be conveniently modified via sketched profile or shape parameters of a spatial transform. New components can be similarly designed by sketching on different projection planes. The convolution surface model lends itself to smooth merging between the overlapping components. Our method overcomes several limitations of previous sketched-based systems, including designing objects of arbitrary genus, objects with semi-sharp features, and the ability to easily generate variants of shapes.}, year = {2004}, pages = {71-83}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue1/v23i1pp071-083.pdf} } @article{CGFv23i1pp085-112:2004, author = {Jan Kautz}, title = {{Hardware Lighting and Shading: a Survey}}, journal = {Computer Graphics Forum}, volume = {23}, number = {1}, abstract = {Traditionally, hardware rasterizers only support the Phong lighting model in combination with Gouraud shading using point light sources. However, the Phong lighting model is strictly empirical and physically implausible. Gouraud shading also tends to undersample the highlight unless a highly tesselated surface is used. Hence, higher-quality hardware accelerated lighting and shading has gained much interest in the recent five years. The research on hardware lighting and shading is two-fold. On the one hand, better lighting models for local illumination (assuming point light sources but evaluated per pixel) were demonstrated to be amenable to hardware implementation. On the other hand, recent research has demonstrated that even area lights, represented as environment maps, can be combined with complex lighting models. In both areas, many articles have been published, making it hard to decide which algorithm is well-suited for which application. This state-of-the-art report will review all relevent articles in both areas, and list advantages and disadvantages of each algorithm.}, year = {2004}, pages = {85-112}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue1/v23i1pp085-112.pdf} } @article{CGFv23i2pp129-141:2004, author = {Cyrille Damez and Nicolas Holzschuch and Francois X. Sillion}, title = {{Space-Time Hierarchical Radiosity with Clustering and Higher-Order Wavelets}}, journal = {Computer Graphics Forum}, volume = {23}, number = {2}, abstract = {We address in this paper the issue of computing diffuse global illumination solutions for animation sequences. The principal difficulties lie in the computational complexity of global illumination, emphasized by the movement of objects and the large number of frames to compute, as well as the potential for creating temporal discontinuities in the illumination, a particularly noticeable artifact. We demonstrate how space-time hierarchical radiosity, i.e. the application to the time dimension of a hierarchical decomposition algorithm, can be effectively used to obtain smooth animations: first by proposing the integration of spatial clustering in a space-time hierarchy; second, by using a higher-order wavelet basis adapted for the temporal dimension. The resulting algorithm is capable of creating time-dependent radiosity solutions efficiently.}, year = {2004}, pages = {129-141}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue2/v23i2pp129-141.pdf} } @article{CGFv23i2pp143-155:2004, author = {A. Formella and K. M{\"u}ller}, title = {{A Viewpoint-Dependent Approach to Ray Trace Free-Form Surfaces}}, journal = {Computer Graphics Forum}, volume = {23}, number = {2}, abstract = {For convincing realistic scenes objects with free-form surfaces are essential. Especially for photorealistic rendering pure polygonal models are often not sufficient. We present a new kind of algorithm to render free-form surfaces in a rendering system based on ray tracing. We describe a triangular patch as usual by its three points and normal vectors, but base the intersection calculation as well on the viewpoint of the camera (or, in general, on the ray itself). Hence, the shape of the object depends to some extent on the sampling rays. However, the resulting differences of, for instance, the shape of the silhouette to the shape of the corresponding shadow is usually not perceived by the observer of the rendered image. Because we perform a direct computation without a tessellation process, the resulting surface, its shadows, and its reflections appear smooth independent of the distance to the camera. Furthermore, the memory consumption depends only linearly on the number of input triangles. Special features like creases, T-vertices, and darts are also well supported. The computed uv-coordinates provide a direct means for texture mapping whose visual appearance improves significantly compared to triangle meshes of the same resolution.}, year = {2004}, pages = {143-155}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue2/v23i2pp143-155.pdf} } @article{CGFv23i2pp157-166:2004, author = {F. Hurtado and M. Noy and J.-M. Robert and V. Sacristan and S. Skiena}, title = {{Visualizing Objects with Mirrors}}, journal = {Computer Graphics Forum}, volume = {23}, number = {2}, abstract = {We present an automatic camera and mirrors placement method for visualizing 3D scenes such that complete and nonredundant visibility is guaranteed, as well as highest image resolution. We provide algorithms and geometries for optimal object-independent mirrors and viewpoint placement for all objects in a specific class. We also briefly consider object-dependent algorithmic problems, where mirrors and viewpoints are positioned as a function of the object.}, year = {2004}, pages = {157-166}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue2/v23i2pp157-166.pdf} } @article{CGFv23i2pp167-172:2004, author = {Y. K. Liu and B. Zalik and H. Yang}, title = {{An Integer One-Pass Algorithm for Voxel Traversal}}, journal = {Computer Graphics Forum}, volume = {23}, number = {2}, abstract = {Voxel traversing along a line in a uniformly divided voxel space is frequently needed in different applications of computer graphics. The paper presents a new integer one-pass algorithm for this problem. In 2D, the proposed approach is based on a modification of the well-known Bresenham algorithm. The algorithm is then extended in 3D where a special case may occur. It is characterized by a simple discriminator. A derivation for this discriminator given in the paper confirms that all calculations can be realized using only integer arithmetic. In this way, the accumulation of rounding errors is completely eliminated, and a robust and compact implementation can be easily achieved. One of the main advantages of the proposed algorithm is that it visits 1–3 voxels during each iteration thus assuring its efficiency. The algorithm has been compared with other algorithms for voxel traversing by measuring spent CPU time. For comparison, Cleary & Wyvill's, Amanatides & Woo's, and Code-based algorithm have been used. The proposed algorithm is faster than the referenced algorithms.}, year = {2004}, pages = {167-172}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue2/v23i2pp167-172.pdf} } @article{CGFv23i2pp173-187:2004, author = {D. Strnad and N. Guid}, title = {{Modeling Trees with Hypertextures}}, journal = {Computer Graphics Forum}, volume = {23}, number = {2}, abstract = {In the paper, a new method for modelling trees at medium detail is presented. The method is based on a volumetric representation of trees, generated by an iterated function system (IFS). Alleviating the modeling restrictions of fractal techniques, extensions to the standard IFS are introduced. Practical aspects of modeling and rendering of trees, such as data structures and bounding volumes, are discussed. The advantages of the new method are described at the end together with some results.}, year = {2004}, pages = {173-187}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue2/v23i2pp173-187.pdf} } @article{CGFv23i2pp189-201:2004, author = {Dan Su and Philip Willis}, title = {{Image Interpolation by Pixel-Level Data-Dependent Triangulation}}, journal = {Computer Graphics Forum}, volume = {23}, number = {2}, abstract = {We present a novel image interpolation algorithm. The algorithm can be used in arbitrary resolution enhancement, arbitrary rotation and other applications of still images in continuous space. High-resolution images are interpolated from the pixel-level data-dependent triangulation of lower-resolution images. It is simpler than other methods and is adaptable to a variety of image manipulations. Experimental results show that the new “mesh image” algorithm is as fast as the bilinear interpolation method. We assess the interpolated images' quality visually and also by the MSE measure which shows our method generates results comparable in quality to slower established methods. We also implement our method in graphics card hardware using OpenGL which leads to real-time high-quality image reconstruction. These features give it the potential to be used in gaming and image-processing applications.}, year = {2004}, pages = {189-201}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue2/v23i2pp189-201.pdf} } @article{CGFv23i2pp203-221:2004, author = {Robert S. Laramee and Helwig Hauser and Helmut Doleisch and Benjamin Vrolijk and Frits H. Post and Daniel Weiskopf}, title = {{The State of the Art in Flow Visualization: Dense and Texture-Based Techniques}}, journal = {Computer Graphics Forum}, volume = {23}, number = {2}, abstract = {Flow visualization has been a very attractive component of scientific visualization research for a long time. Usually very large multivariate datasets require processing. These datasets often consist of a large number of sample locations and several time steps. The steadily increasing performance of computers has recently become a driving factor for a reemergence in flow visualization research, especially in texture-based techniques. In this paper, dense, texture-based flow visualization techniques are discussed. This class of techniques attempts to provide a complete, dense representation of the flow field with high spatio-temporal coherency. An attempt of categorizing closely related solutions is incorporated and presented. Fundamentals are shortly addressed as well as advantages and disadvantages of the methods.}, year = {2004}, pages = {203-221}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue2/v23i2pp203-221.pdf} } @article{CGFv23i2pp223-251:2004, author = {K. W. Brodlie and D. A. Duce and J. R. Gallop and J. P. R. B. Walton and J. D. Wood}, title = {{Distributed and Collaborative Visualization}}, journal = {Computer Graphics Forum}, volume = {23}, number = {2}, abstract = {Visualization is a powerful tool for analyzing data and presenting results in science, engineering and medicine. This paper reviews ways in which it can be used in distributed and/or collaborative environments. Distributed visualization addresses a number of resource allocation problems, including the location of processing close to data for the minimization of data traffic. The advent of the Grid Computing paradigm and the link to Web Services provides fresh challenges and opportunities for distributed visualization-including the close coupling of simulations and visualizations in a steering environment. Recent developments in collaboration have seen the growth of specialized facilities (such as Access Grid) which have supplemented traditional desktop video conferencing using the Internet and multicast communications. Collaboration allows multiple users-possibly at remote sites-to take part in the visualization process at levels which range from the viewing of images to the shared control of the visualization methods. In this review, we present a model framework for distributed and collaborative visualization and assess a selection of visualization systems and frameworks for their use in a distributed or collaborative environment. We also discuss some examples of enabling technology and review recent work from research projects in this field.}, year = {2004}, pages = {223-251}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue2/v23i2pp223-251.pdf} } @article{CGFv23i3pp268-268:2004, author = {Henry Fuchs}, title = {{Immersive Integration of Physical and Virtual Environments}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {We envision future work and play environments in which the user's computing interface is more closely integrated with the physical surroundings than today's conventional computer display screens and keyboards.We are working toward realizable versions of such environments, in which multiple video projectors and digital cameras enable every visible surface to be both measured in 3D and used for display. If the 3D surface positions were transmitted to a distant location, they may also enable distant collaborations to become more like working in adjacent offices connected by large windows. With collaborators at the University of Pennsylvania, Brown University, Advanced Network and Services, and the Pittsburgh Supercomputing Center, we at Chapel Hill have been working to bring these ideas to reality. In one system, depth maps are calculated from streams of video images and the resulting 3D surface points are displayed to the user in head-tracked stereo. Among the applications we are pursuing for this tele-presence technology, is advanced training for trauma surgeons by immersive replay of recorded procedures. Other applications display onto physical objects, to allow more natural interaction with them ``painting'' a dollhouse, for example. More generally, we hope to demonstrate that the principal interface of a future computing environment need not be limited to a screen the size of one or two sheets of paper. Just as a useful physical environment is all around us, so too can the increasingly ubiquitous computing environment be all around us -integrated seamlessly with our physical surroundings.}, year = {2004}, pages = {268--268}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp268-268.pdf} } @article{CGFv23i3pp269-269:2004, author = {Mathieu Desbrun}, title = {{Applied Geometry:Discrete Differential Calculus for Graphics}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Geometry has been extensively studied for centuries, almost exclusively from a differential point of view. However, with the advent of the digital age, the interest directed to smooth surfaces has now partially shifted due to the growing importance of discrete geometry. From 3D surfaces in graphics to higher dimensional manifolds in mechanics, computational sciences must deal with sampled geometric data on a daily basis-hence our interest in Applied Geometry.In this talk we cover different aspects of Applied Geometry. First, we discuss the problem of Shape Approximation, where an initial surface is accurately discretized (i.e., remeshed) using anisotropic elements through error minimization. Second, once we have a discrete geometry to work with, we briefly show how to develop a full- blown discrete calculus on such discrete manifolds, allowing us to manipulate functions, vector fields, or even tensors while preserving the fundamental structures and invariants of the differential case. We will emphasize the applicability of our discrete variational approach to geometry by showing results on surface parameterization, smoothing, and remeshing, as well as virtual actors and thin-shell simulation.Joint work with: Pierre Alliez (INRIA), David Cohen-Steiner (Duke U.), Eitan Grinspun (NYU), Anil Hirani (Caltech), Jerrold E. Marsden (Caltech), Mark Meyer (Pixar), Fred Pighin (USC), Peter Schröder (Caltech), Yiying Tong (USC).}, year = {2004}, pages = {269--269}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp269-269.pdf} } @article{CGFv23i3pp270-270:2004, author = {Philip Dutre}, title = {{Image-based Relighting, and Computer Vision}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Image-based techniques have become very popular over the past couple of years. Ranging from modeling to rendering and lighting, the use of images as direct input for graphics algorithms has become as important as processing polygons or other forms of data.This talk will focus on some of the challenges posed by Image-based relighting. Starting from a set of photographs of an object under various illumination conditions, Image-based relighting computes novel renderings of the objects. Also, the inverse problem stated as ``What is the required lighting configuration to reach a desired illumination on the object?'' will be discussed, as well as some thoughts on how results from computer vision can be used to accelerate the process.}, year = {2004}, pages = {270--270}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp270-270.pdf} } @article{CGFv23i3pp271-279:2004, author = {Jukka Arvo and Mika Hirvikorpi and Joonas Tyystj{\"a}rvi}, title = {{Approximate Soft Shadows win an Image-Space Flood-Fill Algorithm}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Most former soft shadow algorithms have either suffered from restricted self-shadowing capabilities, been too slow for interactive applications, or could only be used with a limited types of geometry. In this paper, we propose an efficient image-based approach for computing soft shadows. Our method is based on shadow mapping and provides the associated benefits. We use pixel-based visibility computations for rendering penumbra regions directly into the screen-space. This is accomplished by using a modified flood-fill algorithm which enables us to implement the algorithm using programmable graphics hardware. Even though the resulting images are most often high quality, we do not claim that the proposed method is physically correct. The computation time and memory requirements for soft shadows depend on image resolution and the number of lights, not geometric scene complexity. Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation I.3.7 [Three-Dimensional Graphics and Realism]: Color, shading, shadowing, and texture}, year = {2004}, pages = {271--279}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp271-279.pdf} } @article{CGFv23i3pp281-290:2004, author = {Chunhui Mei and Jiaoying Shi and Fuli Wu}, title = {{Rendering with Spherical Radiance Transport Maps}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {In this paper, we propose a real-time method for rendering soft shadows and inter-reflections of dynamic objects under complex illumination. In previous methods, many efforts were taken to acquire occlusion and reflection informations for dynamic scene on the fly, and the result image cannot be generated in real time. In our approach, these informations for each object are pre-computed and stored in well-defined Spherical Radiance Transport Maps (SRTMs). For distant complex illumination such as environment illumination and area light source, we decompose the illumination to several hundred directional lights. In rendering, we search in SRTMs for occlusion info which may cause shadows, and reflection info which may cause inter-reflections. Finally we produce realistic soft shadows and inter-reflections efficiently. Our method is related with but different from previous Pre-computed Radiance Transfer techniques which are only suitable for static scene.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: shading and shadowing}, year = {2004}, pages = {281--290}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp281-290.pdf} } @article{CGFv23i3pp291-299:2004, author = {Mateu Sbert and Laszlo Szecsi and Laszlo Szirmay-Kalos}, title = {{Real-time Light Animation}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Light source animation is a particularly hard field of real-time global illumination algorithms since moving light sources result in drastic illumination changes and make coherence techniques less effective. However, the animation of small (point-like) light sources represents a special but practically very important case, for which the reuse of the results of other frames is possible. This paper presents a fast light source animation algorithm based on the virtual light sources illumination method. The speed up is close to the length of the animation, and is due to reusing paths in all frames and not only in the frame where they were obtained. The possible applications of this algorithm are the lighting design and systems to convey shape and features with relighting.}, year = {2004}, pages = {291--299}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp291-299.pdf} } @article{CGFv23i3pp301-310:2004, author = {Amit Shesh and Baoquan Chen}, title = {{SMARTPAPER: An Interactive and User Friendly Sketching System}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {This paper describes an interactive sketching system for 3D design/modeling that diverts from the conventional menu-and-button interfaces of CAD tools. The system, dubbed SMARTPAPER, offers a unified sketching environment that supports direct sketching as well as gestured sketching with more emphasis on the former to encourage natural sketching styles. SMARTPAPER also provides a unified 2D and 3D drawing domain by allowing the user to sketch directly on a 3D model in addition to the usual 2D sketching from scratch. A natural sketching experience is offered by supporting casual sketching consisting of wiggly, discontinuous, overlapping strokes. The system is empowered by an array of seamlessly integrated 2D and 3D features such as 2D sketch cleaning, 3D reconstruction from 2D sketch, 3D transformations, sketching on 3D, and conventional 3D CSG operations like cutting and joining. The key to the success of SMARTPAPER is efficient and robust 3D reconstruction from a single freehand 2D sketch with minimal hints. We have employed and improved Lipson's optimization method, originally designed for offline reconstruction of engineering drawings, in our interactive system by leveraging additional clues obtained by interaction during sketching.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Interaction Techniques, Pen-based Interaction}, year = {2004}, pages = {301--310}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp301-310.pdf} } @article{CGFv23i3pp311-320:2004, author = {Jian. J. Zhang and L. H. You}, title = {{Fast Surface Modelling Using a 6th Order PDE}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Although the control-point based parametric approach is used most widely in free-form surface modelling, complementary techniques co-exist to meet various specialised requirements. The partial differential equation (PDE) based modelling approach is especially suitable for satisfying surface boundary constraints. They are also effective for the generation of families of free-form surfaces, which share a common base and differ in their secondary features. In this paper, we present a fast surface modelling method using a sixth order PDE. This PDE provides enough degrees of freedom not only to accommodate tangent, but also curvature boundary conditions and offers more shape control parameters to serve as user controls for the manipulation of surface shapes. In order to achieve real-time performance, we have constructed a surface function and developed a high-precision approximate solution to the 6th order PDE. Unlike some existing PDE-based techniques, this resolution method can satisfy the boundary conditions exactly, and is able to create free-form surfaces as fast and almost as accurately as the closed-form (analytical) solutions. Due to the fact that it has sufficient degrees of freedom to accommodate the continuity of 3-sided and 4-sided surface patches at their boundaries, this method is able to model complex surfaces consisting of multiple patches. Compared with existing PDE-based modelling methods, this method is both fast and can solve a larger class of surface modelling problems.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Curves, surfaces, solid, and object representations; physically based modelling}, year = {2004}, pages = {311--320}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp311-320.pdf} } @article{CGFv23i3pp321-330:2004, author = {Sebti Foufou and Lionel Garnier}, title = {{Dupin Cyclide Blends Between Quadric Surfaces for Shape Modeling}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {We introduce a novel method to define Dupin cyclide blends between quadric primitives. Dupin cyclides are non-spherical algebraic surfaces discovered by French mathematician Pierre-Charles Dupin at the beginning of the 19th century. As a Dupin cyclide can be fully characterized by its principal circles, we have focussed our study on how to determine principal circles tangent to both quadrics being blended. This ensures that the Dupin cyclide we are constructing constitutes aG1blend. We use the Rational Quadratic BĂ©zier Curve (RQBC) representation of circular arcs to model the principal circles, so the construction of each circle is reduced to the determination of the three control points of the RQBC representing the circle.In this work, we regard the blending of two quadric primitives A and B as two complementary blending operations: primitive A-cylinder and cylinder-primitive B; two Dupin cyclides and a cylinder are then defined for each blending operation. In general the cylinder is not useful and may be reduced to a simple circle. A complete shape design example is presented to illustrate the modeling of Eurographics'04 Hugo using a limited number of quadrics combined using Dupin cyclide blends.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling}, year = {2004}, pages = {321--330}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp321-330.pdf} } @article{CGFv23i3pp331-340:2004, author = {Aravind Krishnaswamy and Gladimir V.G. Baranoski}, title = {{A Biophysically-Based Spectral Model of Light Interaction with Human Skin}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Despite the notable progress in physically-based rendering, there is still a long way to go before we can automatically generate predictable images of biological materials. In this paper, we address an open problem in this area, namely the spectral simulation of light interaction with human skin. We propose a novel biophysically based model that accounts for all components of light propagation in skin tissues, namely surface reflectance, subsurface reflectance and transmittance, and the biological mechanisms of light absorption by pigments in these tissues. The model is controlled by biologically meaningful parameters, and its formulation, based on standard Monte Carlo techniques, enables its straightforward incorporation into realistic image synthesis frameworks. Besides its biophysically-based nature, the key difference between the proposed model and the existing skin models is its comprehensiveness, i.e., it computes both spectral (reflectance and transmittance) and scattering (bidirectional surface-scattering distribution function) quantities for skin specimens. In order to assess the predictability of our simulations, we evaluate their accuracy by comparing results from the model with actual skin measured data. We also present computer generated images to illustrate the flexibility of the proposed model with respect to variations in the biological input data, and its applicability not only in the predictive image synthesis of different skin tones, but also in the spectral simulation of medical conditions.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism}, year = {2004}, pages = {331--340}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp331-340.pdf} } @article{CGFv23i3pp341-350:2004, author = {Brett Desbenoit and Eric Galin and Samir Akkouche}, title = {{Simulating and modeling lichen growth}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {This paper presents a system for modeling lichens and simulating their propagation and growth in a virtual scene. Lichens colonize almost every substrate in nature and play an important role in the visual appearance of a natural object. The propagation of lichens over the substrate is performed by an Open Diffusion Limited Aggregation model constrained by the characteristics of the environment. The designer can control the development of lichens with simple parameters. Rendering the complex geometry and texture of lichens is achieved by instantiating three dimensional lichen models stored in an atlas of shapes created after real world images. The lichens obtained by our approach considerably increase the realism of complex natural scenes.Categories and Subject Descriptors (according to ACMCCS):I.3.3 [Computer Graphics]:Three-Dimensional Graphics and Realism}, year = {2004}, pages = {341--350}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp341-350.pdf} } @article{CGFv23i3pp351-360:2004, author = {Callum Galbraith and Lars M{\"u}ndermann and Brian Wyvill}, title = {{Implicit Visualization and Inverse Modeling of Growing Trees}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {A method is proposed for photo-realistic modeling and visualization of a growing tree. Recent visualization methods have focused on producing smoothly blending branching structures, however, these methods fail to account for the inclusion of non-smooth features such as branch bark ridges and bud scale scars. These features constitute an important visual aspect of a living tree, and are also observed to vary over time. The proposed method incorporates these features by using an hierarchical implicit modeling system, which provides a variety of tools for combining surface components in both smooth and non smooth configurations. A procedural interface to this system supports the use of inverse modeling, which is a global-to-local methodology, where the local properties of plant organs are described in terms of their global position within the tree architecture. Inverse modeling is used to define both the tree structure at any time, and a continuous developmental sequence for the tree from a seedling. These techniques provide an intuitive paradigm for the definition of complex tree growth sequences and their subsequent visualization, based solely on observed phenomena. Thus, a key advantage is that they do not require any knowledge of, or simulation of, the underlying biological processes.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Curve, surface, solid, and object representations I.3.7 [Computer Graphics]: Animation}, year = {2004}, pages = {351--360}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp351-360.pdf} } @article{CGFv23i3pp361-370:2004, author = {Carles Bosch and Xavier Pueyo and Stephane Merillou and Djamchid Ghazanfarpour}, title = {{A Physically-Based Model for Rendering Realistic Scratches}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Individually visible scratches, also called isolated scratches, are very common in real world surfaces. Although their microgeometry is not visible, they are individually perceptible by the human eye, lying into a representation scale between BRDF and texture. In order to simulate this kind of scratches in synthetic images we need to know their position over the surface (texture scale), so we can determine where to use the specific scratch BRDF instead of the ordinary surface BRDF. Computing the BRDF of a scratch is difficult because it depends on the scratch's invisible microgeometry. In this paper, we propose a new physically based model to derive this microgeometry by simulating the formation process of scratches. We allow specifying intuitively the parameters involved in the process such as the scratching tool, the penetration forces, and the material properties of the object. From these parameters, we derive the microgeometries of the scratches by taking into account the real behaviour of the process. This behaviour has been determined by analysing existing models in the field of materials engineering and some ``scratch tests'' that we performed on metals. Our method has the advantages of easily simulating scratches with a wide range of microgeometries and taking into account the variability of their microgeometry along the scratch path. Another contribution is related to the location of the scratches over the surface. Instead of using an image of the paths as in previous work, we present a new representation based on curves defining the paths. This offers an independence on the image resolution or the distance from the observer and accurately provides the scratch direction in order to compute scratch BRDFs.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Color, shading, shadowing, and texture.}, year = {2004}, pages = {361--370}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp361-370.pdf} } @article{CGFv23i3pp371-379:2004, author = {M. Gopi and David Eppstien}, title = {{Single-Strip Triangulation of Manifolds with Arbitrary Topology}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Triangle strips have been widely used for efficient rendering. It is NP-complete to test whether a given triangulated model can be represented as a single triangle strip, so many heuristics have been proposed to partition models into few long strips. In this paper, we present a new algorithm for creating a single triangle loop or strip from a triangulated model. Our method applies a dual graph matching algorithm to partition the mesh into cycles, and then merges pairs of cycles by splitting adjacent triangles when necessary. New vertices are introduced at midpoints of edges and the new triangles thus formed are coplanar with their parent triangles, hence the visual fidelity of the geometry is not changed. We prove that the increase in the number of triangles due to this splitting is 50% in the worst case, however for all models we tested the increase was less than 2%. We also prove tight bounds on the number of triangles needed for a single-strip representation of a model with holes on its boundary. Our strips can be used not only for efficient rendering, but also for other applications including the generation of space filling curves on a manifold of any arbitrary topology.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Geometric algorithms, Triangulation, Stripification. G.2.2 [Graph algorithms]: Hamiltonian Path, Hamiltonian Cycle, Perfect Matching.}, year = {2004}, pages = {371--379}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp371-379.pdf} } @article{CGFv23i3pp381-389:2004, author = {Sebastien Valette and Jean-Marc Chassery}, title = {{Approximated Centroidal Voronoi Diagrams for Uniform Polygonal Mesh Coarsening}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {We present a novel clustering algorithm for polygonal meshes which approximates a Centroidal Voronoi Diagram construction. The clustering provides an efficient way to construct uniform tessellations, and therefore leads to uniform coarsening of polygonal meshes, when the output triangulation has many fewer elements than the input mesh. The mesh topology is also simplified by the clustering algorithm. Based on a mathematical framework, our algorithm is easy to implement, and has low memory requirements. We demonstrate the efficiency of the proposed scheme by processing several reference meshes having up to 1 million triangles and very high genus within a few minutes on a low- end computer.}, year = {2004}, pages = {381--389}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp381-389.pdf} } @article{CGFv23i3pp391-400:2004, author = {Klaus Hildebrandt and Konrad Polthier}, title = {{Anisotropic Filtering of Non-Linear Surface Features}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {A new method for noise removal of arbitrary surfaces meshes is presented which focuses on the preservation and sharpening of non-linear geometric features such as curved surface regions and feature lines. Our method uses a prescribed mean curvature flow (PMC) for simplicial surfaces which is based on three new contributions: 1. the definition and efficient calculation of a discrete shape operator and principal curvature properties on simplicial surfaces that is fully consistent with the well-known discrete mean curvature formula, 2. an anisotropic discrete mean curvature vector that combines the advantages of the mean curvature normal with the special anisotropic behaviour along feature lines of a surface, and 3. an anisotropic prescribed mean curvature flow which converges to surfaces with an estimated mean curvature distribution and with preserved non-linear features. Additionally, the PMC flow prevents boundary shrinkage at constrained and free boundary segments.}, year = {2004}, pages = {391--400}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp391-400.pdf} } @article{CGFv23i3pp401-410:2004, author = {C. Andujar and P. Brunet and A. Chica and I. Navazo and J. Rossignac and A. Vinacua}, title = {{Computing Maximal Tiles and Application to Impostor-Based Simplification}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {The computation of the largest planar region approximating a 3D object is an important problem with wide applications in modeling and rendering. Given a voxelization of the 3D object, we propose an efficient algorithm to solve a discrete version of this problem. The input of the algorithm is the set of grid edges connecting the interior and the exterior of the object (called sticks). Using a voting-based approach, we compute the plane that slices the largest number of sticks and is orientation-compatible with these sticks. The robustness and efficiency of our approach rests on the use of two different parameterizations of the planes with suitable properties. The first of these is exact and is used to retrieve precomputed local solutions of the problem. The second one is discrete and is used in a hierarchical voting scheme to compute the global maximum. This problem has diverse applications that range from finding object signatures to generating simplified models. Here we demonstrate the merits of the algorithm for efficiently computing an optimized set of textured impostors for a given polygonal model.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling}, year = {2004}, pages = {401--410}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp401-410.pdf} } @article{CGFv23i3pp411-420:2004, author = {Parag Chaudhuri and Prem Kalra and Subhashis Banerjee}, title = {{A System for View-Dependent Animation}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {In this paper, we present a novel system for facilitating the creation of stylized view-dependent 3D animation. Our system harnesses the skill and intuition of a traditionally trained animator by providing a convivial sketch based 2D to 3D interface. A base mesh model of the character can be modified to match closely to an input sketch, with minimal user interaction. To do this, we recover the best camera from the intended view direction in the sketch using robust computer vision techniques. This aligns the mesh model with the sketch. We then deform the 3D character in two stages - first we reconstruct the best matching skeletal pose from the sketch and then we deform the mesh geometry. We introduce techniques to incorporate deformations in the view-dependent setting. This allows us to set up view-dependent models for animation.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism - Animation }, year = {2004}, pages = {411--420}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp411-420.pdf} } @article{CGFv23i3pp421-430:2004, author = {Johannes Zander and Tobias Isenberg and Stefan Schlechtweg and Thomas Strothotte}, title = {{High Quality Hatching}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Hatching lines are often used in line illustrations to convey tone and texture of a surface. In this paper we present methods to generate hatching lines from polygonal meshes and render them in high quality either at interactive rates for on-screen display or for reproduction in print. Our approach is based on local curvature information that is integrated to form streamlines on the surface of the mesh. We use a new algorithm that provides an even distribution of these lines. A special processing of these streamlines ensures high quality line rendering for both intended output media later on. While the streamlines are generated in a preprocessing stage, hatching lines are rendered either for vector-based printer output or on-screen display, the latter allowing for interaction in terms of changing the view parameters or manipulating the entire line shading model at run-time using a virtual machine.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation-Display algorithms; I.3.3 [Computer Graphics]: Picture/Image Generation-Line and curve generation }, year = {2004}, pages = {421--430}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp421-430.pdf} } @article{CGFv23i3pp431-440:2004, author = {Daisuke Tasaki and Shinji Mizuno and Minoru Okada}, title = {{Virtual Drypoint by a Model-driven Strategy}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {In this paper we propose a method to synthesize a virtual copperplate print image based on physical model as a non-photorealistic rendering in Computer Graphics. In particular we pick out the drypoint from many existing copperplate printing techniques. A drypoint print has a remarkable feature that ridged burrs are arising out of the copperplate and the printed lines are slightly ragged and fuzzy. Our method consists of four sub-processes: plate making, ink applying, wiping and printing. Each process simulates the physical actions and phenomena observed in the actual copperplate printing. In this study we use a small-scale print and an actual print created by a real copperplate artist for some experiments to indicate effects and availability of proposed method to synthesize a print image with the feature of drypoint. Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism}, year = {2004}, pages = {431--440}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp431-440.pdf} } @article{CGFv23i3pp441-450:2004, author = {Shuzhen Wang and Wolfgang Heidrich}, title = {{The Design of an Inexpensive Very High Resolution Scan Camera System}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {We describe a system for transforming an off-the-shelf flatbed scanner into a $200 scan backend for large format cameras. While we describe both software and hardware aspects, the focus of the paper is on software issues such as color calibration and removal of scanner artifacts. With current scanner technology, the resulting camera system is capable of taking black&white, color, or near-infrared photographs with up to 490 million pixels. Our analysis shows that we achieve actual optical resolutions close to the theoretical maximum, and that color reproduction is comparable to commercial camera systems. We believe that the camera system described here has many potential applications in image-based modeling and rendering, cultural heritage projects, and professional digital photography.}, year = {2004}, pages = {441--450}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp441-450.pdf} } @article{CGFv23i3pp451-460:2004, author = {Ramesh Raskar and Jeroen Baar and Thomas Willwacher and Srinivas Rao}, title = {{Quadric Transfer for Immersive Curved Screen Displays}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Curved screens are increasingly being used for high-resolution immersive visualization environments. We describe a new technique to display seamless images using overlapping projectors on curved quadric surfaces such as spherical or cylindrical shape. We exploit a quadric image transfer function and show how it can be used to achieve sub-pixel registration while interactively displaying two or three-dimensional datasets for a head-tracked user. Current techniques for automatically registered seamless displays have focused mainly on planar displays. On the other hand, techniques for curved screens currently involve cumbersome manual alignment to make the installation conform to the intended design. We show a seamless real-time display system and discuss our methods for smooth intensity blending and efficient rendering.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism- Virtual reality}, year = {2004}, pages = {451--460}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp451-460.pdf} } @article{CGFv23i3pp461-468:2004, author = {Eric Bourque and Gregory Dudek}, title = {{Procedural Texture Matching and Transformation}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {We present a technique for creating a smoothly varying sequence of procedural textures that interpolates between arbitrary input samples of texture. This texture transformation uses a library of procedural shaders and selects the correct shaders and associated parameters to accomplish the task.In general, selecting a procedural texture from a library, or finding the correct parameters to produce a smooth texture transition can be complex and time consuming. We propose a strategy for automating this process. While superficially this problem appears intractable for both humans and computational systems, its natural characteristics make a computational solution feasible. We present an algorithm and experimental results demonstrating this approach.Transformation between two textures can then be achieved procedurally, while enforcing perceptual similarity constraints between adjacent texture frames. We describe a technique for efficiently sampling the parameter domain of a shader based on a texture similarity function to create a smooth path through its texture range. In the case of evolving between several shaders, a method is described to obtain the best jump-points which can be used to connect different shaders smoothly in texture space. Several examples of the technique are shown, and future directions as well as potential problems are discussed.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Texture}, year = {2004}, pages = {461--468}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp461-468.pdf} } @article{CGFv23i3pp469-478:2004, author = {Tino Weinkauf and Holger Theisel and Hans-Christian Hege and Hans-Peter Seidel}, title = {{Topological Construction and Visualization of Higher Order 3D Vector Fields}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {We present the first algorithm for constructing 3D vector fields based on their topological skeleton. The skeleton itself is modeled by interactively moving a number of control polygons. Then a piecewise linear vector field is automatically constructed which has the same topological skeleton as modeled before. This approach is based on a complete segmentation of the areas around critical points into sectors of different flow behavior. Based on this, we present the first approach to visualizing higher order critical points of 3D vector fields.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Line and Curve Generation I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism}, year = {2004}, pages = {469--478}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp469-478.pdf} } @article{CGFv23i3pp479-488:2004, author = {D. Weiskopf}, title = {{Dye Advection Without the Blur: A Level-Set Approach for Texture-Based Visualization of Unsteady Flow}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Dye advection is an intuitive and versatile technique to visualize both steady and unsteady flow. Dye can be easily combined with noise-based dense vector field representations and is an important element in user-centric visual exploration processes. However, fast texture-based implementations of dye advection rely on linear interpolation operations that lead to severe diffusion artifacts. In this paper, a novel approach for dye advection is proposed to avoid this blurring and to achieve long and clearly defined streaklines or extended streak-like patterns. The interface between dye and background is modeled as a level-set within a signed distance field. The level-set evolution is governed by the underlying flow field and is computed by a semi-Lagrangian method. A reinitialization technique is used to counteract the distortions introduced by the level-set evolution and to maintain a level-set function that represents a local distance field. This approach works for 2D and 3D flow fields alike. It is demonstrated how the texture-based level-set representation lends itself to an efficient GPU implementation and therefore facilitates interactive visualization.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism}, year = {2004}, pages = {479--488}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp479-488.pdf} } @article{CGFv23i3pp489-497:2004, author = {Benjamin Mora and David S. Evert}, title = {{Instant Volumetric Understanding with Order-Independent Volume Rendering}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Rapid, visual understanding of volumetric datasets is a crucial outcome of a good volume rendering application, but few current volume rendering systems deliver this result. Our goal is to reduce the volumetric surfing that is required to understand volumetric features by conveying more information in fewer images. In order to achieve this goal, and in contrast with most current methods which still use optical models and alpha blending, our approach reintroduces the order-independent contribution of every sample along the ray in order to have an equiprobable visualization of all the volume samples. Therefore, we demonstrate how order independent sampling can be suitable for fast volume understanding, show useful extensions to MIP and X-ray like renderings, and, finally, point out the special advantage of using stereo visualization in these models to circumvent the lack of depth cues.Categories and Subject Descriptors: I.3.3 [Computer Graphics]: Picture/Image, Generation,I.3.7 [Computer Graphics]: Three-Dimensional graphics and realism.}, year = {2004}, pages = {489--497}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp489-497.pdf} } @article{CGFv23i3pp499-508:2004, author = {C. Andujar and P. Vazquez and M. Fairen}, title = {{Way-Finder: guided tours through complex walkthrough models}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {The exploration of complex walkthrough models is often a difficult task due to the presence of densely occluded regions which pose a serious challenge to online navigation. In this paper we address the problem of algorithmic generation of exploration paths for complex walkthrough models. We present a characterization of suitable properties for camera paths and we discuss an efficient algorithm for computing them with little or no user intervention. Our approach is based on identifying the free-space structure of the scene (represented by a cell and portal graph) and an entropy-based measure of the relevance of a view-point. This metric is key for deciding which cells have to be visited and for computing critical way-points inside each cell. Several results on different model categories are presented and discussed.}, year = {2004}, pages = {499--508}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp499-508.pdf} } @article{CGFv23i3pp509-518:2004, author = {Fabrice Lamarche and Stephane Donikian}, title = {{Crowd of Virtual Humans: a New Approach for Real Time Navigation in Complex and Structured Environments}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {The navigation activity is an every day practice for any human being capable of locomotion. Our objective in this work is to reproduce this crucial human activity inside virtual environments. Putting together the high complexity of a realistic environment such as a city, a big amount of virtual humans and the real-time constraint requires to optimize each aspect of the animation process. In this paper, we present a suitable topological structuring of the geometric environment to allow fast path finding as well as an efficient reactive navigation algorithm for virtual humans evolving inside a crowd.}, year = {2004}, pages = {509--518}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp509-518.pdf} } @article{CGFv23i3pp519-528:2004, author = {Mankyu Sung and Michael Gleicher and Stephen Chenney}, title = {{Scalable behaviors for crowd simulation}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Crowd simulation for virtual environments offers many challenges centered on the trade-offs between rich behavior, control and computational cost. In this paper we present a new approach to controlling the behavior of agents in a crowd. Our method is scalable in the sense that increasingly complex crowd behaviors can be created without a corresponding increase in the complexity of the agents. Our approach is also more authorable; users can dynamically specify which crowd behaviors happen in various parts of an environment. Finally, the character motion produced by our system is visually convincing. We achieve our aims with a situation-based control structure. Basic agents have very limited behaviors. As they enter new situations, additional, situation-specific behaviors are composed on the fly to enable agents to respond appropriately. The composition is done using a probabilistic mechanism. We demonstrate our system with three environments including a city street and a theater.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Animation}, year = {2004}, pages = {519--528}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp519-528.pdf} } @article{CGFv23i3pp529-538:2004, author = {S. Hasegawa and M. Sato}, title = {{Real-time Rigid Body Simulation for Haptic Interactions Based on Contact Volume of Polygonal Objects}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {This paper proposes a new method for real-time rigid body simulations for haptic interactions based on a penalty method regarding contact volume. Analytical methods for calculation of contact forces require too much time to maintain fast update rates for haptic controls. In addition, they prohibit direct connection of haptic interfaces.Penalty methods, which employ spring-damper models for calculation of contact forces, offer a very rapid rate of iterations. In addition, they permit direct connection of haptic interfaces. Penalty methods are good for haptic interactions. However, previous penalty methods do not regard distribution of contact forces over the contact area. For that reason, they can't calculate normal and friction forces on face-face contacts correctly.We propose a distributed spring-damper model on a contact area to solve these problems. We analyze three-dimensional geometries of the intersecting portion on the polyhedral objects. Then, we integrate forces and torques of distributed spring-damper models.We implement a proposed simulator and compare it with a point-based penalty method and constraint method. The comparison shows that the proposed simulator improves accuracy of the simulation of face-face contact and friction forces and the simulation speed. In addition, we attach a six degree-of-freedom (6-DOF) haptic interface to the simulator. Users can feel 6-DOF force feedback and input 6-DOF motions.Categories and Subject Descriptors (according to ACM CCS): I.6.5 [Model Development]: Modeling methodologies, H.5.2 [User Interfaces]: Haptic I/O, I.3.6 [Methodology and Techniques]: Interaction techniques}, year = {2004}, pages = {529--538}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp529-538.pdf} } @article{CGFv23i3pp539-545:2004, author = {Yoshinori Dobashi and Tsuyoshi Yamamoto and Tomoyuki Nishita}, title = {{Synthesizing Sound from Turbulent Field using Sound Textures for Interactive Fluid Simulation}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Sound is an indispensable element for the simulation of a realistic virtual environment. Therefore, there has been much recent research focused on the simulation of realistic sound effects. This paper proposes a method for creating sound for turbulent phenomena such as fire. In a turbulent field, the complex motion of vortices leads to the generation of sound. This type of sound is called a vortex sound. The proposed method simulates a vortex sound by computing vorticity distributions using computational fluid dynamics. Sound textures for the vortex sound are first created in a pre-process step. The sound is then created at interactive rates by using these sound textures. The usefulness of the proposed method is demonstrated by applying it to the simulation of the sound of fire and other turbulent phenomena.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism - Animation; I.6.8 [Simulation and Modeling]: Types of Simulation - Animation; I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism; I.6.3 [Simulation and Modeling]: Applications; H.5.5 [Information Interfaces and Presentation]: Sound and Music Computing - Methodologies and techniques, Modeling.}, year = {2004}, pages = {539--545}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp539-545.pdf} } @article{CGFv23i3pp547-556:2004, author = {Jeffrey L. Schoner and Jochen Lang and Hans-Peter Seidel}, title = {{Measurement-Based Interactive Simulation of Viscoelastic Solids}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Animation of viscoelastic solids in entertainment and medical applications as well as scientific simulation can be improved through observations of real world objects. This paper presents a method for simulating viscoelastic solids in real-time for visual and haptic display along with a method for determining the parameters of the the underlying model from automated physical measurements of real world objects. The viscoelastic model is a novel extension of the discrete Green's function matrix for linear elasticity, which combines static behavior represented by Green's functions with dynamic behavior expressed by differential equations inspired by particle systems. We describe a novel estimation method of dynamic contact behavior for heterogeneous complex objects based on these measurements. For this estimation, our method relies only on measurement data previously used in the acquisition less realistic elastostatic models. In this way our method allows more physically accurate realism in animation of viscoelastic solids without large additional computational costs or any measurements besides those associated with related methods for elastostatic solids.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Physically based modeling I.3.7 [Computer Graphics]: Virtual reality, animation}, year = {2004}, pages = {547--556}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp547-556.pdf} } @article{CGFv23i3pp557-566:2004, author = {Avneesh Sud and Miguel A. Otaduy and Dinesh Manocha}, title = {{DiFi: Fast 3D Distance Field Computation Using Graphics Hardware}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {We present an algorithm for fast computation of discretized 3D distance fields using graphics hardware. Given a set of primitives and a distance metric, our algorithm computes the distance field for each slice of a uniform spatial grid baly rasterizing the distance functions of the primitives. We compute bounds on the spatial extent of the Voronoi region of each primitive. These bounds are used to cull and clamp the distance functions rendered for each slice. Our algorithm is applicable to all geometric models and does not make any assumptions about connectivity or a manifold representation. We have used our algorithm to compute distance fields of large models composed of tens of thousands of primitives on high resolution grids. Moreover, we demonstrate its application to medial axis evaluation and proximity computations. As compared to earlier approaches, we are able to achieve an order of magnitude improvement in the running time.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Distance fields, Voronoi regions, graphics hardware, proximity computations}, year = {2004}, pages = {557--566}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp557-566.pdf} } @article{CGFv23i3pp567-576:2004, author = {Jan Klein and Gabriel Zachmann}, title = {{Point Cloud Collision Detection}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {In the past few years, many efficient rendering and surface reconstruction algorithms for point clouds have been developed. However, collision detection of point clouds has not been considered until now, although this is a prerequisite to use them for interactive or animated 3D graphics.We present a novel approach for time-critical collision detection of point clouds. Based solely on the point representation, it can detect intersections of the underlying implicit surfaces. The surfaces do not need to be closed.We construct a point hierarchy where each node stores a sufficient sample of the points plus a sphere covering of a part of the surface. These are used to derive criteria that guide our hierarchy traversal so as to increase convergence. One of them can be used to prune pairs of nodes, the other one is used to prioritize still to be visited pairs of nodes. At the leaves we efficiently determine an intersection by estimating the smallest distance.We have tested our implementation for several large point cloud models. The results show that a very fast and precise answer to collision detection queries can always be given.Categories and Subject Descriptors (according to ACM CCS): G.1.2 [Numerical Analysis]: Approximation of surfaces and contours I.3.5 [Computer Graphics]: Computational Geometry and Object-Modeling[Geometric algorithms, languages and systems; object hierarchy; physically-based modeling] I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism[Animation; virtual reality]}, year = {2004}, pages = {567--576}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp567-576.pdf} } @article{CGFv23i3pp577-584:2004, author = {Xiaobin Wu and J{\"o}rg Peters}, title = {{Interference Detection for Subdivision Surfaces}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Accurate and robust interference detection and ray-tracing of subdivision surfaces requires safe linear approximations. Approximation of the limit surface by the subdivided control polyhedron can be both inaccurate and, due to the exponential growth of the number of facets, costly.This paper shows how a standard intersection hierarchy, such as an OBB tree, can be made safe and efficient for subdivision surface interference detection. The key is to construct, on the fly, optimally placed facets, whose spherical offsets tightly enclose the limit surface. The spherically offset facets can be locally subdivided and they can be efficiently intersected based on standard triangle-triangle interference detection.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling}, year = {2004}, pages = {577--584}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp577-584.pdf} } @article{CGFv23i3pp585-593:2004, author = {Laszlo Szecsi and Mateu Sbert and Laszlo Szirmay-Kalos}, title = {{Combined Correlated and Importance Sampling in Direct Light Source Computation and Environment Mapping}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {This paper presents a general variance reduction method that is a quasi-optimal combination of correlated and importance sampling. The weights of the combination are selected automatically in order to keep the merits of both importance and correlated sampling. The proposed sampling method is used for efficient direct light source computation of large area sources and for the calculation of the reflected illumination of environment maps. Importance sampling would be good in these cases if the sources are hidden, while correlated sampling is efficient if the sources are fully visible. The proposed method automatically detects the particular case and provides results that inherit the advantages of both techniques.}, year = {2004}, pages = {585--593}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp585-593.pdf} } @article{CGFv23i3pp595-603:2004, author = {Ingo Wald and Johannes G{\"u}nther and Philipp Slusallek}, title = {{Balancing Considered Harmful - Faster Photon Mapping using the Voxel Volume Heuristic -}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Photon mapping is one of the most important algorithms for computing global illumination. Especially for efficiently producing convincing caustics, there are no real alternatives to photon mapping. On the other hand, photon mapping is also quite costly: Each radiance lookup requires to find the k nearest neighbors in a kd-tree, which can be more costly than shooting several rays. Therefore, the nearest-neighbor queries often dominate the rendering time of a photon map based renderer.In this paper, we present a method that reorganizes - i.e. un balances - the kd-tree for storing the photons in a way that allows for finding the k-nearest neighbors much more efficiently, thereby accelerating the radiance estimates by a factor of 1.2–3.4. Most importantly, our method still finds exactly the same k-nearest-neighbors as the original method, without introducing any approximations or loss of accuracy. The impact of our method is demonstrated with several practical examples.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Global Illumination I.3.7 [Computer Graphics]: Raytracing}, year = {2004}, pages = {595--603}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp595-603.pdf} } @article{CGFv23i3pp605-614:2004, author = {Jean-Philippe Farrugia and Bernard Peroche}, title = {{A Progressive Rendering Algorithm Using an Adaptive Perceptually Based Image Metric }}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {In this paper, we propose to solve the global illumination problem through a progressive rendering method relying on an adaptive sampling of the image space. The refinement of this sample scheme is driven by an image metric based on a powerful vision model. A Delaunay triangulation of the sampled points is followed by a classification of these triangles into three classes. By interpolating each triangle according to the class it belongs to, we can obtain a high quality image by computing only a fraction of all the pixels and thus saving computation time.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Perceptual Rendering, Global illumination}, year = {2004}, pages = {605--614}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp605-614.pdf} } @article{CGFv23i3pp615-624:2004, author = {Jiri­ Bittner and Michael Wimmer and Harald Piringer and Werner Purgathofer}, title = {{Coherent Hierarchical Culling: Hardware Occlusion Queries Made Useful}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {We present a simple but powerful algorithm for optimizing the usage of hardware occlusion queries in arbitrary complex scenes. Our method minimizes the number of issued queries and reduces the delays due to the latency of query results. We reuse the results of occlusion queries from the last frame in order to initiate and schedule the queries in the next frame. This is done by processing nodes of a spatial hierarchy in a front-to-back order and interleaving occlusion queries with rendering of certain previously visible nodes. The proposed scheduling of the queries makes use of spatial and temporal coherence of visibility. Despite its simplicity, the algorithm achieves good culling efficiency for scenes of various types. The implementation of the algorithm is straightforward and it can be easily integrated in existing real-time rendering packages based on common hierarchical data structures.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism}, year = {2004}, pages = {615--624}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp615-624.pdf} } @article{CGFv23i3pp625-633:2004, author = {Daniel Weiskopf and Tobias Schafhitzel and Thomas Ertl}, title = {{GPU-Based Nonlinear Ray Tracing}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {In this paper, we present a mapping of nonlinear ray tracing to the GPU which avoids any data transfer back to main memory. The rendering process consists of the following parts: ray setup according to the camera parameters, ray integration, ray-object intersection, and local illumination. Bent rays are approximated by polygonal lines that are represented by textures. Ray integration is based on an iterative numerical solution of ordinary differential equations whose initial values are determined during ray setup. To improve the rendering performance, we propose acceleration techniques such as early ray termination and adaptive ray integration. Finally, we discuss a variety of applications that range from the visualization of dynamical systems to the general relativistic visualization in astrophysics and the rendering of the continuous refraction in media with varying density.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism}, year = {2004}, pages = {625--633}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp625-633.pdf} } @article{CGFv23i3pp635-642:2004, author = {Ming Li and Marcus Magnor and Hans-Peter Seidel}, title = {{Hardware-Accelerated Rendering of Photo Hulls}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {This paper presents an efficient hardware-accelerated method for novel view synthesis from a set of images or videos. Our method is based on the photo hull representation, which is the maximal photo-consistent shape. We avoid the explicit reconstruction of photo hulls by adopting a view-dependent plane-sweeping strategy. From the target viewpoint slicing planes are rendered with reference views projected onto them. Graphics hardware is exploited to verify the photo-consistency of each rasterized fragment. Visibilities with respect to reference views are properly modeled, and only photo-consistent fragments are kept and colored in the target view. We present experiments with real images and animation sequences. Thanks to the more accurate shape of the photo hull representation, our method generates more realistic rendering results than methods based on visual hulls. Currently, we achieve rendering frame rates of 2–3 fps. Compared to a pure software implementation, the performance of our hardware-accelerated method is approximately 7 times faster.Categories and Subject Descriptors (according to ACM CCS): CR Categories: I.3.3 [Computer Graphics]: Picture/Image Generation; I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism.}, year = {2004}, pages = {635--642}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp635-642.pdf} } @article{CGFv23i3pp643-652:2004, author = {Jainhua Wu and Leif Kobbelt}, title = {{Optimized Sub-Sampling of Point Sets for Surface Splatting}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Using surface splats as a rendering primitive has gained increasing attention recently due to its potential for high-performance and high-quality rendering of complex geometric models. However, as with any other rendering primitive, the processing costs are still proportional to the number of primitives that we use to represent a given object. This is why complexity reduction for point-sampled geometry is as important as it is, e.g., for triangle meshes. In this paper we present a new sub-sampling technique for dense point clouds which is specifically adjusted to the particular geometric properties of circular or elliptical surface splats. A global optimization scheme computes an approximately minimal set of splats that covers the entire surface while staying below a globally prescribed maximum error toleranceΔ. Since our algorithm converts pure point sample data into surface splats with normal vectors and spatial extent, it can also be considered as a surface reconstruction technique which generates a hole-free piecewise linearC−1continuous approximation of the input data. Here we can exploit the higher flexibility of surface splats compared to triangle meshes. Compared to previous work in this area we are able to obtain significantly lower splat numbers for a given error tolerance.}, year = {2004}, pages = {643--652}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp643-652.pdf} } @article{CGFv23i3pp653-660:2004, author = {Gael Guennebaud and Loic Barthe and Mathias Paulin}, title = {{Deferred Splatting}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {In recent years it has been shown that, above a certain complexity, points become the most efficient rendering primitives. Although the programmability of the lastest graphics hardware allows efficient implementation of high quality surface splatting algorithms, their performance remains below those obtained with simpler point based rendering algorithms when they are used for scenes of high complexity. In this paper, our goal is to apply high quality point based rendering algorithms on complex scenes. For this purpose, we show how to take advantage of temporal coherency in a very accurate hardware accelerated point selection algorithm allowing the expensive computations to be peformed only on visible points. Our algorithm is based on a multi-pass hardware accelerated EWA splatting. It is also suitable for any rendering application since no pre-process is needed and no assumption is made on the data structure. In addition, we briefly discuss the association of our method with other existing culling techniques and optimization for particular applications.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Viewing algorithms}, year = {2004}, pages = {653--660}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp653-660.pdf} } @article{CGFv23i3pp661-668:2004, author = {S{\"o}ren Grimm and Stefan Bruckner and Armin Kanitsar and Eduard Gr{\"o}ller}, title = {{VOTS: VOlume doTS as a Point-Based Representation of Volumetric Data}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {We present Volume dots (Vots), a new primitive for volumetric data modelling, processing, and rendering. Vots are a point-based representation of volumetric data. An individual Vot is specified by the coefficients of a Taylor series expansion, i.e. the function value and higher order derivatives at a specific point. A Vot does not only represent a single sample point, it represents the underlying function within a region. With the Vots representation we have a more intuitive and high-level description of the volume data. This allows direct analytical examination and manipulation of volumetric datasets. Vots enable the representation of the underlying scalar function with specified precision. User-centric importance sampling is also possible, i.e., unimportant volume parts are still present but represented with just very few Vots. As proof of concept, we show Maximum Intensity Projection based on Vots.Categories and Subject Descriptors (according to ACM CCS): I.3.6 [Computer Graphics]: Graphics Data Structures and Data Types}, year = {2004}, pages = {661--668}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp661-668.pdf} } @article{CGFv23i3pp669-676:2004, author = {Volker Blanz and Kristina Scherbaum and Thomas Vetter and Hans-Peter Seidel}, title = {{Exchanging Faces in Images}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Pasting somebody's face into an existing image with traditional photo retouching and digital image processing tools has only been possible if both images show the face from the same viewpoint and with the same illumination. However, this is rarely the case for given pairs of images. We present a system that exchanges faces across large differences in viewpoint and illumination. It is based on an algorithm that estimates 3D shape and texture along with all relevant scene parameters, such as pose and lighting, from single images. Manual interaction is reduced to clicking on a set of about 7 feature points, and marking the hairline in the target image. The system can be used for image processing, virtual try-on of hairstyles, and face recognition. By separating face identity from imaging conditions, our approach provides an abstract representation of images and a novel, high-level tool for image manipulation.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Animation}, year = {2004}, pages = {669--676}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp669-676.pdf} } @article{CGFv23i3pp677-686:2004, author = {Yang Wang and Xiaolei Huang and Chan-Su Lee and Song Zhang and Zhiguo Li and Dimitris Samaras and Dimitris Metaxas and Ahmed Elgammal and Peisen Huang}, title = {{High Resolution Acquisition, Learning and Transfer of Dynamic 3-D Facial Expressions}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {Synthesis and re-targeting of facial expressions is central to facial animation and often involves significant manual work in order to achieve realistic expressions, due to the difficulty of capturing high quality dynamic expression data. In this paper we address fundamental issues regarding the use of high quality dense 3-D data samples undergoing motions at video speeds, e.g. human facial expressions. In order to utilize such data for motion analysis and re-targeting, correspondences must be established between data in different frames of the same faces as well as between different faces. We present a data driven approach that consists of four parts: 1) High speed, high accuracy capture of moving faces without the use of markers, 2) Very precise tracking of facial motion using a multi-resolution deformable mesh, 3) A unified low dimensional mapping of dynamic facial motion that can separate expression style, and 4) Synthesis of novel expressions as a combination of expression styles. The accuracy and resolution of our method allows us to capture and track subtle expression details. The low dimensional representation of motion data in a unified embedding for all the subjects in the database allows for learning the most discriminating characteristics of each individual's expressions as that person's “expression style”. Thus new expressions can be synthesized, either as dynamic morphing between individuals, or as expression transfer from a source face to a target face, as demonstrated in a series of experiments.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Animation; I.3.5 [Computer Graphics]: Curve, surface, solid, and object representations; I.3.3 [Computer Graphics]: Digitizing and scanning; I.2.10 [Artificial intelligence]: Motion ; I.2.10 [Artificial intelligence]: Representations, data structures, and transforms; I.2.10 [Artificial intelligence]: Shape; I.2.6 [Artificial intelligence]: Concept learning}, year = {2004}, pages = {677--686}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp677-686.pdf} } @article{CGFv23i3pp687-695:2004, author = {Kyunggun Na and Moonryul Jung}, title = {{Hierarchical Retargetting of Fine Facial Motions}}, journal = {Computer Graphics Forum}, volume = {23}, number = {3}, abstract = {We present a novel technique for retargetting captured facial animation to new facial models. We use dense motion data that can express fine motions such as wrinkles. We use a normal mesh, which is a special multi-resolution mesh, to represent source and target models. A normal mesh is defined by the base mesh and sequence of normal offsets from it. Our retargetting consists of two steps: base mesh and detail mesh retargetting. For base mesh retargetting, we use an example-based technique to take advantage of the intuition of the user in specifying the similarity between source and target expressions. In detail mesh retargetting, the variations of normal offsets in the source mesh are hierarchically computed and transferred to the target mesh. Our retargetting scheme is able to produce robust and delicate results for unusual target models from highly detailed motion data.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three Dimensional Graphics and Realism - Animation; I.3.5 [Computer Graphics]: Computational Geometry and Object Modelling - hierarchy and geometric transformation, object hierarchy}, year = {2004}, pages = {687--695}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue3/v23i3pp687-695.pdf} } @article{CGFv23i4pp697-714:2004, author = {Chandrajit Bajaj and Insung Ihm and Jungki Min and Jinsang Oh}, title = {{SIMD Optimization of Linear Expressions for Programmable Graphics Hardware}}, journal = {Computer Graphics Forum}, volume = {23}, number = {4}, abstract = {The increased programmability of graphics hardware allows efficient graphical processing unit (GPU) implementations of a wide range of general computations on commodity PCs. An important factor in such implementations is how to fully exploit the SIMD computing capacities offered by modern graphics processors. Linear expressions in the form of , where A is a matrix, and and are vectors, constitute one of the most basic operations in many scientific computations. In this paper, we propose a SIMD code optimization technique that enables efficient shader codes to be generated for evaluating linear expressions. It is shown that performance can be improved considerably by efficiently packing arithmetic operations into four-wide SIMD instructions through reordering of the operations in linear expressions. We demonstrate that the presented technique can be used effectively for programming both vertex and pixel shaders for a variety of mathematical applications, including integrating differential equations and solving a sparse linear system of equations using iterative methods.}, year = {2004}, pages = {697--714}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue4/v23i4pp697-714.pdf} } @article{CGFv23i4pp715-725:2004, author = {Haitao Zhang and Feng Qiu and Arie Kaufman}, title = {{Fast Hybrid Approach for Texturing Point Models}}, journal = {Computer Graphics Forum}, volume = {23}, number = {4}, abstract = {We present three methods for texturing point models from sample textures. The first method, the point parameterization method, uses a fast distortion-bounded parameterization algorithm to flatten the point model's surface into one or more 2D patches. The sample texture is mapped onto these patches and alpha blending is used to minimize the discontinuity in the gaps between the patches. The second method is based on neighborhood matching where a color is assigned to each point by searching the best match within an irregular neighborhood. The hybrid method combines the former two methods, capitalizing on the advantages of both. The point parameterization method is used first to color most of the points, and the point neighborhood-matching method is then applied to the points belonging to the gaps between the parameterized patches to minimize the discontinuity. We opt for fast texture generation, while some discontinuities may appear in the gaps of anisotropic textures.}, year = {2004}, pages = {715--725}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue4/v23i4pp715-725.pdf} } @article{CGFv23i4pp727-739:2004, author = {S. Schein and G. Elber}, title = {{Placement of Deformable Objects}}, journal = {Computer Graphics Forum}, volume = {23}, number = {4}, abstract = {With the increasing complexity of photorealistic scenes, the question of building and placing objects in three-dimensional scenes is becoming ever more difficult. While the question of placement of rigid objects has captured the attention of researchers in the past, this work presents an intuitive and interactive scheme to properly place deformable objects with the aid of free-form deformation tools. The presented scheme can also be used to animate the locomotion of nonrigid objects, most noticeably animals, and adapt the motion to arbitrary terrain. The automatic construction of our free-form deformation tool is completely hidden from the end user, and hence, circumvents the difficulties typically faced in manipulating these deformation functions. Further, a precise bound on the error that is introduced by applying free-form deformations to polygonal models is presented, along with an almost-optimal adaptive refinement algorithm to achieve a certain accuracy in the mapping.}, year = {2004}, pages = {727--739}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue4/v23i4pp727-739.pdf} } @article{CGFv23i4pp741-759:2004, author = {M. Platings and A. M. Day}, title = {{Compression of Large-Scale Terrain Data for Real-Time Visualization Using a Tiled Quad Tree}}, journal = {Computer Graphics Forum}, volume = {23}, number = {4}, abstract = {The aim of the rapid world modeling project is to implement a system to visualize the topography of the entire world on consumer-level hardware. This presents a significant problem in terms of both storage requirements and rendering speed. This paper presents the ‘Tiled Quad Tree’, a technique and format for the storage of digital terrain models, to work as part of an integrated system for the visualization of global terrain data. We show how this format efficiently stores and compresses elevation data, in a way that allows the data to be read very rapidly from hard disk or similar storage medium, to facilitate real-time rendering. The results of compressing several distinct data sets are presented.}, year = {2004}, pages = {741--759}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue4/v23i4pp741-759.pdf} } @article{CGFv23i4pp761-781:2004, author = {Roland Schregle and Jan Wienold}, title = {{Physical Validation of Global Illumination Methods: Measurement and Error Analysis}}, journal = {Computer Graphics Forum}, volume = {23}, number = {4}, abstract = {In this paper, we present a physical validation of global illumination algorithms based on measurements from a simple experimental setup. The validation methodology emphasizes tractability and error minimization. To this end, we discuss issues such as the acquisition and accurate simulation of material bidirectional reflection distribution functions (BRDFs) and the light source distribution, as well as error analysis. In addition, we present a nearest-neighbor resampling technique for BRDFs and a simple method for extracting the light source distribution from digitized high dynamic range (HDR) images. Finally, we compare the measurements to a forward and backward raytracing solution (photon map and RADIANCE, respectively) in a set of case studies.}, year = {2004}, pages = {761--781}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue4/v23i4pp761-781.pdf} } @article{CGFv23i4pp783-797:2004, author = {Giuseppe Patane and Michela Spagnuolo and Bianca Falcidieno}, title = {{Para-Graph: Graph-Based Parameterization of Triangle Meshes with Arbitrary Genus}}, journal = {Computer Graphics Forum}, volume = {23}, number = {4}, abstract = {This paper describes a novel approach to the parameterization of triangle meshes representing 2-manifolds with an arbitrary genus. A topology-based decomposition of the shape is computed and used to segment the shape into primitives, which define a chart decomposition of the mesh. Then, each chart is parameterized using an extension of the barycentric coordinates method. The charts are all 0-genus and can be of three types only, depending on the number of boundary components. The chart decomposition and the parameterization are used to define a shape graph where each node represents one primitive and the arcs code the adjacency relationships between the primitives. Conical and cylindrical primitives are coded together with their skeletal lines that are computed from and aligned with their parameterization. The application of the parameterization approach to remeshing guarantees that extraordinary vertices are localized only where two patches share a boundary and they are not scattered on the whole surface.}, year = {2004}, pages = {783--797}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue4/v23i4pp783-797.pdf} } @article{CGFv23i4pp799-812:2004, author = {Raquel Urtasun and Pascal Glardon and Ronan Boulic and Daniel Thalmann and Pascal Fua}, title = {{Style-Based Motion Synthesis}}, journal = {Computer Graphics Forum}, volume = {23}, number = {4}, abstract = {Representing motions as linear sums of principal components has become a widely accepted animation technique. While powerful, the simplest version of this approach is not particularly well suited to modeling the specific style of an individual whose motion had not yet been recorded when building the database: it would take an expert to adjust the PCA weights to obtain a motion style that is indistinguishable from his. Consequently, when realism is required, the current practice is to perform a full motion capture session each time a new person must be considered. In this paper, we extend the PCA approach so that this requirement can be drastically reduced: for whole classes of cyclic and noncyclic motions such as walking, running or jumping, it is enough to observe the newcomer moving only once at a particular speed or jumping a particular distance using either an optical motion capture system or a simple pair of synchronized video cameras. This one observation is used to compute a set of principal component weights that best approximates the motion and to extrapolate in real-time realistic animations of the same person walking or running at different speeds, and jumping a different distance.}, year = {2004}, pages = {799--812}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue4/v23i4pp799-812.pdf} } @article{CGFv23i4pp813-823:2004, author = {M. B. Vieira and P. P. Martins and A. A. Araujo and M. Cord and S. Philipp-Foliguet}, title = {{Smooth Surface Reconstruction Using Tensor Fields as Structuring Elements}}, journal = {Computer Graphics Forum}, volume = {23}, number = {4}, abstract = {We propose a new strategy to estimate surface normal information from highly noisy sparse data. Our approach is based on a tensor field morphologically adapted to infer normals. It acts as a three-dimensional structuring element of smooth surfaces. Robust orientation inference for all input elements is performed by morphological operations using the tensor field. A general normal estimator is defined by combining the inferred normals, their confidences and the tensor field. This estimator can be used to directly reconstruct the surface or give input normals to other reconstruction methods. We present qualitative and quantitative results to show the behavior of the original methods and ours. A comparative discussion of these results shows the efficiency of our propositions.}, year = {2004}, pages = {813--823}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue4/v23i4pp813-823.pdf} } @article{CGFv23i4pp825-838:2004, author = {Antonio W. Vieira and Thomas Lewiner and Luiz Velho and Helio Lopes and Geovan Tavares}, title = {{Stellar Mesh Simplification Using Probabilistic Optimization}}, journal = {Computer Graphics Forum}, volume = {23}, number = {4}, abstract = {This paper proposes the stellar mesh simplification method, a fast implementation of the Four-Face Cluster (FFC) algorithm. In this method, a probabilistic optimization heuristic substitutes the priority queue of the original method, which results in a 40% faster algorithm with the same order of distortion. It extends naturally to a progressive and/or multiresolution scheme for combinatorial surfaces. This work also presents a simple way to encode the hierarchy of the resulting multiresolution meshes. This work also focuses on important aspects for the development of a practical and robust implementation of this simplification technique, and on the analysis of the influence of the parameters.}, year = {2004}, pages = {825--838}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue4/v23i4pp825-838.pdf} } @article{CGFv23i4ppi-i.pdf:2004, author = {David Duke and Roberto Scopigno}, title = {{Editorial}}, journal = {Computer Graphics Forum}, volume = {23}, number = {4}, abstract = {}, year = {2004}, pages = {i--i}, ISSN = {0167-7055}, publisher = {The Eurographics Association and Blackwell Publishing Ltd}, URL = {http://www.eg.org/EG/CGF/volume23/issue4/v23i4ppi-i.pdf.pdf} }