Volume 20 (2001)

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3D Metamorphosis Between Different Types of Geometric Models
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Breen, David E.; Mauch, Sean; Whitaker, Ross T.; Mao, Jia
We present a powerful morphing technique based on level set methods, that can be combined with a variety of scan conversion/model processing techniques. Bringing these techniques together creates a general morphing approach that allows a user to morph a number of geometric model types in a single animation. We have developed techniques for converting several types of geometric models (polygonal meshes, CSG models and MRI scans) into distance volumes, the volumetric representation required by our level set morphing approach. The combination of these two capabilities allows a user to create a morphing sequence regardless of the model type of the source and target objects, freeing him/her to use whatever model type is appropriate for a particular animation.
Accurate and Fast Proximity Queries Between Polyhedra Using Convex Surface Decomposition
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Ehmann, Stephen A.; Lin, Ming C.
The need to perform fast and accurate proximity queries arises frequently in physically-based modeling, simulation, animation, real-time interaction within a virtual environment, and game dynamics. The set of proximity queries include intersection detection, tolerance verification, exact and approximate minimum distance computation, and (disjoint) contact determination. Specialized data structures and algorithms have often been designed to perform each type of query separately. We present a unified approach to perform any of these queries seamlessly for general, rigid polyhedral objects with boundary representations which are orientable 2-manifolds. The proposed method involves a hierarchical data structure built upon a surface decomposition of the models. Furthermore, the incremental query algorithm takes advantage of coherence between successive frames. It has been applied to complex benchmarks and compares very favorably with earlier algorithms and systems.
Adaptive Implicit Surface Polygonization Using Marching Triangles
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Akkouche, Samir; Galin, Eric
This paper presents several improvements to the marching triangles algorithm for general implicit surfaces. The original method generates equilateral triangles of constant size almost everywhere on the surface. We present several modifications to adapt the size of the triangles to the curvature of the surface. As cracks may arise in the resulting polygonization, we propose a specific crack-closing method invoked at the end of the mesh growing step. Eventually, we show that the marching triangles can be used as an incremental meshing technique in an interactive modeling environment. In contrast to existing incremental techniques based on spatial subdvision, no extra data-structure is needed to incrementally edit skeletal implicit surfaces, which saves both memory and computation time.
An Adaptive Method for Indirect Illumination Using Light Vectors
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Serpaggi, Xavier; Peroche, Bernard
In computer graphics, several phenomema need to be taken into account when it comes to the field of photo-realism. One of the most relevant is obviously the notion of global, and more precisely indirect, illumination. In "classical" ray-tracing if you are not under the light, then you are in a shadow. A great amount of work has been carried out which proposes ray-tracing based solutions to take into account the fact that "there is a certain amount of light in shadows". All of these methods carry the same weaknesses: high computation time and a lot of parameters you need to manage to get something out of the method. This paper proposes a generic computation method of indirect illumination based on Monte Carlo sampling and on the sequential analysis theory, which is faster and more automatic than classical methods.
Adaptive Nonlinear Finite Elements for Deformable Body Simulation Using Dynamic Progressive Meshes
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Wu, Xunlei; Downes, Michael S.; Goktekin, Tolga; Tendick, Frank
Realistic behavior of deformable objects is essential for many applications such as simulation for surgical training. Existing techniques of deformable modeling for real time simulation have either used approximate methods that are not physically accurate or linear methods that do not produce reasonable global behavior. Nonlinear finite element methods (FEM) are globally accurate, but conventional FEM is not real time. In this paper, we apply nonlinear FEM using mass lumping to produce a diagonal mass matrix that allows real time computation. Adaptive meshing is necessary to provide sufficient detail where required while minimizing unnecessary computation. We propose a scheme for mesh adaptation based on an extension of the progressive mesh concept, which we call dynamic progressive meshes.
Adaptive Representation of Specular Light
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Briere, Normand; Poulin, Pierre
Caustics produce beautiful and intriguing illumination patterns. However, their complex behavior makes them difficult to simulate accurately in all but the simplest configurations. To capture their appearance, we present an adaptive approach based upon light beams. Exploiting the coherence between the light rays forming a beam greatly reduces the number of samples required for precise illumination reconstruction. The beams characterize the light distribution due to interactions with specular surfaces in 3D space. They thus allow for the treatment of illumination within single-scattering participating media. A hierarchical structure enclosing the light beams possesses inherent properties to detect efficiently all beams reaching any 3D point, to adapt itself according to illumination effects in the final image, and to reduce memory consumption via caching.
Alain Fournier, 1943-2000 An Appreciation
(Blackwell Publishers Ltd and the Eurographics Association., 2001) Fiume, E.
Animation of Soap Bubble Dynamics, Cluster Formation and Collision
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Durikovic, Roman
What is happening when a soap bubble floats on the air? How do bubbles coalesce to form beautiful three-dimensional clusters? The physical-based model and animation described herein provide the answers. This paper deals with a complete computer simulation of soap bubbles from a dynamic perspective, which should prove to be of great interest to physicists and mathematicians. We discuss the dynamic formation of irregular bubble clusters and how to animate bubbles. The resulting model takes into account surface tension, film elasticity, and shape variations due to gravity and external wind forces.
Antialiasing of Environment Maps
(Blackwell Publishers Ltd and the Eurographics Association., 2001) Schilling, Andreas
Environment maps, like texture maps or any other maps consisting of discretely stored data have to be properly filtered, if they are being resampled in the process of rendering an image. For environment maps, this is especially important, as the sampling rate is subject to extreme changes due to the curvature of the reflecting surfaces. However, for the same reason, the antialiasing is especially difficult to perform, as the sampling rate has to be determined for each pixel. We introduce a method to perform this calculation and determine the parameters for anisotropic filtering of the environment map. Instead of the BRDF, we employ roughness pyramids to account for the properties of the reflecting surface. The principles that are used to perform this antialiasing can be applied for antialiasing reflected textures in general e.g. in ray tracing.
Are Points the Better Graphics Primitives?
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Gross, Markus
Since the early days of graphics the computer based representation of three-dimensional geometry has been one of the core research fields. Today, various sophisticated geometric modelling techniques including NURBS or implicit surfaces allow the creation of 3D graphics models with increasingly complex shape. In spite of these methods the triangle has survived over decades as the king of graphics primitives meeting the right balance between descriptive power and computational burden. As a consequence, today's consumer graphics hardware is heavily tailored for high performance triangle processing. In addition, a new generation of geometry processing methods including hierarchical representations, geometric filtering, or feature detection fosters the concept of triangle meshes for graphics modelling.Unlike triangles, points have amazingly been neglected as a graphics primitive. Although being included in APIs since many years, it is only recently that point samples experience a renaissance in computer graphics. Conceptually, points provide a mere discretization of geometry without explicit storage of topology. Thus, point samples reduce the representation to the essentials needed for rendering and enable us to generate highly optimized object representations. Although the loss of topology poses great challenges for graphics processing, the latest generation of algorithms features high performance rendering, point/pixel shading, anisotropic texture mapping, and advanced signal processing of point sampled geometry.This talk will give an overview of how recent research results in the processing of triangles and points are changing our traditional way of thinking of surface representations in computer graphics - and will discuss the question: Are Points the Better Graphics Primitives?
Artist-Directed Inverse-Kinematics Using Radial Basis Function Interpolation
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Rose III, Charles F.; Sloan, Peter-Pike J.; Cohen, Michael F.
One of the most common tasks in computer animation is inverse-kinematics, or determining a joint configuration required to place a particular part of an articulated character at a particular location in global space. Inverse-kinematics is required at design-time to assist artists using commercial 3D animation packages, for motion capture analysis, and for run-time applications such as games.We present an efficient inverse-kinematics methodology based on the interpolation of example motions and positions. The technique is demonstrated on a number of inverse-kinematics positioning tasks for a human figure. In addition to simple positioning tasks, the method provides complete motion sequences that satisfy an inverse-kinematic goal. The interpolation at the heart of the algorithm allows an artist's influence to play a major role in ensuring that the system always generates plausible results. Due to the lightweight nature of the algorithm, we can position a character at extremely high frame rates, making the technique useful for time-critical run-time applications such as games.
Automatic Lighting Design using a Perceptual Quality Metric
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Shacked, Ram; Lischinski, Dani
Lighting has a crucial impact on the appearance of 3D objects and on the ability of an image to communicate information about a 3D scene to a human observer. This paper presents a new automatic lighting design approach for comprehensible rendering of 3D objects. Given a geometric model of a 3D object or scene, the material properties of the surfaces in the model, and the desired viewing parameters, our approach automatically determines the values of various lighting parameters by optimizing a perception-based image quality objective function. This objective function is designed to quantify the extent to which an image of a 3D scene succeeds in communicating scene information, such as the 3D shapes of the objects, fine geometric details, and the spatial relationships between the objects.Our results demonstrate that the proposed approach is an effective lighting design tool, suitable for users without expertise or knowledge in visual perception or in lighting design.
A Camera Engine for Computer Games: Managing the Trade-Off Between Constraint Satisfaction and Frame Coherence
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Halper, Nicolas; Helbing, Ralf; Strothotte, Thomas
Many computer games treat the user in the "1st person" and bind the camera to his or her view. More sophistication in a game can be achieved by enabling the camera to leave the users' viewpoint. This, however, requires new methods for automatic, dynamic camera control. In this paper we present methods and tools for such camera control. We emphasize guiding camera control by constraints; however, optimal constraint satisfaction tends to lead to the camera jumping around too much. Thus, we pay particular attention to a trade-off between constraint satisfaction and frame coherence. We present a new algorithm for dynamic consideration of the visibility of objects which are deemed to be important in a given game context.
Coarse-to-fine surface simplification with geometric guarantees
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Boissonnat, Jean-Daniel; Cazals, Frederic
Let PC be a 3D point cloud and ? be a positive value called tolerance. We aim at constructing a triangulated surface S based on a subset PCU of PC such that all the points in PCL=PC?PCU are at distance at most ? from a facet of S. (PCU and PCL respectively stand for Point Cloud Used and Point Cloud Left.) We call this problem simplification with geometric guarantees.This paper presents a new framework to simplify with geometric guarantees. The approach relies on two main ingredients. First an oracle providing information on the surface being reconstructed even though the triangulated surface itself has not been computed. Second, a reconstruction algorithm providing incremental updates of the reconstructed surface, as well as a fast point-to-triangles distance computation. The oracle is used to guess a subset of the point cloud from which a triangulated surface is reconstructed. It relies on an implicit surface the triangulated surface is an approximation of, and is therefore available before the triangle mesh. The point-to-triangles distance computation and the local updates are then invoked to insert new vertices until the tolerance is met.We also present a detailed experimental study which shows the efficiency of the simplification process both in terms of simplification rate and running time.To the best of our knowledge, this algorithm is the first one performing coarse-to-fine surface simplification with geometric guarantees.
Constrained Fairing for Meshes
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Liu, Xinguo; Bao, Hujun; Heng, PhengAnn; Wong, TienTsin; Peng, Qunsheng
In this paper, we present a novel fairing algorithm for the removal of noise from uniform triangular meshes without shrinkage and serious distortion. The key feature of this algorithm is to keep all triangle centers invariant at each smoothing step by including some constraints in the energy minimization functional. The constrained functional is then minimized efficiently using an iterative method. Further, we apply this smoothing technique to a multiresolution representation to remove arbitrary levels of detail. A volume-preserving decimation algorithm is presented to generate the multiresolution representation. The experimental results demonstrate the combined algorithm's stability and efficiency.
Control of Feature-point-driven Facial Animation Using a Hypothetical Face
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Su, Ming-Shing; Ko, Ming-Tat; Cheng, Kuo-Young
A new approach to the generation of a feature-point-driven facial animation is presented. In the proposed approach, a hypothetical face is used to control the animation of a face model. The hypothetical face is constructed by connecting some predefined facial feature points to create a net so that each facet of the net is represented by a Coon's surface. Deformation of the face model is controlled by changing the shape of the hypothetical face, which is performed by changing the locations of feature points and their tangents. Experimental results show that this hypothetical-face-based method can generate facial expressions which are visually almost identical to those of a real face.
CP3: Robust, Output-sensitive Display of Convex Polyhedra in Scanline Mode
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Barkan, Ella; Gordon, Dan
A new technique is developed for displaying disjoint convex polyhedra. The method has the following properties: It is output-sensitive, displays the objects in scanline mode, and it is naturally robust. There is no complex data structure uniting the different polyhedra, so dynamic insertions and deletions are simple. Its robustnes is based on a novel method of comparing depths by representative "axes" of objects instead of surfaces. The method is based on two extensions of the "critical-points" method for polygon scan conversion: One extension allows the efficient display of planar graphs in scanline mode, and another extension is into the third dimension. Test runs indicate that it compares extremely favorably with other methods that operate in scanline mode, as well as with standard software and hardware techniques of medium-level workstations.
Detection of Salient Curvature Features on Polygonal Surfaces
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Watanabe, Kouki; Belyaev, Alexander G.
We develop an approach for stable detection of perceptually salient curvature features on surfaces approximated by dense triangle meshes. The approach explores an "area degenerating" effect of the focal surface near its singularities and combines together a new approximations of the mean and Gaussian curvatures, nonlinear averaging of curvature maps, histogram-based curvature extrema filtering, and an image processing skeletonization procedure adapted for triangular meshes. Finally we use perceptually significant curvature extrema triangles to enhance the Garland-Heckbert mesh decimation method.
Displacement Mapping using Scan Conversion Hardware Architectures
(Blackwell Publishers Ltd and the Eurographics Association., 2001) Doggett, Michael; Kugler, Anders; Strasser, Wolfgang
This paper presents a novel algorithm and architectures for perspective correct displacement of the surface geometry of a polygonal model using a displacement map. This new displaced surface geometry is passed onto a traditional rendering pipeline. The algorithm uses a multiple pass approach in which the geometry is displaced in the first pass and then the displaced geometry is rendered. The significant features of the algorithm are that the surface is displaced after its triangle mesh is transformed into screen space and that it uses only bi-linear interpolation for calculating the displaced geometry allowing a cheap incremental scan-line implementation. A hardware architecture based on this algorithm is presented along with possible alternative implementations. The technique presented here allows greater photorealism by using increased detail without an increase in bandwidth for geometry or calculation time for transformation.
Drawing for Illustration and Annotation in 3D
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Bourguignon, David; Cani, Marie-Paule; Drettakis, George
We present a system for sketching in 3D, which strives to preserve the degree of expression, imagination, and simplicity of use achieved by 2D drawing. Our system directly uses user-drawn strokes to infer the sketches representing the same scene from different viewpoints, rather than attempting to reconstruct a 3D model. This is achieved by interpreting strokes as indications of a local surface silhouette or contour. Strokes thus deform and disappear progressively as we move away from the original viewpoint. They may be occluded by objects indicated by other strokes, or, in contrast, be drawn above such objects. The user draws on a plane which can be positioned explicitly or relative to other objects or strokes in the sketch. Our system is interactive, since we use fast algorithms and graphics hardware for rendering. We present applications to education, design, architecture and fashion, where 3D sketches can be used alone or as an annotation of an existing 3D model.

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