Issue 3

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https://diglib.eg.org/handle/10.2312/101

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Now showing 1 - 20 of 57

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.
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.
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.
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.
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.
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.
A Dynamic Motion Control Technique for Human-like Articulated Figures
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Oshita, Masaki; Makinouchi, Akifumi
This paper presents a dynamic motion control technique for human-like articulated figures in a physically based character animation system. This method controls a figure such that the figure tracks input motion specified by a user. When environmental physical input such as an external force or a collision impulse are applied to the figure, this method generates dynamically changing motion in response to the physical input. We have introduced comfort and balance control to compute the angular acceleration of the figure's joints. Our algorithm controls the several parts of a human-like articulated figure separetely through the minimum number of degrees-of-freedom. Using this approach, our algorithm simulates realistic human motions at efficient computational cost. Unlike existing dynamic simulation systems, our method assumes that input motion is already realistic, and is aimed at dynamically changing the input motion in real-time only when unexpected physical input is applied to the figure. As such, our method works efficiently in the framework of current computer games.
Fast Cloth Animation on Walking Avatars
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Vassilev, T.; Spanlang, B.; Chrysanthou, Y.
This paper describes a fast technique for animating clothing on walking humans. It exploits a mass-spring cloth model but applies a new velocity directional modification approach to overcome its super-elasticity. The algorithm for cloth-body collision detection and response is based on image-space interference tests, unlike the existing ones that use object-space checks. The modern workstations' graphics hardware is used not only to compute the depth maps of the body but also to interpolate the body normal vectors and velocities of each vertex. As a result the approach is very fast and makes it possible to produce animation at a rate of three to four frames per second.
Fast simulation and rendering techniques for fluid objects
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Kunimatsu, A.; Watanabe, Y.; Fujii, H.; Saito, T.; Hiwada, K.; Takahashi, T.; Ueki, H.
Movies with actions and light effects of fluid objects are aesthetically pleasing and interesting. Until now, the calculation costs of simulation and rendering of fluid objects have been very high. Using a modern PC system and appropriate methods, we achieved a time of 10-20 seconds per frame for this application. Our system uses a full Navier-Stokes equation solver with uniform Eulerian mesh, marching cube isosurface techniques, Catmull-Clark subdivision surface techniques, ray tracing techniques on each vertex and conventional polygon base rendering by HW accelerator. In this paper, we describe the components of our system and the reasons for choosing them. By measuring CPU times of each process for some movie scenes of fluid objects, we evaluate this system. We consider what factors are important for creating movies of fluid objects with short TAT.
Fast Visualization of Object Contours by Non-Photorealistic Volume Rendering
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Csebfalvi, Balazs; Mroz, Lukas; Hauser, Helwig; Konig, Andreas; Groller, Eduard
In this paper we present a fast visualization technique for volumetric data, which is based on a recent non-photorealistic rendering technique. Our new approach enables alternative insights into 3D data sets (compared to traditional approaches such as direct volume rendering or iso-surface rendering). Object contours, which usually are characterized by locally high gradient values, are visualized regardless of their density values. Cumbersome tuning of transfer functions, as usually needed for setting up DVR views is avoided. Instead, a small number of parameters is available to adjust the non-photorealistic display. Based on the magnitude of local gradient information as well as on the angle between viewing direction and gradient vector, data values are mapped to visual properties (color, opacity), which then are combined to form the rendered image (MIP is proposed as the default compositing stragtegy here). Due to the fast implementation of this alternative rendering approach, it is possible to interactively investigate the 3D data, and quickly learn about internal structures. Several further extensions of our new approach, such as level lines are also presented in this paper.
Feature Sensitive Remeshing
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Vorsatz, J.; Rossl, C.; Kobbelt, L. P.; Seidel, H.-P.
Remeshing artifacts are a fundamental problem when converting a given geometry into a triangle mesh. We propose a new remeshing technique that is sensitive to features. First, the resolution of the mesh is iteratively adapted by a global restructuring process which additionally optimizes the connectivity. Then a particle system approach evenly distributes the vertices across the original geometry. To exactly find the features we extend this relaxation procedure by an effective mechanism to attract the vertices to feature edges. The attracting force is imposed by means of a hierarchical curvature field and does not require any thresholding parameters to classify the features.
Flexible Image-Based Photometric Reconstruction using Virtual Light Sources
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Gibson, Simon; Howard, Toby; Hubbold, Roger
Photometric reconstruction is the process of estimating the illumination and surface reflectance properties of an environment, given a geometric model of the scene and a set of photographs of its surfaces. For mixed-reality applications, such data is required if synthetic objects are to be correctly illuminated or if synthetic light sources are to be used to re-light the scene. Current methods of estimating such data are limited in the practical situations in which they can be applied, due to the fact that the geometric and radiometric models of the scene which are provided by the user must be complete, and that the position (and in some cases, intensity) of the light sources must also be specified a-priori. In this paper, a novel algorithm is presented which overcomes these constraints, and allows photometric data to be reconstructed in less restricted situations. This is achieved through the use of virtual light sources which mimic the effect of direct illumination from unknown luminaires, and indirect illumination reflected off unknown geometry. The intensity of these virtual light sources and the surface material properties are estimated using an iterative algorithm which attempts to match calculated radiance values to those observed in photographs. Results are presented for both synthetic and real scenes that show the quality of the reconstructed data and its use in off-line mixed-reality applications.
Generalized Stochastic Sampling Method for Visualization and Investigation of Implicit Surfaces
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Tanaka, Satoshi; Shibata, Akihiro; Yamamoto, Hiroaki; Kotsuru, Hisakiyo
Recently we proposed the stochastic sampling method (SSM), which can numerically generate sample points on complicated implicit surfaces quickly and uniformly. In this paper we generalize the method in two aspects: (1) We introduce two kinds of boundary conditions, so that we can sample a finite part of an open surface spreading infinitely. (2) We generalize the stochastic differential equation used in the SSM, so that its solutions can satisfy plural constraint conditions simultaneously. The first generalization enables us to visualize cut views of open surfaces. The second generalization enables us to visualize intersections of static and moving implicit surfaces, which leads to detailed investigation of intersections and other interesting applications such as visualization of contour maps.
Global Illumination as a Combination of Continuous Random Walk and Finite-Element Based Iteration
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Szirmay-Kalos, Laszlo; Csonka, Ferenc; Antal, Gyorgy
The paper introduces a global illumination method that combines continuous and finite-element approaches, pre-serving the speed of finite-element based iteration and the accuracy of continuous random walks. The basic idea is to decompose the radiance function to a finite-element component that is only a rough estimate and to a difference component that is obtained by Monte-Carlo techniques. Iteration and random walk are handled uniformly in the framework of stochastic iteration. This uniform treatment allows the finite-element component to be built up adap-tively aiming at minimizing the Monte-Carlo component. The method is also suited for interactive walkthrough animation in glossy scenes since when the viewpoint changes, only the small Monte-Carlo component needs to be recomputed.

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