Volume 20 (2001)

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Valence-Driven Connectivity Encoding for 3D Meshes
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Alliez, Pierre; Desbrun, Mathieu
In this paper, we propose a valence-driven, single-resolution encoding technique for lossless compression of triangle mesh connectivity. Building upon a valence-based approach pioneered by Touma and Gotsman22 , we design a new valence-driven conquest for arbitrary meshes that always guarantees smaller compression rates than the original method. Furthermore, we provide a novel theoretical entropy study of our technique, hinting the optimality of the valence-driven approach. Finally, we demonstrate the practical efficiency of this approach (in agreement with the theoretical prediction) on a series of test meshes, resulting in the lowest compression ratios published so far, for both irregular and regular meshes, small or large.
Real-Time Volume Deformations
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Westermann, Rudiger; Rezk-Salama, Christof
Real-time free-form deformation tools are primarily based on surface or particle representations to allow for interactive modification and fast rendering of complex models. The efficient handling of volumetric representations, however, is still a challenge and has not yet been addressed sufficiently. Volumetric models, on the other hand, form an important class of representation in many applications. In this paper we present a novel approach to the real-time deformation of scalar volume data sets taking advantage of hardware supported 3D texture mapping. In a prototype implementation a modeling environment has been designed that allows for interactive manipulation of arbitrary parts of volumetric objects. In this way, any desired shape can be modeled and used subsequently in various applications. The underlying algorithms have wide applicability and can be exploited effectively for volume morphing and medical data processing.
Texture Mapping with Hard Constraints
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Eckstein, Ilya; Surazhsky, Vitaly; Gotsman, Craig
We show how to continuously map a texture onto a 3D triangle mesh when some of the mesh vertices are constrained to have given (u, v) coordinates. This problem arises frequently in interactive texture mapping applications and, to the best of our knowledge, a complete and efficient solution is not available. Our techniques always guarantee a solution by introducing extra (Steiner) vertices in the triangulation if needed. We show how to apply our methods to texture mapping in multi-resolution scenarios and image warping and morphing.
The John Lansdown Award
(Blackwell Publishers Ltd and the Eurographics Association., 2001) Jones, Huw; Willis, Phil
Guided Exploration with Dynamic Potential Fields: the Cubical Path System
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Beckhaus, Steffi; Ritter, Felix; Strothotte, Thomas
Exploring unknown models or scenes is a highly interactive and dynamic process. Systems for automatic presentation of models or scenes either require cinematographic rules, direct human interaction, framesets, or pre-calculation of paths to a known goal. In this paper we present a system which can deal with rapidly changing user interest in objects of a scene or model as well as with dynamic models and changes of the camera position introduced interactively by the user or through cuts. We describe CubicalPath, a new potential field-based camera control system that helps with the exploration of virtual environments.
Spatial Patches - A Primitive for 3D Model Representation
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Ivanov, D.; Kuzmin, Ye.
The commonly used solution for real-life 3D model representation is polygonal spatially consistent geometry, with texture, and, optionally, bump or displacement maps attached. Although the idea of displacement mapping is well known, there are just a few approaches to its efficient implementation. In this paper we develop a technique that allows for efficient representation and rendering of 3D models by getting a new angle on the displacement mapping concept. We introduce a new primitive that is defined as the range image of a small part of the model's surface; therefore, it is called a spatial patch. The whole model is just a collection of patches with no connectivity information between them. Such a representation can be directly acquired by 3D scanning machinery, and stored in a compact uniform form. It also allows for efficient visualization, which is the major focus of this paper. Thus, we present the logical structure of a rendering unit based on conventional z-buffering, and discuss the involved algorithms in detail. These algorithms benefit from modern features of computing units for which we believe the proposed technique can be used in a wide range of applications dealing with real-life 3D data.
A Recursive Subdivision Algorithm for Piecewise Circular Spline
(Blackwell Publishers Ltd and the Eurographics Association., 2001) Nasri, Ahmad H.; Van Overveld, C. W. A. M.; Wyvill, Brian
We present an algorithm for generating a piecewise G1 circular spline curve from an arbitrary given control polygon. For every corner, a circular biarc is generated with each piece being parameterized by its arc length. This is the first subdivision scheme that produces a piecewise biarc curve that can interpolate an arbitrary set of points. It is easily adopted in a recursive subdivision surface scheme to generate surfaces with circular boundaries with pieces parameterized by arc length, a property not previously available. As an application, a modified version of Doo-Sabin subdivision algorithm is outlined making it possible to blend a subdivision surface with other surfaces having circular boundaries such as cylinders.
Visualizing Stars and Emission Nebulas
(Blackwell Publishers Ltd and the Eurographics Association., 2001) Nadeau, David R.; Genetti, Jon D.; Napear, Steve; Pailthorpe, Bernard; Emmart, Carter; Wesselak, Erik and Davidson, Dennis
We describe star and nebula visualization techniques used to create a 3D volumetric visualization of the Orion Nebula. The nebula's ionization layer is modeled first as a surface model, derived from infrared and visible light observations. The surface model is imported into a volume scene graph-based visualization system that uses procedural volume modeling to simulate the nebula's emissive gas layers. Additional scene graphs model proplyds and shock fronts within the nebula. Stars are rendered using Gaussian spots that are attenuated with distance. Finally, eighty-six separate volumes are voxelized from these scene graphs, then simultaneously volume rendered.
Incremental Updates for Rapid Glossy Global Illumination
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Granier, Xavier; Drettakis, George
We present an integrated global illumination algorithm including non-diffuse light transport which can handle complex scenes and enables rapid incremental updates. We build on a unified algorithm which uses hierarchical radiosity with clustering and particle tracing for diffuse and non-diffuse transport respectively. We present a new algorithm which chooses between reconstructing specular effects such as caustics on the diffuse radiosity mesh, or special purpose caustic textures, when high frequencies are present. Algorithms are presented to choose the resolution of these textures and to reconstruct the high-frequency non-diffuse lighting effects. We use a dynamic spatial data structure to restrict the number of particles re-emitted during the local modifications of the scene. By combining this incremental particle trace with a line-space hierarchy for incremental update of diffuse illumination, we can locally modify complex scenes rapidly. We also develop an algorithm which, by permitting slight quality degradation during motion, achieves quasi-interactive updates. We present an implementation of our new method and its application to indoors and outdoors scenes.
Visual Perception in Realistic Image Synthesis
(Blackwell Publishers Ltd and the Eurographics Association, 2001) McNamara, Ann
Realism is often a primary goal in computer graphics imagery, and we strive to create images that are perceptually indistinguishable from an actual scene. Rendering systems can now closely approximate the physical distribution of light in an environment. However, physical accuracy does not guarantee that the displayed images will have authentic visual appearance. In recent years the emphasis in realistic image synthesis has begun to shift from the simulation of light in an environment to images that look as real as the physical environment they portray. In other words the computer image should be not only physically correct but also perceptually equivalent to the scene it represents. This implies aspects of the Human Visual System (HVS) must be considered if realism is required. Visual perception is employed in many different guises in graphics to achieve authenticity. Certain aspects of the visual system must be considered to identify the perceptual effects that a realistic rendering system must achieve in order to reproduce effectively a similar visual response to a real scene. This paper outlines the manner in which knowledge about visual perception is increasingly appearing in state-of-the-art realistic image synthesis. After a brief overview of the HVS, this paper is organized into four sections, each exploring the use of perception in realistic image synthesis, each with slightly different emphasis and application. First, Tone Mapping Operators, which attempt to map the vast range of computed radiance values to the limited range of display values, are discussed. Then perception based image quality metrics, which aim to compare images on a perceptual rather than physical basis, are presented. These metrics can be used to evaluate, validate and compare imagery. Thirdly, perception driven rendering algorithms are described. These algorithms focus on embedding models of the HVS directly into global illumination computations in order to improve their efficiency. Finally, techniques for comparing computer graphics imagery against the real world scenes they represent are discussed.
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.
Eurographics
(Blackwell Publishers Ltd and the Eurographics Association., 2001)
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.
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.
Visualization of Isosurfaces with Parametric Cubes
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Mora, B.; Jessel, J.P.; Caubet, R.
To render images from volume datasets, an interpolation method also called reconstruction is needed. The level of details of the resultant image closely depends on the filter used for reconstruction. We propose here a new filter producing C1 continue surfaces. The provided image quality is better than current high-quality algorithms, like splatting or trilinear raycasting, where tiny details are often eliminated. In contrast with other studied high quality filters that are practically unusable, our algorithm has been implemented interactively on a modest platform thanks to an efficient implementation using parametric cubes. We also demonstrate the interest of a min-max octree in the visualization of isosurfaces interactively thresholded.
A Unified Subdivision Scheme for Polygonal Modeling
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Maillot, Jerome; Stam, Jos
Subdivision rules have traditionally been designed to generate smooth surfaces from polygonal meshes. In this paper we propose to employ subdivision rules as a polygonal modeling tool, specifically to add additional level of detail to meshes. However, existing subdivision schemes have several undesirable properties making them ill suited for polygonal modeling. In this paper we propose a general set of subdivision rules which provides users with more control over the subdivision process. Most existing subdivision schemes are special cases. In particular, we provide subdivision rules which blend approximating spline based schemes with interpolatory ones. Also, we generalize subdivision to allow any number of refinements to be performed in a single step.
Tensor Topology Tracking: A Visualization Method for Time-Dependent 2D Symmetric Tensor Fields
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Tricoche, X.; Scheuermann, G.; Hagen, H.
Topological methods produce simple and meaningful depictions of symmetric, second order two-dimensional tensor fields. Extending previous work dealing with vector fields, we propose here a scheme for the visualization of time-dependent tensor fields. Basic notions of unsteady tensor topology are discussed. Topological changes - known as bifurcations - are precisely detected and identified by our method which permits an accurate tracking of degenerate points and related structures.
Rendering Natural Waters
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Premoze, Simon; Ashikhmin, Michael
Creating and rendering realistic water is one of the most daunting tasks in computer graphics. Realistic rendering of water requires that the sunlight and skylight illumination are correct, the water surface is modeled accurately and that the light transport within water body is properly handled. This paper describes a method for wave generation on a water surface using a physically-based approach. The wave generation uses data from the oceanographical observations and it is controlled by intuitive parameters such as wind speed and wind direction. The optical behavior of the water surfaces is complex but is well-described in the ocean science literature. We present a simple and intuitive light transport approach that is easy to use for many different water types such as deep ocean water, muddy coastal water, and fresh water bodies. We demonstrate our model for a number of water and atmospheric conditions.
Fast and Controllable Simulation of the Shattering of Brittle Objects
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Smith, Jeffrey; Witkin, Andrew; Baraff, David
We present a method for the rapid and controllable simulation of the shattering of brittle objects under impact. An object is represented as a set of point masses connected by distance-preserving linear constraints. This use of constraints, rather than stiff springs, gains us a significant advantage in speed while still retaining fine control over the fracturing behavior. The forces exerted by these constraints during impact are computed using Lagrange multipliers. These constraint forces are then used to determine when and where the object will break, and to calculate the velocities of the newly created fragments. We present the details of our technique together with examples illustrating its use.An earlier version of this paper was presented at Graphics Interface 2000, held in Montreal, Canada.
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.

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