EG2002

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Interactive High-Quality Volume Rendering with Flexible Consumer Graphics Hardware
(Eurographics Association, 2002) Engel, Klaus; Ertl, Thomas
Recently, the classic rendering pipeline in 3D graphics hardware has become flexible by means of programmable geometry engines and rasterization units. This development is primarily driven by the mass market of computer games and entertainment software, whose demand for new special effects and more realistic 3D environments induced a reconsideration of the once static rendering pipeline. Besides the impact on visual scene complexity in computer games, these advances in flexibility provide an enormous potential for new volume rendering algorithms. Thereby, they make yet unseen quality as well as improved performance for scientific visualization possible and allow to visualize hidden features contained within volumetric data. The goal of this report is to deliver insight into the new possibilities that programmable state-of-the-art graphics hardware offers to the field of interactive, high-quality volume rendering. We cover different slicing approaches for texture-based volume rendering, non-polygonal iso-surfaces, dot-product shading, environment-map shading, shadows, pre- and post-classification, multi-dimensional classification, high-quality filtering, pre-integrated classification and pre-integrated volume rendering, large volume visualization and volumetric effects.
3D Data Acquisition
(Eurographics Association, 2002) Scopigno,Roberto; Andujar, Carlos; Goesele,Michael; Lensch, Hendrik P. A.
3D scanners and image acquisition systems are rapidly becoming more affordable and allow to build highly accurate models of real 3D objects in a cost- and time-effective manner. This tutorial will present the potential of this technology, review the state of the art in model acquisition methods, and will discuss the 3D acquisition pipeline from physical acquisition until the final digital model. First, different scanning techniques such as time-of-flight or structured light approaches will briefly be presented. Other acquisition related issues including the design of the scanning studio will be discussed and evaluated. In the area of registration, we will consider both the problems of initially aligning individual scans, and of refining this alignment with variations of the Iterative Closest Point method. For scan integration and mesh reconstruction, we will compare various methods for computing interpolating and approximating surfaces. We will then look at various ways in which surface properties such as color and reflectance can be extracted from acquired imagery. Finally, we will examine techniques for the efficient management and rendering of very large, attribute-rich meshes, including methods for the construction of simplified triangle-based representation and sample-based rendering approaches.
Adaptive Compression of Human Animation Data
(Eurographics Association, 2002) Ahmed, Amr Adel Hassan; Hilton, Adrian; Mokhtarian, Farzin
In this paper we introduce an adaptive motion compression technique using the discrete wavelet transform. Based on the analysis of human animation data, and its frequency contents, the wavelet analysis is utilised to achieve motion compression. It has been found that even with high compression ratios (up to 86%), the compressed animation is visually very close to the original animation. This property is potentially useful for many areas of animation such as motion interpolation/blending and networked virtual environments. One of our motivations is that motion blending/interpolation between motion capture samples is one of the successful techniques for synthesis of novel realistic human animation. One of the major concerns of that method is the increase of the database size with the large number of samples required to synthesise a wide range of movements. Previous research has addressed this issue by trying to reduce the number of samples required for interpolation. The approach that we introduce in this paper is to reduce the individual sample’s size using compression. Integration of both these approaches promises to allow a realistic animation with reduced database size. In networked virtual environments and on-line games, compressing the animation data can reduce the transmission load and help in achieving real-time performance and realism with reduced cost.
Interactive Visualization with Programmable Graphics Hardware
(Eurographics Association, 2002) Ertl, Thomas
One of the main scientific goals of visualization is the development of algorithms and appropriate data models which facilitate interactive visual analysis and direct manipulation of the increasingly large data sets which result from simulations running on massive parallel computer systems, from measurements employing fast highresolution sensors, or from large databases and hierarchical information spaces. This task can only be achieved with the optimization of all stages of the visualization pipeline: filtering, compression, and feature extraction of the raw data sets, adaptive visualization mappings which allow the users to choose between speed and accuracy, and exploiting new graphics hardware features for fast and high-quality rendering. The recent introduction of advanced programmability in widely available graphics hardware has already led to impressive progress in the area of volume visualization. However, besides the acceleration of the final rendering, flexible graphics hardware is increasingly being used also for the mapping and filtering stages of the visualization pipeline, thus giving rise to new levels of interactivity in visualization applications. The talk will present recent results of applying programmable graphics hardware in various visualization algorithms covering volume data, flow data, terrains, NPR rendering, and distributed and remote applications.
Dependent Tests Driven Filtering in Monte-Carlo Global Illumination
(Eurographics Association, 2002) Csonka, Ferenc; Szirmay-Kalos, Laszlo; Kelemen, Csaba; Antal, György
This paper presents a multi-phase algorithm to solve the global illumination problem. In the first phase dependent tests are applied, i.e. the random walks of different pixels are built from the same random numbers. The result of the first phase is used to identify homogeneous pixel groups in the image. The criterion of the formation of such groups is that averaging the color inside these groups should result in less error than handling the pixels independently. The second phase of the algorithm is a conventional random walk method that uses independent random samples in different pixels. The final result is calculated as the average of the results of the dependent tests and the lowpass filtered version of the independent tests. This low-pass filter averages the pixel values inside the homogenous groups. The algorithm takes advantage of the fact that the image can contain larger homogeneous regions that can be calculated from much less number of samples. Thus we can focus on those pixels where significant changes happen.
Mesh Decimation for Displacement Mapping
(Eurographics Association, 2002) Collins, Gordon; Hilton, Adrian
We present a mesh decimation algorithm for triangular meshes. Unlike other decimation algorithms we are not concerned with geometric error but with the existence of a displacement mapping which can map between the original and decimated meshes. We use the implicit function theorem to derive a condition which ensures the existence of a displacement map. The algorithm is applied to some standard scanned models and reduction rates around 99% are seen.
From Textual Chats to Interest Groups in 3D Virtual Space
(Eurographics Association, 2002) Masa, Michal; Zara, Jiri
While the textual chat is a highly popular tool for various kinds of social interactions, its extension to the visual three-dimensional domain remains almost untouched and without practical utilization yet. This paper discusses advantages and disadvantages of spatial virtual environment when used as a platform for connecting people and serving for social and cultural interaction. The differences between textual chat and interest groups in virtual reality are highlighted with the aim to overcome the gap between well-established chat technology and promising but still a bit exotic virtual reality approach. Theoretical analysis is followed by several examples taken from experimental setup.
Function-defined shape node for VRML
(Eurographics Association, 2002) Lai, Feng Min; Sourin, Alexei
This paper describes how the web-based visualisation can be greatly improved using the function-based shape modelling technique. We propose the function-defined VRML shape node, which allows the content creators to describe any complex models with relatively small functions compared to the large-size polygonal mesh based VRML nodes. The design, the implementation details, and the application examples of the proposed node are discussed. The software is available for downloading from the project website.
Using pre-integrated Transfer Functions in an Interactive Software System for Volume
(Eurographics Association, 2002) Knittel, Guenter
We explore possibilities to implement classification based on pre-integrated transfer functions in a software system for high-speed volume rendering. The major obstacle to remove is the large size of the multi-dimensional look-up tables. For high rendering performance, all parameters must be available in the L1-cache of the CPU, which is usually by far too small to hold the required tables. We discuss a cache-efficient and fast approximate solution and present a comparison to the standard classification method with respect to performance and image quality.
Visibility Preprocessing Using Spherical Sampling of Polygonal Patches
(Eurographics Association, 2002) Meruvia Pastor, Oscar E.
A technique is presented that permits fast view-reconstruction of individual objects. This method improves a previous approach to solve the problem of approximated view reconstruction by combining clustering of polygons with visibility bitfields to determine visibility for novel viewpoints. The technique consists of three steps: patch creation, spherical sampling, and rendering. In the first stage, the input 3D model is tiled in polygonal patches. In the sampling stage images of the model are taken from several points on the surface of a viewing sphere. Patch-ID bitfields, which are structures that contain visibility information, are computed for each picture. In the rendering stage, a subset of the viewpoints computed for sampling is selected depending on the viewers position on the viewing sphere and the bitfields of the selected viewpoints are used to rebuild the visible parts of the model from the new viewpoint. The overall system presented here makes a very efficient use of memory resources, and involves practically no overhead during rendering while significantly improving frame rate during interaction with large models. Although the technique is not conservative, our results show that the reconstructed views are practically identical to the original views of the model.
View-Dependent Rendering for Polygonal Datasets
(Eurographics Association, 2002) El- Sana, Jihad; De Floriani, Leila; Puppo, Enrico; Shamir, Arik
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Distance fields applied to character animation
(Eurographics Association, 2002) Rudomin, Isaac; Castillo, J.
A general hybrid geometric-physical method that is useful for animating characters with skin, clothing and a MPEG-4 compatible face is presented. This method uses an approximation to the underlying musculo-skeletal structure of the body and face to generate a distance field, used for collision detection purposes, and skin/clothing consisting of a particle-spring mesh. The results obtained deliver animation with plausible dynamics for fairly detailed models at around 60fps on a PIII computer with Nvidia Gforce2 graphics. The main contribution is to show that similar algorithms can be used for skin, clothing and facial animation, at interactive rates.
A Convolution-Based Algorithm for Animated Water Waves
(Eurographics Association, 2002) Loviscach, Jörn
A non-linear partial differential equation solver is too sophisticated for computer graphics applications if they are only used to render effects like circular waves and ship wakes. We present an approach which simulates waves through a convolution algorithm. It handles both gravity waves and capillary waves; the latter are often neglected even though they dominate small-scale behavior. The algorithm can be integrated into a complete solution architecture: First, standard commercial 3-D software is used to prepare an animated scene with objects traveling on a water surface. Based on the movements of these objects, waves are calculated and added as bump and displacement maps to the 3-D model.
Improved Integration for Cloth Simulation
(Eurographics Association, 2002) Parks, David L.; Forsyth, David A.
Most methods of cloth simulation produce animations that do not move very freely; the result often looks like the material is “swimming”. The primary sources of this phenomenon are the non-physical dissipation terms often added to the mechanics to ensure stability in the simulation, and the numerical damping that is implicit in the choice of ODE integration schemes. By disposing of the additional dissipation terms and choosing a new integrator, the generalized-a method, that was designed to safely integrate mechanical systems with extraneous high-frequency signals in their temporal component, we obtain more realistic results often with the about the same amount of computation.
The Voronoi-Quadtree: construction and visualization
(Eurographics Association, 2002) Coll, Narcís; Boada, Imma; Sellares, J.A.
We define a quadtree-based planar Voronoi diagram codification, the Voronoi-Quadtree, valid for generalized sites (points, line-segments, curve-arc segments, ...) and for different distance functions (Euclidean metrics, convex distance functions, ...).We present an algorithm for constructing, at a prefixed level of detail, the Voronoi-Quadtree associated to a Voronoi diagram determined by a set of sites and a given distance function. A second algorithm that, taking as input a Voronoi-Quadtree, visualizes a polygonal approximation of the boundary of the Voronoi diagram is also described.
Visual Data Mining
(Eurographics Association, 2002) Keim, Daniel A.; Müller, Wolfgang; Schumann, Heidrun
Never before in history has data been generated at such high volumes as it is today. Exploring and analyzing the vast volumes of data has become increasingly difficult. Information visualization and visual data mining can help to deal with the flood of information. The advantage of visual data exploration is that the user is directly involved in the data mining process. There are a large number of information visualization techniques that have been developed over the last two decades to support the exploration of large data sets. In this star report, we provide an overview of information visualization and visual data mining techniques, and illustrate them using a few examples.
Real-Time Animated Grass
(Eurographics Association, 2002) Bakay, Brook; Lalonde, Paul; Heidrich, Wolfgang
We present a simple method to render fields of grass, animated in the wind, in real-time. The technique employs vertex shaders to render displacement maps with Russian-doll style transparent shells. Animation is achieved by translating the surface according to a local wind vector while preserving the length of the blades of grass. This technique achieves convincing results on current consumer graphics hardware and can be applied to other similar surfaces such as hair and fur.
Reverse Diffusion for Smooth Buildup of Progressivly Transmitted Geometry
(Eurographics Association, 2002) Buelow, Thomas
In this paper we consider 3D object surfaces which can be represented as scalar functions defined on the sphere. These objects can be modeled as series of spherical harmonic functions. A simple progressive transmission scheme could be implemented which transmits the expansion coefficients one by one and thus implements a coarse to fine reconstruction. The buildup of the object according to this scheme is not completely smooth: Wavy patterns appear which disappear in subsequent stages and are replaced by finer spurious patterns and so on. We propose a remedy for this behavior which is based on the simulation of a reversed diffusion process on the sphere.
Feature interference in free form template matching
(Eurographics Association, 2002) Song, Y.; Vergeest, J. S. M.; Horvath, I.
Template matching is a useful method in the reconstruction of free form surfaces. In this paper, matching of free form surfaces with parameterized templates is studied with the emphasis on feature interference. By their definitions in 3- Dimensional space, free form features are introduced, analyzed and parameterized first. An optimization function based on a Hausdorff-like shape distance measuring method is proposed and applied as measuring method between the digitalized model surface and the parameterized feature template. The proposed method not only can fit isolated free form features, but also works when a feature is interfered by other free form features in some specified conditions. A series of numerical experiments have been conducted to demonstrate the proposed methods based on ACIS and Open Inventor. Fitting strategies are proposed as well.
Adaptive Tessellation for Trimmed NURBS Surface
(Eurographics Association, 2002) YingLiang, Ma; Hewitt, Terry
We present an adaptive method for tessellating the trimmed NURBS surface in the parametric domain. Given a model space tolerance ε, the algorithm first splits the NURBS surface in both the U and V directions to fit within the bounding box of the outer trimming loop. Then we subdivide the surface into Bézier patches recursively until the control net of the Bézier patch is flat enough and within the tolerance ε. By building up the quadtrees of inner trimming loops, we use the scanline algorithm to remove the patches inside the inner trimming loops. Finally, we close the inner trimming loops with a set of triangles. The resulting tessellation contains both quadrilaterals and triangles.

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