Volume 21 (2002)

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Techniques for Realistic Visualization of Fluids: A Survey
(Blackwell Publishers Ltd and the Eurographics Association, 2002) Adabala, Neeharika; Manohar, Swami
Visualization of fluids has wide applications in science, engineering and entertainment. Various methodologies of visualizing fluids have evolved which emphasize on capturing different aspects of the fluids accurately. In this survey the existing methods for realistic visualization of fluids are reviewed. The approaches are classified based on the key concept they rely on for fluid modeling. This classification allows for easy selection of the method to be adopted for visualization given an application. It also enables identification of alternative techniques for fluid modeling.
Towards Interactive Real-Time Crowd Behavior Simulation
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Ulicny, Branislav; Thalmann, Daniel
While virtual crowds are becoming common in non-real-time applications, the real-time domain is still relativelyunexplored. In this paper we discuss the challenges involved in creating such simulations, especially the needto efficiently manage variety. We introduce the concept of levels of variety. Then we present our work oncrowd behaviour simulation aimed at interactive real-time applications such as computer games or virtualenvironments. We define a modular behavioural architecture of a multi-agent system allowing autonomous andscripted behaviour of agents supporting variety. Finally we show applications of our system in a virtual realitytraining system and a virtual heritage reconstruction.ACM CSS: I.3.7 Three-Dimensional Graphics and Realism-Animation, I.2.11 Distributed ArtificialIntelligence-Multi-agent systems
Eurographics Italy 1st Conference
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Bordegoni, Monica
Flattening 3D objects using silhouettes
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Martin, D.; Fekete, J.D.; Torres, J. C.
An important research area in non-photorealistic rendering is the obtention of silhouettes. There are many methods to do this using 3D models and raster structures, but these are limited in their ability to create stylised silhouettes while maintaining complete flexibility. These limitations do not exist in illustration, as each element is plane and the interaction between them can be eliminated by locating each one in a different layer. This is the approach presented in this paper: a 3D model is flattened into plane elements ordered in space, which allows the silhouettes to be drawn with total flexibility.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Line and Curve Generation
Metamorphosis of Polyhedral Surfaces using Decomposition
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Shlafman, Shymon; Tal, Ayellet; Katz, Sagi
This paper describes an algorithm for morphing polyhedral surfaces based on their decompositions into patches. The given surfaces need neither be genus-zero nor two-manifolds. We present a new algorithm for decomposing surfaces into patches. We also present a new projection scheme that handles topologically cylinder-like polyhedral surfaces. We show how these two new techniques can be used within a general framework and result with morph sequences that maintain the distinctive features of the input models.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computational Geometry and Object Modeling]: Boundary representations I.3.7 [Three-Dimensional Graphics and Realism]: Animation
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Free-form sketching with variational implicit surfaces
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Karpenko, Olga; Hughes, John F.; Raskar, Ramesh
With the advent of sketch-based methods for shape construction, there's a new degree of power available in the rapid creation of approximate shapes. Sketch [Zeleznik, 1996] showed how a gesture-based modeler could be used to simplify conventional CSG-like shape creation. Teddy [Igarashi, 1999] extended this to more free-form models, getting much of its power from its 'inflation' operation (which converted a simple closed curve in the plane into a 3D shape whose silhouette, from the current point of view, was that curve on the view plane) and from an elegant collection of gestures for attaching additional parts to a shape, cutting a shape, and deforming it.But despite the powerful collection of tools in Teddy, the underlying polygonal representation of shapes intrudes on the results in many places. In this paper, we discuss our preliminary efforts at using variational implicit surfaces [Turk, 2000] as a representation in a free-form modeler. We also discuss the implementation of several operations within this context, and a collection of user-interaction elements that work well together to make modeling interesting hierarchies simple. These include 'stroke inflation' via implicit functions, blob-merging, automatic hierarchy construction, and local surface modification via silhouette oversketching. We demonstrate our results by creating several models.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Modeling packages I.3.6 [Computer Graphics]: Interaction techniques
Book Reviews
(Blackwell Publishers Ltd and the Eurographics Association, 2002) Howard, Toby
Vortex Tracking and Visualisation in a Flow Past a Tapered Cylinder
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Reinders, Freek; Sadarjoen, I. Ari; Vrolijk, Benjamin; Post, Frits H.
In this paper we explore a novel combined application of two of our existing visualisation techniques to thetracking of 3D vortex tubes in an unsteady flow. The applied techniques are the winding-angle vortex extractiontechnique based on streamline geometry, and the attribute-based feature tracking technique. We have applied theseto the well-known case of an unsteady 3D flow past a tapered cylinder.First, 2D vortices are detected in a number of horizontal slices for each time step, by means of the winding-anglevortex extraction method. For each 2D vortex a number of attributes are calculated and stored. These vorticesare visualised by a special type of ellipse icons, showing the position, shape and rotational direction and speed ineach slice.Next, for each time step, 3D vortex tubes are constructed from the 2D vortices by applying the feature trackingprocedure in a spatial dimension to connect the corresponding vortices in adjacent slices. The result is a graphattribute set with the 2D vortex attributes in the nodes and the spatial correspondences as edges.Finally, the 3D vortex tubes are tracked in time using the same tracking procedure, for finding the correspondingtubes in successive time steps. The result is a description of the evolution of the 3D vortices. An interactive, time-dependentvisualisation is generated using the temporal correspondences of each vortex tube. This analysis revealsa number of interesting patterns.ACM CSS: I.3.8 Computer Graphics-Applications
Hardware-Based Volumetric Knit-Wear
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Daubert, Katja; Seidel, Hans-Peter
We present a hardware-based, volumetric approach for rendering knit wear at very interactive rates. A single stitch is represented by a volumetric texture with each voxel storing the main direction of the strands of yarn inside it. We render the knit wear in layers using an approximation of the Banks model. Our hardware implementation allows specular and diffuse material properties to change from one voxel to the next. This enables us to represent yarn made up of different components or render garments with complicated color patterns. Furthermore, our approach can handle self-shadowing of the stitches, and can easily be adapted to also include view-independent scattering. The resulting shader lends itself naturally to mip-mapping, and requires no reordering of the base geometry, making it versatile and easy to use.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Hardware Applications Volumetric Textures
13th Eurographics Workshop on Rendering
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Debevec, Paul; Gibson, Simon
Efficient Multidimensional Sampling
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Kollig, Thomas; Keller, Alexander
Image synthesis often requires the Monte Carlo estimation of integrals. Based on a generalized concept of stratification we present an efficient sampling scheme that consistently outperforms previous techniques. This is achieved by assembling sampling patterns that are stratified in the sense of jittered sampling and N-rooks sampling at the same time. The faster convergence and improved anti-aliasing are demonstrated by numerical experiments.Categories and Subject Descriptors (according to ACM CCS): G.3 [Probability and Statistics]: Probabilistic Algorithms (including Monte Carlo); I.3.2 [Computer Graphics]: Picture/Image Generation; I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism.
Report of the Statutory Auditors to the General Meeting of the Members of Eurographics Association Geneva
(Blackwell Publishers, Inc and the Eurographics Association, 2002)
Web 2D Graphics File Formats
(Blackwell Publishers Ltd and the Eurographics Association, 2002) Duce, David; Herman, Ivan; Hopgood, Bob
The earliest Web browsers focussed on the display of textual information. When graphics were added, essentially only image graphics and image file formats were supported. For a significant range of applications, image graphics has severe limitations, for example in terms of file size, download time and inability to interact with and modify the graphics client-side. Vector graphics may be more appropriate in these cases, and this has become possible through the introduction of the WebCGM and Scalable Vector Graphics (SVG) formats, both of which are open standards, the former from ISO/IEC and W3C and the latter from W3C. This paper reviews the background to Web graphics, presents the WebCGM file format, and gives a more detailed exposition of the most recent format, SVG. The paper concludes with reflections on the current state of this area and future prospects.
23rd Eurographics General Assembly
(Blackwell Publishers, Inc and the Eurographics Association, 2002)
Editorial
(Blackwell Publishers Ltd and the Eurographics Association, 2002)
Multiresolution Surfaces having Arbitrary Topologies by a Reverse Doo Subdivision Method
(Blackwell Publishers Ltd and the Eurographics Association, 2002) Samavati, Faramarz; Mahdavi-Amiri, Nezam; Bartels, Richard
We have shown how to construct multiresolution structures for reversing subdivision rules using global least squares models (Samavati and Bartels, Computer Graphics Forum, 18(2):97-119, June 1999). As a result, semiorthogonal wavelet systems have also been generated. To construct a multiresolution surface of an arbitrary topology, however, biorthogonal wavelets are needed. In Bartels and Samavati (Journal of Computational and Applied Mathematics, 119:29-67, 2000) we introduced local least squares models for reversing subdivision rules to construct multiresolution curves and tensor product surfaces, noticing that the resulting wavelets were biorthogonal (under an induced inner product). Here, we construct multiresolution surfaces of arbitrary topologies by locally reversing the Doo subdivision scheme. In a Doo subdivision, a coarse surface is converted into a fine one by the contraction of coarse faces and the addition of new adjoining faces. We propose a novel reversing process to convert a fine surface into a coarse one plus an error. The conversion has the property that the subdivision of the resulting coarse surface is locally closest to the original fine surface, in the least squares sense, for two important face geometries. In this process, we first find those faces of the fine surface which might have been produced by the contraction of a coarse face in a Doo subdivision scheme. Then, we expand these faces. Since the expanded faces are not necessarily joined properly, several candidates are usually at hand for a single vertex of the coarse surface. To identify the set of candidates corresponding to a vertex, we construct a graph in such a way that any set of candidates corresponds to a connected component. The connected components can easily be identified by a depth first search traversal of the graph. Finally, vertices of the coarse surface are set to be the average of their corresponding candidates, and this is shown to be equivalent to local least squares approximation for regular arrangements of triangular and quadrilateral faces.
Geometric Approximations Towards Free Specular Comic Shading
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Winnemoller, Holger; Bangay, Shaun
We extend the standard solution to comic rendering with a comic-style specular component. To minimise the computational overhead associated with this extension, we introduce two optimising approximations; the perspective correction angle and the vertex face-orientation measure. Both of these optimisations are generally applicable, but they are especially well suited for applications where a physically correct lighting simulation is not required. Using our optimisations we achieve performances comparable to the standard solution. As our approximations favour large models, we even outperform the standard approach for models consisting of 10,000 triangles or more, which we can render exceeding 40 frames per second, including the specular component.Categories and Subject Descriptors (according to ACM CSS): I.3.3 [Computer Graphics] Picture/Image Generation: Display algorithms; I.3.7 [Computer Graphics] Three-Dimensional Graphics and Realism: Color, shading, shadowing, and texture; I.4.3 [Image Processing and Computer Vision] Enhancements: Geometric Correction.
3rd Eurographics Workshop on Parallel Graphics and Visualization
(Blackwell Publishers Ltd and the Eurographics Association, 2002)

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