Issue 4

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    Computer Graphics forum
    (Blackwell Publishing, Inc and Eurographics Association, 2003) Duke, David; Scopigno, Roberto
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    Soft Object Modelling with Generalised ChainMail - Extending the Boundaries of Web-based Graphics
    (Blackwell Publishing, Inc and Eurographics Association, 2003) Li, Ying; Brodlie, Ken
    Soft object modelling is crucial in providing realistic simulation of many surgical procedures. High accuracy is achievable using the Finite Element Method (FEM), but significant computational power is required. We are interested in providing Web-based surgical training simulation where such computational power is not available, but in return lower accuracy is often sufficient. A useful alternative to FEM is the 3D ChainMail algorithm that models elements linked in a regular, rectangular mesh, mimicking the behaviour of chainmail armour. An important aspect is the ability to make topology changes for example by cutting - an aspect that FEM finds difficult. Our contribution is to extend the 3D ChainMail technique to arbitrary grids in 2D and 3D. This extends the range of applications that can be addressed by the ChainMail approach, to include surfaces and volumes defined on triangular and tetrahedral meshes. We have successfully deployed the algorithm in a Web-based environment, using VRML and Java linked through the External Authoring Interface.ACM CSS: I.3.5 Computer graphics: Computional Geometry and Object Modelling, I.3.2 Computer Graphics: Graphics Systems, J.3 Life and Medical Sciences
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    Granada, 4 September 2003
    (Blackwell Publishing, Inc and Eurographics Association, 2003)
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    The State of the Art in Flow Visualisation: Feature Extraction and Tracking
    (Blackwell Publishing, Inc and Eurographics Association, 2003) Post, Frits H.; Vrolijk, Benjamin; Hauser, Helwig; Laramee, Robert S.; Doleisch, Helmut
    Flow visualisation is an attractive topic in data visualisation, offering great challenges for research. Very large data sets must be processed, consisting of multivariate data at large numbers of grid points, often arranged in many time steps. Recently, the steadily increasing performance of computers again has become a driving force for new advances in flow visualisation, especially in techniques based on texturing, feature extraction, vector field clustering, and topology extraction.In this article we present the state of the art in feature-based flow visualisation techniques. We will present numerous feature extraction techniques, categorised according to the type of feature. Next, feature tracking and event detection algorithms are discussed, for studying the evolution of features in time-dependent data sets. Finally, various visualisation techniques are demonstrated.ACM CSS: I.3.8 Computer Graphics-applications
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    Auditor-s Report
    (Blackwell Publishing, Inc and Eurographics Association, 2003)
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    Siggraph 2003
    (Blackwell Publishing, Inc and Eurographics Association, 2003) Laycock, S. D.; Laycock, R. G.
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    A Survey of Inverse Rendering Problems
    (Blackwell Publishing, Inc and Eurographics Association, 2003) Patow, Gustavo; Pueyo, Xavier
    Inverse rendering problems usually represent extremely complex and costly processes, but their importance in many research areas is well known. In particular, they are of extreme importance in lighting engineering, where potentially costly mistakes usually make it unfeasible to test design decisions on a model. In this survey we present the main ideas behind these kinds of problems, characterize them, and summarize work developed in the area, revealing problems that remain unsolved and possible areas of further research.ACM CSS: I.3.6 Computer Graphics Methodology and Techniques I.3.7 Computer Graphics-Three-Dimensional Graphics and Realism I.4.1 Image Processing and Computer Vision Digitization and Image Capture I.4.7 Image Processing and Computer Vision Feature Measurement I.4.8 Image Processing and Computer Vision Scene Analysis
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    A Survey of Real-time Soft Shadows Algorithms
    (Blackwell Publishing, Inc and Eurographics Association, 2003) Hasenfratz, J. -M.; Lapierre, M.; Holzschuch, N.; Sillion, F.; Artis GRAVIR/IMAG-INRIA
    Recent advances in GPU technology have produced a shift in focus for real-time rendering applications, whereby improvements in image quality are sought in addition to raw polygon display performance. Rendering effects such as antialiasing, motion blur and shadow casting are becoming commonplace and will likely be considered indispensable in the near future. The last complete and famous survey on shadow algorithms — by Woo et al. [52] in 1990 — has to be updated in particular in view of recent improvements in graphics hardware, which make new algorithms possible. This paper covers all current methods for real-time shadow rendering, without venturing into slower, high quality techniques based on ray casting or radiosity. Shadows are useful for a variety of reasons: first, they help understand relative object placement in a 3D scene by providing visual cues. Second, they dramatically improve image realism and allow the creation of complex lighting ambiances. Depending on the application, the emphasis is placed on a guaranteed framerate, or on the visual quality of the shadows including penumbra effects or “soft shadows”. Obviously no single method can render physically correct soft shadows in real time for any dynamic scene! However our survey aims at providing an exhaustive study allowing a programmer to choose the best compromise for his/her needs. In particular we discuss the advantages, limitations, rendering quality and cost of each algorithm. Recommendations are included based on simple characteristics of the application such as static/moving lights, single or multiple light sources, static/dynamic geometry, geometric complexity, directed or omnidirectional lights, etc. Finally we indicate which methods can efficiently exploit the most recent graphics hardware facilities.
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    Bias Compensation for Photon Maps
    (Blackwell Publishing, Inc and Eurographics Association, 2003) Roland Schregle
    Density estimation techniques such as the photon map method rely on a particle transport simulation to reconstruct indirect illumination, which is proportional to the particle density. In the photon map framework, particles are usually located using nearest-neighbour methods due to their generality. However, these methods have an inherent tradeoff between local bias and noise in the reconstructed illumination, which depends on the density estimate bandwidth. This paper presents a bias compensating operator for nearest-neighbour density estimation which adapts the bandwidth according to the estimated bias in the reconstructed illumination.ACM CSS: I.3.7 Three-Dimensional Graphics and Realism Raytracing
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    EG2003 Medical Prize Competition
    (Blackwell Publishing, Inc and Eurographics Association, 2003) John, Nigel W.
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    Automatic View Selection Using Viewpoint Entropy and its Application to Image-Based Modelling
    (Blackwell Publishing, Inc and Eurographics Association, 2003) Vazquez, Pere-Pau; Feixas, Miquel; Sbert, Mateu; Heidrich, Wolfgang
    In the last decade a new family of methods, namely Image-Based Rendering, has appeared. These techniques rely on the use of precomputed images to totally or partially substitute the geometric representation of the scene. This allows to obtain realistic renderings even with modest resources. The main problem is the amount of data needed, mainly due to the high redundancy and the high computational cost of capture. In this paper we present a new method to automatically determine the correct camera placement positions in order to obtain a minimal set of views for Image-Based Rendering. The input is a 3D polyhedral model including textures and the output is a set of views that sample all visible polygons at an appropriate rate. The viewpoints should cover all visible polygons with an adequate quality, so that we sample the polygons at sufficient rate. This permits to avoid the excessive redundancy of the data existing in several other approaches. We also reduce the cost of the capturing process, as the number of actually computed reference views decreases. The localization of interesting viewpoints is performed with the aid of an information theory-based measure, dubbed viewpoint entropy. This measure is used to determine the amount of information seen from a viewpoint. Next we develop a greedy algorithm to minimize the number of images needed to represent a scene. In contrast to other approaches, our system uses a special preprocess for textures to avoid artifacts appearing in partially occluded textured polygons. Therefore no visible detail of these images is lost.ACM CSS: I.3.7 Computer Graphics'-Three-Dimensional Graphics and Realism
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    Ray Tracing Surfaces with Contours
    (Blackwell Publishing, Inc and Eurographics Association, 2003) Balsys, Ronald J.; Suffern, Kevin G.
    We present two algorithms for ray tracing surfaces with contour lines that are level surfaces of scalar fields. One algorithm renders the contours as bands of constant finite width, while the other renders them as one pixel wide anti-aliased lines. The algorithms work with mathematically defined implicit and parametric surfaces, and triangle meshes. The contours can help visualize the surfaces, and visualize functions defined on the surfaces, such as their curvature properties.
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    New Eurographics Fellow
    (Blackwell Publishing, Inc and Eurographics Association, 2003)
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    BRDF Measurement Modelling using Wavelets for Efficient Path Tracing
    (Blackwell Publishing, Inc and Eurographics Association, 2003) Claustres, L.; Paulin, M.; Boucher, Y.
    Physically based rendering needs numerical models from real measurements, or analytical models from material definitions, of the Bidirectional Reflectance Distribution Function (BRDF). However, measured BRDF data sets are too large and provide no functionalities to be practically used in Monte Carlo path tracing algorithms. In this paper, we present a wavelet-based generic BRDF model suitable for both physical analysis and path tracing. The model is based on the separation of spectral and geometrical aspect of the BRDF and allows a compact and efficient representation of isotropic, anisotropic and/or spectral BRDFs. After a brief survey of BRDF and wavelet theory, we present our software architecture for generic wavelet transform and how to use it to model BRDFs. Then, modelling results are presented on real and virtual BRDF measurements. Finally, we show how to exploit the multiresolution property of the wavelet encoding to reduce the variance by importance sampling in a path tracing algorithm.ACM CSS: I.3.7 Computer Graphics-Three-Dimensional Graphics and Realism