VisSym01: Joint Eurographics - IEEE TCVG Symposium on Visualization

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Space-Efficient Boundary Representation of Volumetric Objects
(The Eurographics Association, 2001) Mroz, Lukas; Hauser, Helwig; David S. Ebert and Jean M. Favre and Ronald Peikert
In this paper we present a compression technique for efficiently representing boundary objects from volumetric data-sets. Exploiting spatial coherency within object contours, we are able to reduce the size of the volumetric boundary down to the size of just a few images. Allowing for direct volume rendering of the down-scaled data in addition to compression ratios up to 250:1, interactive volume visualization becomes possible, even over the Internet and on low-end hardware.
Progressive View-Dependent Isosurface Propagation
(The Eurographics Association, 2001) Liu, Zhiyan; Finkelstein, Adam; Li, Kai; David S. Ebert and Jean M. Favre and Ronald Peikert
This paper proposes a new isosurface extraction algorithm that extracts portions of the isosurface in a view-dependent manner by ray casting and propagation. The algorithm casts rays through a volume to find visible active cells as seeds and then propagates their polygonal isosurface into the neighboring cells. Small pieces of the isosurface are generated by distance-limited propagation and joined together to form the final surface. We demonstrate that this progressive algorithm generates an approximate result quickly and refines it to the final correct image over time. In addition, the algorithm scales with the resolution of the display and supports adaptive-resolution visualization.
Preserving the Mental Map using Foresighted Layout
(The Eurographics Association, 2001) Diel, Stepahn; Görg, Carsten; Kerren, Andreas; David S. Ebert and Jean M. Favre and Ronald Peikert
First we introduce the concept of graph animations as a sequence of evolving graphs and a generic algorithm which computes a Foresighted Layout for dynamically drawing these graphs while preserving the mental map. The algorithm is generic in the sense that it takes a static graph drawing algorithm as a parameter. In other words, trees can be animated with a static tree layouter, graphs with a static Sugiyama-style layouter or a spring embedder, etc. Second we discuss applications of Foresighted Layout in algorithm animation and visualization of navigation behaviour.
Interactive and Multi-modal Visualization for Neuroendoscopic Interventions
(The Eurographics Association, 2001) Bartz, Dirk; Straßer, Wolfgang; Gürvit, Özlem; Freudenstein, Dirk; Skalej, Martin; David S. Ebert and Jean M. Favre and Ronald Peikert
Based on the VIVENDI-framework for virtual endoscopy, we present a system for the interactive and multi-modal representation of important anatomical structures for neuroendoscopic interventions. A serious problem of neuroendoscopic interventions is the possibility of injuring a blood vessel while performing endoscopic surgery inside the human brain. Besides the sudden loss of optical visibility due to the red-out of the injured vessel, a potential lethal mass bleeding can be the fatal outcome of the intervention. To avoid accidental lesions, we represent the relevant information using multiple volumetric MRI-based representations of the respective organs.
Interacting with Stock Market Data in a Virtual Environment
(The Eurographics Association, 2001) Nesbitt, Keith; David S. Ebert and Jean M. Favre and Ronald Peikert
Virtual Environment technology enables new styles of user interfaces that provide multi-sensory interactions. For example, interfaces can be designed which immerse the user in a 3D space and provide multi-sensory feedback. Many information spaces are multivariate, large and abstract in nature. It has been a goal of Virtual Environments to widen the human to computer bandwidth and so assist in the interpretation of these spaces by providing models that allow the user to interact 'naturally'. One goal for this interaction may be to uncover useful patterns within the data. This paper describes a Virtual Environment system called the "Workbench" and explains three models of stock market data that have been developed for this environment. The aim of this work is to provide models that allow analysts to explore for new trading patterns in the stock market data. Some early results of this work are discussed.
Salient Representation of Volume Data
(The Eurographics Association, 2001) Hladuvka, Jiri; König, Andreas; Gröller, Eduard; David S. Ebert and Jean M. Favre and Ronald Peikert
We introduce a novel method for identification of objects of interest in volume data. Our approach conveys the information contained in two essentially different concepts, the object s boundaries and the narrow solid structures, in an easy and uniform way. The second order derivative operators in directions reaching minimal response are employed for this task. To show the superior performance of our method, we provide a comparison with its main competitor surface extraction from areas of maximal gradient magnitude. We show that our approach provides the possibility to represent volume data by a subset of a nominal size.
A Hardware-Assisted Visibility-Ordering Algorithm With Applications To Volume Rendering
(The Eurographics Association, 2001) Krishnan, Shankar; Silva, Cláudio T.; Wei, Bin; David S. Ebert and Jean M. Favre and Ronald Peikert
We propose a hardware-assisted visibility ordering algorithm. From a given viewpoint, a (back-to-front) visibility ordering of a set of objects is a partial order on the objects such that if object A obstructs object B, then B precedes A in the ordering. Such orderings are useful because they are the building blocks of other rendering algorithms such as direct volume rendering of unstructured grids. The traditional way to compute the visibility order is to build a set of visibility relations (e.g., B < p A), and then run a topological sort on the set of relations to actually get the partial ordering. Our technique instead works by assigning a layer number to each primitive, which directly determines the visibility ordering. Objects that have the same layer number are independent, and have no obstruction between each other. We use a simple technique which exploits a combination of the z- and stencil buffers to compute the layer number of each primitive. One application of our technique is to obtain a fast unstructured volume rendering algorithm. In this paper, we present our technique and its implementation in OpenGL. We also discuss its performance and some optimizations on some recent graphics hardware architectures.
Extraction of Crack-free Isosurfaces from Adaptive Mesh Refinement Data
(The Eurographics Association, 2001) Weber, Gunther H.; Kreylos, Oliver; Ligocki, Terry J.; Shalf, John M.; Hagen, Hans; Hamann, Bernd; Joy, Kenneth I.; David S. Ebert and Jean M. Favre and Ronald Peikert
Adaptive mesh refinement (AMR) is a numerical simulation technique used in computational fluid dynamics (CFD). It permits the efficient simulation of phenomena characterized by substantially varying scales in complexity of local behavior of certain variables. By using a set of nested grids at different resolutions, AMR combines the simplicity of structured rectilinear grids with the possibility to adapt to local changes in complexity and spatial resolution. Hierarchical representations of scientific data pose challenges when isosurfaces are extracted. Cracks can arise at the boundaries between regions represented at different resolutions. We present a method for the extraction of isosurfaces from AMR data that avoids cracks at the boundaries between levels of different resolution.
Comparative Visualization of Instabilities in Crash-Worthiness Simulations
(The Eurographics Association, 2001) Sommer, Ove; Ertl, Thomas; David S. Ebert and Jean M. Favre and Ronald Peikert
Since crash-worthiness simulations get more and more important as part of the car development process in order to reduce the cost of development, enhance the product quality, and minimize the time-to-market, the reliability of the simulation results plays a decisive role concerning their significance. Recently the simulation departments of several automotive companies started investigating the quantity and reason for deviations during a number of simulation runs on the same input model. In this case study we discuss different measurements for instability and present a texture-based visualization method which allows the engineers to efficiently explore the simulation results by interactively hiding finite element structures with nearly constant crash performance. Furthermore, we describe those parts of our prototype which use a CORBA layer for providing the same view on a set of simulation results and allowing the visual comparison by using the marker functionality.
I/O-Conscious Volume Rendering
(The Eurographics Association, 2001) Yang, Chuan-Kai; Chiueh, Tzi-cker; David S. Ebert and Jean M. Favre and Ronald Peikert
Most existing volume rendering algorithms assume that data sets are memory-resident and thus ignore the performance overhead of disk I/O. While this assumption may be true for high-performance graphics machines, it does not hold for most desktop personal workstations. To minimize the end-to-end volume rendering time, this work re-examines implementation strategies of the ray casting algorithm, taking into account both computation and I/O overheads. Specifically, we developed a data-driven execution model for ray casting that achieves the maximum overlap between rendering computation and disk I/O. Together with other performance optimizations, on a 300-MHz Pentium-II machine, without directional shading, our implementation is able to render a 128x128 greyscale image from a 128x128x128 data set with an average end-to-end delay of 1 second, which is very close to the memory-resident rendering time. With a little modification, this work can also be extended to do out-of-core visualization as well.
Volume Rendering Data with Uncertainty Information
(The Eurographics Association, 2001) Djurcilov, Suzana; Kim, Kwansik; Lermusiaux, Pierre F. J.; Pang, Alex; David S. Ebert and Jean M. Favre and Ronald Peikert
This paper explores two general methods for incorporating volumetric uncertainty information in direct volume rendering. The goal is to produce volume rendered images that depict regions of high (or low) uncertainty in the data. The first method involves incorporating the uncertainty information directly into the volume rendering equation. The second method involves post-processing information of volume rendered images to composite uncertainty information. We present some initial findings on what mappings provide qualitatively satisfactory results and what mappings do not. Results are considered satisfactory if the user can identify regions of high or low uncertainty in the rendered image. We also discuss the advantages and disadvantages of both approaches.
Three-dimensional Reconstruction and Visualization of the Cerebral Cortex in Primates
(The Eurographics Association, 2001) Demelio, Sergio; Bettio, Fabio; Gobbetti, Enrico; Luppino, Giuseppe; David S. Ebert and Jean M. Favre and Ronald Peikert
We present a prototype interactive application for the direct analysis in three dimensions of the cerebral cortex in primates. The paper provides an overview of the current prototype system and presents the techniques used for reconstructing the cortex shape from data derived from histological sections as well as for rendering it at interactive rates. Results are evaluated by discussing the analysis of the right hemisphere of the brain of a macaque monkey used for neuroanatomical tract-tracing experiments.
Improved visualization in virtual colonoscopy using image-based rendering
(The Eurographics Association, 2001) Serlie, Iwo; Vos, Frans; Gelder, Rogier van; Stoker, Jaap; Truyen, Roel; Gerritsen, Frans; Nio, Yung; Post, Frits; David S. Ebert and Jean M. Favre and Ronald Peikert
Virtual colonoscopy (VC) is a patient-friendly alternative for colorectal endoscopic examination. We explore visualization aspects of VC such as surface in view, navigation and communication of a diagnosis. A series of unfolded cubes presents an animated full 360-degree omnidirectional field-of-view to the physician, to facilitate thorough and rapid inspection. For communication between physicians a tool has been designed that uses image-based rendering. Clinical evaluation has shown a reduction in inspection time from 19 minutes to 7 minutes without loss of sensitivity. With current virtual colonoscopy using a 2-sided view only 94% of the surface is available for exploration. In our approach the surface in view is increased to potentially 100%. Thus, the entire colon can be explored with better confidence that no regions are missed.
Automotive Soiling Simulation Based On Massive Particle Tracing
(The Eurographics Association, 2001) Roettger, Stefan; Schulz, Martin; Bartelheimer, Wolf; Ertl, Thomas; David S. Ebert and Jean M. Favre and Ronald Peikert
In the automotive industry Lattice-Boltzmann type flow solvers like PowerFlow from Exa Corporation are becoming increasingly important. In contrast to the traditional finite volume approach PowerFlow utilizes a hierachical cartesian grid for flow simulation. In this case study we show how to take advantage of these hierarchical grids in order to extend an existing Lattice-Boltzmann CFD environment with an automotive soiling simulation system. To achieve this, we chose to constantly generate a huge number of massive particles in user manipulable particle emitters. The process of tracing these particles step by step thus creates evolving particle streams, which can be displayed interactively by our visualization system. Each particle is created with stochastically varying diameter, specific mass and initial velocity, whereas already existing particles may decay because of aging, when leaving the simulation domain or when colliding with the vehicle s surface. On the one hand the display of these animated particles is a very natural and intuitive way to explore a CFD data set. On the other hand animated massive particles can be easily utilized for driving an automotive soiling simulation just by coloring the particles hit points on the vehicle s surface.
A Case Study in Multi-Sensory Investigation of Geoscientific Data
(The Eurographics Association, 2001) Harding, Chris; Kakadiaris, Ioannis A.; Casey, John F.; Loftin, R. Bowen; David S. Ebert and Jean M. Favre and Ronald Peikert
In this paper, we report our ongoing research into multi-sensory investigation of geoscientific data. Our Geoscientific Data Investigation System (GDIS) integrates three-dimensional, interactive computer graphics, touch (haptics) and real-time sonification into a multi-sensory Virtual Environment. GDIS has been used to investigate geological structures on the high-resolution bathymetry data from the Mid-Atlantic Ridge. Haptic force feedback was used to precisely digitize line features on three-dimensional morphology and to feel surface properties via varying friction settings; additional, overlapping data can be perceived via sound (sonification). We also report on the results of a psycho-acoustic study about the absolute recognition of sound signals, and on the actual feedback that we have received from a number of geoscientists during a recent major geoscience conference.
Multiresolution Maximum Intensity Volume Rendering by Morphological Pyramids
(The Eurographics Association, 2001) Roerdink, Jos B.T.M.; David S. Ebert and Jean M. Favre and Ronald Peikert
We propose a multiresolution representation for maximum intensity projection (MIP) volume rendering, based on morphological pyramids which allow progressive refinement and have the property of perfect reconstruction. The pyramidal analysis and synthesis operators are composed of morphological erosion and dilation, combined with dyadic downsampling for analysis and dyadic upsampling for synthesis. The structure of the multiresolution MIP representation is very similar to wavelet splatting, the main differences being that (i) linear summation of voxel values is replaced by maximum computation, and (ii) linear wavelet filters are replaced by (nonlinear) morphological filters.
Visualization of Thermal Flows in an Automotive Cabin with Volume Rendering Method
(The Eurographics Association, 2001) Ono, Kenji; Matsumoto, Hideki; Himeno, Ryutaro; David S. Ebert and Jean M. Favre and Ronald Peikert
A predictive system of thermal flow with quick turnaround time in a passenger compartment has been developed. An efficient method based on the Cartesian mesh system was used to reduce the period of analysis. The computed temperature in an automotive cabin was visualized by volume rendering techniques using an RVSLIB software library developed by NEC. Consecutive images of the flow were converted into MPEG1 movies, which gave us an overall understanding of the flow. The visualization results indicate that the present system is capable to sufficiently predict the thermal environment in a vehicle cabin at early stage of vehicle development.
The Rendering of Unstructured Grids Revisited
(The Eurographics Association, 2001) Westermann, Rüdiger; David S. Ebert and Jean M. Favre and Ronald Peikert
In this paper we propose a technique for resampling scalar fields given on unstructured tetrahedral grids. This technique takes advantage of hardware accelerated polygon rendering and 2D texture mapping and thus avoids any sorting of the tetrahedral elements. Using this technique, we have built a visualization tool that enables us to either resample the data onto arbitrarily sized Cartesian grids, or to directly render the data on a slice-by-slice basis. Since our approach does not rely on any pre-processing of the data, it can be utilized efficiently for the display of time-dependent unstructured grids where geometry as well as topology change over time.
Subdivision Surfaces for Scattered-data Approximation
(The Eurographics Association, 2001) Bertram, Martin; Hagen, Hans; David S. Ebert and Jean M. Favre and Ronald Peikert
We propose a modified Loop subdivision surface scheme for the approximation of scattered data in the plane. Starting with a triangulated set of scattered data with associated function values, our scheme applies linear, stationary subdivision rules resulting in a hierarchy of triangulations that converge rapidly to a smooth limit surface. The novelty of our scheme is that it applies subdivision only to the ordinates of control points, whereas the triangulated mesh in the plane is fixed. Our subdivision scheme defines locally supported, bivariate basis functions and provides multiple levels of approximation with triangles. We use our subdivision scheme for terrain modeling.
Virtual Colon Flattening
(The Eurographics Association, 2001) Bartroli, A. Vilanova; R.Wegenkittl,; König, A.; Gröller, E.; Sorantin, E.; David S. Ebert and Jean M. Favre and Ronald Peikert
We present a new method to visualize virtual endoscopic views. We propose to flatten the organ by the direct projection of the surface onto a set of cylinders. Two sampling strategies are presented and the introduced distortions are studied. A non-photorealistic technique is presented to enhance the perception of the images. Finally, an approximate but real-time endoscopic fly-through is possible by using the data obtained by the projection technique.

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