VisSym04: Joint Eurographics - IEEE TCVG Symposium on Visualization

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Accuracy Evaluation of Different Centerline Approximations of Blood Vessels
(The Eurographics Association, 2004) Cruz, A. La; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
Accurate determination of the vessel axis is a prerequisite for automated visualization and quantification of artery diseases. This paper presents an evaluation of different methods for approximating the centerline of the vessel in a phantom simulating the peripheral arteries. Six algorithms were used to determine the centerline of a synthetic peripheral arterial vessel. They are based on: ray casting using thresholds and maximum gradient-like stop criterion, pixel motion estimation between successive images called block matching, center of gravity and shape based segmentation. The Randomized Hough Transform and ellipse fitting have been used as shape based segmentation techniques. Since in the synthetic data set the centerline is known, an estimation of the error can be calculated in order to determine the accuracy achieved by a given method.
Case Study: Visualization of annotated DNA sequences
(The Eurographics Association, 2004) Peeters, Tim; Fiers, Mark; Wetering, Huub van de; Nap, Jan-Peter; Wijk, Jarke J. van; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
DNA sequences and their annotations form ever expanding data sets. Proper explorations of such data sets require new tools for visualization and analysis. In this case study, we have defined the requirements for a visualization tool for annotated DNA sequences.We have implemented these requirements in a new and flexible tool for browsing and comparing annotated DNA sequences interactively and in real-time. The use of standard information visualization techniques, such as linked windows, perspective walls, and smooth interaction, enables genome researchers to obtain better insight in large DNA data sets in an effective, efficient, and attractive way.
Interactively Visualizing Procedurally Encoded Scalar Fields
(The Eurographics Association, 2004) Jang, Yun; Weiler, Manfred; Hopf, Matthias; Huang, Jingshu; Ebert, David S.; Gaither, Kelly P.; Ertl, Thomas; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
While interactive visualization of rectilinear gridded volume data sets can now be accomplished using texture mapping hardware on commodity PCs, interactive rendering and exploration of large scattered or unstructured data sets is still a challenging problem. We have developed a new approach that allows the interactive rendering and navigation of procedurally-encoded 3D scalar fields by reconstructing these fields on PC class graphics processing units. Since the radial basis functions (RBFs) we use for encoding can provide a compact representation of volumetric scalar fields, the large grid/mesh traditionally needed for rendering is no longer required and ceases to be a data transfer and computational bottleneck during rendering. Our new approach will interactively render RBF encoded data obtained from arbitrary volume data sets, including both structured volume models and unstructured scattered volume models. This procedural reconstruction of large data sets is flexible, extensible, and can take advantage of the Moore's Law cubed increase in performance of graphics hardware.
Superquadric Tensor Glyphs
(The Eurographics Association, 2004) Kindlmann, Gordon; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
Tensor field visualization is a challenging task due in part to the multi-variate nature of individual tensor samples. Glyphs convey tensor variables by mapping the tensor eigenvectors and eigenvalues to the orientation and shape of a geometric primitive, such as a cuboid or ellipsoid. Though widespread, cuboids and ellipsoids have problems of asymmetry and visual ambiguity. Cuboids can display misleading orientation for tensors with underlying rotational symmetry. Ellipsoids differing in shape can be confused, from certain viewpoints, because of similarities in profile and shading. This paper addresses the problems of asymmetry and ambiguity with a new tunable continuum of glyphs based on superquadric surfaces. Superquadric tensor glyphs enjoy the necessary symmetry properties of ellipsoids, while also imitating cuboids and cylinders to better convey shape and orientation, where appropriate. The new glyphs are demonstrated on fields of diffusion tensors from the human brain.
Surface Techniques for Vortex Visualization
(The Eurographics Association, 2004) Garth, Christoph; Tricoche, Xavier; Salzbrunn, Tobias; Bobach, Tom; Scheuermann, Gerik; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
This paper presents powerful surface based techniques for the analysis of complex flow fields resulting from CFD simulations. Emphasis is put on the examination of vortical structures. An improved method for stream surface computation that delivers accurate results in regions of intricate flow is presented, along with a novel method to determine boundary surfaces of vortex cores. A number of surface techniques are presented that aid in understanding the flow behavior displayed by these surfaces. Furthermore, a scheme for phenomenological extraction of vortex core lines using stream surfaces is discussed and its accuracy is compared to one of the most established standard techniques.
Software Landscapes: Visualizing the Structure of Large Software Systems
(The Eurographics Association, 2004) Balzer, Michael; Noack, Andreas; Deussen, Oliver; Lewerentz, Claus; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
Modern object-oriented programs are hierarchical systems with many thousands of interrelated subsystems. Visualization helps developers to better comprehend these large and complex systems. This paper presents a three-dimensional visualization technique that represents the static structure of object-oriented programs using landscape-like distributions of three-dimensional objects on a two-dimensional plane. The familiar landscape methaphor facilitates intuitive navigation and comprehension. The visual complexity is reduced by adjusting the transparency of object surfaces to the distance of the viewpoint. An approach called Hierarchical Net is proposed for a clear representation of the relationsships between the subsystems.
Generalized Distance Transforms and Skeletons in Graphics Hardware
(The Eurographics Association, 2004) Strzodka, R.; Telea, A.; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
We present a framework for computing generalized distance transforms and skeletons of two-dimensional objects using graphics hardware. Our method is based on the concept of footprint splatting. Combining different splats produces weighted distance transforms for different metrics, as well as the corresponding skeletons and Voronoi diagrams. We present a hierarchical acceleration scheme and a subdivision scheme that allows visualizing the computed skeletons with subpixel accuracy in real time. Our splatting approach allows one to easily change all the metric parameters, treat any 2D boundaries, and easily produce both DTs and skeletons. We illustrate the method by several examples.
Volume Visualization and Visual Queries for Large High-Dimensional Datasets
(The Eurographics Association, 2004) Reina, G.; Ertl, T.; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
We propose a flexible approach for the visualization of large, high-dimensional datasets. The raw, highdimensional data is mapped into an abstract 3D distance space using the FastMap algorithm, which helps, together with other linear preprocessing steps, to make changes to the resulting 3D representation within a few seconds. Thus exploration of such datasets is a less tedious task compared to other techniques. We use volumes with four components to enable the user to brush an attribute selection onto the volume for inspection. We exploit multiple transfer functions for displaying these attributes and also to filter one attribute with values of another. An advantage of this volume sampling approach is that the rendering performance is independent of the dataset size. The drawback of limited resolution can be overcome by providing a linked detail view for a freely selectable portion of space. Examples of the inspection and filtering possibilities using a silvicultural dataset illustrate the strengths of our approach.
Texture-Based Flow Visualization on Isosurfaces from Computational Fluid Dynamics
(The Eurographics Association, 2004) Laramee, Robert S.; Schneider, Jürgen; Hauser, Helwig; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
Isosurfacing, by itself, is a common visualization technique for investigating 3D vector fields. Applying texturebased flow visualization techniques to isosurfaces provides engineers with even more insight into the characteristics of 3D vector fields. We apply a method for producing dense, texture-based representations of flow on isosurfaces. It combines two well know scientific visualization techniques, namely iso-surfacing and texture-based flow visualization, into a useful hybrid approach. The method is fast and can generate dense representations of flow on isosurfaces with high spatio-temporal correlation at 60 frames per second. The method is applied in the context of CFD simulation data, namely, the investigation of a common swirl flow pattern and the visualization of blood flow.
Auralization I: Vortex Sound Synthesis
(The Eurographics Association, 2004) Shin, Youngin; Bajaj, Chandrajit; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
Auralization is the process of extracting and displaying meaningful information in the form of sound from data. Through not only visualization but also auralization, users may have better understandings of the data, especially when it is visually complicated. In this work, a field auralization technique is introduced, which objective is at the sound synthesis from field information represented as 3D time-varying volume data. Our technique takes a hybrid approach between parameter mapping and direct simulation. During preprocessing, acoustic strengths are computed at each vertex at each time step of volume data. During interaction, users navigate within the volume space and audio frames are computed by integrating the radiations from the sources. A number of problems inherent in this problem and our solutions are discussed.
Boundary Switch Connectors for Topological Visualization of Complex 3D Vector Fields
(The Eurographics Association, 2004) Weinkauf, T.; Theisel, H.; Hege, H.-C.; Seidel, H.-P.; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
One of the reasons that topological methods have a limited popularity for the visualization of complex 3D flow fields is the fact that their topological structures contain a number of separating stream surfaces. Since these stream surfaces tend to hide each other as well as other topological features, for complex 3D topologies the visualizations become cluttered and hardly interpretable. One solution of this problem is the recently introduced concept of saddle connectors which treats separation surfaces emanating from critical points. In this paper we extend this concept to separation surfaces starting from boundary switch curves. This way we obtain a number of particular stream lines called boundary switch connectors. They connect either two boundary switch curves or a boundary switch curve with a saddle. We discuss properties and computational issues of boundary switch connectors and apply them to topologically complex flow data.
Graph Drawing by Subspace Optimization
(The Eurographics Association, 2004) Koren, Yehuda; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
We show a novel approach for accelerating the computation of graph drawing algorithms. The method is based on the notion that we can find a subspace with a relatively low dimensionality that captures the "nice" layouts of the graph. This way each axis of the drawing is a linear combination of a few basis vectors, instead of being an arbitrary vector in Rn (n is the number of nodes). We describe ways of constructing these basis vectors and also algorithms for optimizing the graph drawing in the resulting subspace.
Medical Applications of Multi-Field Volume Rendering and VR Techniques
(The Eurographics Association, 2004) Kniss, Joe; Schulze, Jürgen P.; Wössner, Uwe; Winkler, Peter; Lang, Ulrich; Hansen, Charles; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
This paper reports on a new approach for visualizing multi-field MRI or CT datasets in an immersive environment with medical applications. Multi-field datasets combine multiple scanning modalities into a single 3D, multivalued, dataset. In our approach, they are classified and rendered using real-time hardware accelerated volume rendering, and displayed in a hybrid work environment, consisting of a dual power wall and a desktop PC. For practical reasons in this environment, the design and use of the transfer functions is subdivided into two steps, classification and exploration. The classification step is done at the desktop, taking advantage of the 2D mouse as a high accuracy input device. The exploration process takes place on the powerwall.We present our new approach, describe the underlying implementation issues, report on our experiences with different immersive environments, and suggest ways it can be used for collaborative medical diagnosis and treatment planning.
Efficient Isosurface Tracking Using Precomputed Correspondence Table
(The Eurographics Association, 2004) Ji, Guangfeng; Shen, Han-Wei; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
Feature tracking is a useful method for visualizing and analyzing time-varying scalar fields. It allows scientists to focus on regions of interest and track their evolution and interaction over time. To allow the user to freely explore the data set, features must be tracked in an efficient manner. In this paper, we present an efficient time-varying isosurface tracking algorithm. Unlike the previous algorithms which compute the corresponding isosurface components in the adjacent time steps by performing expensive computation at run time, our algorithm can rapidly identify corresponding isosurfaces by performing simple table lookup operations. This table, called the correspondence lookup table, can be computed at a preprocessing stage. The idea behind our approach is that the correspondence relationship can only change at critical isovalues in R3 or R4 and remains unchanged between adjacent pairs of critical isovalues. With our algorithm, isosurfaces can be tracked in an efficient manner with minimal overhead.
Case Study: Visual Analysis of Complex, Time-Dependent Simulation Results of a Diesel Exhaust System
(The Eurographics Association, 2004) Doleisch, Helmut; Mayer, Michael; Gasser, Martin; Wanker, Roland; Hauser, Helwig; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
In previous work we have presented visualization techniques that provide engineers with a high degree of interactivity and flexibility for analyzing large, time-dependent, and high-dimensional data sets resulting from CFD (computational fluid dynamics) simulations. In this case study we apply our techniques in the fields of the automotive engineering industry and demonstrate how users benefit from using them during their routine analysis, as well as for exploring new phenomena. For coping with some of the special requirements in this application, we adapted and extended parts of the system. A comparison of two related cases of a diesel exhaust system is presented, and some important questions about these cases are addressed.
Visual Triangulation of Network-Based Phylogenetic Trees
(The Eurographics Association, 2004) Brandes, U.; Dwyer, T.; Schreiber, F.; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
Phylogenetic trees are built by examining differences in the biological traits of a set of species. An example of such a trait is a biological network such as a metabolic pathway, common to all species but with subtle differences in each. Phylogenetic trees of metabolic pathways represent multiple aspects of similarity and hypothetical evolution in a single, yet complex structure that is difficult to understand and interpret. We present a visualization method that facilitates analysis of such structures by presenting multiple coordinated perspectives simultaneously. Each of these perspectives constitutes a useful visualization in its own right, but it is only together that they unfold their full explorative power.
Techniques for Visualizing Multi-Valued Flow Data
(The Eurographics Association, 2004) Urnessy, Timothy; Interrante, Victoria; Longmire, Ellen; Marusic, Ivan; Ganapathisubramani, Bharathram; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
In this paper we discuss several techniques to display multiple scalar distributions within an image depicting a 2D flow field. We first address how internal contrast and mean luminance can effectively be used to represent a scalar distribution in addition to an underlying flow field. Secondly, we expand upon a current technique to more effectively use luminance ramps over dense streamlines to represent direction of flow. Lastly, we present a new method, based on embossing, to encode the out-of-plane component of a 3D vector field defined over a 2D domain. Throughout this paper, we limit our focus to the visualization of steady flows.
Visual Component Analysis
(The Eurographics Association, 2004) Müller, Wolfgang; Alexa, Marc; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
We propose to integrate information visualization techniques with factor analysis. Specifically, a principal direction derived from a principal component analysis (PCA) of the data is displayed together with the data in a scatterplot matrix. The direction can be adjusted to coincide with visual trends in the data. Projecting the data onto the orthogonal subspace allows determining the next direction. The set of directions identified in this way forms an orthogonal space, which represents most of the variation in the data. We call this process visual component analysis (VCA). Furthermore, it is quite simple to integrate VCA with clustering. The user fits poly-lines to the displayed data, and the poly-lines implicitly define clusters. Per-cluster projection leads to the definition of per-cluster components.
Ray Casting Curved-Quadratic Elements
(The Eurographics Association, 2004) Wiley, D. F.; Childs, H. R.; Hamann, B.; Joy, K. I.; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
We present a method for ray casting curved-quadratic elements in 3D. The advantages of this approach is that a curved element can be directly visualized. Conventionally, higher-order elements are tessellated with several linear elements so that standard visualization techniques can be applied to the linear elements. Our method primarily focuses on how to find an approximation to the intersection between a ray and a curved-quadratic element. Once this approximation is found, conventional accumulation and color mapping techniques can be applied to the approximation to produce a volumetric visualization of the element. A cutting plane implementation is also shown that leverages the ray casting technique.
Illustrating Surfaces in Volume
(The Eurographics Association, 2004) Yuan, Xiaoru; Chen, Baoquan; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
This paper presents a novel framework for illustrating surfaces in a volume. Surfaces are illustrated by drawing only feature lines, such as silhouettes, valleys, ridges, and surface hatching strokes, and are embedded in volume renderings. This framework promises effective illustration of both surfaces and volumes without occluding or cluttering each other. A two-step approach has been taken: the first step depicts surfaces; the second step performs volume rendering, at the same time embedding surfaces from the first step. We introduce Procedurally Perturbed Image Processing (PIP), a new method for enhancing both feature detection and depiction of surfaces. We also present implementation strategies, especially those leveraging modern graphics hardware, for delivering an interactive rendering system. Our implementation results have shown that this mixed form of rendering improves volume visualization and is efficient.

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