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.
Adaptive Volume Construction from Ultrasound Images of a Human Heart
(The Eurographics Association, 2004) Reis, Gerd; Bertram, Martin; Lengen, Rolf H. van; Hagen, Hans; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
We present a volume modelling approach based on sequences of two-dimensional ultrasound images. Though generally applicable to arbitrary freehand ultrasound, our method is designed for the reconstruction of timevarying volumes from ultrasound images of a human heart. Since the reliability of the reconstructed data depends very much on the spatial density of ultrasound images, we apply a hierarchical modelling approach. The volume produced for each time step is represented as adaptive mesh refinement (AMR) data such that regions of low reliability in the reconstructed volume can be recognized by their coarse resolution.
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.
A Botanically Inspired High-Dimensional Visualization with Multivariate Glyphs
(The Eurographics Association, 2004) Chlan, E. B.; Rheingans, Penny; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
It is difficult for the average viewer to assimilate and comprehend huge amounts of high-dimensional data. It is important to present data in a way that allows the user a high level understanding of the overall organization and structure without losing the ability to study low level detail as needed. Although hierarchically clustered data is already organized, many current means of presenting such data give the user little more than an overview of the organization. It would be useful to see more information about the data even at a high level and to examine specific clusters as needed. We want to understand the relationships of the clusters in terms of the underlying data, and to understand the extent and variability of the data without requiring examination of each data item. To meet these goals, we present an aesthetically appealing visualization based on botanical trees which preserves the natural order of hierarchically organized data. Hierarchical data is rendered as a simple branched tree. The tree gives an overview of the relationships among various clusters and is supplemented with two glyphs which allow the user to focus in on specific clusters of the data at different levels of detail. At a medium level of focus, a cluster glyph based on a radial, space filling approach shows the subtree rooted at a specified cluster. At a low level of detail, the branch glyph allows the viewer to see not only aggregate information about the cluster but the extent and variability of the component clusters.
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.
Browsing and Visualizing Digital Bibliographic Data
(The Eurographics Association, 2004) Klink, Stefan; Ley, Michael; Rabbidge, Emma; Reuther, Patrick; Walter, Bernd; Weber, Alexander; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
Access to publications is provided by conventional libraries, digital libraries operated by learned societies or commercial publishers, and a huge number of web sites maintained by the scientists themselves or their institutions. But comprehensive meta-indices in combination with a helpful graphical user interface for this increasing number of information sources are missing for most areas of science. Our DBLP (Digital Bibliography & Library Project) Computer Science Bibliography is a major service used by thousands of computer scientists. It provides fundamental support for scientists searching for publications or other scientists in similar communities. For better assistance we developed a new browser prototype which has a user-friendly interface and plays a central role in the search and browsing of the data. The DBL-Browser provides smart search functions and several textual and graphical visualization models. This paper gives an overview of some important research issues within the field of bibliographical information retrieval and visualization. After introducing the whole framework, the DBL-Browser itself and various visualization models are described.
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.
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.
A Cluster-Space Visual Interface for Arbitrary Dimensional Classification of Volume Data
(The Eurographics Association, 2004) Tzeng, Fan-Yin; Ma, Kwan-Liu; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
In volume visualization, users typically specify transfer functions to classify the data and assign visual attributes to each material class. Higher-dimensional classification makes it easier to differentiate material classes since more data properties are considered. One of the difficulties in using higher-dimensional classification is the absence of appropriate user interfaces. We introduce an intuitive user interface that allows the user to work in the cluster space, which shows the material classes with a set of material widgets, rather than work in the transfer function space. This interface not only provides the user the capability to specify arbitrary-dimensional transfer functions, but also allows the user to operate directly on the classification and visualization results.
DTI Visualization with Streamsurfaces and Evenly-Spaced Volume Seeding
(The Eurographics Association, 2004) Vilanova, A.; Berenschot, G.; Pul, C. van; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
Experimental evidence has shown that water diffusion is anisotropic in organized tissues such as white matter or muscles. Diffusion Tensor Imaging is a non-invasive MR technique that measures water diffusion. DTI is used to visualize linear structures such as fibers. In this paper, we present a visualization tool for DTI data. A new algorithm to visualize linear structures in areas of crossing or converging fibers is presented. Usually the user defines an area from where the fibers are generated. In this way, the user can miss part of the information, if the area is not correctly defined. We present a method to visualize the structures in the whole volume with an evenly-spaced distance between them. Some results obtained by our partners using the DTI tool will be presented.
Efficient Display of Background Objects for Virtual Endoscopy using Flexible First-Hit Ray Casting
(The Eurographics Association, 2004) Neubauer, A.; Forster, M.; Wegenkittl, R.; Mroz, L.; Bühler, K.; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
Many applications of virtual endoscopy require the display of background objects behind the semi-transparent surface of the investigated organ. This paper deals with pre-processing and visualization of background objects for virtual endoscopy. A new first-hit ray casting technique for efficient perspective iso-surfacing of arbitrarily selected objects of interest is described: Visualization is performed without the use of dedicated hardware or data structures limiting flexibility (e.g., polygonal meshes or distance fields). The speedup is gained by exploiting inter-pixel coherency and by finding a near-optimal compromise between reduction of ray-tracking distances and limitation of the administrational cost associated with this reduction. The algorithm was developed by enhancing the previously published cell-based first-hit ray casting algorithm. This paper describes the original algorithm and explains the extensions needed to achieve interactive rendering of background objects.
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.
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.
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.
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.
High-Quality Lighting and Efficient Pre-Integration for Volume Rendering
(The Eurographics Association, 2004) Lum, Eric B.; Wilson, Brett; Ma, Kwan-Liu; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
Pre-integrated volume rendering is an effective technique for generating high-quality visualizations. The precomputed lookup tables used by this method are slow to compute and can not include truly pre-integrated lighting due to space constraints. The lighting for pre-integrated rendering is therefore subject to the same sampling artifacts as in standard volume rendering. We propose methods to speed up lookup table generation and minimize lighting artifacts. The incremental subrange integration method we describe allows interactive lookup table generation in O(n<sup>2</sup>) time without the need for approximation or hardware assistance. The interpolated preintegrated lighting algorithm eliminates discontinuities by linearly interpolating illumination along the view direction. Both methods are applicable to any pre-integrated rendering method, including cell projection, ray casting, and hardware-accelerated algorithms.
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.
Interaction Spaces in Data and Information Visualization
(The Eurographics Association, 2004) Ward, M.; Yang, J.; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
User interaction plays an integral part in the effective visualization of data and information. Typical interaction operations include navigation, selection, and distortion. A problem that can occur when these operations are speci£ed using direct manipulation is determining which object or space is the focus of the interaction. In some operations the user wants to indicate a region of an image, while in others the focus might be the data being projected or the surface upon which the projection is occurring. In this paper we attempt to identify a complete list of spaces within which interactive operations can occur in data and information visualization. These interaction spaces help disambiguate the focus of interactive operations, and their study can potentially reveal new and powerful methods for supporting the visual exploration process. We de£ne the distinctions between the spaces and provide examples of interactions within each space.
Interactive High Quality Trimmed NURBS Visualization Using Appearance Preserving Tessellation
(The Eurographics Association, 2004) Guthe, M.; Balázs, Á.; Klein, R.; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
Trimmed NURBS models are the standard representation used in CAD/CAM systems and accurate visualization of large trimmed NURBS models at interactive frame rates is of great interest for industry. To visualize the quality of a surface several techniques like isophotes, reflection lines, etc. are used. Most existing approaches transform the NURBS surfaces into a fine polygonal representation and build static levels of detail from this representation. This polygonal approximation together with its normals are adjusted in a semi-automatic procedure to achieve the desired visual fidelity during visualization. Since this approach allows only for a fixed maximum accuracy and does not support deformable models, another more recent approach is to keep the NURBS representation and generate view-dependent LODs on the fly up to the currently required preciseness. However, so far this approach took only into account the geometric error of an approximation and thus neglected the various illumination artifacts introduced by the chosen (possibly view-dependent) triangulation. Although this problem can be solved by using normal maps, the resolution of the normal maps again limits the accuracy. Furthermore, the normal map generation requires a preprocessing step which prevents the support of deformable NURBS models. In this paper we present a novel automatic tessellation algorithm that considers the illumination artifacts and is well suited both for the generation of static and dynamic LOD schemes with guaranteed visual fidelity. Our new method is also capable of high quality visualization of further attributes like curvature, temperature, etc. on surfaces with little or no modification.
Interactive TreemapsWith Detail on Demand to Support Information Search in Documents
(The Eurographics Association, 2004) Schlechtweg, Stefan; Schulze-Wollgast, Petra; Schumann, Heidrun; Oliver Deussen and Charles Hansen and Daniel Keim and Dietmar Saupe
This paper addresses the issue of how information visualization techniques can be used to assist full-text search in electronic documents. Our approach supports multiple term queries with interactive treemaps. We use a treemap to visualize the basic structure of the document and exploit color coding to show the distribution of query terms on various levels of the hierarchy. Furthermore, we include filtering techniques to concentrate on those parts of the structure that actually contain the requested information, and, finally provide interactive tools to give access to detailed information whenever the user wishes.

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