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Keynote Address

Visualization for Knowledge Workers, St. Eick
Abstract: Visualization has had a huge impact on Science and is beginning to emerge into the mainstream. Notable successes have been in focused domains including, for example, medical imaging and weather forecasting. Many believe that we are on the cusp of broad, deployment of this technology. It has the potential to touch all knowledge workers and become the next user interface for business decision making. To help deliver on this promise we have developed a suite of visualization components providing a rich user experience, a visualization workbench for rapidly scripting applications, and exercised the workbench to address several customer behavior-related and network management-oriented problems. We are finding that the visualization techniques gaining the most traction with these new users are related to, but different from those developed in the scientific community.

Research Papers 1 - Feature Tracking and Visualization Systems

Attribute-Based Feature Tracking, F. Reinders, F.H. Post, H.J.W. Spoelder
Abstract: Visualization of time-dependent data is an enormous task because of the immense amount of data involved. However, most of the time the scientist is mainly interested in the evolution of certain features. Therefore, it suffices to show the evolution of these features. The task of the visualization system is to extract the features from all frames, to determine the correspondence between features in successive frames, and finally to visualize the tracking results. This paper describes a tracking system that uses feature data to solve the correspondence problem. It tracks feature paths and determines their evolution in time. The feature data consists of basic attributes such as position, size, and mas. For each set of attributes a number of correspondence functions can be tested which results in a correspondence factor. This factor makes it possible to quantify the goodness of the match between two features in successive time frames. Since thealgorithm uses only a small data set, it is feasible to perform an extensive multi-pass search for continuing paths.

Vission: An Object Oriented Dataflow System for Simulation and Visualization, A. Telea, J.J. van Wijk
Abstract: Scientific visualization and simulation specification and monitoring are sometimes addressed by object-oriented environments. Even though object orientation powerfully and elegantly models many application domains, integration of OO libraries in such systems remains a difficult task. The elegance and simplicity of object orientation is often lost in the integration phase, so combining OO and dataflow concepts is usually limited. We propose a system for visualization and simulation with a generic object-oriented way to simulation design, control and interactivity, which merges OO and dataflow modelling in a single abstraction. Advantages of the proposed system over similar tools are presented and illustrated by a comprehensive set of examples.

A Client-side Approach towards Platform Independent Molecular Visualization over the World Wide Web, M. Bender, H. Hagen, A. Seck
Abstract: A web-based, entirely platform independent Molecular Visualization System has been developed using state of the art Internet programming techniques. This system offers the visualization of various molecular models, molecular surfaces and chemical or physical molecular properties which can be displayed at the same time. The system itself has been developed using the Java programming language, which allows flexible and platform independent use, perfect integration with the World Wide Web and due to its object-oriented structure easy extension and maintenance. All necessary calculations, e.g. the calculation of a Richards' Contact Surface or an Isosurface, take place on the client's side exploiting the computational power of modern desktop workstations and personal computers. This powerful approach offers new possibilities in Teaching, Web Publishing and Drug Design.

Research Papers 2 - Medical Imaging

Fast Volume Rotation using Binary Shear-Warp Factorization, B. Csebfalvi
Abstract: This paper presents a fast volume rotation technique based on binary shear-warp factorization. Unlike many acceleration algorithms this method does not trade image quality for speed and does not require any specialized hardware either. In order to skip precisely the empty regions along the rays to be evaluated a binary volume is generated indicating the locations of the transparent cells. This mask is rotated by an incremental binary shear transformation, executing bitwise boolean operations on integers storing the bits of the binary volume. The ray casting is accelerated using the transformed mask and an appropriate lookup-table technique for finding the first non-transparent cell along each ray.

VIVENDI - A Virtual Ventricle Endoscopy System for Virtual Medicine, D. Bartz, M. Skalej
Abstract: Virtual Medicine is an emerging and challenging field in Computer Graphics. Numerous visualization methods are used to model and render data of different modalities. In this paper, we present a new endoscopy system for virtual medicine. The main purpose of this system is to provide support for the planning of complicated endoscopic interventions inside of the ventricular system of the human brain. Although, our current focus is on ventricle endoscopy, this system is applicable to other areas as well. In order to achieve interactive framerates on workstations with medium graphics performance, we apply an efficient implementation of a basic algorithms for general visibility queries.

Real-Time Maximum Intensity Projection, L. Mroz, A. König, E.Gröller
Abstract: Maximum Intensity Projection (MIP) is a volume rendering technique which is used to extract high-intensity structures from volumetric data. At each pixel the highest data value encountered along the corresponding viewing ray is determined. MIP is commonly used to extract vascular structures from medical MRI data sets (angiography). The usual way to compensate for the loss of spatial and occlusion information in MIP images is to view the data from different view points by rotating them.As the generation of MIP is usually non-interactive, this is done by calculating multiple images offline and playing them back as an animation. In this paper a new algorithm is proposed which is capable of interactively generating Maximum Intensity Projection images using parallel projection and templates. Voxels of the data set which will never contribute to a MIP due to their neighborhood are removed during a preprocessing step. The remaining voxels are stored in a way which guarantees optimal cache coherency regardless of the viewing direction. For use on low-end hardware, a preview-mode is included which renders only more significant parts of the volume during user interaction. Furthermore we demonstrate the usability of our data structure for extensions of the MIP technique like MIP with depth-shading and Local Maximum Intensity Projection (LMIP).

Case Studies 1 - Flow, Meteorological, and Molecular Visualization

Exploring Instationary Fluid Flows by Interactive Volume Movies, T. Glau
Abstract: Volume rendering offers the unique ability to represent inner object data and to realize enclosed structures "at first sight". Unlike software-based methods, the use of more and more available special-purpose hardware allows volume rendering at interactive frame rates - a crucial criterion for acceptance in industrial applications, e.g. CFD analysis. Careful optimizations and the exclusive use of hardware-accelerated data manipulation facilities even enable volume rendered movies supporting real time interactivity. This article presents the most important features and implementation issues of an OpenInventor-based stereoscopic, VR-featured volume rendering system for instationary datasets.

Where Weather Meets the Eye -- A Case Study on a Wide Range of Meteorological Visualisations for Diverse Audiences, H. Haase, M. Bock, E. Hergenröther, C. Knöpfle, H.-J. Koppert, F. Schröder, A. Trembilski, J. Weidenhausen
Abstract: Sophisticated visualisation enables experts as well as lay persons to extract knowledge from complex data. This is particularly true for visualising the massive amounts of data involved in meteorological observations and simulations. These are of interest to scientists, to forecasters, and to the general public. The paper presents and discusses a range of solutions for meteorlogical visualisation. Topics covered include systems for the production of TV weather forecasts, for the analysis of simulation output by experts, for personalised weather information in the Web, and for meteorological visualisation using Virtual Studio and Augmented Reality technology.

Visualization of Molecules with Positional Uncertainty, P. Rheingans, S. Joshi
Abstract: Designing new and better chemotherapeutic compounds requires an understanding of the mechanism by which the drugs exert their biological effects. This involves consideration of the geometry of the active site, determination of the geometry of the drug, and analysis of the fit between them. This problem of drug-substrate fit, often called the docking problem, can be greatly influenced by uncertainty in the position of drug side chains. Traditional molecular graphics techniques fail to capture the distribution of likely atom positions. This paper describes a range of techniques for showing atom positions as probability distributions that more completely describe parameters which determine fit.

Research Papers 3 - Flow Visualization

Visualization of Global Flow Structures Using Multiple Levels of Topology, W. de Leeuw, R. van Liere
Abstract: The technique for visualizing topological information in fluid flows is well known. However, when the technique is used in complex and information rich data sets, the result will be a cluttered image which is difficult to interpret. This paper presents a technique for the visualization of multi-level topology in flow data sets. It provides the user with a mechanism to visualize the topology without excessive cluttering while maintaining the global structure of the flow.

2D Vector Field Visualization Using furlike texture, L. Khouas, C. Odet, D. Friboulet
Abstract: This paper presents a new technique for 2D vector field visualization. Our approach is based on the use of a furlike texture. For this purpose, we have first developed a texture model that allows two dimensional synthesis of 3D furlike texture. The technique is based on a non stationary two dimensional AutoRegressive synthesis (2D AR). The texture generator allows local control of orientation and length of the synthesized texture (the orientation and length of filaments). This texture model is then used to represent 2D vector fields. We can use orientation, length, density and color attributes of our furlike texture to visualize local orientation and magnitude of a 2D vector field. The visual representations produced are satisfying since complete information about local orientation is easily perceived. We will show that the technique can also produce LIC-like texture. In addition, due to the AR formulation, the obtained technique is computationnally efficient.

Geometric Methods for Vortex Extraction, I. Ari Sadarjoen, F.H. Post
Abstract: This paper presents two vortex detection methods which are based on the geometric properties of streamlines. Unlike traditional vortex detection methods, which are based on point-samples of physical quantities, one of our methods is also effective in detecting weak vortices. In addition, it allows for quantitative feature extraction by calculating numerical attributes of vortices. Results are also presented of applying these methods to CFD simulation data sets.

Research Papers 4 - Information Visualization

Procedural Shape Generation for Multi-dimensional Data Visualization, D.S. Ebert, R.M. Rohrer, C.D. Shaw, P. Panda, J.M. Kukla, D. Aaron Roberts
Abstract: Visualization of multi-dimensional data is a challenging task. The goal is not the display of multiple data dimensions, but user comprehension of the multi-dimensional data. This paper explores several techniques for perceptually motivated procedural generation of shapes to increase the comprehension of multi-dimensional data. Our glyph-based system allows the visualization of both regular and irregular grids of volumetric data. A glyph's location, 3D size, color, and opacity encode up to 8 attributes of scalar data per glyph. We have extended the system's capabilities to explore shape variation as a visualization attribute. We use procedural shape generation techniques because they allow flexibility, data abstraction, and freedom from specification of detailed shapes. We have explored three procedural shape generation techniques: fractal detail generation, superquadrics, and implicit surfaces. These techniques allow from 1 to 14 additional data dimensions to be visualized using glyph shape.

Skeletal Images as Visual Cues in Graph Visualization, I. Herman, M.S. Marshall, G. Melancon, D.J. Duke, M. Delest, J.-P. Domenger
Abstract: The problem of graph layout and drawing is fundamental to many approaches to the visualization of relational information structures. As the data set grows, the visualization problem is compounded by the need to reconcile the user's need for orientation cues with the danger of information overload. Put simply: How can we limit the number of visual elements on the screen so as not to overwhelm the user yet retain enough information that the user is able to navigate and explore the data set confidently? How can we provide orientational cues so that a user can understand the location of the current viewpoint in a large data set? These are problems inherent not only to graph drawing but information visualization in general. We propose a method which extracts the significant features of a directed acyclic graph as the basis for navigation (Note: The color figures and a demonstration applet are available at the web site: http://www.cwi.nl/InfoVisu).

Visualization by Examples: Mapping Data to Visual Representations Using Few Correspondences, M. Alexa, W. Müller
Abstract: In this paper we propose a new approach for the generation of visual scales for the visualization of scalar and multivariate data. Based on the specification of only a few correspondences between the data set and elements of a space of visual representations complex visualization mappings are produced. The foundation of this approach is the introduction of a multidimensional space of visual representations. The mapping between these spaces can be defined by approximating or satisfying the user defined relations between data values and visual atributes.

Case Studies 2 - Medical Applications

Parallel Ray Casting of Visible Human on Distributed Memory Architectures,C. Bajaj, I. Ihm, G. Koo, S. Park
Abstract: This paper proposes a new parallel ray-casting scheme for very large volume data on a distributed-memory architecture. Our method, based on data compression, attempts to enhance the speedup of parallel rendering by quickly reconstructing data from local memory rather than expensively fetching them from remote memory spaces. Furthermore, it takes the advantages of both object-order and image-order traversal algorithms: It exploits object-space and image-space coherence, respectively, by traversing volumes block-wise and using a run-time quadtree which is maintained dynamically against pixels' opacity values. We report experimental results on Cray T3E for the Visible Man dataset.

Analysis and Visualization of the Brain Shift Phenomenon, C. Luerig, P. Hastreiter, C. Nimsky, T. Ertl
Abstract: In this paper we present a method for analyzing the brain shift. The brain shift is a brain deformation phenomenon, that occurs during surgical operations on the opened head. This deformation makes navigation within the brain very difficult for the surgeon, as preoperative magnetic resonance images invalidate very quickly after the beginning of the operation. Up to now not enough is known about this deformation phenomenon in order to come up with solutions for corrective action. The aim of the tool which is presented here is to prepare ground for a better understanding by visualizing the deformation between two 3D brain data sets, where one has been taken preoperatively and the second one during the operation after the brain shift has occured. We propose a new method for the modeling of the deformation by means of efficient distance determination of two deformable surface approximations. Color coding and semi-transparent overlay of the surfaces provides qualitative and quantitative information about the brain shift. The provided insight may lead to a prediction method in future.

Advances in Quality Control of Intraoperative Radiotherapy, S. Walter, G. Straßmann, M. Schmitt
Abstract: Intra Operative Radiotherapy is a kind of Brachytherapy where the remains of a surgically not completely removed tumour are irradiated at the open situ of the patient. The current main drawback of this radiation treatment is the insufficient documentation of the applied radiation and the lack of a possibility for an individual treatment planning. This work presents a system that is a common development of the Fraunhofer IGD and the St{\"a}dtische Klinik Offenbach and MedCom GmbH that offers a possibility for interactive supervision of the placement of the irradiation flabs, the creation of a documentation of the applied isodose as well as the possibility for an individual intra operative radiation treatment planning.

Research Papers 5 - Large Data Sets and Scattered Data

On Simulated Annealing and the Construction of Linear Spline Approximations for Scattered Data, O. Kreylos, B. Hamann
Abstract: We describe a method to create optimal linear spline approximations to arbitrary functions of one or two variables, given as scattered data without known connectivity. We start with an initial approximation consisting of a fixed number of vertices and improve this approximation by choosing different vertices, governed by a simulated annealing algorithm. In the case of one variable, the approximation is defined by line segments; in the case of two variables, the vertices are connected to define a Delaunay triangulation of the selected subset of sites in the plane. In a second version of this algorithm, specifically designed for the bivariate case, we choose vertex sets and also change the triangulation to achieve both optimal vertex placement and optimal triangulation. We then create a hierarchy of linear spline approximations, each one being a superset of all lower-resolution ones.

Parallel Multipipe Rendering for Very Large Isosurface Visualization, T. Udeshi, Ch.D. Hansen
Abstract: In exploratory scientific visualization, isosurfaces are typically created with an explicit polygonal representation for the surface using a technique such as Marching Cubes. This surface is subsequently rendered with an attached graphics hardware accelerator such as the SGI Infinite Reality. For even moderate data sets, Marching Cubes can generate an extraordinary number of polygons, which take time to construct and to render. As the isovalue is changed, the resulting surface, and perhaps the topology, is modified making display lists impractical. Current generation of high-end graphics adapters, such as the SGI Infinite Reality, have a quoted maximum polygon rendering rate of around 10M polygons/second. However, in practice this rate is difficult to achieve primarily due to geometry traversal (appropriate display list) and pixel coverage of the polygons. As a result, when viewing isosurfaces of large, greater than 1GByte, data sets rendering becomes a bottle neck. We have recently seen the attachment of multiple graphics adapters on high-end SGI Onyx2 supercomputers. The multiple graphics pipes can be used for multiple users or they can be combined to provide a single user the power of parallel rendering. Until recently, there has not been much experimentation with this configuration for polygon rendering. To address the rendering bottleneck, we have developed a multipipe strategy for parallel rendering using a combination of CPUs and parallel graphics adaptors. The multipipe system uses multiple graphics adapters in parallel, the so called  SGI Onyx2 Reality Monster. In this paper, we discuss the issues of using the multiple pipes in a Sort-Last fashion which out performs a single graphics adaptor for a surprisingly low number of polygons.

Efficient Ray Intersection for Visualization and Navigation of Global Terrain using Spherical Height-Augmented Quadtrees, Z. Wartell, W. Ribarsky, L. Hodges
Abstract: We present an algorithm for efficiently computing ray intersections with multi-resolution global terrain partitioned by spheroidal height-augmented quadtrees. While previous methods support terrain defined on a Cartesian coordinate system, our methods support terrain defined on a two-parameter ellipsoidal coordinate system. This curvilinear system is necessary for an accurate model of global terrain. Supporting multi-resolution terrain and quadtrees on this curvilinear coordinate system raises a surprising number of complications. We describe the complexities and present solutions. The final algorithm is suited for interactive terrain selection, collision detection and simple LOS (line-of-site) queries on global terrain.

Research Papers 6 - Geometry and Grid Visualization

Geodesic Flow on Polyhedral Surfaces, K. Polthier, M. Schmies
Abstract: On a curved surface the front of a point wave evolves in concentric circles which start to overlap and branch after a certain time. This evolution is described by the geodesic flow and helps to understand the geometry of surfaces. In this paper we compute the evolution of distance circles on polyhedral surfaces and develop a method to visualize the set of circles, their overlapping, branching, and their temporal evolution simultaneously. We consider the evolution as an interfering wave on the surface, and extend isometric texture maps to efficiently handle the branching and overlapping of the wave.

A Comparison of Error Indicators on Nested Grids for Multilevel Visualization, T. Gerstner, M. Rumpf, U. Weikard
Abstract: Multiresolution visualization methods have recently become an indispensable ingredient of real time interactive post processing. Here local error indicators serve as criteria where to refine the data representation on the physical domain. In this article we give an overview on different types of error measurement on nested grids and compare them for selected applications in 2D as well as in 3D. Furthermore, it is pointed out that a certain saturation of the considered error indicator plays an important role in multilevel visualization and can be reused for the evaluation of data bounds in hierarchical searching or for a multilevel backface culling ofisosurfaces.

New Approaches for Particle Tracing on Sparse Grids, C. Teitzel, T. Ertl
Abstract: Flow visualization tools based on particle methods continue to be an important utility of flow simulation. Additionally, sparse grids are of increasing interest in numerical simulations. In [Teitzel-etal-98:Springer],  we presented the advantages of particle tracing on uniform sparse grids. Here we present and compare two different approaches to accelerate particle tracing on sparse grids. Furthermore, a new approach is presented in order to perform particle tracing on curvilinear sparse grids. The method for curvilinear sparse grids consists of a modified Stencil Walk algorithm and especially adapted routines to compute, store, and handle the required Jacobians. The accelerating approaches are on the on hand an adaptive method, where an error criterion is used to skip basis functions subspaces with minor contribution coefficients, and on the other hand the so-called combination technique, which uses a specific selection of small full grids to emulate sparse grids.

Case Studies 3 - Information Visualization and Web-based Visualization

Application of Information Visualization to the Analysis of Software Release History, H. Gall, M. Jazayeri, C. Riva
Abstract: We present our experiences in applying information visualization techniques to the study of the evolution of a large telecommunication software system. We used the third dimension to portray the temporal evolution of the system and color to display software attributes. The visualization was surprisingly successful in uncovering interesting and useful patterns in the system’s evolution. To do the visualization, we built a tool that combines off-the-shelf components: a database for storing software release data, VRML for displaying and navigating three-dimensional data, and a web browser for the user-interface. The tool is published on the web. The tool is capable of providing effective views of data that are always kept by software development organizations but are often ignored. Information visualization makes it possible to exploit such historical data about past projects to help in the planning stages of future software projects.

Internet-Based Front-End to Network Simulator, T. He
Abstract: We present an Java-based interactive visual interface to the network simulator. Having successfully incorporated the network visualization technologies, our system provides an effective front-end interface supporting real time control and monitoring of the back-end simulator through Internet or Intranet.

Visualization of Grinding Processes, M. Fiege, G. Scheuermann, M. Muenchhofen, H. Hagen
Abstract: In grinding technology, the application of superabrasives and increasing demands for higher productivity and higher quality require an appropriate selection of optimum set-up parameters. An efficient way to determine and test these parameters is modeling and simulating the grinding process. A visualization of the simulation-data can support the choice of the parameters and increase the knowledge of the complex grinding process. This paper describes a web-based visualization tool on the basis of a kinematic simulation. The tool allows the visualization of the surface of an already ground workpiece as well as the changing shape of the workpiece during the grinding process. Two methods for the visualization of the grinding-objects are implemented. One method describes the scene with the Virtual Reality Modeling Language, the other one uses a renderer to create the images.

Research Papers 7 - Volume Visualization

Efficiently Rendering Large Volume Data Using Texture Mapping Hardware, X. Tong, W. Wang, W. Tsang, Z. Tang
Abstract: Volume rendering with texture mapping hardware is a fast volume rendering method available on high-end workstations. However, limited texture memory prevents the method from being used to render large volume data efficiently. In this paper, we propose a new approach to accelerate volume rendering with texture mapping hardware. Based on a new volume-loading pipeline, the volume data is preprocessed efficiently before rendering. Only the volume data that contains object voxels are loaded into texture memory and resampled for rendering. Moreover, for modified classification threshold, our algorithm classifies and processes the raw volume data nearly in real time. Test show that about 40% to 60% rendering time is saved in our method for large volume data.

Interactive Direct Volume Rendering of Time-Varying Data, J. Clyne, J. Dennis
Abstract: Previous efforts aimed at improving direct volume rendering performance in order to achieve interactive frame rates have focused largely on time-invariant, 3D datasets. Little work has been done in the area of interactive direct volume rendering of time-varying data, such as is commonly found in Computation Fluid Dynamics (CFD) simulations. Until recently, the additional costs imposed by time-varying data have made consideration of interactive direct volume rendering impractical. We present a volume rendering system based on a parallel implementation of the Shear-Warp Factorization algorithm that is capable of rendering time-varying 128^3 datasets at interactive speeds. A number of advances in computing have made this achievement possible: availability of inexpensive, high-performance I/O systems; high-bandwidth, commodity networking; commercial, microprocessor-based, shared-memory multiprocessors; and new, highly-optimized rendering algorithms.

A Methodology for Comparing Direct Volume Rendering Algorithms Using a Projection-Based Data Level Approach, K. Kim, A. Pang
Abstract: Identifying and visualizing uncertainty together with the data is a well recognized problem. One of the culprits that introduce uncertainty in the visualization pipeline is the visualization algorithm itself. Uncertainties introduced this way usually arise from approximations and manifests themselves as artifacts in the resulting images. In this paper, we focus on comparing different direct volume rendering (DVR) algorithms and their artifacts as a result of DVR algorithm selections and their associated parameter settings. We present a new data level comparison methodology that uses differences in intermediate rendering information. In particular, we extend the traditional image level comparison techniques to include data level comparison techniques. In image level comparisons, quantized pixel values are the starting point for comparison measurements. In contrast, data level comparison techniques have the advantage of accessing and evaluating the intermediate 3D information during the rendering process. Our data level approach overcomes limitations of image level approaches and provide capabilities to compare application dependent details as well as general rendering qualities. One of the key challenges with our data level comparison approach is finding a common base for comparing the rich variety of DVR algorithms. In this paper, we present how a projection algorithm can be used as a base for comparing other DVR algorithms.In addition, a set of projection-based metrics are derived to quantify the comparison measurements among DVR algorithms. The results presented in this paper complement our earlier findings where a ray-based approach was used as the base for comparing other DVR algorithms.

Helwig Löffelmann & Kei Nam Tsoi (Joe), 1998-1999, mailto:helwig@cg.tuwien.ac.at & mailto:joe@cg.tuwien.ac.at.