VisSym00: Joint Eurographics - IEEE TCVG Symposium on Visualization

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Skeleton Graph Generation for Feature Shape Description
(The Eurographics Association, 2000) Reinders, Freek; Jacobson, Melvin E.D.; Post, Frits H.; W. de Leeuw and R. van Liere
An essential step in feature extraction is the calculation of attribute sets describing the characteristics of a feature. Often, attribute sets include the position, size, and orientation of the feature. These attributes are very important, but they do not provide a good approximation of the shape of a feature. For better shape description, a more sophisticated method is needed. This paper describes a method that extracts a binary skeleton of a feature, and transforms it into a graphical representation: the skeleton-graph. This graph represents the original skeleton with controlled precision, and contains the essential topology and geometry of the skeleton. In addition, distance information is used to generate a simplified reconstruction of the original 3D feature shape, which can also be used as an iconic object for visualization.
Squarified Treemaps
(The Eurographics Association, 2000) Bruls, Mark; Huizing, Kees; Wijk, Jarke J. van; W. de Leeuw and R. van Liere
An extension to the treemap method for the visualization of hierarchical information, such as directory structures and organization structures, is presented. The standard treemap method often gives thin, elongated rectangles. As a result, rectangles are difficult to compare and to select. A new method is presented to generate lay-outs in which the rectangles approximate squares. To strenghten the visualization of the structure, shaded frames are used around groups of related nodes.
ViSSh: A Data Visualisation Spreadsheet
(The Eurographics Association, 2000) Nunez, Fabian; Blake, Edwin; W. de Leeuw and R. van Liere
We describe a data visualisation system which uses spreadsheets as its user interface metaphor. Similar systems implemented in the past were hampered by the contradiction between an imperative formula language and the declarative spreadsheet framework. We have analysed spreadsheets from a data visualisation point of view, and built a system that is an improvement over past efforts. Our prototype combines the following three techniques: we store lists of values in each spreadsheet cell; we use a functional programming language as the formula language and we make use of lazy evaluation. The novel combination of these techniques makes our system consistently declarative in nature, and gives it several advantages such as small, uncluttered visual programs, the ability to deal with
A Case Study of Isosurface Extraction Algorithm Performance
(The Eurographics Association, 2000) Sutton, Philip M.; Hansen, Charles D.; Shen, Han-Wei; Schikore, Dan; W. de Leeuw and R. van Liere
Isosurface extraction is an important and useful visualization method. Over the past ten years, the field has seen numerous isosurface techniques published, leaving the user in a quandary about which one should be used. Some papers have published complexity analysis of the techniques, yet empirical evidence comparing different methods is lacking. This case study presents a comparative study of several representative isosurface extraction algorithms. It reports and analyzes empirical measurements of execution times and memory behavior for each algorithm. The results show that asymptotically optimal techniques may not be the best choice when implemented on modern computer architectures.
Appearance-Based Virtual-View Generation for Fly Through in a Real Dynamic Scene
(The Eurographics Association, 2000) Baba, Shigeyuki; Saito, Hideo; Vedula, Sundar; Cheung, Kong Man; Kanade, Takeo; W. de Leeuw and R. van Liere
We present appearance-based virtual view generation which allows viewers to fly through a real dynamic scene. The scene is captured by synchronized multiple cameras. Arbitrary views are generated by interpolating two original camera-view images near the given viewpoint. The quality of the generated synthetic view is determined by the precision, consistency and density of correspondences between the two images. All or most of previous work that uses interpolation extracts the correspondences from these two images. However, not only is it difficult to do so reliably (the task requires a good stereo algorithm), but also the two images alone sometimes do not have enough information, due to problems such as occlusion. Instead, we take advantage of the fact that we have many views, from which we can extract much more reliable and comprehensive 3D geometry of the scene as a 3D model. The dense and precise correspondences between the two images, to be used for interpolation, are derived from this constructed 3D model. Our method of 3D modeling from multiple images uses the Multiple Baseline Stereo method and Shape from Silhouette method.
Hardware Accelerated Wavelet Transformations
(The Eurographics Association, 2000) Hopf, Matthias; Ertl, Thomas; W. de Leeuw and R. van Liere
Wavelets and related multiscale representations are important means for edge detection and processing as well as for segmentation and registration. Due to the computational complexity of these approaches no interactive visualization of the extraction process is possible nowadays. By using the hardware of modern graphics workstations for accelerating wavelet decomposition and reconstruction we realize a first important step for removing lags in the visualization cycle.
Improving Angular Resolution in Visualizations of Geographic Networks
(The Eurographics Association, 2000) Brandes, Ulrik; Shubina, Galina; Tamassia, Roberto; W. de Leeuw and R. van Liere
In visualizations of large-scale transportation and communications networks, node coordinates are usually fixed to preserve the underlying geography, while links are represented as geodesics for simplicity. This often leads to severe readability problems due to poor angular resolution, i.e. small angles formed by lines converging in a node. We present a new method using automatically routed cubic curves that both preserves node coordinates and eliminates the resolution problem. The approach is applied to representations in the plane and on the sphere, showing European train connections and Internet traffic, respectively.
Drawing Relational Schemas
(The Eurographics Association, 2000) Battista, Giuseppe Di; Didimo, Walter; Patrignani, Maurizio; Pizzonia, Maurizio; W. de Leeuw and R. van Liere
A wide number of practical applications would benefit from automatically generated graphical representations of relational schemas, in which tables are represented by boxes, and table attributes correspond to distinct stripes inside each table. Links, connecting two attributes of two different tables, represent relational constraits or join paths, and may attach arbitrarily to the left or to the right side of the stripes representing the attributes. To our knowledge no drawing technique is available to automatically produce diagrams in such strongly constrained drawing convention. In this paper we provide a polynomial time algorithm solving this problem and test its efficiency and effectiveness against a large test suite.
Contextual Visualization of Actor Status in Social Networks
(The Eurographics Association, 2000) Brandes, Ulrik; Wagner, Dorothea; W. de Leeuw and R. van Liere
We propose a novel information visualization approach for an analytical method applied in the social sciences. In social network analysis, social structures are formally represented as graphs, and structural properties of these graphs are assumed to be useful in the explanation of social phenomena. A particularly important such property is the relative status of actors in a given network. Since operationalizations of status are aggregate indices of vertices, researchers are not only interested in status, but also in the context leading to these values, i.e. the underlying social network. We therefore visualize the network in a layered fashion, mapping status scores to vertical coordinates. The resulting problem of determining horizontal positions of vertices such that the overall layout is readable, is algorithmically difficult, yet well-studied in the literature on graph drawing. We outline a customized approach that routinely produces satisfactory pictures at interactive speed.
Progressive Volume Models for Rectilinear Data using Tetrahedral Coons Volumes
(The Eurographics Association, 2000) Holliday, David J.; Nielson, Gregory M.; W. de Leeuw and R. van Liere
We present a new technique for modeling rectilinear volume data. The algorithm produces a trivariate model, F(x; y; z), which is piecewise defined over tetrahedra that fits the volume data to within a user specified tolerance. The technique is adaptive leading to an efficient model that is more complex where the data demands it. The novelty of the present technique is that a valid tetrahedrization is not required. Tetrahedral cells are subdivided as required by the error condition only. This type of cellular decomposition leads to a continuous model by the use of a tetrahedral Coons volume which has the ability to interpolate to arbitrary boundary data.
Towards visual matching as a way of transferring pre-operative surgery planning
(The Eurographics Association, 2000) Buck, Stijn De; Cleynenbreugel, Johan Van; Marchal, Guy; Suetens, Paul; W. de Leeuw and R. van Liere
This paper presents a case study towards intra-operative visualization of pre-operative medical images and surgery planning information. We describe a two stage procedure to provide a surgeon with valuable information during surgery, by augmenting live video with a 3D visualization of surgery planning. A first stage consists of automatic determination of the intrinsic parameters of the video camera by means of one image of a calibration object. It comprises an automatic ellipse extraction and a solution to the 2D-3D correspondence problem. With the intrinsic camera parameters known, we perform a second stage to compute the extrinsic camera parameters with respect to the patient under surgery, allowing us to position and visualize the medical images in the right place. Techniques are investigated to visualize and manipulate the pre-operative medical images in order to cope with changes in the surgery scene.
DAG Drawing from an Information Visualization Perspective
(The Eurographics Association, 2000) Melancon, G.; Herman, I.; W. de Leeuw and R. van Liere
When dealing with a graph, any visualization strategy must rely on a layout procedure at least to initiate the process. Because the visualization process evolves within an interactive environment the choice of this layout procedure is critical and will often be based on efficiency. This paper compares two popular layout strategies, one based on the extraction of a spanning tree, the other based on edge crossing minimization of directed acyclic graphs. The comparison is made based on a large number of experimental evidence gathered through random graph generation. The main conclusion of these experiments is that, contrary to the popular belief, usage of edge crossing minimization algorithms may be extremely useful and advantageous, even under the heavy requirements of information visualization.
Case Study: Resource Steering in a Visualization System
(The Eurographics Association, 2000) Chi, Ed H.; Riedl, John T.; W. de Leeuw and R. van Liere
Visual computational steering environments extend traditional visualization environments by enabling the user to interactively steer the computations applied to the data. In this paper, we develop a new type of computational steering. Resource steering extends current visual steering techniques by providing machine resource estimation and control to the user. With resource steering, the user controls the execution of the computation on a parallel or distributed computer based on experimentally or theoretically derived estimates of the parallel performance of the computation. We demonstrate this extended steering model by applying it to an information visualization system that analyzes genetic sequence similarity reports. We show how our extended steering model enhances the user s ability to control visualization computations.
Very Large Scale Visualization Methods for Astrophysical Data
(The Eurographics Association, 2000) Hanson, Andrew J.; Fu, Chi-Wing; Wernert, Eric A.; W. de Leeuw and R. van Liere
We address the problem of interacting with scenes that contain a very large range of scales. Computer graphics environments normally deal with only a limited range of orders of magnitude before numerical error and other anomalies begin to be apparent, and the effects vary widely from environment to environment. Applications such as astrophysics, where a single scene could in principle contain visible objects from the subatomic scale to the intergalactic scale, provide a good proving ground for the multiple scale problem. In this context, we examine methods for interacting continuously with simultaneously active astronomical data sets ranging over 40 or more orders of magnitude. Our approach relies on utilizing a single scale of order 1.0 for the definition of all data sets. Where a single object, like a planet or a galaxy, may require moving in neighborhoods of vastly different scales, we employ multiple scale representations for the single object; normally, these are sparse in all but a few neighborhoods. By keying the changes of scale to the pixel size, we can restrict all data set scaling to roughly four orders of magnitude. Navigation problems are solved by designing constraint spaces that adjust properly to the large scale changes, keeping navigation sensitivity at a relatively constant speed in the user s screen space.
Variational Approach to Vector Field Decomposition
(The Eurographics Association, 2000) Polthier, Konrad; Preuß, Eike; W. de Leeuw and R. van Liere
For the feature analysis of vector fields we decompose a given vector field into three components: a divergence-free, a rotation-free, and a harmonic vector field. This Hodge-type decomposition splits a vector field using a variational approach, and allows to locate sources, sinks, and vortices as extremal points of the potentials of the components. Our method applies to discrete tangential vector fields on surfaces, and is of global nature. Results are presented of applying the method to test cases and a CFD flow.
Design of Visualizations for Urban Modeling
(The Eurographics Association, 2000) Pinnel, L. Denise; Dockrey, Matthew; Brush, A.J. Bernheim; Borning, Alan; W. de Leeuw and R. van Liere
Urban planning experts often use computer models to help evaluate alternative land use policies, particularly as they interact with transportation and environmental decisions. The greatly increased data volume provided by new land use models makes their effective use difficult without suitable visualization tools. We present UrbanView, a visualization system for urban modeling, and describe a user study to determine appropriate visualizations for the urban modeling domain.
SMARTLINK: An Agent for Supporting Dataflow Application Construction
(The Eurographics Association, 2000) Telea, Alexandru; Wijk, Jarke J. van; W. de Leeuw and R. van Liere
Visual programmable dataflow systems are an effective way to build a large class of visualization applications from existing software modules. However, the appeal of dataflow systems is often decreased as their users have to get familiar with libraries containing hundreds of different modules. Classical documentation systems such as hypertext or example suites are not always effective, as they lack the context of the user s questions and problems. We present a new visual dataflow programming assistant that is simple to use, offers context-sensitive help derived from the user s own behavior, and smoothly integrates in the effective point-andclick visual programming metaphor.We illustrate our approach with real-life usage examples.
Hybrid Model for Vascular Tree Structures
(The Eurographics Association, 2000) Puig, Anna; Tost, Dani; Navazo, Isabel; W. de Leeuw and R. van Liere
This paper proposes a new representation scheme of the cerebral blood vessels. This model provides information on the semantics of the vascular structure: the topological relationships between vessels and the labeling of vascular accidents such as aneurysms and stenoses. In addition, the model keeps information of the inner surface geometry as well as of the vascular map volume properties, i.e. the tissue density, the blood flow velocity and the vessel wall elasticity. The model can be constructed automatically in a pre-process from a set of segmented MRA images. Its memory requirements are optimized on the basis of the sparseness of the vascular structure. It allows fast queries and efficient traversals and navigations. The visualizations of the vessel surface can be performed at different levels of detail. The direct rendering of the volume is fast because the model provides a natural way to skip over empty data. The paper analyzes the memory requirements of the model along with the costs of the most important operations on it.
Direct Volume Rendering from Photographic Data
(The Eurographics Association, 2000) Ebert, David; McClanahan, Tim; Rheingans, Penny; Yoo, Terry; W. de Leeuw and R. van Liere
Direct volume rendering from photographic volume data has the potential to create realistic images of internal volume structure, as well as the structure of boundaries within the volume. While possession of the photographic volume simplifies color calculations in voxel illumination, it complicates opacity calculation. This paper describes a framework for addressing illumination challenges in photographic volume data and presents initial results.
Hierarchical Data Representations Based on Planar Voronoi Diagrams
(The Eurographics Association, 2000) Schussman, Shirley; Bertram, Martin; Hamann, Bernd; Joy, Kenneth I.; W. de Leeuw and R. van Liere
Multiresolution representation of high-dimensional scattered data is a fundamental problem in scientific visualization. This paper introduces a data hierarchy of Voronoi diagrams as a versatile solution. Given an arbitrary set of points in the plane, our goal is the construction of an approximation hierarchy using the Voronoi diagram as the essential building block. We have implemented two Voronoi diagram-based algorithms to demonstrate their usefulness for hierarchical scattered data approximation. The first algorithm uses a constant function to approximate the data within each Voronoi cell, and the second algorithm uses the Sibson interpolant [14].

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