VisSym03: Joint Eurographics - IEEE TCVG Symposium on Visualization

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Using Graphs for Fast Error Term Approximation of Time-varying Datasets
(The Eurographics Association, 2003) Nuber, C.; LaMar, E. C.; Pascucci, V.; Hamann, B.; Joy, K. I.; G.-P. Bonneau and S. Hahmann and C. D. Hansen
We present a method for the efficient computation and storage of approximations of error tables used for error estimation of a region between different time steps in time-varying datasets. The error between two time steps is defined as the distance between the data of these time steps. Error tables are used to look up the error between different time steps of a time-varying dataset, especially when run time error computation is expensive. However, even the generation of error tables itself can be expensive. For n time steps, the exact error look-up table (which stores the error values for all pairs of time steps in a matrix) has a memory complexity and pre-processing time complexity of O(n2), and O(1) for error retrieval. Our approximate error look-up table approach uses trees, where the leaf nodes represent original time steps, and interior nodes contain an average (or best-representative) of the children nodes. The error computed on an edge of a tree describes the distance between the two nodes on that edge. Evaluating the error between two different time steps requires traversing a path between the two leaf nodes, and accumulating the errors on the traversed edges. For n time steps, this scheme has a memory complexity and pre-processing time complexity of O(nlog(n)), a significant improvement over the exact scheme; the error retrieval complexity is O(log(n)). As we do not need to calculate all possible n2 error terms, our approach is a fast way to generate the approximation.
Shrouds: Optimal Separating Surfaces for Enumerated Volumes
(The Eurographics Association, 2003) Nielson, Gregory M.; Graf, Gary; Holmes, Ryan; Huang, Adam; Phielipp, Mariano; G.-P. Bonneau and S. Hahmann and C. D. Hansen
We describe new techniques for computing a smooth triangular mesh surface that surrounds an enumerated volume consisting of a collection of points from a 3D rectilinear grid. The surface has the topology of an isosurface computed by a marching cubes method applied to a field function that has the value one at the points in the volume and zero for points not in the volume. The vertices are confined to the edges of the grid that penetrate this separating surface and the precise positions are computed so as to optimize a certain energy functional applied to the surface. We use efficient iterative methods to compute the optimal separating surfaces. We lift the concept of energy functionals for planar curves to isosurfaces by means of the 4*-network which is a unique collection of orthogonal planar polygons lying on the isosurface. The general strategy that we describe here leads to methods that are simple, efficient, and effective.
Detection of constrictions on closed polyhedral surfaces
(The Eurographics Association, 2003) Hétroy, F.; Attali, D.; G.-P. Bonneau and S. Hahmann and C. D. Hansen
We define constrictions on a surface as simple closed geodesic curves, i.e. curves whose length is locally minimal. They can be of great interests in order to cut the surface in smaller parts. In this paper, we present a method to detect constrictions on closed triangulated surfaces. Our algorithm is based on a progressive approach. First, the surface is simplified by repeated edge collapses. The simplification continues until we detect an edge whose collapse would change the topology of the surface. It happens when three edges of the surface form a triangle that does not belong to the surface. The three edges define what we call a seed curve and are used to initialize the search of a constriction. Secondly, the constriction is progressively constructed by incrementally refining the simplified surface until the initial surface is retrieved. At each step of this refinement process, the constriction is updated. Some experimental results are provided.
Anti-Aliased Volume Extraction
(The Eurographics Association, 2003) Lakare, Sarang; Kaufman, Arie; G.-P. Bonneau and S. Hahmann and C. D. Hansen
We present a technique to extract regions from a volumetric dataset without introducing any aliasing so that the extracted volume can be explored using direct volume rendering techniques. Extracting regions using binary masks generated by contemporary segmentation approaches typically introduces aliasing at the boundary of the extracted regions. This aliasing is especially visible when the dataset is visualized using direct volume rendering. Our algorithm uses the binary mask only to locate the boundary. The main idea of the algorithm is to retain the natural fuzziness at the boundary of a region even after it is extracted. To achieve that, intensities of the boundary voxels are flipped so that they are now representing a fuzzy boundary with the empty region surrounding it, while preserving the boundary position.
Hardware-assisted View-dependent Isosurface Extraction using Spherical Partition
(The Eurographics Association, 2003) Gao, Jinzhu; Shen, Han-Wei; G.-P. Bonneau and S. Hahmann and C. D. Hansen
Extracting only the visible portion of an isosurface can improve both the computation efficiency and the rendering speed. However, the visibility test overhead can be quite high for large scale data sets. In this paper, we present a view-dependent isosurface extraction algorithm utilizing occlusion query hardware to accelerate visible isosurface extraction. A spherical partition scheme is proposed to traverse the data blocks in a layered front-to-back order. Such traversal order helps our algorithm to identify the visible isosurface blocks more quickly with fewer visibility queries. Our algorithm can compute a more complete isosurface in a smaller amount of time, and thus is suitable for time-critical visualization applications.
Interactive Feature Specification for Focus+Context Visualization of Complex Simulation Data
(The Eurographics Association, 2003) Doleisch, Helmut; Gasser, Martin; Hauser, Helwig; G.-P. Bonneau and S. Hahmann and C. D. Hansen
Visualization of high-dimensional, large data sets, resulting from computational simulation, is one of the most challenging fields in scientific viualization. When visualization aims at supporting the analysis of such data sets, feature-based approches are very useful to reduce the amount of data which is shown at each instance of time and guide the user to the most interesting areas of the data. When using feature-based visualization, one of the most difficult questions is how to extract or specify the features. This is mostly done (semi-)automatic up to now. Especially when interactive analysis of the data is the main goal of the visualization, tools supporting interactive specification of features are needed. In this paper we present a framework for flexible and interactive specification of high-dimensional and/or complex features in simulation data. The framework makes use of multiple, linked views from information as well as scientific visualization and is based on a simple and compact feature definition language (FDL). It allows the definition of one or several features, which can be complex and/or hierarchically described by brushing multiple dimensions (using non-binary and composite brushes). The result of the specification is linked to all views, thereby a focus+context style of visualization in 3D is realized. To demonstrate the usage of the specification, as well as the linked tools, applications from flow simulation in the automotive industry are presented.
Improving Topological Segmentation of Three-dimensional Vector Fields
(The Eurographics Association, 2003) Mahrous, Karim M.; Bennett, Janine C.; Hamann, Bernd; Joy, Kenneth I.; G.-P. Bonneau and S. Hahmann and C. D. Hansen
We present three enhancements to accelerate the extraction of separatrices of three-dimensional vector fields, using intelligently selected "sample" streamlines. These enhancements reduce the number of needed sample streamlines and their propagation length. Inflow/outflow matching supports the simultaneous extraction of topologically significant inflow and outflow separatrices in a single pass. An adaptive sampling approach is introduced and used to seed streamlines in a more meaningful and efficient manner. Cell-locking is a new concept that isolates regions of a data set that do not contain separatrices. This concept makes streamline propagation more efficient as streamlines are not propagated through cells that do not influence or contain separatrices. These enhancements enable us to perform separatrix construction for three-dimensional vector field data requiring less overall computation.
Visual Hierarchical Dimension Reduction for Exploration of High Dimensional Datasets
(The Eurographics Association, 2003) Yang, J.; Ward, M.O.; Rundensteiner, E.A.; Huang, S.; G.-P. Bonneau and S. Hahmann and C. D. Hansen
Traditional visualization techniques for multidimensional data sets, such as parallel coordinates, glyphs, and scatterplot matrices, do not scale well to high numbers of dimensions. A common approach to solving this problem is dimensionality reduction. Existing dimensionality reduction techniques usually generate lower dimensional spaces that have little intuitive meaning to users and allow little user interaction. In this paper we propose a new approach to handling high dimensional data, named Visual Hierarchical Dimension Reduction (VHDR), that addresses these drawbacks. VHDR not only generates lower dimensional spaces that are meaningful to users, but also allows user interactions in most steps of the process. In VHDR, dimensions are grouped into a hierarchy, and lower dimensional spaces are constructed using clusters of the hierarchy. We have implemented the VHDR approach into XmdvTool, and extended several traditional multidimensional visualization methods to convey dimension cluster characteristics when visualizing the data set in lower dimensional spaces. Our case study of applying VHDR to a real data set supports our belief that this approach is effective in supporting the exploration of high dimensional data sets.
Path Seeds and Flexible Isosurfaces Using Topology for Exploratory Visualization
(The Eurographics Association, 2003) Carr, Hamish; Snoeyink, Jack; G.-P. Bonneau and S. Hahmann and C. D. Hansen
Morse theory and the Reeb graph give topological summaries of the behaviour of continuous scalar functions. The contour tree augments the Reeb graph for the isosurfaces in a volume to store seed sets, which are starting points for extracting isosurfaces by the continuation method. We replace the minimal seed sets of van Kreveld et al. with path seeds, which generate paths that correspond directly to the individual components of an isosurface. From a path we get exactly one seed per component, which reduces storage and simplifies isosurface extraction. Moreover, the correspondence allows us to extend the contour spectrum of Bajaj et al. to an interface that we call flexible isosurfaces, in which individual contours with different isovalues can be displayed, manipulated and annotated. The largest contour segmentation, in which separate surfaces are generated for each local maximum of the field, is a special case of the flexible isosurface.
Adaptive Smooth Scattered-data Approximation for Large-scale Terrain Visualization
(The Eurographics Association, 2003) Bertram, Martin; Tricoche, Xavier; Hagen, Hans; G.-P. Bonneau and S. Hahmann and C. D. Hansen
We present a fast method that adaptively approximates large-scale functional scattered data sets with hierarchical B-splines. The scheme is memory efficient, easy to implement and produces smooth surfaces. It combines adaptive clustering based on quadtrees with piecewise polynomial least squares approximations. The resulting surface components are locally approximated by a smooth B-spline surface obtained by knot removal. Residuals are computed with respect to this surface approximation, determining the clusters that need to be recursively refined, in order to satisfy a prescribed error bound. We provide numerical results for two terrain data sets, demonstrating that our algorithm works efficiently and accurate for large data sets with highly non-uniform sampling densities.
Detecting Critical Regions in Scalar Fields
(The Eurographics Association, 2003) Weber, Gunther H.; Scheuermann, Gerik; Hamann, Bernd; G.-P. Bonneau and S. Hahmann and C. D. Hansen
Trivariate data is commonly visualized using isosurfaces or direct volume rendering. When exploring scalar fields by isosurface extraction it is often difficult to choose isovalues that convey "useful" information. The significance of visualizations using direct volume rendering depends on the choice of good transfer functions. Understanding and using isosurface topology can help in identifying "relevant" isovalues for visualization via isosurfaces and can be used to automatically generate transfer functions. Critical isovalues indicate changes in topology of an isosurface: the creation of new surface components, merging of surface components or the formation of holes in a surface component. Interesting isosurface behavior is likely to occur at and around critical isovalues. Current approaches to detect critical isovalues are usually limited to isolated critical points. Data sets often contain regions of constant value (i.e., mesh edges, mesh faces, or entire mesh cells). We present a method that detects critical points, critical regions and corresponding critical isovalues for a scalar field defined by piecewise trilinear interpolation over a uniform rectilinear grid. We describe how to use the resulting list of critical regions/points and associated values to examine trivariate data.
Rendering Vector Data over Global, Multi-resolution 3D Terrain
(The Eurographics Association, 2003) Wartell, Zachary; Kang, Eunjung; Wasilewski, Tony; Ribarsky, William; Faust, Nickolas; G.-P. Bonneau and S. Hahmann and C. D. Hansen
Modern desktop PCs are capable of taking 2D Geographic Information System (GIS) applications into the realm of interactive 3D virtual worlds. In prior work we developed and presented graphics algorithms and data management methods for interactive viewing of a 3D global terrain system for desktop and virtual reality systems. In this paper we present a key data structure and associated render-time algorithm for the combined display of multi-resolution 3D terrain and traditional GIS polyline vector data. Such vector data is traditionally used for representing geographic entities such as political borders, roads, rivers and cadastral information
MCMR: A Fluid View on Time Dependent Volume Data
(The Eurographics Association, 2003) Leeuw, Wim de; Liere, Robert van; G.-P. Bonneau and S. Hahmann and C. D. Hansen
Mass Conservative Motion Reconstruction is a new method for estimating motion in time dependent volume data. A time dependent vector field representing the movement of the data is computed from a sequence of scalar volume data sets. The principle of mass conservation in a continuum is used during the reconstruction. Standard flow visualization techniques are used for the visualization of the derived vector field. This paper presents the underlying concepts of MCMR, its implementation, its accuracy and applicability.
A Robust Level-Set Algorithm for Centerline Extraction
(The Eurographics Association, 2003) Telea, Alexandru; Vilanova, Anna; G.-P. Bonneau and S. Hahmann and C. D. Hansen
We present a robust method for extracting 3D centerlines from volumetric datasets. We start from a 2D skeletonization method to locate voxels centered with respect to three orthogonal slicing directions. Next, we introduce a new detection criterion to extract the centerline voxels from the above skeletons, followed by a thinning, reconnection, and a ranking step. Overall, the proposed method produces centerlines that are object-centered, connected, one voxel thick, robust with respect to object noisiness, handles arbitrary object topologies, comes with a simple pruning threshold, and is fast to compute. We compare our results with two other methods on a variety of real-world datasets
Case Study: Comparing Two Methods for Filtering External Motion in 4D Confocal Microscopy Data
(The Eurographics Association, 2003) Leeuw, Wim de; Liere, Robert van; G.-P. Bonneau and S. Hahmann and C. D. Hansen
In this case study, we compare two methods for filtering external motion in time dependent volume data sets acquired from confocal microscopy. The pros and cons of a landmark based and a voxel based method are discussed. We show that filtering external motion is an essential first step for the visualization of confocal data.
Interaction of Light and Tensor Fields
(The Eurographics Association, 2003) Zheng, Xiaoqiang; Pang, Alex; G.-P. Bonneau and S. Hahmann and C. D. Hansen
We present three new ways of looking at tensor volumes. All three methods are based on the interaction of simulated light and the tensor field. Conceptually, rays are shot from a certain direction into the tensor volume. These rays are influenced by the surrounding tensor field and bent as they traverse through the volume. The tensor is visualized by both the nature of the bent rays and by the collection of rays deposited on a receiving plate. The former is similar to streamlines, but shows paths of greatest influence by the tensor field. The latter is similar to caustic effects from photon maps, but shows the convergence or divergence of the rays through the tensor volume. We also use the concept of treating the tensor volume as a special lens that distorts an image. Using backward ray tracing through the tensor volume, we generate image distortions that also show internal properties of the tensor field. A key advantage of these techniques is that they can work directly with non-symmetric tensor fields without first decomposing them into components. Color images can also be found in www.soe.ucsc.edu/research/avis/tensorray.html.
Visualizing Spatial Distribution Data Sets
(The Eurographics Association, 2003) Luo, Alison; Kao, David; Pang, Alex; G.-P. Bonneau and S. Hahmann and C. D. Hansen
In this paper, we define distributions as a new data type and address the challenges of visualizing spatial distribution data sets. Numerous visualization techniques exist today for dealing with scalar data. That is, there is a scalar value at each spatial location, which may also be changing over time. Likewise, techniques exist for dealing with vector, tensor and multivariate data sets. However, there is currently no systematic way of dealing with distribution data where there is a collection of values for the same variable at every location and time. Distribution data is increasingly becoming more common as computers and sensor technologies continue to improve. They have also been used in a number of fields ranging from agriculture, engineering design and manufacturing to weather forecasting. Rather than developing specialized visualization techniques for dealing with distribution data, the approach presented in this paper is to find a systematic way of extending existing visualization methods to handle this new data type. For example, we would like to be able to generate isosurfaces of 3D scalar distribution data sets, or generate streamlines of vector distribution data sets. In order to accomplish this goal, we propose the use of a set of mathematically and procedurally defined operators that allow us to work directly on distributions. Color images can also be found in www.cse.ucsc.edu/research/avis/operator.html.
Accelerated Force Computation for Physics-Based Information Visualization
(The Eurographics Association, 2003) Hao, Ming C.; Dayal, Umeshwar; Cotting, Daniel; Holenstein, Thomas; Gross, Markus; G.-P. Bonneau and S. Hahmann and C. D. Hansen
Visualization of similarity is an emerging technique for analyzing relation-based data sets. A common way of computing the respective layouts in an information space is to employ a physics-based mass-spring system. Force computation, however, is costly and of order N2. In this paper, we propose a new acceleration method to adopt a well-known optimized force-computation algorithm which drastically reduces the computation time to the order of N log N. The basic idea is to derive a two-pass, "prediction and correction" procedure including a customized potential function. We have applied this method to two different applications: web access and sales analysis. Both demonstrate the efficiency and versatility of the presented method.
Analysis of the HDAF for Interpolation and Noise Suppression in Volume Rendering
(The Eurographics Association, 2003) Andersson, Kristoffer; Kakadiaris, Ioannis A.; Papadakis, Manos; Kouri, Donald J.; Hoffman, David K.; G.-P. Bonneau and S. Hahmann and C. D. Hansen
In this paper, we evaluate the HDAF (Hermite Distributed Approximating Functionals) family of interpolation and derivative functions, with respect to their accuracy for reliable volume rendering, and compare them with other interpolation and derivative estimation filters. We utilize several different evaluation methods, both analytical and experimental. The former includes the order of decay of the global error, the local spatial error, and the behavior of the filters in the frequency domain. In the experimental part, visualizations of both synthetic and medical data are produced and studied. We show that the HDAFs exhibit superior behavior if the volumetric data are distorted by high frequency noise, and perform well under noise free conditions. This due to their ability to adjust the range of recovered frequencies.
Feature Flow Fields
(The Eurographics Association, 2003) Theisel, H.; Seidel, H.-P.; G.-P. Bonneau and S. Hahmann and C. D. Hansen
Feature tracking algorithms for instationary vector fields are usually based on a correspondence analysis of the features at different time steps. This paper introduces a method for feature tracking which is based on the integration of stream lines of a certain vector field called feature flow field. We analyze for which features the method of feature flow fields can be applied, we show how events in the flow can be detected using feature flow fields, and we show how to construct the feature flow fields for particular classes of features. Finally, we apply the technique to track critical points in a 2D instationary vector field.

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