VisSym03: Joint Eurographics - IEEE TCVG Symposium on Visualization

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https://diglib.eg.org/handle/10.2312/402

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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.
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.
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.
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.
ShellSplatting: Interactive Rendering of Anisotropic Volumes
(The Eurographics Association, 2003) Botha, Charl P.; Post, Frits H.; G.-P. Bonneau and S. Hahmann and C. D. Hansen
This work presents an extension of shell rendering that is more flexible and yields higher quality volume renderings. Shell rendering consists of efficient data-structures and methods to manipulate and render structures with non-precise boundaries in volume data. We have updated these algorithms by creating an implementation that makes effective use of ubiquitously available commercial graphics hardware. More significantly, we have extended the algorithm to make use of elliptical Gaussian splats instead of straight-forward voxel projection. This dramatically increases the quality of the renderings, especially with anisotropically sampled volumes. The use of the graphics hardware alleviates the performance penalty of using splats.
Vector Field Visualization using Markov Random Field Texture Synthesis
(The Eurographics Association, 2003) Taponecco, Francesca; Alexa, Marc; G.-P. Bonneau and S. Hahmann and C. D. Hansen
Vector field visualization aims at generating images in order to convey the information existing in the data. We use Markov Random Field (MRF) texture synthesis methods to generate the visualization from a set of sample textures. MRF texture synthesis methods allow generating images that are locally similar to a given example image. We extend this idea for vector field visualization by identifying each vector value with a representative example image, e.g. a strongly directed texture that is rotated according to a 2D vector. The visualization is synthesized pixel by pixel, where each pixel is chosen from the sample texture according to the vector values of the local pixel. The visualization locally communicates the vector information as each pixel is chosen from a sample that is representative of the vector. Furthermore it is smooth, as MRF texture synthesis searches for best fitting neighborhoods. This leads to dense and smooth visualizations with the additional freedom to use arbitrary representation textures for any vector value.
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.
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.
ISOSLIDER: A System for Interactive Exploration of Isosurfaces
(The Eurographics Association, 2003) Chhugani, Jatin; Vishwanath, Sudhir; Cohen, Jonathan; Kumar, Subodh; G.-P. Bonneau and S. Hahmann and C. D. Hansen
We present ISOSLIDER, a system for interactive exploration of isosurfaces of a scalar field. Our algorithm focuses on fast update of isosurfaces for interactive display as a user makes small changes to the isovalue of the desired surface. We exploit the coherence of this update. Larger changes are supported as well. The update to the isosurface is made at a correct level of detail so that not too many operations need be performed nor too many triangles need be rendered. ISOSLIDER does not need to retain the entire volume in the main memory and stores most data out of core. The central idea of the ISOSLIDER algorithm is to determine salient isovalues where surface topology changes and pre-encode these changes so as to facilitate fast updates to the triangulation.
Post-Convolved Splatting
(The Eurographics Association, 2003) Neophytou, Neophytos; Mueller, Klaus; G.-P. Bonneau and S. Hahmann and C. D. Hansen
One of the most expensive operations in volume rendering is the interpolation of samples in volume space. The number of samples, in turn, depends on the resolution of the final image. Hence, viewing the volume at high magnification will incur heavy computation. In this paper, we explore an approach that limits the number of samples to the resolution of the volume, independent of the magnification factor, using a cheap post-convolution process on the interpolated samples to generate the missing samples. For X-ray, this post-convolution is needed only once, after the volume is fully projected, while in full volume rendering, the post-convolution must be applied before each shading and compositing step. Using this technique, we are able to achieve speedups of two and more, without compromising rendering quality. We demonstrate our approach using an image-aligned sheet-buffered splatting algorithm, but our conclusions readily generalize to any volume rendering algorithm that advances across the volume in a slice-based fashion.
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.
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
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.
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
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.
Efficient Visualization of Large Medical Image Datasets on Standard PC Hardware
(The Eurographics Association, 2003) Pekar, V.; Hempel, D.; Kiefer, G.; Busch, M.; Weese, J.; G.-P. Bonneau and S. Hahmann and C. D. Hansen
Fast and accurate algorithms for medical image processing and visualization are becoming increasingly important due to routine acquisition and processing of rapidly growing amounts of data in clinical practice. At the same time, standard computer hardware is becoming sufficiently powerful to be used in applications which previously required expensive and inflexible special-purpose hardware. We present an efficient volume rendering approach using the example of maximum intensity projection (MIP), which is an important clinical tool. The method systematically exploits the properties of general-purpose hardware such as hierarchical cache memories and superscalar processing. In order to optimize the cache efficiency, the dataset is processed in blocks which fit into the processor cache. The innermost ray casting loop is transformed such that the arithmetic operations and memory accesses can be processed in parallel on current general-purpose processors. Combined with other optimization strategies, such as vectorization and block-wise ray skipping, this approach yields near-interactive frame rates for large clinical datasets using a standard dual-processor PC. Data compression and simplification methods have intentionally not been used in order to demonstrate the achievable performance without any quality reductions. Some of the presented ideas can be applied to other computationally intensive image processing tasks.
Isosurfaces on Optimal Regular Samples
(The Eurographics Association, 2003) Carr, Hamish; Theußl, Thomas; Möller, Torsten; G.-P. Bonneau and S. Hahmann and C. D. Hansen
Volumetric samples on Cartesian lattices are less efficient than samples on body-centred cubic (BCC) lattices. We show how to construct isosurfaces on BCC lattices using several different algorithms. Since the mesh that arises from BCC lattices involves a large number of cells, we show two alternate methods of reducing the number of cells by clumping tetrahedra into either octahedra or hexahedra. We also propose a theoretical model for estimating triangle counts for various algorithms, and present experimental results to show that isosurfaces generated using one of our algorithms can be competitive with isosurfaces generated using Marching Cubes on similar Cartesian grids
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.
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.

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