VisSym02: Joint Eurographics - IEEE TCVG Symposium on Visualization

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View-Dependent Multiresolution Splatting of Non-Uniform Data
(The Eurographics Association, 2002) Jang, Justin; Ribarsky, William; Shaw, Christopher D.; Faust, Nickolas; D. Ebert and P. Brunet and I. Navazo
This paper develops an approach for the splat-based visualization of large scale, non-uniform data. A hierarchical structure is generated that permits detailed treatment at the leaf nodes of the non-uniform distribution. A set of levels of detail (LODs) are generated based on the levels of the hierarchy. These yield two metrics, one in terms of the spatial extent of the bounding box containing the splat and one in terms of the variation of the scalar field over this box. The former yields a view-dependent choice of LODs while the latter yields a view-independent LOD based on the field variation. To show the utility of this general approach it is applied to a set of application data for a whole earth environment and some test data. Performance results are given.
Vortex Tracking in Scale-Space
(The Eurographics Association, 2002) Bauer, Dirk; Peikert, Ronald; D. Ebert and P. Brunet and I. Navazo
Scale-space techniques have become popular in computer vision for their capability to access the multiscale information inherently contained in images. We show that the field of flow visualization can benefit from these techniques, too, yielding more coherent features and sorting out numerical artifacts as well as irrelevant large-scale features. We describe an implementation of scale-space computation using finite elements and show that performance is sufficient for computing a scale-space of time-dependent CFD data. Feature tracking, if available, allows to process the information provided by scale-space not just visually but also algorithmically. We present a technique for extending a class of feature extraction schemes by an additional dimension, resulting in an efficient solution of the tracking problem.
Volume Rendering Multivariate Data to Visualize Meteorological Simulations: A Case Study
(The Eurographics Association, 2002) Kniss, Joe; Hansen, Charles; D. Ebert and P. Brunet and I. Navazo
High resolution computational weather models are becoming increasing complex. However, the analysis of these models has not benefited from recent advancements in volume visualization. This case study applies the ideas and techniques from multi-dimensional transfer function based volume rendering to the multivariate weather simulations. The specific goal of identifying frontal zones is addressed. By combining temperature and humidity as a multivariate field, the frontal zones are more readily identified thereby assisting the meteorologists in their analysis tasks.
Speech and Gesture Multimodal Control of a Whole Earth 3D Visualization Environment
(The Eurographics Association, 2002) Krum, David M.; Omoteso, Olugbenga; Ribarsky, William; Starner, Thad; Hodges, Larry F.; D. Ebert and P. Brunet and I. Navazo
A growing body of research shows several advantages to multimodal interfaces including increased expressiveness, flexibility, and user freedom. This paper investigates the design of such an interface that integrates speech and hand gestures. The interface has the additional property of operating relative to the user and can be used while the user is in motion or standing at a distance from the computer display. The paper then describes an implementation of the multimodal interface for a whole Earth 3D visualization which presents navigation interface challenges due to the large magnitude of scale and extended spaces that are available. The characteristics of the multimodal interface are examined, such as speed, recognizability of gestures, ease and accuracy of use, and learnability under likely conditions of use. This implementation shows that such a multimodal interface can be effective in a real environment and sets some parameters for the design and use of such interfaces.
Comparison of Morphological Pyramids for Multiresolution MIP Volume Rendering
(The Eurographics Association, 2002) Roerdink, Jos B.T.M.; D. Ebert and P. Brunet and I. Navazo
We recently proposed a multiresolution representation for maximum intensity projection (MIP) volume rendering based on morphological adjunction pyramids which allow progressive refinement and have the property of perfect reconstruction. In this algorithm the pyramidal analysis and synthesis operators are composed of morphological erosion and dilation, combined with dyadic downsampling for analysis and dyadic upsampling for synthesis. Here we introduce an alternative pyramid scheme in which a morphological opening instead of an erosion is used for pyramidal analysis. As a result, the approximation accuracy when rendering from higher levels of the pyramid is improved.
Shear-Warp Deluxe: The Shear-Warp Algorithm Revisited
(The Eurographics Association, 2002) Sweeney, Jon; Mueller, Klaus; D. Ebert and P. Brunet and I. Navazo
Despite continued advances in volume rendering technology, the Shear-Warp algorithm, although conceived as early as 1994, still remains the world s fastest purely software-based volume rendering algorithm. The impressive speed of near double-digit framerates for moderately sized datasets, however, does come at the price of reduced image quality and memory consumption. In this paper, we present the implementation and impact of certain measures that seek to address these shortcomings. Specifically, we investigate the effects of: (i) post-interpolated classification and shading, (ii) matched volume sampling on zoom, (iii) the interpolation of intermediate slices to reduce inter-slice aliasing, and (iv) the re-use of encoded RLE runs for more than one major viewing direction to preserve memory. We also study a new variation of the shear-warp algorithm that operates on body-centered cubic grids. We find that the reduction of the number of voxels that this grid affords translates into direct savings in rendering times, with minimal degradation in image quality.
A Continuous Skeletonization Method Based on Level Sets
(The Eurographics Association, 2002) Rumpf, Martin; Telea, Alexandru; D. Ebert and P. Brunet and I. Navazo
A robust and efficient method in 2D and 3D for the calculation of skeletons for arbitrary objects is presented. The method is based on the calculation of the distance function with respect to the object boundary. This is combined, in a post processing step, with a new indicator to identify the skeleton, which coincides with the singularity set of the distance map. The indicator is defined as a suitable function of certain local momenta of this distance map and allows a robust and accurate computation of the distance from the skeleton set. This distance is then extended, again via the level set method, onto the whole space. Several applications in 2D and 3D are presented.
Interactive Visualization and Steering of CFD Simulations
(The Eurographics Association, 2002) Kreylos, O.; Tesdall, A. M.; Hamanny, B.; Hunter, J. K.; Joy, K. I.; D. Ebert and P. Brunet and I. Navazo
We describe a system that supports real-time interactive visualization of computational fluid dynamics (CFD) simulations. The system allows a user to place and manipulate visualization primitives, such as isolines and streamlines, during an ongoing simulation process. A user can interactively select and designate regions of the computational mesh for refinement as the simulation progresses, perform remeshing, and see the effects of the refinement on the simulation in real time. The system is being used for the study of two open problems in compressible fluid dynamics. We can interactively explore solutions as they are computed, identify flow field regions containing features of interest, and refine the grid in those regions in order to obtain a better result locally. The ability to visualize "live" data, and to make changes to the computational setup in real time, has helped us to understand the underlying fundamental CFD simulation issues of these problems in shorter times than would otherwise have been possible.
Feature-Preserving Volume Filtering
(The Eurographics Association, 2002) Neumann, László; Csébfalvi, Balázs; Viola, Ivan; Mlejnek, Matej; Gröller, Eduard; D. Ebert and P. Brunet and I. Navazo
In this paper a feature-preserving volume filtering method is presented. The basic idea is to minimize a threecomponent global error function penalizing the density and gradient errors and the curvature of the unknown filtered function. The optimization problem leads to a large linear equation system defined by a sparse coefficient matrix. We will show that such an equation system can be efficiently solved in frequency domain using fast Fourier transformation (FFT). For the sake of clarity, first we illustrate our method on a 2D example which is a dedithering problem. Afterwards the 3D extension is discussed in detail since we propose our method mainly for volume filtering. We will show that the 3D version can be efficiently used for elimination of the typical staircase artifacts of direct volume rendering without losing fine details. Unlike local filtering techniques, our novel approach ensures a global smoothing effect. Previous global 3D methods are restricted to binary volumes or segmented iso-surfaces and they are based on area minimization of one single reconstructed surface. In contrast, our method is a general volume-filtering technique, implicitly smoothing all the iso-surfaces at the same time. Although the strength of the presented algorithm is demonstrated on a specific 2D and a specific 3D application, it is considered as a general mathematical tool for processing images and volumes.
Adding a scalar value to texture-based vector field representations by local contrast analysis
(The Eurographics Association, 2002) Sanna, A.; Zunino, C.; Montrucchio, B.; Montuschi, P.; D. Ebert and P. Brunet and I. Navazo
Several algorithms can effectively represent vector fields by texture-based representations, visualizing at most all information on the field: direction, orientation, and local magnitude. An open problem still remains the mapping on textures of adjunctive information such as temperature, pressure, and so on, without using colors. This article addresses this issue by proposing a technique to add a scalar value denoting streamlines by means of different levels of contrast. Both streamline starting tones and the range of tones depend on the scalar value to be mapped; in this way, areas visualized by different contrast levels are represented. Two examples show the effectiveness of the proposed technique.
STATISTICAL COMPUTATION OF SALIENT ISO-VALUES
(The Eurographics Association, 2002) Tenginakai, Shivaraj; Machiraju, Raghu; D. Ebert and P. Brunet and I. Navazo
Detection of the salient iso-values in a volume dataset is often the first step towards its exploration. An error-and-trail approach is often used; new semi-automatic techniques either make assumptions about their data [4] or present multiple criteria for analysis. Determining if a dataset satisfies an algorithm s assumptions, or the criteria to be used in an analysis are both non-trivial tasks. The use of a dataset s statistical signatures, local higher order moments (LHOMs), to characterize its salient iso-values was presented in [10]. In this paper we propose a computational algorithm that uses LHOMs for expedient estimation of salient iso-values. As LHOMs are model independent statistical signatures our algorithm does not impose any assumptions on the data. Further, the algorithm has a single criterion for characterization of the salient iso-values, and the search for this criterion is easily automated. Examples from medical and computational domains are used to demonstrate the effectiveness of the proposed algorithm.
Visualization of Bibliographic Networks with a Reshaped Landscape Metaphor
(The Eurographics Association, 2002) Brandes, U.; Willhalm, T.; D. Ebert and P. Brunet and I. Navazo
We describe a novel approach to visualize bibliographic networks that facilitates the simultaneous identification of clusters (e.g., topic areas) and prominent entities (e.g., surveys or landmark papers). While employing the landscape metaphor proposed in several earlier works, we introduce new means to determine relevant parameters of the landscape. Moreover, we are able to compute prominent entities, clustering of entities, and the landscape s surface in a surprisingly simple and uniform way. The effectiveness of our network visualizations is illustrated on data from the graph drawing literature.
Visualizing and Investigating Multidimensional Functions
(The Eurographics Association, 2002) Santos, S. R. dos; Brodlie, K. W.; D. Ebert and P. Brunet and I. Navazo
This paper addresses the problem of visualizing multidimensional scalar functions. These functions are often encountered in fields such as Engineering, Mathematics, and Physics to understand and model complex phenomena. We propose a novel method based on the dimension reduction philosophy called HyperCell. Its basic concept is to represent the function by means of dynamic orthogonal low (ID, 2D, or 3D) dimensional subspaces, called Cells. Firstly the user defines a N-dimensional region of interest, in which the data can be visualized. Then the user interactively creates cells by selecting up to three dimensions from the function domain. A cell can be visualized using a standard visualization algorithm such as isosurfacing or volume rendering. The analysis of the function is done by investigating several cells, which can be sampled simultaneously at different regions of interest in N-Space. The HyperCell method allows several useful operations to help the exploratory process such as navigation and rotation in N-Space, and brushing.
Locating Closed Streamlines in 3D Vector Fields
(The Eurographics Association, 2002) Wischgoll, Thomas; Scheuermann, Gerik; D. Ebert and P. Brunet and I. Navazo
The analysis and visualization of flows is a central problem in visualization. Topology based methods have gained increasing interest in recent years. This article describes a method for the detection of closed streamlines in 3D flows. It is based on a special treatment of cases where a streamline reenters a cell to prevent infinite cycling during streamline calculation. The algorithm checks for possible exits of a loop of crossed faces and detects structurally stable closed streamlines. These global features are not detected by conventional topology and feature detection algorithms.
Direct Volume Rendering of Photographic Volumes Using Multi-Dimensional Color-Based Transfer Functions
(The Eurographics Association, 2002) Morris, Christopher J.; Ebert, David; D. Ebert and P. Brunet and I. Navazo
Traditionally, volume rendering of medical data has been comprised of transfer functions that map a scalar value, usually a MRI or CT intensity, to an opacity. Corresponding color maps are either selected regardless of the actual physical color of the volume (i.e. greyscale) or predetermined as in photographic volumes. Rarely has the voxel color been used as a means to define the associated opacity value. By using transfer functions that map multichannel color values(RGB or CIE L¤u¤v¤) to opacity, we can generate compelling and informative renderings that provide consistent boundary extraction throughout the volume. We present renderings of the Visible Human photographic volume using multi-dimensional color-based transfer functions. These functions were constructed by using gradient boundary enhancement techniques in conjunction with volume illustration techniques and incorporating the first and second directional derivatives along the gradient direction. We empirically compare the effectiveness of using the color-based transfer functions and discuss their applications and potential for future development.
Secondary Task Display Attributes - Optimizing Visualizations for Cognitive Task Suitability and Interference Avoidance
(The Eurographics Association, 2002) Chewar, C. M.; McCrickard, D. Scott; Ndiwalana, Ali; North, Chris; Pryor, Jon; Tessendorf, David; D. Ebert and P. Brunet and I. Navazo
We found that established display design guidelines for focal images cannot be extended to images displayed as a secondary task in a dual-task situation. This paper describes an experiment that determines a new ordering guideline for secondary task image attributes according to human cognitive ability to extract information. The imperative for alternate guidelines is based on the difference in an image s ability to convey meaning, which decreases when moved from a focal to a secondary task situation. Secondary task attribute ordering varies with the level of degradation in the primary task. Furthermore, attribute effectiveness may be particular to types of visual operations relating to cognitive tasks.
An Evaluation of Information Visualization in Attention-Limited Environments
(The Eurographics Association, 2002) Somervell, Jacob; McCrickard, D. Scott; North, Chris; Shukla, Maulik; D. Ebert and P. Brunet and I. Navazo
People often need to quickly access or maintain awareness of secondary information while busy with other primary tasks. Information visualizations provide rapid, effective access to information, but are generally designed to be examined by users as the primary focus of their attention. The goal of this research is to discover how to design information visualizations intended for the periphery and to understand how quickly and effectively people can interpret information visualizations while they are busily performing other tasks. We evaluated how several factors of a visualization (visual density, presence time, and secondary task type) impact people s abilities to continue with a primary task and to complete secondary tasks related to the visualization. Our results suggest that, with relaxed time pressure, reduced visual information density and a single well-defined secondary task, people can effectively interpret visualizations with minimal distraction to their primary task.
Octreemizer: A Hierarchical Approach for Interactive Roaming Through Very Large Volumes
(The Eurographics Association, 2002) Plate, John; Tirtasana, Michael; Carmona, Rhadamés; Fröhlich, Bernd; D. Ebert and P. Brunet and I. Navazo
We have developed a hierarchical paging scheme for handling very large volumetric data sets at interactive frame rates. Our system trades texture resolution for speed and uses effective prediction strategies. We have tested our approach for datasets with up to 16GB in size and show that it works well with less than 500MB of main memory cache for 64MB of 3D-texture memory. Our approach makes it feasible to deal with these volumes on desktop machines.
A Generic Solution for Hardware-Accelerated Remote Visualization
(The Eurographics Association, 2002) Stegmaier, Simon; Magallón, Marcelo; Ertl, Thomas; D. Ebert and P. Brunet and I. Navazo
This paper presents a generic solution for hardware-accelerated remote visualization that works transparently for all OpenGL-based applications and OpenGL-based scene graphs. Universality is achieved by taking advantage of dynamic linking, efficient data transfer by means of VNC. The proposed solution does not require any modifications of existing applications and allows for remote visualization with different hardware architectures involved in the visualization process. The library s performance is evaluated using standard OpenGL example programs and by volume rendering substantial data sets.
Bag-of-Particles as a Deformable Model
(The Eurographics Association, 2002) Stahl, D.; Ezquerra, N.; Turk, G.; D. Ebert and P. Brunet and I. Navazo
We present an interactive, physically-based, elastically deformable model using a particle system to model surfaces with interior volumes that can be haptically felt. Oriented particles used in existing surface-only models, and unoriented particles used in volume-only simulations are combined to form a bag-of-particles. Multiple species of surface and volume particles, coupled with prede£ned interspecies parameters, determine the elastic properties of a bag. Starting with an object represented as a 3D voxel bitmap of connected components, the gradient of its distance map gives a vector £eld, or gradient map, that captures the static shape of an object and provides shape-maintaining forces. The gradient map enables the user to de£ne the geometry of the simulated objects, and provides feedback reaction forces allowing a user to feel the model. A bag-of-particles model can simulate several objects in the same scene, as well as objects composed of different materials, such as organs with multiple tissue types. We demonstrate the bag-of-particles approach using a number of different data sources, and apply it to modeling myocardium dynamics.

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