VisSym02: Joint Eurographics - IEEE TCVG Symposium on Visualization

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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.
AUFLIC: An Accelerated Algorithm For Unsteady Flow Line Integral Convolution
(The Eurographics Association, 2002) Liu, ZhanPing; II, Robert James Moorhead; D. Ebert and P. Brunet and I. Navazo
UFLIC (Unsteady Flow Line Integral Convolution) is an effective texture synthesis technique to visualize unsteady flow with enhanced temporal coherence, but it is time-consuming to generate. This paper presents an accelerated algorithm, called AUFLIC (Accelerated UFLIC), to speed up the UFLIC generation. Our algorithm saves, re-uses, and updates pathlines in the value scattering processes. A flexible seeding strategy is introduced so that a seed particle may be directly extracted from the previous scattering processes to make best use of the saved pathline so as to reduce computationally expensive pathline integration calculations. A dynamic activation-deactivation scheme is employed to maintain the fewest necessary pathlines. Avoiding excessive pathlines achieves acceleration and nearly-constant memory consumption. With very low memory cost, AUFLIC cuts UFLIC generation time nearly in half without any image quality degradation.
An Augmented Fast Marching Method for Computing Skeletons and Centerlines
(The Eurographics Association, 2002) Telea, Alexandru; Wijk, Jarke J. van; D. Ebert and P. Brunet and I. Navazo
We present a simple and robust method for computing skeletons for arbitrary planar objects and centerlines for 3D objects. We augment the Fast Marching Method (FMM) widely used in level set applications 11 by computing the paramterized boundary location every pixel came from during the boundary evolution. The resulting parameter field is then thresholded to produce the skeleton branches created by boundary features of a given size. The presented algorithm is straightforward to implement, has low memory costs and short execution times, and is robust with respect to the used threshold and initial shape noisiness. The produced skeletons are very similar to the ones delivered by more complex algorithms. Various 2D and 3D applications are presented.
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.
Best Quadratic Spline Approximation for Hierarchical Visualization
(The Eurographics Association, 2002) Wiley, D. F.; Childs, H. R.; Hamann, B.; Joy, K. I.; Max, N. L.; D. Ebert and P. Brunet and I. Navazo
We present a method for hierarchical data approximation using quadratic simplicial elements for domain decomposition and field approximation. Higher-order simplicial elements can approximate data better than linear elements. Thus, fewer quadratic elements are required to achieve similar approximation quality. We use quadratic basis functions and compute best quadratic simplicial spline approximations that are C0-continuous everywhere. We adaptively refine a simplicial approximation by identifying and bisecting simplicial elements with largest errors. It is possible to store multiple approximation levels of increasing quality. We have tested the suitability and efficiency of our hierarchical data approximation scheme by applying it to several data sets.
Cell-Based First-Hit Ray Casting
(The Eurographics Association, 2002) Neubauer, A.; Mroz, L.; Hauser, H.; Wegenkittl, R.; D. Ebert and P. Brunet and I. Navazo
Cell-based first-hit ray casting is a new technique for fast perspective volume visualization. This technique, based on the well known ray casting algorithm, performs iso-surfacing and supports interactive threshold adjustment. It is accelerated by the reduction of average ray path lengths to only a few steps per pixel. The volume is divided into cubic sub volumes. Each sub volume that is intersected by an iso-surface is projected to the image plane. A local ray casting step within the sub volume is performed for each pixel covered by the projection. Cell-based first-hit ray casting is perfectly suited whenever fast perspective iso-surfacing is required. This paper describes the basic algorithm, presents possible optimizations and evaluates the performance of the algorithm for one specific application, the post-implantation assessment of endovascular stent placement. It will be shown that the algorithm, though executed on a single processor machine without any hardware acceleration, performs well for view points inside as well as outside the stented blood vessel and significantly outperforms an optimized, yet more conventional ray casting technique.
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.
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.
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.
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.
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.
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.
Interactive Previewing for Transfer Function Specification in Volume Rendering
(The Eurographics Association, 2002) Botha, Charl P.; Post, Frits H.; D. Ebert and P. Brunet and I. Navazo
This paper presents a new technique for supplying meaningful visual feedback during direct volume rendering transfer function specification. The technique uses meta-data calculated during a pre-processing step to generate interactively an approximate volume rendering that is voxel-registered with a single user-selected slice. Because of the registration, this preview can easily be alpha-blended with a grey-scale image of the data that is being volume rendered. In this way, the user gets real-time visual feedback on her transfer function specification with regards to both the expected composited optical properties and the "fidelity" (how closely the rendering matches the original data) of the resulting rendering.
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.
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.
A Novel Approach To Vortex Core Region Detection
(The Eurographics Association, 2002) Jiang, Ming; Machiraju, Raghu; Thompson, David; D. Ebert and P. Brunet and I. Navazo
In this paper we present a simple and efficient vortex core region detection algorithm based on ideas derived from combinatorial topology. These ideas originated from Sperner s lemma, which by itself is of little value to detecting vortex cores. However, we take these ideas from the lemma and apply them in a point-based fashion to detecting vortex core regions. The resulting algorithms for both 2D and 3D are quite simple and very efficient compared to existing ones. We applied our algorithms to both numerically simulated and procedurally generated datasets to illustrate the efficacy of our approach.
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.
An Open Toolkit for Prototyping Reverse Engineering Visualizations
(The Eurographics Association, 2002) Telea, Alexandru; Maccari, Alessandro; Riva, Claudio; D. Ebert and P. Brunet and I. Navazo
Maintenance and evolution of complex software systems (such as mobile telephones) involves activities such as reverse engineering (RE) and software visualization. Although several RE tools exist, we found their architecture hard to adapt to the domain and problem specific requirements posed by our current practice in Nokia. In this paper, we present an open architecture which allows easy prototyping of RE data exploration and visualization scenarios for a large range of domain models. We pay special attention to the visual and interactive requirements of the reverse engineering process. We compare our toolkit with other existing reverse engineering visual tools and outline the differences.
Parallel and Out-of-core View-dependent Isocontour Visualization Using Random Data Distribution
(The Eurographics Association, 2002) Zhang, Xiaoyu; Bajaj, Chandrajit; Ramachandran, Vijaya; D. Ebert and P. Brunet and I. Navazo
In this paper we describe a parallel and out-of-core view-dependent isocontour visualization algorithm that efficiently extracts and renders the visible portions of an isosurface from large datasets. The algorithm first creates an occlusion map using ray-casting and nearest neighbors. With the occlusion map constructed, the visible portion of the isosurface is extracted and rendered. All steps are in a single pass with minimal communication overhead. The overall workload is well balanced among parallel processors using random data distribution. Volumetric datasets are statically partitioned onto the local disks of each processor and loaded only when necessary. This out-of-core feature allows it to handle scalably large datasets. We additionally demonstrate significant speedup of the view-dependent isocontour visualization on a commodity off-the-shelf PC cluster.
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.

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