EuroVis06: Joint Eurographics - IEEE VGTC Symposium on Visualization

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https://diglib.eg.org/handle/10.2312/399

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3D Soft Segmentation and Visualization of Medical Data Based on Nonlinear Diffusion and Distance Functions
(The Eurographics Association, 2006) Petersch, B.; Serrano-Serrano, O.; Hönigmann, D.; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
Visualization of medical 3D data is a complex problem, since the raw data is often unsuitable for standard techniques like Direct Volume Rendering. Some kind of pre-treatment is necessary, usually segmentation of the structures of interest, which in turn is a difficult task. Most segmentation techniques yield a model without indicating any uncertainty. Visualization then can be misleading, especially if the original data is of poor contrast. We address this dilemma proposing a geometric approach based on distance on image manifolds and an alternative approach based on nonlinear diffusion. An effective algorithm solving Hamilton-Jacobi equations allows for computing a distance function for 2D and 3D manifolds at interactive rates. An efficient implementation of a semi-implicit operator splitting scheme accomplishes interactivity for the diffusion-based strategy. We establish a model which incorporates local information about its reliability and can be visualized with standard techniques. When interpreting the result of the segmentation in a diagnostic setting, this information is of utmost importance.
Affiliation Dynamics with an Application to Movie-Actor Biographies
(The Eurographics Association, 2006) Brandes, Ulrik; Hoefer, Martin; Pich, Christian; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
We propose a visualization approach for dynamic affiliation networks in which events are characterized by a set of descriptors. It uses a radial ripple metaphor to display the passing of time and conveys relations among the different constituents through appropriate layout. Our method is particularly suitable when assuming an egocentric perspective, and we illustrate it on movie-actor biographies.
The alpha -histogram: Using Spatial Coherence to Enhance Histograms and Transfer Function Design
(The Eurographics Association, 2006) Lundström, Claes; Ynnerman, Anders; Ljung, Patric; Persson, Anders; Knutsson, Hans; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
The high complexity of Transfer Function (TF) design is a major obstacle to widespread routine use of Direct Volume Rendering, particularly in the case of medical imaging. Both manual and automatic TF design schemes would benefit greatly from a fast and simple method for detection of tissue value ranges. To this end, we introduce the a-histogram, an enhancement that amplifies ranges corresponding to spatially coherent materials. The properties of the a-histogram have been explored for synthetic data sets and then successfully used to detect vessels in 20 Magnetic Resonance angiographies, proving the potential of this approach as a fast and simple technique for histogram enhancement in general and for TF construction in particular.
Application-Oriented Extensions of Profile Flags
(The Eurographics Association, 2006) Mlejnek, Matej; Ermes, Pierre; Vilanova, Anna; Rijt, Rob van der; Bosch, Harrie van den; Gerritsen, Frans; Gröller, M. Eduard; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
This paper discusses two applications of probing dense volumetric data for MR orthopedics and dynamic contrast enhanced MRI mammography. In order not to reduce the context information and to extract the essential part of the data, we apply Profile Flags. A Profile Flag is a 3D glyph for probing and annotating the volumetric data. The first application area deals with visualization of T2 profiles for interactive inspection of knee cartilage and detection of lesions. In the second application, we present the usability the Profile Flags for measuring of time-signal profiles for a set of time-dependent MR volumes. Several extensions of the basic Profile Flag concept are described in detail and discussed. These extensions include selection of a set of profiles based on spatial as well as curve differences, automatic positioning of the Profile Flags, and adaptation for probing of time-varying volumetric data. Additionally, we include the evaluation of the used methods by our medical partners.
Automating Transfer Function Design for Volume Rendering Using Hierarchical Clustering of Material Boundaries
(The Eurographics Association, 2006) ereda, Petr; Vilanova, Anna; Gerritsen, Frans A.; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
Transfer function design plays a crucial role in direct volume rendering. Furthermore, it has a major influence on the efficiency of the visualization process. We have developed a framework that facilitates the semi-automatic design of transfer functions. Similarly to other approaches we generate clusters in the transfer function domain. We created a real-time interaction with a hierarchy of clusters. This interaction effectively substitutes cumbersome settings of clustering thresholds. Our framework is also able to easily combine different clustering criteria. We have developed two similarity measures for clustering of material boundaries. One is based on the similarity of the boundaries in the transfer function domain and the other on their spatial relation. We use the LH space as the transfer function domain. This space facilitates the clustering of material boundaries. We demonstrate our approach on several examples.
A Case Study: Visualizing Material Point Method Data
(The Eurographics Association, 2006) Bigler, James; Guilkey, James; Gribble, Christiaan; Hansen, Charles; Parker, Steven G.; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
The Material Point Method is used for complex simulation of solid materials represented using many individual particles. Visualizing such data using existing polygonal or volumetric methods does not accurately encapsulate both the particle and macroscopic properties of the data. In this case study we present various methods used to visualize the particle data as spheres and explain and evaluate two methods of augmenting the visualization using silhouette edges and advanced illumination such as ambient occlusion.We also present informal feedback received from the application scientists who use these methods in their workflow.
Combining Extended Table Lens and Treemap Techniques for Visualizing Tabular Data
(The Eurographics Association, 2006) Telea, Alexandru; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
We present a framework for visualizing large tabular data that combines two views: the table view and the treemap view. The table view extends the known table lens as follows: We cluster related elements to reduce subsampling artifacts and achieve table size independent rendering time; we use multiple-column sorting to create scenariospecific data hierarchies on the fly; and we use shaded cushions to show data structure and variation. Hierarchies built in the table view are shown in a customizable treemap view. One can choose both layout and rendering by a few clicks, effectively creating visual scenarios on-the-fly. We illustrate our framework on real-life stock data.
CVSgrab: Mining the History of Large Software Projects
(The Eurographics Association, 2006) Voinea, S. L.; Telea, A.; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
Many software projects use Software Configuration Management systems to support their development process. Such systems accumulate in time large amounts of information useful for process accounting and auditing. We study how software developers can get insight in this information in order to understand the project context and the product artifacts. To this end, we propose several new techniques for visual mining of project evolution. Central to our approach is a file-based evolution visualization, where each project is shown as a set of horizontal stripes depicting files along the time axis. We propose several mechanisms for interactively building layouts in this display, and for correlating the evolution with the results of various software metrics. We demonstrate the usefulness of our approach on real- life data sets.
D2VR: High-Quality Volume Rendering of Projection-based Volumetric Data
(The Eurographics Association, 2006) Rautek, Peter; Csébfalvi, Balázs; Grimm, Sören; Bruckner, Stefan; Gröller, Eduard; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
Volume rendering techniques are conventionally classified as either direct or indirect methods. Indirect methods require to transform the initial volumetric model into an intermediate geometrical model in order to efficiently visualize it. In contrast, direct volume rendering (DVR) methods can directly process the volumetric data. Modern CT scanners usually provide data as a set of samples on a rectilinear grid, which is computed from the measured projections by discrete tomographic reconstruction. Therefore the rectilinear grid can already be considered as an intermediate volume representation. In this paper we introduce direct direct volume rendering (D2VR). D2VR does not require a rectilinear grid, since it is based on an immediate processing of the measured projections. Arbitrary samples for ray casting are reconstructed from the projections by using the Filtered Back-Projection algorithm. Our method removes a lossy resampling step from the classical volume rendering pipeline. It provides much higher accuracy than traditional grid-based resampling techniques do. Furthermore we also present a novel high-quality gradient estimation scheme, which is also based on the Filtered Back-Projection algorithm.
Data Reconstruction and Visualization Techniques for Forensic Pathology
(The Eurographics Association, 2006) Ehlert, Alexander; Salah, Zein; Bartz, Dirk; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
Forensic pathology is largely concerned with the determination of the cause and manner of deaths after accidents, or other circumstances in criminal investigations. A major task in that process is the documentation of surface injuries, which is traditionally done by drawing sketches, photography, or more recently by photogrammetry to generate a three-dimensional digital lesion cartography of the body surface. In this paper, we describe a semi-automatic processing pipeline how data from 3D photogrammetry is combined and used to generate a visual surface representation of accident victims. In that course, a number of steps are performed to provide a high-quality interactive, point-based visualization of the acquired data, which can be used in a more routine way than previous forensic surface methods.
Direct Isosurface Extraction from Scattered Volume Data
(The Eurographics Association, 2006) Rosenthal, Paul; Linsen, Lars; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
Isosurface extraction is a standard visualization method for scalar volume data and has been subject to research for decades. Nevertheless, to our knowledge, no isosurface extraction method exists that directly extracts surfaces from scattered volume data without 3D mesh generation or reconstruction over a structured grid. We propose a method based on spatial domain partitioning using a kd-tree and an indexing scheme for efficient neighbor search. Our approach consists of a geometry extraction and a rendering step. The geometry extraction step computes points on the isosurface by linearly interpolating between neighboring pairs of samples. The neighbor information is retrieved by partitioning the 3D domain into cells using a kd-tree. The cells are merely described by their index and bitwise index operations allow for a fast determination of potential neighbors. We use an angle criterion to select appropriate neighbors from the small set of candidates. The output of the geometry step is a point cloud representation of the isosurface. The final rendering step uses point-based rendering techniques to visualize the point cloud. Our direct isosurface extraction algorithm for scattered volume data produces results of quality close to the results from standard isosurface extraction algorithms for gridded volume data (like marching cubes). In comparison to 3D mesh generation algorithms (like Delaunay tetrahedrization), our algorithm is about one order of magnitude faster for the examples used in this paper.
Efficient Surface Reconstruction from Noisy Data using Regularized Membrane Potentials
(The Eurographics Association, 2006) Jalba, A. C.; Roerdink, J. B. T. M.; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
We present a novel, physically-motivated method for surface reconstruction that can recover smooth surfaces from noisy and sparse data sets, without using orientation information. A new volumetric technique based on regularized-membrane potentials for aggregating the input sample points is introduced, which manages improved noise tolerability and outlier removal, without sacrificing much with respect to detail (feature) recovery. In this method, sample points are first aggregated on a volumetric grid. A labeling algorithm that relies on intrinsic properties of the smooth scalar field emerging after aggregation is used to classify grid points as exterior or interior to the surface. We also introduce a mesh-smoothing paradigm based on a mass-spring system, enhanced with a bending-energy minimizing term to ensure that the final triangulated surface is smoother than piecewise linear. The method compares favorably with respect to previous approaches in terms of speed and flexibility.
Enhanced Visualizations of Thermographic Data in Process Industry
(The Eurographics Association, 2006) Seipel, S.; Forsberg, A.- K.; Wesslén, D.; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
In this paper, we describe an improved method for visualization of thermographic data in the paper and pulp process industry. We present an application that allows process operators to freely choose how absolute temperatures and time varying changes of thermographic scans should be mapped to colors and/or 3D shapes. Of the possible combinations, we selected two different forms of 3D visualizations and an existing conventional 2D map visualization. We then evaluated these visualization forms with regard to their effectiveness in experimental field studies. The field tests were carried out to measure the operators performance in early detection of insulation damages on lime kilns. The results we obtained from the study show that the two new forms of 3D visualization lead to a reduction of the detection times by about two-thirds and one-third, respectively, when compared to the conventional 2D map representation. Since lime kiln monitoring is based on the rather generic method of continuous thermographic imaging, we suggest that these results also hold for the control and surveillance of other processes.
Enhancing Slice-based Visualizations of Medical Volume Data
(The Eurographics Association, 2006) Tietjen, Christian; Meyer, Björn; Schlechtweg, Stefan; Preim, Bernhard; Hertel, Ilka; Strauß, Gero; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
Slice-based visualizations of CT and MRI data are frequently used for diagnosis, intervention planning and intraoperative navigation since they allow a precise analysis and localization. We present new techniques to enhance the visualization of cross sectional medical image data. Our work is focussed on intervention planning and intraoperative navigation. We address the following problems of slice-based visualization in these areas: the lack of a graphical overview on the positions of anatomic structures, the localization of a target structure and the display of safety zones around pathologic structures. To improve the overview, we introduce LIFTCHARTs, attached as vertical bars to a slice-based visualization. For localizing target structures, we introduce halos. These techniques restrict the occlusion of the original data to a minimum and avoid any modification of the original data. To demonstrate the usability of these visualization techniques, we show two application scenarios in which the techniques come into operation.
Evaluating the Effectiveness of Tree Visualization Systems for Knowledge Discovery
(The Eurographics Association, 2006) Wang, Yue; Teoh, Soon Tee; Ma, Kwan-Liu; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
User studies, evaluations, and comparisons of tree visualization systems have so far focused on questions that can readily be answered by simple, automated queries without needing visualization. Studies are lacking on the actual use of tree visualization in discovering intrinsic, hidden, non-trivial and potentially valuable knowledge. We have thus formulated a set of tree exploration tasks not previously considered and have performed user studies and analysis to determine how visualization helps users to perform these tasks. In our study, we evaluated three systems: RINGS (a node-link representation), Treemap (a containment representation), and Windows Explorer. Our findings suggest a few ways that tree visualization helps users to perceive different aspects of hierarchical structured information. We then explain how these visual representations are able to trigger human perception to make these discoveries.
Fast Ray Traversal of Tetrahedral and Hexahedral Meshes for Direct Volume Rendering
(The Eurographics Association, 2006) Marmitt, Gerd; Slusallek, Philipp; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
The importance of high-performance rendering of unstructured or curvilinear data sets has increased significantly, mainly due to its use in scientific simulations such as computational fluid dynamics and finite element computations. However, the unstructured nature of these data sets lead to rather slow implementations for ray tracing. The approaches discussed in this paper are fast and scalable towards realtime ray tracing applications. We evaluate new algorithms for rendering tetrahedral and hexahedral meshes. In each algorithm, the first cell along a ray is found using common realtime ray tracing techniques. For traversing subsequent cells within the volume, Plücker coordinates as well as ray-bilinear patch intersection tests are used. Since the volume is rendered directly, all algorithms are applicable for isosurface rendering, maximum-intensity projection, and emissionabsorption models.
GPU-Accelerated Volume Splatting With Elliptical RBFs
(The Eurographics Association, 2006) Neophytou, Neophytos; Mueller, Klaus; McDonnell, Kevin T.; Hong, Wei; Guan, Xin; Qin, Hong; Kaufman, Arie; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
Radial Basis Functions (RBFs) have become a popular rendering primitive, both in surface and in volume rendering. This paper focuses on volume visualization, giving rise to 3D kernels. RBFs are especially convenient for the representation of scattered and irregularly distributed point samples, where the RBF kernel is used as a blending function for the space in between samples. Common representations employ radially symmetric RBFs, and various techniques have been introduced to render these, also with efficient implementations on programmable graphics hardware (GPUs). In this paper, we extend the existing work to more generalized, ellipsoidal RBF kernels, for the rendering of scattered volume data. We devise a post-shaded kernel-centric rendering approach, specifically designed to run efficiently on GPUs, and we demonstrate our renderer using datasets from subdivision volumes and computational science.
GPU-Based Hyperstreamlines for Diffusion Tensor Imaging
(The Eurographics Association, 2006) Reina, G.; Bidmon, K.; Enders, F.; Hastreiter, P.; Ertl, T.; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
We propose a new approach for the visualization of hyperstreamlines, which offers potential for better scalability than the conventional polygon-based approach. Our method circumvents the bandwidth bottleneck between the CPU and GPU by transmitting a small set of parameters for each tube segment and generates the surface directly on the GPU using the classical sphere tracing approach. This reduces the load on the CPU that would otherwise need to provide a suitable level-of-detail representation of the scene, while offering even higher quality in the resulting surfaces since every fragment is traced individually. We demonstrate the effectiveness of this approach by comparing it to the performance and output of conventional visualization tools in the application area of diffusion tensor imaging of human brain MR scans. The method presented here can also be utilized to generate other types of surfaces on the GPU that are too complex to handle with direct ray casting and can therefore be adapted for other applications.
GPUFLIC: Interactive and Accurate Dense Visualization of Unsteady Flows
(The Eurographics Association, 2006) Li, Guo-Shi; Tricoche, Xavier; Hansen, Charles; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
The paper presents an efficient and accurate implementation of Unsteady Flow LIC (UFLIC) on the Graphics Processing Unit (GPU). We obtain the same, high quality texture representation of unsteady two-dimensional flows as the original, time-consuming method but leverage the features of today s commodity hardware to achieve interactive frame rates. Despite a remarkable number of recent contributions in the field of texture-based visualization of time-dependent vector fields, the present paper is the first to provide a faithful implementation of that prominent technique fully supported by the graphics pipeline.
A Granular Three Dimensional Multiresolution Transform
(The Eurographics Association, 2006) Entezari, Alireza; Meng, Tai; Bergner, Steven; Möller, Torsten; Beatriz Sousa Santos and Thomas Ertl and Ken Joy
We propose a three dimensional multi-resolution scheme to represent volumetric data in resolutions which are powers of two, resolving the rigidity of the commonly used separable Cartesian multi-resolution schemes in 3D that only allow for change of resolution by a power of eight. Through in-depth comparisons with the counterpart resampling solutions on the Cartesian lattice, we demonstrate the superiority of our subsampling scheme. We derive and document the Fourier domain analysis of this representation. Using such an analysis one can obtain ideal and discrete multidimensional filters for this multi-resolution scheme.

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