EuroVis08: Joint Eurographics - IEEE VGTC Symposium on Visualization

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https://diglib.eg.org/handle/10.2312/397

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Illustrative Parallel Coordinates
(The Eurographics Association and Blackwell Publishing Ltd., 2008) McDonnell, Kevin T.; Mueller, Klaus; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Illustrative parallel coordinates (IPC) is a suite of artistic rendering techniques for augmenting and improving parallel coordinate (PC) visualizations. IPC techniques can be used to convey a large amount of information about a multidimensional dataset in a small area of the screen through the following approaches: (a) edge-bundling through splines; (b) visualization of "branched" clusters to reveal the distribution of the data; (c) opacity-based hints to show cluster density; (d) opacity and shading effects to illustrate local line density on the parallel axes; and (e) silhouettes, shadows and halos to help the eye distinguish between overlapping clusters. Thus, the primary goal of this work is to convey as much information as possible in a manner that is aesthetically pleasing and easy to understand for non-experts.
Computing Local Signed Distance Fields for Large Polygonal Models
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Chang, Byungjoon; Cha, Deukhyun; Ihm, Insung; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
The signed distance field for a polygonal model is a useful representation that facilitates efficient computation in many visualization and geometric processing tasks. Often it is more effective to build a local distance field only within a narrow band around the surface that holds local geometric information for the model. In this paper, we present a novel technique to construct a volumetric local signed distance field of a polygonal model. To compute the local field efficiently, exactly those cells that cross the polygonal surface are found first through a new voxelization method, building a list of intersecting triangles for each boundary cell. After their neighboring cells are classified, the triangle lists are exploited to compute the local signed distance field with minimized voxel-totriangle distance computations. While several efficient methods for computing the distance field, particularly those harnessing the graphics processing unit's (GPU's) processing power, have recently been proposed, we focus on a CPU-based technique, intended to deal flexibly with large polygonal models and high-resolution grids that are often too bulky for GPU computation.
Visual Clustering in Parallel Coordinates
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Zhou, Hong; Yuan, Xiaoru; Qu, Huamin; Cui, Weiwei; Chen, Baoquan; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Parallel coordinates have been widely applied to visualize high-dimensional and multivariate data, discerning patterns within the data through visual clustering. However, the effectiveness of this technique on large data is reduced by edge clutter. In this paper, we present a novel framework to reduce edge clutter, consequently improving the effectiveness of visual clustering. We exploit curved edges and optimize the arrangement of these curved edges by minimizing their curvature and maximizing the parallelism of adjacent edges. The overall visual clustering is improved by adjusting the shape of the edges while keeping their relative order. The experiments on several representative datasets demonstrate the effectiveness of our approach.
Centrality Based Visualization of Small World Graphs
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Ham, Frank van; Wattenberg, Martin; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Current graph drawing algorithms enable the creation of two dimensional node-link diagrams of huge graphs. However, for graphs with low diameter (of which "small world" graphs are a subset) these techniques begin to break down visually even when the graph has only a few hundred nodes. Typical algorithms produce images where nodes clump together in the center of the screen, making it hard to discern structure and follow paths. This paper describes a solution to this problem, which uses a global edge metric to determine a subset of edges that capture the graph's intrinsic clustering structure. This structure is then used to create an embedding of the graph, after which the remaining edges are added back in. We demonstrate applications of this technique to a number of real world examples.
Virtual Klingler Dissection: Putting Fibers into Context
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Schultz, Thomas; Sauber, Natascha; Anwander, Alfred; Theisel, Holger; Seidel, Hans-Peter; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Fiber tracking is a standard tool to estimate the course of major white matter tracts from diffusion tensor magnetic resonance imaging (DT-MRI) data. In this work, we aim at supporting the visual analysis of classical streamlines from fiber tracking by integrating context from anatomical data, acquired by a T1-weighted MRI measurement. To this end, we suggest a novel visualization metaphor, which is based on data-driven deformation of geometry and has been inspired by a technique for anatomical fiber preparation known as Klingler dissection. We demonstrate that our method conveys the relation between streamlines and surrounding anatomical features more effectively than standard techniques like slice images and direct volume rendering. The method works automatically, but its GPU-based implementation allows for additional, intuitive interaction.
Towards Closing the Analysis Gap: Visual Generation of Decision Supporting Schemes from Raw Data
(The Eurographics Association and Blackwell Publishing Ltd., 2008) May, Thorsten; Kohlhammer, Jörn; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
The derivation, manipulation and verification of analytical models from raw data is a process which requires a transformation of information across different levels of abstraction. We introduce a concept for the coupling of data classification and interactive visualization in order to make this transformation visible and steerable for the human user. Data classification techniques generate mappings that formally group data items into categories. Interactive visualization includes the user into an iterative refinement process. The user identifies and selects interesting patterns to define these categories. The following step is the transformation of a visible pattern into the formal definition of a classifier. In the last step the classifier is transformed back into a pattern that is blended with the original data in the same visual display. Our approach allows in intuitive assessment of a formal classifier and its model, the detection of outliers and the handling of noisy data using visual pattern-matching. We instantiated the concept using decision trees for classification and KVMaps as the visualization technique. The generation of a classifier from visual patterns and its verification is transformed from a cognitive to a mostly pre-cognitive task.
Extraction Of Feature Lines On Surface Meshes Based On Discrete Morse Theory
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Sahner, Jan; Weber, Britta; Prohaska, Steffen; Lamecker, Hans; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
We present an approach for extracting extremal feature lines of scalar indicators on surface meshes, based on discrete Morse Theory. By computing initial Morse-Smale complexes of the scalar indicators of the mesh, we obtain a candidate set of extremal feature lines of the surface. A hierarchy of Morse-Smale complexes is computed by prioritizing feature lines according to a novel criterion and applying a cancellation procedure that allows us to select the most significant lines. Given the scalar indicators on the vertices of the mesh, the presented feature line extraction scheme is interpolation free and needs no derivative estimates. The technique is insensitive to noise and depends only on one parameter: the feature significance. We use the technique to extract surface features yielding impressive, non photorealistic images.
Automatic Detection and Visualization of Distinctive Structures in 3D Unsteady Multi-fields
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Jänicke, Heike; Böttinger, Michael; Tricoche, Xavier; Scheuermann, Gerik; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Current unsteady multi-field simulation data-sets consist of millions of data-points. To efficiently reduce this enormous amount of information, local statistical complexity was recently introduced as a method that identifies distinctive structures using concepts from information theory. Due to high computational costs this method was so far limited to 2D data. In this paper we propose a new strategy for the computation that is substantially faster and allows for a more precise analysis. The bottleneck of the original method is the division of spatio-temporal configurations in the field (light-cones) into different classes of behavior. The new algorithm uses a density-driven Voronoi tessellation for this task that more accurately captures the distribution of configurations in the sparsely sampled high-dimensional space. The efficient computation is achieved using structures and algorithms from graph theory. The ability of the method to detect distinctive regions in 3D is illustrated using flow and weather simulations.
Quality Isosurface Mesh Generation Using an Extended Marching Cubes Lookup Table
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Raman, Sundaresan; Wenger, Rephael; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Concurrent Viewing of Multiple Attribute-Specific Subspaces
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Sisneros, Robert; Johnson, C. Ryan; Huang, Jian; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
In this work we present a point classification algorithm for multi-variate data. Our method is based on the concept of attribute subspaces, which are derived from a set of user specified attribute target values. Our classification approach enables users to visually distinguish regions of saliency through concurrent viewing of these subspaces in single images. We also allow a user to threshold the data according to a specified distance from attribute target values. Based on the degree of thresholding, the remaining data points are assigned radii of influence that are used for the final coloring. This limits the view to only those points that are most relevant, while maintaining a similar visual context.
Abstractive Representation and Exploration of Hierarchically Clustered Diffusion Tensor Fiber Tracts
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Chen, Wei; Zhang, Song; Correia, Stephen; Ebert, David S.; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Diffusion tensor imaging (DTI) has been used to generate fibrous structures in both brain white matter and muscles. Fiber clustering groups the DTI fibers into spatially and anatomically related tracts. As an increasing number of fiber clustering methods have been recently developed, it is important to display, compare, and explore the clustering results efficiently and effectively. In this paper, we present an anatomical visualization technique that reduces the geometric complexity of the fiber tracts and emphasizes the high-level structures. Beginning with a volumetric diffusion tensor image, we first construct a hierarchical clustering representation of the fiber bundles. These bundles are then reformulated into a 3D multi-valued volume data. We then build a set of geometric hulls and principal fibers to approximate the shape and orientation of each fiber bundle. By simultaneously visualizing the geometric hulls, individual fibers, and other data sets such as fractional anisotropy, the overall shape of the fiber tracts are highlighted, while preserving the fibrous details. A rater with expert knowledge of white matter structure has evaluated the resulting interactive illustration and confirmed the improvement over straightforward DTI fiber tract visualization.
A Four-level Focus + Context Approach to Interactive Visual Analysis of Temporal Features in Large Scientific Data
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Muigg, Philipp; Kehrer, Johannes; Oeltze, Steffen; Piringer, Harald; Doleisch, Helmut; Preim, Bernhard; Hauser, Helwig; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
In this paper we present a new approach to the interactive visual analysis of time-dependent scientific data - both from measurements as well as from computational simulation - by visualizing a scalar function over time for each of tenthousands or even millions of sample points. In order to cope with overdrawing and cluttering, we introduce a new four-level method of focus+context visualization. Based on a setting of coordinated, multiple views (with linking and brushing), we integrate three different kinds of focus and also the context in every single view. Per data item we use three values (from the unit interval each) to represent to which degree the data item is part of the respective focus level. We present a color compositing scheme which is capable of expressing all three values in a meaningful way, taking semantics and their relations amongst each other (in the context of our multiple linked view setup) into account. Furthermore, we present additional image-based postprocessing methods to enhance the visualization of large sets of function graphs, including a texture-based technique based on line integral convolution (LIC). We also propose advanced brushing techniques which are specific to the timedependent nature of the data (in order to brush patterns over time more efficiently). We demonstrate the usefulness of the new approach in the context of medical perfusion data.
Visual Analysis and Semantic Exploration of Urban LIDAR Change Detection
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Butkiewicz, Thomas; Chang, Remco; Wartell, Zachary; Ribarsky, William; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Many previous approaches to detecting urban change from LIDAR point clouds interpolate the points into rasters, perform pixel-based image processing to detect changes, and produce 2D images as output. We present a method of LIDAR change detection that maintains accuracy by only using the raw, irregularly spaced LIDAR points, and extracts relevant changes as individual 3D models. We then utilize these models, alongside existing GIS data, within an interactive application that allows the chronological exploration of the changes to an urban environment. A three-tiered level-of-detail system maintains a scale-appropriate, legible visual representation across the entire range of view scales, from individual changes such as buildings and trees, to groups of changes such as new residential developments, deforestation, and construction sites, and finally to larger regions such as neighborhoods and districts of a city that are emerging or undergoing revitalization. Tools are provided to assist the visual analysis by urban planners and historians through semantic categorization and filtering of the changes presented.
TimeRadarTrees: Visualizing Dynamic Compound Digraphs
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Burch, Michael; Diehl, Stephan; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
The evolution of dependencies in information hierarchies can be modeled by sequences of compound digraphs with edge weights. In this paper we present a novel approach to visualize such sequences of graphs. It uses radial tree layout to draw the hierarchy, and circle sectors to represent the temporal change of edges in the digraphs. We have developed several interaction techniques that allow the users to explore the structural and temporal data. Smooth animations help them to track the transitions between views. The usefulness of the approach is illustrated by examples from very different application domains.
A Screen Space Quality Method for Data Abstraction
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Johansson, Jimmy; Cooper, Matthew; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
The rendering of large data sets can result in cluttered displays and non-interactive update rates, leading to time consuming analyses. A straightforward solution is to reduce the number of items, thereby producing an abstraction of the data set. For the visual analysis to remain accurate, the graphical representation of the abstraction must preserve the significant features present in the original data. This paper presents a screen space quality method, based on distance transforms, that measures the visual quality of a data abstraction. This screen space measure is shown to better capture significant visual structures in data, compared with data space measures. The presented method is implemented on the GPU, allowing interactive creation of high quality graphical representations of multivariate data sets containing tens of thousands of items
Navigation and Exploration of Interconnected Pathways
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Streit, Marc; Kalkusch, M.; Kashofer, K.; Schmalstieg, Dieter; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Visualizing pathways, i. e. models of cellular functional networks, is a challenging task in computer assisted biomedicine. Pathways are represented as large collections of interwoven graphs, with complex structures present in both the individual graphs and their interconnections. This situation requires the development of novel visualization techniques to allow efficient visual exploration. We present the Caleydo framework, which incorporates a number of approaches to handle such pathways. Navigation in the network of pathways is facilitated by a hierarchical approach which dynamically selects a working set of individual pathways for closer inspection. These pathways are interactively rendered together with visual interconnections in a 2.5D view using graphics hardware acceleration. The layout of individual graphs is not computed automatically, but taken from the KEGG and BioCarta databases, which use layouts that life scientists are familiar with. Therefore they encode essential meta-information. While the KEGG and BioCarta pathways use a pre-defined layout, interactions such as linking+ brushing, neighborhood search or detail on demand are still fully interactive in Caleydo. We have evaluated Caleydo with pathologists working on the determination of unknown gene functions. Informal experiences confirm that Caleydo is useful in both generating and validating such hypotheses. Even though the presented techniques are applied to medical pathways, the proposed way of interaction is not limited to cellular processes and therefore has the potential to open new possibilities in other fields of application.
Interactive Visualization for Memory Reference Traces
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Choudhury, A. N. M. Imroz; Potter, Kristin C.; Parker, Steven G.; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
We present the Memory Trace Visualizer (MTV), a tool that provides interactive visualization and analysis of the sequence of memory operations performed by a program as it runs. As improvements in processor performance continue to outpace improvements in memory performance, tools to understand memory access patterns are in- creasingly important for optimizing data intensive programs such as those found in scientific computing. Using visual representations of abstract data structures, a simulated cache, and animating memory operations, MTV can expose memory performance bottlenecks and guide programmers toward memory system optimization opportu- nities. Visualization of detailed memory operations provides a powerful and intuitive way to expose patterns and discover bottlenecks, and is an important addition to existing statistical performance measurements.
Sound Tracing: Rendering Listener Specific Acoustic Room Properties
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Bellmann, Jens; Michel, Frank; Deines, Eduard; Hering-Bertram, Martin; Mohring, Jan; Hagen, Hans; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
We present an acoustic rendering approach visualizing the listener-specific contribution of frequency-dependent pressure fields on a scene geometry with acoustic reflection and scattering properties. Our method facilitates the evaluation of simulated acoustics showing the effect of simulation parameters like absorption and scattering. The image-based spatial localization of acoustic properties is complementary to the auditive evaluation by means of auralization. Our core contribution is a pressure-based acoustic rendering equation and a corresponding raytracing method applying techniques from photorealistic rendering to the field of simulated room acoustics. Applications are directed at the visualization of interference patterns and analyzing the impact of acoustic reflection parameters.
Interactive Exploratory Visualization of 2D Vector Fields
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Isenberg, Tobias; Everts, Maarten H.; Grubert, Jens; Carpendale, Sheelagh; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
In this paper we present several techniques to interactively explore representations of 2D vector fields. Through a set of simple hand postures used on large, touch-sensitive displays, our approach allows individuals to customdesign glyphs (arrows, lines, etc.) that best reveal patterns of the underlying dataset. Interactive exploration of vector fields is facilitated through freedom of glyph placement, glyph density control, and animation. The custom glyphs can be applied individually to probe specific areas of the data but can also be applied in groups to explore larger regions of a vector field. Re-positionable sources from which glyphs - animated according to the local vector field - continue to emerge are used to examine the vector field dynamically. The combination of these techniques results in an engaging visualization with which the user can rapidly explore and analyze varying types of 2D vector fields, using a virtually infinite number of custom-designed glyphs.
Visual Abstractions of Solvent Pathlines near Protein Cavities
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Bidmon, Katrin; Grottel, Sebastian; Bös, Fabian; Pleiss, Jürgen; Ertl, Thomas; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Water is known to play a crucial role in protein structure, flexibility and activity. The use of molecular dynamics simulations allows detailed studies of complex protein-solvent interactions. Cluster analysis and density-based approaches have been successfully used for the identification and analysis of conserved water molecules and hydration patterns of proteins. However, appropriate tools for analysing long-time molecular dynamics simulations with respect to tracking and visualising the paths of solvent molecules are lacking. Our method focuses on visualising the solvent paths entering and leaving cavities of the protein and allows to study the route and dynamics of the exchange of tightly bound internal water molecules with the bulk solvent. The proposed visualisation also represents dynamic properties such as direction and velocity in the solvent. Especially, by clustering similar pathlines with respect to designated properties the visualisation can be abstracted to represent the principal paths of solvent molecules through the cavities. Its application in the analysis of long-time scale molecular dynamics simulations not only confirmed conjectures based on previous manual observations made by chance, but also led to novel insights into the dynamical and structural role of water molecules and its interplay with protein structure.

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