27-Issue 3

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https://diglib.eg.org/handle/10.2312/136

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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.
Animating Causal Overlays
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Bartram, Lyn; Yao, Miao; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Most approaches to representing causality, such as the common causal graph, require a separate and static view, but in many cases it is useful to add the dimension of causality to the context of an existing visualization. Building on research from perceptual psychology that shows the perception of causality is a low-level visual event derived from certain types of motion, we are investigating how to add animated causal representations, called visual causal vectors, onto other visualizations. We refer to these as causal overlays. Our initial experimental results show this approach has great potential but that extra cues are needed to elicit the perception of causality when the motions are overlaid on other graphical objects. In this paper we describe the approach and report on a study that examined two issues of this technique: how to accurately convey the causal flow and how to represent the strength of the causal effect.
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.
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.
Classification and Uncertainty Visualization of Dendritic Spines from Optical Microscopy Imaging
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Janoos, Firdaus; Nouansengsy, Boonthanome; Xu, Xiaoyin; Machiraju, Raghu; Wong, Stephen T. C.; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Abstract Neuronal dendrites and their spines affect the connectivity of neural networks, and play a significant role in many neurological conditions. Neuronal function is observed to be closely correlated with the appearance, disappearance and morphology of the spines. Automatic 3-D reconstruction of neurons from light microscopy images, followed by the identification, classification and visualization of dendritic spines is therefore essential for studying neuronal physiology and biophysical properties. In this paper, we present a method to reconstruct dendrites using a surface representation of the dendrite. The 1-D skeleton of the dendritic surface is then extracted by a medial geodesic function that is robust and topologically correct. This is followed by a Bayesian identification and classification of the spines. The dendrite and spines are visualized in a manner that displays the spines' types and the inherent uncertainty in identification and classification. We also describe a user study conducted to validate the accuracy of the classification and the efficacy of the visualization.
Code Flows: Visualizing Structural Evolution of Source Code
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Telea, Alexandru; Auber, David; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Understanding detailed changes done to source code is of great importance in software maintenance. We present Code Flows, a method to visualize the evolution of source code geared to the understanding of fine and mid-level scale changes across several file versions. We enhance an existing visual metaphor to depict software structure changes with techniques that emphasize both following unchanged code as well as detecting and highlighting important events such as code drift, splits, merges, insertions and deletions. The method is illustrated with the analysis of a real-world C++ code system.
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.
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.
COPERNICUS: Context-Preserving Engine for Route Navigation with Interactive User-modifiable Scaling
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Ziegler, Hartmut; Keim, Daniel A.; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
In this paper, we present an automated system for generating context-preserving route maps that depict navigation routes as a path between nodes and edges inside a topographic network. Our application identifies relevant context information to support navigation and orientation, and generates customizable route maps according to design principles that communicate all relevant context information clearly visible on one single page. Interactive scaling allows seamless transition between the original undistorted map and our new map design, and supports userspecified scaling of regions of interest to create personalized driving directions according to the drivers needs.
Density Displays for Data Stream Monitoring
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Hao, Ming; Keim, Daniel A.; Dayal, Umeshwar; Oelke, Daniela; Tremblay, Chantal; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
In many business applications, large data workloads such as sales figures or process performance measures need to be monitored in real-time. The data analysts want to catch problems in flight to reveal the root cause of anomalies. Immediate actions need to be taken before the problems become too expensive or consume too many resources. In the meantime, analysts need to have the "big picture" of what the information is about. In this paper, we derive and analyze two real-time visualization techniques for managing density displays: (1) circular overlay displays which visualize large volumes of data without data shift movements after the display is full, thus freeing the analyst from adjusting the mental picture of the data after each data shift; and (2) variable resolution density displays which allow users to get the entire view without cluttering. We evaluate these techniques with respect to a number of evaluation measures, such as constancy of the display and usage of display space, and compare them to conventional displays with periodic shifts. Our real time data monitoring system also provides advanced interactions such as a local root cause analysis for further exploration. The applications using a number of real-world data sets show the wide applicability and usefulness of our ideas.
Discrete Multi-Material Interface Reconstruction for Volume Fraction Data
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Anderson, John C.; Garth, C.; Duchaineau, Mark A.; Joy, Kenneth I.; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
We present the results from a user study looking at the ability of observers to mentally integrate wind direction and magnitude over a vector field. The data set chosen for the study is an MM5 (PSU/NCAR Mesoscale Model) simulation of Hurricane Lili over the Gulf of Mexico as it approaches the southeastern United States. Nine observers participated in the study. This study investigates the effect of layering on the observer's ability to determine the magnitude and direction of a vector field. We found a tendency for observers to underestimate the magnitude of the vectors and a counter-clockwise bias when determining the average direction of a vector field. We completed an additional study with two observers to try to uncover the source of the counter-clockwise bias. These results have direct implications to atmospheric scientists, but may also be able to be applied to other fields that use 2D vector fields.
Evaluation of Illustration-inspired Techniques for Time-varying Data Visualization
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Joshi, Alark; Rheingans, Penny; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Illustration-inspired techniques have provided alternative ways to visualize time-varying data. Techniques such as speedlines, flow ribbons, strobe silhouettes and opacity-based techniques provide temporal context to the current timestep being visualized. We evaluated the effectiveness of these illustrative techniques by conducting a user study. We compared the ability of subjects to visually track features using snapshots, snapshots augmented by illustration techniques, animations, and animations augmented by illustration techniques. User accuracy, time required to perform a task, and user confidence were used as measures to evaluate the techniques. The results indicate that the use of illustration-inspired techniques provides a significant improvement in user accuracy and the time required to complete the task. Subjects performed significantly better on each metric when using augmented animations as compared to augmented snapshots.
Exploratory Visualization of Animal Kinematics Using Instantaneous Helical Axes
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Keefe, Daniel F.; O'Brien, Trevor M.; Baier, David B.; Gatesy, Stephen M.; Brainerd, Elizabeth L.; Laidlaw, David H.; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
We present novel visual and interactive techniques for exploratory visualization of animal kinematics using instantaneous helical axes (IHAs). The helical axis has been used in orthopedics, biomechanics, and structural mechanics as a construct for describing rigid body motion. Within biomechanics, recent imaging advances have made possible accurate high-speed measurements of individual bone positions and orientations during experiments. From this high-speed data, instantaneous helical axes of motion may be calculated. We address questions of effective interactive, exploratory visualization of this high-speed 3D motion data. A 3D glyph that encodes all parameters of the IHA in visual form is presented. Interactive controls are used to examine the change in the IHA over time and relate the IHA to anatomical features of interest selected by a user. The techniques developed are applied to a stereoscopic, interactive visualization of the mechanics of pig mastication and assessed by a team of evolutionary biologists who found interactive IHA-based analysis a useful addition to more traditional motion analysis techniques.
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.
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.
FromWeb Data to Visualization via Ontology Mapping
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Gilson, Owen; Silva, Nuno; Grant, Phil W.; Chen, Min; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
In this paper, we propose a novel approach for automatic generation of visualizations from domain-specific data available on the web. We describe a general system pipeline that combines ontology mapping and probabilistic reasoning techniques. With this approach, a web page is first mapped to a Domain Ontology, which stores the semantics of a specific subject domain (e.g., music charts). The Domain Ontology is then mapped to one or more Visual Representation Ontologies, each of which captures the semantics of a visualization style (e.g., tree maps). To enable the mapping between these two ontologies, we establish a Semantic Bridging Ontology, which specifies the appropriateness of each semantic bridge. Finally each Visual Representation Ontology is mapped to a visualization using an external visualization toolkit. Using this approach, we have developed a prototype software tool, SemViz, as a realisation of this approach. By interfacing its Visual Representation Ontologies with public domain software such as ILOG Discovery and Prefuse, SemViz is able to generate appropriate visualizations automatically from a large collection of popular web pages for music charts without prior knowledge of these web pages.
Generating Color Palettes using Intuitive Parameters
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Wijffelaars, Martijn; Vliegen, Roel; Wijk, Jarke J. van; Linden, Erik-Jan van der; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Color is widely used in data visualization to show data values. The proper selection of colors is critical to convey information correctly. In this paper, we present a technique for generating univariate lightness ordered palettes. These are specified via intuitive input parameters that are used define the appearance of the palette: number of colors, hue, lightness, saturation, contrast and hue range. The settings of the parameters are used to generate curves through CIELUV color space. This color space is used in order to correctly translate the requirements in terms of perceptual properties to a set of colors. The presented palette generation method enables users to specify palettes that have these perceptual properties, such as perceived order, equal perceived distance and equal importance. The technique has been integrated in MagnaView, a system for multivariate data visualization.
Geometry-driven Visualization of Microscopic Structures in Biology
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Mosaliganti, Kishore; Machiraju, Raghu; Huang, Kun; Leone, Gustavo; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
At a microscopic resolution, biological structures are composed of cells, red blood corpuscles (RBCs), cytoplasm and other microstructural components. There is a natural pattern in terms of distribution, arrangement and packing density of these components in biological organization. In this work, we propose to use N-point correlation functions to guide the analysis and exploration process in microscopic datasets. These functions provide useful feature spaces to aid segmentation and visualization tasks. We show 3D visualizations of mouse placenta tissue layers and mouse mammary ducts as well as 2D segmentation/tracking of clonal populations. Further confidence in our results stems from validation studies that were performed with manual ground-truth for segmentation.
GPU Local Triangulation: an Interpolating Surface Reconstruction Algorithm
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Buchart, Carlos; Borro, Diego; Amundarain, Aiert; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
A GPU capable method for surface reconstruction from unorganized point clouds without additional information, called GLT (GPU Local Triangulation), is presented. The main objective of this research is the generation of a GPU interpolating reconstruction based on local Delaunay triangulations, inspired by a pre-existing reconstruction algorithm. Current graphics hardware accelerated algorithms are approximating approaches, where the final triangulation is usually performed through either marching cubes or marching tetrahedras. GPU-compatible methods and data structures to perform normal estimation and the local triangulation have been developed, plus a variation of the Bitonic Merge Sort algorithm to work with multi-lists. Our method shows an average gain of one order of magnitude over previous research.
Illustrative Hybrid Visualization and Exploration of Anatomical and Functional Brain Data
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Jainek, Werner M.; Born, Silvia; Bartz, Dirk; Straßer, Wolfgang; Fischer, Jan; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Common practice in brain research and brain surgery involves the multi-modal acquisition of brain anatomy and brain activation data. These highly complex three-dimensional data have to be displayed simultaneously in order to convey spatial relationships. Unique challenges in information and interaction design have to be solved in order to keep the visualization sufficiently complete and uncluttered at the same time. The visualization method presented in this paper addresses these issues by using a hybrid combination of polygonal rendering of brain structures and direct volume rendering of activation data. Advanced rendering techniques including illustrative display styles and ambient occlusion calculations enhance the clarity of the visual output. The presented rendering pipeline produces real-time frame rates and offers a high degree of configurability. Newly designed interaction and measurement tools are provided, which enable the user to explore the data at large, but also to inspect specific features closely. We demonstrate the system in the context of a cognitive neurosciences dataset. An initial informal evaluation shows that our visualization method is deemed useful for clinical research.

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