27-Issue 3

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

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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.
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.
Physically-based Dye Advection for Flow Visualization
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Li, Guo-Shi; Tricoche, Xavier; Hansen, Charles; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Dye advection is widely used in experimental flow analysis but has seen less use for visualization in computational fluid dynamics. One possible reason for this disconnect is the inaccuracy of the texture-based approach, which is prone to artifacts caused by numeric diffusion and mass fluctuation. In this paper, we introduce a novel 2D dye advection scheme for flow visualization based on the concept of control volume analysis typically used in computational fluid dynamics. The evolution of dye patterns in the flow field is achieved by advecting individual control volumes, which collectively cover the entire spatial domain. The local variation of dye material, represented as a piecewise quasi-parabolic function, is integrated within each control volume resulting in mass conserving transport without excessive numerical diffusion. Due to its physically based formulation, this approach is capable of conveying intricate flow structures not shown in the traditional dye advection schemes while avoiding visual artifacts.
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.
Visual Comparison of Hierarchically Organized Data
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Holten, Danny; Wijk, Jarke J. van; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
We provide a novel visualization method for the comparison of hierarchically organized data. Our technique visualizes a pair of hierarchies that are to be compared and simultaneously depicts how these hierarchies are related by explicitly visualizing the relations between matching subhierarchies. Elements that are unique to each hierarchy are shown, as well as the way in which hierarchy elements are relocated, split or joined. The relations between hierarchy elements are visualized using Hierarchical Edge Bundles (HEBs). HEBs reduce visual clutter, they visually emphasize the aforementioned splits, joins, and relocations of subhierarchies, and they provide an intuitive way in which users can interact with the relations. The focus throughout this paper is on the comparison of different versions of hierarchically organized software systems, but the technique is applicable to other kinds of hierarchical data as well. Various data sets of actual software systems are used to show how our technique can be employed to easily spot splits, joins, and relocations of elements, how sorting both hierarchies with respect to each other facilitates comparison tasks, and how user interaction is supported.
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.
Particle Level Set Advection for the Interactive Visualization of Unsteady 3D Flow
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Cuntz, Nicolas; Kolb, Andreas; Strzodka, Robert; Weiskopf, Daniel; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Typically, flow volumes are visualized by defining their boundary as iso-surface of a level set function. Grid-based level sets offer a good global representation but suffer from numerical diffusion of surface detail, whereas particlebased methods preserve details more accurately but introduce the problem of unequal global representation. The particle level set (PLS) method combines the advantages of both approaches by interchanging the information between the grid and the particles. Our work demonstrates that the PLS technique can be adapted to volumetric dye advection via streak volumes, and to the visualization by time surfaces and path volumes. We achieve this with a modified and extended PLS, including a model for dye injection. A new algorithmic interpretation of PLS is introduced to exploit the efficiency of the GPU, leading to interactive visualization. Finally, we demonstrate the high quality and usefulness of PLS flow visualization by providing quantitative results on volume preservation and by discussing typical applications of 3D flow visualization.
Interactive Visualization of Multimodal Volume Data for Neurosurgical Tumor Treatment
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Rieder, Christian; Ritter, Felix; Raspe, Matthias; Peitgen, Heinz-Otto; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
We present novel interactive methods for the visualization of multimodal volume data as used in neurosurgical therapy planning. These methods allow surgeons to explore multimodal volumes and focus on functional data and lesions. Computer graphics techniques are proposed to create expressive visualizations at interactive frame rates to reduce time-consuming and complex interaction with the medical data. Contributions of our work are the distance-based enhancements of functional data and lesions which allows the surgeon to perceive functional and anatomical structures at once and relate them directly to the intervention. In addition we propose methods for the visual exploration of the path to the structures of interest, to enhance anatomical landmarks, and to provide additional depth indicators. These techniques have been integrated in a visualization prototype that provides interaction capabilities for finding the optimal therapeutic strategy for the neurosurgeon.
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.
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.
Visualizing Genome Expression and Regulatory Network Dynamics in Genomic and Metabolic Context
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Westenberg, Michel A.; Hijum, S. A. F. T. van; Kuipers, O. P.; Roerdink, Jos B. T. M.; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
DNA microarrays are used to measure the expression levels of thousands of genes simultaneously. In a time series experiment, the gene expressions are measured as a function of time. We present an application for integrated visualization of genome expression and network dynamics in both regulatory networks and metabolic pathways. Integration of these two levels of cellular processes is necessary, since it provides the link between the measure- ments at the transcriptional level (gene expression levels approximated from microarray data) and the phenotype (the observable characteristics of an organism) at the functional and behavioral level. The integration requires visualization approaches besides traditional clustering and statistical analysis methods. Our application can (i) visualize the data from time series experiments in the context of a regulatory network and KEGG metabolic pathways; (ii) identify and visualize active regulatory subnetworks from the gene expression data; (iii) perform a statistical test to identify and subsequently visualize pathways that are affected by differentially expressed genes. We present a case study, which demonstrates that our approach and application both facilitates and speeds up data analysis tremendously in comparison to a more traditional approach that involves many manual, laborious, and error-prone steps.
Lagrangian Visualization of Flow-Embedded Surface Structures
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Garth, Christoph; Wiebel, Alexander; Tricoche, Xavier; Joy, Ken; Scheuermann, Gerik; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
The notions of Finite-Time Lyapunov Exponent (FTLE) and Lagrangian Coherent Structures provide a strong framework for the analysis and visualization of complex technical flows. Their definition is simple and intuitive, and they are built on a deep theoretical foundation. We apply these concepts to enable the analysis of flows in the immediate vicinity of the boundaries of flow-embedded objects by limiting the Lagrangian analysis to surfaces closely neighboring these boundaries. To this purpose, we present an approach to approximate FTLE fields over such surfaces. Furthermore, we achieve an effective depiction of boundary-related flow structures such as separation and attachment over object boundaries and specific insight into the surrounding flow using several specifically chosen visualization techniques. We document the applicability of our methods by presenting a number of application examples.
Raycasting of Light Field Galleries from Volumetric Data
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Rezk-Salama, Christof; Todt, Severin; Kolb, Andreas; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
The paper describes a technique to generate high-quality light field representations from volumetric data. We show how light field galleries can be created to give unexperienced audiences access to interactive high-quality volume renditions. The proposed light field representation is lightweight with respect to storage and bandwidth capacity and is thus ideal as exchange format for visualization results, especially for web galleries. The approach expands an existing sphere-hemisphere parameterization for the light field with per-pixel depth. High-quality paraboloid maps from volumetric data are generated using GPU-based ray-casting or slicing approaches. Different layers, such as isosurfaces, but not restricted to, can be generated independently and composited in real time. This allows the user to interactively explore the model and to change visibility parameters at run-time.
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.
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.
Investigative Visual Analysis of Global Terrorism
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Wang, Xiaoyu; Miller, Erin; Smarick, Kathleen; Ribarsky, William; Chang, Remco; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Recent increases in terrorist activity around the world have made analyzing and understanding such activities more critical than ever. With the help of organizations such as the National Center for the Study of Terrorism and Responses to Terrorism (START), we now have detailed historical information on each terrorist event around the world since 1970. However, due to the size and complexity of the data, identifying terrorists' patterns and trends has been difficult. To better enable investigators in understanding terrorist activities, we propose a visual analytical system that focuses on depicting one of the most fundamental concepts in investigative analysis, the five W's (who, what, where, when, and why). Views in our system are highly correlated, and each represents one of the W's. With this approach, an investigator can interactively explore terrorist activities efficiently and discover reasons of attacks (why) by identifying patterns temporally (when), geo-spatially (where), between multiple terrorist groups (who), and across different methods or modes of attacks (what). By coupling a global perspective with the details gleaned from asking these five questions, the system allows analysts to think both tactically and strategically.
Topology-Preserving lambda_2-based Vortex Core Line Detection for Flow Visualization
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Schafhitzel, Tobias; Vollrath, Joachim E.; Gois, Joao P.; Weiskopf, Daniel; Castelo, Antonio; Ertl, Thomas; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
We propose a novel vortex core line extraction method based on the lambda_2 vortex region criterion in order to improve the detection of vortex features for 3D flow visualization. The core line is defined as a curve that connects lambda_2 minima restricted to planes that are perpendicular to the core line. The basic algorithm consists of the following stages: (1) lambda_2 field construction and isosurface extraction; (2) computation of the curve skeleton of the lambda_2 isosurface to build an initial prediction for the core line; (3) correction of the locations of the prediction by searching for lambda_2 minima on planes perpendicular to the core line. In particular, we consider the topology of the vortex core lines, guaranteeing the same topology as the initial curve skeleton. Furthermore, we propose a geometry-guided definition of vortex bifurcation, which represents the split of one core line into two parts. Finally, we introduce a user-guided approach in order to narrow down vortical regions taking into account the graph of lambda_2 along the computed vortex core line. We demonstrate the effectiveness of our method by comparing our results to previous core line detection methods with both simulated and experimental data; in particular, we show robustness of our method for noise-affected data.

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