EuroVis08: Joint Eurographics - IEEE VGTC Symposium on Visualization
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Item Visual Inspection of Multivariate Graphs(The Eurographics Association and Blackwell Publishing Ltd., 2008) Pretorius, A. Johannes; Wijk, Jarke J. van; A. Vilanova, A. Telea, G. Scheuermann, and T. MoellerMost graph visualization techniques focus on the structure of graphs and do not offer support for dealing with node attributes and edge labels. To enable users to detect relations and patterns in terms of data associated with nodes and edges, we present a technique where this data plays a more central role. Nodes and edges are clustered based on associated data. Via direct manipulation users can interactively inspect and query the graph. Questions that can be answered include, "which edge types are activated by specific node attributes?" and, "how and from where can I reach specific types of nodes?" To validate our approach we contrast it with current practice. We also provide several examples where our method was used to study transition graphs that model real-world systems.Item 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. MoellerWater 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.Item 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. MoellerIllustration-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.Item 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. MoellerDye 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.Item 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. MoellerColor 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.Item Results of a User Study on 2D Hurricane Visualization(The Eurographics Association and Blackwell Publishing Ltd., 2008) Martin, Joel P.; II, J. Edward Swan; II, Robert J. Moorhead; Liu, Zhanping; Cai, Shangshu; A. Vilanova, A. Telea, G. Scheuermann, and T. MoellerWe 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.Item 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. MoellerWe 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.Item 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. MoellerWe 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.Item 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. MoellerIn 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.Item 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. MoellerRecent 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.Item Interaction-Dependent Semantics for Illustrative Volume Rendering(The Eurographics Association and Blackwell Publishing Ltd., 2008) Rautek, Peter; Bruckner, Stefan; Gröller, M. Eduard; A. Vilanova, A. Telea, G. Scheuermann, and T. MoellerIn traditional illustration the choice of appropriate styles and rendering techniques is guided by the intention of the artist. For illustrative volume visualizations it is difficult to specify the mapping between the 3D data and the visual representation that preserves the intention of the user. The semantic layers concept establishes this mapping with a linguistic formulation of rules that directly map data features to rendering styles. With semantic layers fuzzy logic is used to evaluate the user defined illustration rules in a preprocessing step. In this paper we introduce interaction-dependent rules that are evaluated for each frame and are therefore computationally more expensive. Enabling interaction-dependent rules, however, allows the use of a new class of semantics, resulting in more expressive interactive illustrations. We show that the evaluation of the fuzzy logic can be done on the graphics hardware enabling the efficient use of interaction-dependent semantics. Further we introduce the flat rendering mode and discuss how different rendering parameters are influenced by the rule base. Our approach provides high quality illustrative volume renderings at interactive frame rates, guided by the specification of illustration rules.Item Animating Causal Overlays(The Eurographics Association and Blackwell Publishing Ltd., 2008) Bartram, Lyn; Yao, Miao; A. Vilanova, A. Telea, G. Scheuermann, and T. MoellerMost 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.Item 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. MoellerA 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.Item 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. MoellerIn 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.Item 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. MoellerTypically, 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.Item 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. MoellerIn 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.Item 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. MoellerThe 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.Item 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. MoellerWe 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.Item 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. MoellerWe 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.Item 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. MoellerThe 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.