EuroVis12: Eurographics Conference on Visualization

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https://diglib.eg.org/handle/10.2312/393

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A Quantized Boundary Representation of 2D Flows
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Levine, Joshua; Jadhav, Shreeraj; Bhatia, Harsh; Pascucci, Valerio; Bremer, Peer-Timo; S. Bruckner, S. Miksch, and H. Pfister
Analysis and visualization of complex vector fields remain major challenges when studying large scale simulation of physical phenomena. The primary reason is the gap between the concepts of smooth vector field theory and their computational realization. In practice, researchers must choose between either numerical techniques, with limited or no guarantees on how they preserve fundamental invariants, or discrete techniques which limit the precision at which the vector field can be represented. We propose a new representation of vector fields that combines the advantages of both approaches. In particular, we represent a subset of possible streamlines by storing their paths as they traverse the edges of a triangulation. Using only a finite set of streamlines creates a fully discrete version of a vector field that nevertheless approximates the smooth flow up to a user controlled error bound. The discrete nature of our representation enables us to directly compute and classify analogues of critical points, closed orbits, and other common topological structures. Further, by varying the number of divisions (quantizations) used per edge, we vary the resolution used to represent the field, allowing for controlled precision. This representation is compact in memory and supports standard vector field operations.
Drawing Large Graphs by Low-Rank Stress Majorization
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Khoury, Marc; Hu, Yifan; Krishnan, Shankar; Scheidegger, Carlos; S. Bruckner, S. Miksch, and H. Pfister
Optimizing a stress model is a natural technique for drawing graphs: one seeks an embedding into Rd which best preserves the induced graph metric. Current approaches to solving the stress model for a graph with jVj nodes and jEj edges require the full all-pairs shortest paths (APSP) matrix, which takes O(jVj2 log jEj+jVjjEj) time and O(jVj2) space. We propose a novel algorithm based on a low-rank approximation to the required matrices. The crux of our technique is an observation that it is possible to approximate the full APSP matrix, even when only a small subset of its entries are known. Our algorithm takes time O(kjVj+jVj logjVj+jEj) per iteration with a preprocessing time of O(k3 +k(jEj+jVj logjVj)+k2jVj) and memory usage of O(kjVj), where a user-defined parameter k trades off quality of approximation with running time and space. We give experimental results which show, to the best of our knowledge, the largest (albeit approximate) full stress model based layouts to date.
Visualization of Global Correlation Structures in Uncertain 2D Scalar Fields
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Pfaffelmoser, Tobias; Westermann, Rüdiger; S. Bruckner, S. Miksch, and H. Pfister
Visualizing correlations, i.e., the tendency of uncertain data values at different spatial positions to change contrarily or according to each other, allows inferring on the possible variations of structures in the data. Visualizing global correlation structures, however, is extremely challenging, since it is not clear how the visualization of complicated long-range dependencies can be integrated into standard visualizations of spatial data. Furthermore, storing correlation information imposes a memory requirement that is quadratic in the number of spatial sample positions. This paper presents a novel approach for visualizing both positive and inverse global correlation structures in uncertain 2D scalar fields, where the uncertainty is modeled via a multivariate Gaussian distribution. We introduce a new measure for the degree of dependency of a random variable on its local and global surroundings, and we propose a spatial clustering approach based on this measure to classify regions of a particular correlation strength. The clustering performs a correlation filtering, which results in a representation that is only linear in the number of spatial sample points. Via cluster coloring the correlation information can be embedded into visualizations of other statistical quantities, such as the mean and the standard deviation. We finally propose a hierarchical cluster subdivision scheme to further allow for the simultaneous visualization of local and global correlations.
A Design Study of Direct-Touch Interaction for Exploratory 3D Scientific Visualization
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Klein, Tijmen; Guéniat, Florimond; Pastur, Luc; Vernier, Frédéric; Isenberg, Tobias; S. Bruckner, S. Miksch, and H. Pfister
We present an interaction design study of several non-overlapping direct-touch interaction widgets, postures, and bi-manual techniques to support the needs of scientists who are exploring a dataset. The final interaction design supports navigation/zoom, cutting plane interaction, a drilling exploration, the placement of seed particles in 3D space, and the exploration of temporal data evolution. To ground our design, we conducted a requirements analysis and used a participatory design approach throughout development. We chose simulations in the field of fluid mechanics as our example domain and, in the paper, discuss our choice of techniques, their adaptation to our target domain, and discuss how they facilitate the necessary combination of visualization control and data exploration. We evaluated our resulting interactive data exploration system with seven fluid mechanics experts and report on their qualitative feedback. While we use flow visualization as our application domain, the developed techniques were designed with generalizability in mind and we discuss several implications of our work on further development of direct-touch data exploration techniques for scientific visualization in general.
Preface and Table of Contents
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Stefan Bruckner and Silvia Miksch and Hanspeter Pfister
Interactive Visualization of Generalized Virtual 3D City Models using Level-of-Abstraction Transitions
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Semmo, Amir; Trapp, Matthias; Kyprianidis, Jan Eric; Döllner, Jürgen; S. Bruckner, S. Miksch, and H. Pfister
Virtual 3D city models play an important role in the communication of complex geospatial information in a growing number of applications, such as urban planning, navigation, tourist information, and disaster management. In general, homogeneous graphic styles are used for visualization. For instance, photorealism is suitable for detailed presentations, and non-photorealism or abstract stylization is used to facilitate guidance of a viewer's gaze to prioritized information. However, to adapt visualization to different contexts and contents and to support saliencyguided visualization based on user interaction or dynamically changing thematic information, a combination of different graphic styles is necessary. Design and implementation of such combined graphic styles pose a number of challenges, specifically from the perspective of real-time 3D visualization. In this paper, the authors present a concept and an implementation of a system that enables different presentation styles, their seamless integration within a single view, and parametrized transitions between them, which are defined according to tasks, camera view, and image resolution. The paper outlines potential usage scenarios and application fields together with a performance evaluation of the implementation.
MatchPad: Interactive Glyph-Based Visualization for Real-Time Sports Performance Analysis
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Legg, Philip; Chung, David H. S.; Parry, Matthew L.; Jones, Mark W.; Long, Rhys; Griffiths, Iwan W.; Chen, Min; S. Bruckner, S. Miksch, and H. Pfister
Today real-time sports performance analysis is a crucial aspect of matches in many major sports. For example, in soccer and rugby, team analysts may annotate videos during the matches by tagging specific actions and events, which typically result in some summary statistics and a large spreadsheet of recorded actions and events. To a coach, the summary statistics (e.g., the percentage of ball possession) lacks sufficient details, while reading the spreadsheet is time-consuming and making decisions based on the spreadsheet in real-time is thereby impossible. In this paper, we present a visualization solution to the current problem in real-time sports performance analysis. We adopt a glyph-based visual design to enable coaching staff and analysts to visualize actions and events at a glance . We discuss the relative merits of metaphoric glyphs in comparison with other types of glyph designs in this particular application. We describe an algorithm for managing the glyph layout at different spatial scales in interactive visualization. We demonstrate the use of this technical approach through its application in rugby, for which we delivered the visualization software, MatchPad, on a tablet computer. The MatchPad was used by the Welsh Rugby Union during the Rugby World Cup 2011. It successfully helped coaching staff and team analysts to examine actions and events in detail whilst maintaining a clear overview of the match, and assisted in their decision making during the matches. It also allows coaches to convey crucial information back to the players in a visually-engaging manner to help improve their performance.
Employing 2D Projections for Fast Visual Exploration of Large Fiber Tracking Data
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Poco, Jorge; Eler, Danilo M.; Paulovich, Fernando; Minghim, Rosane; S. Bruckner, S. Miksch, and H. Pfister
Fiber tracts detection is an increasingly common technology for diagnosis and also understanding of brain function. Although tools for tracing and presenting brain fibers are advanced, it is still difficult for physicians or students to explore the dataset in 3D due to their intricate topology. In this work we present a visual exploration approach for fiber tracts data aimed at supporting exploration of such data. The work employs a local, precise and fast 2D multidimensional projection technique that allows a large number of fibers to be handled simultaneously and to select groups of bundled fibers for further exploration. In this approach, a DTI feature dataset, including curvature as well as spatial features, is projected on a 2D or 3D view. By handling groups formed in this view, exploration is linked to corresponding brain fibers in object space. The link exists in both directions and fibers selected in object space are also mapped to feature space. Our approach also allows users to modify the projection, controlling and improving, if necessary, the definition of groups of fibers for small and large datasets, due to the local nature of the projection. Compared to other related work, the method presented here is faster for creating visual representations, making it possible to explore complete sets of fibers tracts up to 250K fibers, which was not possible previously. Additionally, the ability to change configuration of the feature space representation adds a high degree of flexibility to the process.
Comparative Visual Analysis of 2D Function Ensembles
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Piringer, Harald; Pajer, Stephan; Berger, Wolfgang; Teichmann, Heike; S. Bruckner, S. Miksch, and H. Pfister
In the development process of powertrain systems, 2D function ensembles frequently occur in the context of multirun simulations. An analysis has many facets, including distributions of extracted features, comparisons between ensemble members and target functions, and details-on-demand. The primary contribution of this paper is a design study of an interactive approach for a comparative visual analysis of 2D function ensembles. The design focuses on a tight integration of domain-oriented and member-oriented visualization techniques, and it seeks to preserve the mental model of 2D functions on multiple levels of detail. In this context, we propose a novel focus+context approach for visualizations relying on data-driven placement which is based on labeling. We also extend work on feature-preserving downsampling of 2D functions. Our design supports a comparison of 2D functions based on juxtaposition, overlay, and explicit differences. It also enables an analysis in terms of extracted scalar features and 1D aggregations. An evaluation illustrates a workflow in our application context. User feedback indicates a time saving of 70% for common tasks and a qualitative gain for the entire development process.
Conceptualizing Visual Uncertainty in Parallel Coordinates
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Dasgupta, Aritra; Chen, Min; Kosara, Robert; S. Bruckner, S. Miksch, and H. Pfister
Uncertainty is an intrinsic part of any visual representation in visualization, no matter how precise the input data. Existing research on uncertainty in visualization mainly focuses on depicting data-space uncertainty in a visual form. Uncertainty is thus often seen as a problem to deal with, in the data, and something to be avoided if possible. In this paper, we highlight the need for analyzing visual uncertainty in order to design more effective visual representations. We study various forms of uncertainty in the visual representation of parallel coordinates and propose a taxonomy for categorizing them. By building a taxonomy, we aim to identify different sources of uncertainty in the screen space and relate them to different effects of uncertainty upon the user. We examine the literature on parallel coordinates and apply our taxonomy to categorize various techniques for reducing uncertainty. In addition, we consider uncertainty from a different perspective by identifying cases where increasing certain forms of uncertainty may even be useful, with respect to task, data type and analysis scenario. This work suggests that uncertainty is a feature that can be both useful and problematic in visualization, and it is beneficial to augment an information visualization pipeline with a facility for visual uncertainty analysis.
Scalable Detection of Spatiotemporal Encounters in Historical Movement Data
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Bak, Peter; Marder, Mattias; Harary, Sivan; Yaeli, Avi; Ship, Harold J.; S. Bruckner, S. Miksch, and H. Pfister
The widespread adoption of location-aware devices is resulting in the generation of large amounts of spatiotemporal movement data, collected and stored in digital repositories. This forms a fertile ground for domain experts and scientists to analyze such historical data and discover interesting movement behavioral patterns. Experts in many domains, such as transportation, logistics and retail, are interested in detecting and understanding movement patterns and behavior of objects in relation to each other. Their insights can point to optimization potential and reveal deviations from planned behavior. In this paper, we focus on the detection of the encounter patterns as one possible type in movement behavior. These patterns refer to objects being close to one another in terms of space and time. We define scalability as a core requirement when dealing with historical movement data, in order to allow the domain expert to set parameters of the encounter detection algorithm. Our approach leverages a designated data structure and requires only a single pass over chronological data, thus resulting in highly scalable and fast technique to detect encounters. Consequently, users are able to explore their data by interactively specifying the spatial and temporal windows that define encounters. We evaluate our proposed method as a function of its input parameters and data size. We instantiate the proposed method on urban public transportation data, where we found a large number of encounters. We show that single encounters emerge into higher level patterns that are of particular interest and value to the domain.
Visualization of Advection-Diffusion in Unsteady Fluid Flow
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Karch, Grzegorz Karol; Sadlo, Filip; Weiskopf, Daniel; Munz, Claus-Dieter; Ertl, Thomas; S. Bruckner, S. Miksch, and H. Pfister
Advection has been the standard transport mechanism in flow visualization. Diffusion, in contrast, has not been considered important in visual flow field analysis so far, although it is inherent to many physical processes. We present a novel technique that allows for interactive 3D visualization of both advection and diffusion in unsteady fluid flow. We extend texture-based flow visualization, which is advection-oriented, by diffusion. Our finite volume approach based on WENO (weighted essentially non-oscillatory) reconstruction is well parallelizable and features low numerical diffusion at interactive rates. Our scheme contributes to three different applications: (a) highquality dye advection at low numerical diffusion, (b) physically-based dye advection accounting for diffusivity of virtual media, and (c) visualization of advection-diffusion fluxes in physical media where the velocity field is accompanied by a concentration field. Interactive rendering of the virtual dye is accomplished by ray casting. We apply our GPU implementation to CFD examples of thermal convection and evaporation phenomena.
Visualization of 4D Blood-Flow Fields by Spatiotemporal Hierarchical Clustering
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Pelt, Roy van; Jacobs, Sander; Romeny, Bart ter Haar; Vilanova, Anna; S. Bruckner, S. Miksch, and H. Pfister
Advancements in the acquisition and modeling of flow fields result in unsteady volumetric flow fields of unprecedented quality. An important example is found in the analysis of unsteady blood-flow data. Preclinical research strives for a better understanding of correlations between the hemodynamics and the progression of cardiovascular diseases. Modern-day computer models and MRI acquisition provide time-resolved volumetric blood-flow velocity fields. Unfortunately, these fields often remain unexplored, as high-dimensional data are difficult to conceive. We present a spatiotemporal, i.e., four-dimensional, hierarchical clustering, yielding a sparse representation of the velocity data. The clustering results underpin an illustrative visualization approach, facilitating visual analysis. The hierarchy allows an intuitive level-of-detail selection, largely retaining important flow patterns. The clustering employs dissimilarity measures to construct the hierarchy. We have adapted two existing measures for steady vector fields for use in the spacetime domain. Because of the inherent computational complexity of the multidimensional clustering, we introduce a coarse hierarchical clustering approach, which closely approximates the full hierarchy generation, and considerably improves the performance. The resulting clusters are visualized by representative patharrows, in combination with an illustrative anatomical context. We present various seeding approaches and visualization styles, providing sparse overviews of the unsteady behavior of volumetric flow fields.
Nearly Recurrent Components in 3D Piecewise Constant Vector Fields
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Szymczak, Andrzej; Brunhart-Lupo, Nicholas; S. Bruckner, S. Miksch, and H. Pfister
We present an algorithm for computing nearly recurrent components, that represent areas of close to circulating or stagnant flow, for 3D piecewise constant (PC) vector fields defined on regular grids. Using a number of analytical and simulated data sets, we demonstrate that nearly recurrent components can provide interesting insight into the topological structure of 3D vector fields. Our approach is based on prior work on Morse decompositions for PC vector fields on surfaces and extends concepts previously developed with this goal in mind to the case of 3D vector fields defined on regular grids. Our contributions include a description of trajectories of 3D piecewise constant vector fields and an extension of the transition graph, a finite directed graph that represents all trajectories, to the 3D case. Nearly recurrent components are defined by strongly connected components of the transition graph.
Tracing Tuples Across Dimensions: A Comparison of Scatterplots and Parallel Coordinate Plots
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Kuang, Xiaole; Zhang, Haimo; Zhao, Shengdong; McGuffin, Michael J.; S. Bruckner, S. Miksch, and H. Pfister
One of the fundamental tasks for analytic activity is retrieving (i.e., reading) the value of a particular quantity in an information visualization. However, few previous studies have compared user performance in such value retrieval tasks for different visualizations. We present an experimental comparison of user performance (time and error distance) across four multivariate data visualizations. Three variants of scatterplot (SCP) visualizations, namely SCPs with common vertical axes (SCP-common), SCPs with a staircase layout (SCP-staircase), and SCPs with rotated axes between neighboring cells (SCP-rotated), and a baseline parallel coordinate plots (PCP) were compared. Results show that the baseline PCP is better than SCP-rotated and SCP-staircase under all conditions, while the difference between SCP-common and PCP depends on the dimensionality and density of the dataset. PCP shows advantages over SCP-common when the dimensionality and density of the dataset are low, but SCP- common eventually outperforms PCP as data dimensionality and density increase. The results suggest guidelines for the use of SCPs and PCPs that can benefit future researchers and practitioners.
Rolled-out Wordles: A Heuristic Method for Overlap Removal of 2D Data Representatives
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Strobelt, Hendrik; Spicker, Marc; Stoffel, Andreas; Keim, Daniel; Deussen, Oliver; S. Bruckner, S. Miksch, and H. Pfister
When representing 2D data points with spacious objects such as labels, overlap can occur. We present a simple algorithm which modifies the (Mani-)Wordle idea with scan-line based techniques to allow a better placement. We give an introduction to common placement techniques from different fields and compare our method to these techniques w.r.t. euclidean displacement, changes in orthogonal ordering as well as shape and size preservation. Especially in dense scenarios our method preserves the overall shape better than known techniques and allows a good trade-off between the other measures. Applications on real world data are given and discussed.
Computing Voronoi Treemaps: Faster, Simpler, and Resolution-independent
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Nocaj, Arlind; Brandes, Ulrik; S. Bruckner, S. Miksch, and H. Pfister
Voronoi treemaps represent hierarchies as nested polygons. We here show that, contrary to the apparent popular belief, utilization of an algorithm for weighted Voronoi diagrams is not only feasible, but also more efficient than previous low-resolution approximations, even when the latter are implemented on graphics hardware. More precisely, we propose an instantiation of Lloyd's method for centroidal Voronoi diagrams with Aurenhammer's algorithm for power diagrams that yields an algorithm running in O(n log n) rather than Ω(n2) time per iteration, with n the number of sites. We describe its implementation and present evidence that it is faster also in practice.
StratomeX: Visual Analysis of Large-Scale Heterogeneous Genomics Data for Cancer Subtype Characterization
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Lex, Alexander; Streit, Marc; Schulz, Hans-Joerg; Partl, Christian; Schmalstieg, Dieter; Park, Peter J.; Gehlenborg, Nils; S. Bruckner, S. Miksch, and H. Pfister
Identification and characterization of cancer subtypes are important areas of research that are based on the integrated analysis of multiple heterogeneous genomics datasets. Since there are no tools supporting this process, much of this work is done using ad-hoc scripts and static plots, which is inefficient and limits visual exploration of the data. To address this, we have developed StratomeX, an integrative visualization tool that allows investigators to explore the relationships of candidate subtypes across multiple genomic data types such as gene expression, DNA methylation, or copy number data. StratomeX represents datasets as columns and subtypes as bricks in these columns. Ribbons between the columns connect bricks to show subtype relationships across datasets. Drill-down features enable detailed exploration. StratomeX provides insights into the functional and clinical implications of candidate subtypes by employing small multiples, which allow investigators to assess the effect of subtypes on molecular pathways or outcomes such as patient survival. As the configuration of viewing parameters in such a multi-dataset, multi-view scenario is complex, we propose a meta visualization and configuration interface for dataset dependencies and data-view relationships. StratomeX is developed in close collaboration with domain experts.We describe case studies that illustrate how investigators used the tool to explore subtypes in large datasets and demonstrate how they efficiently replicated findings from the literature and gained new insights into the data.
The World's Languages Explorer: Visual Analysis of Language Features in Genealogical and Areal Contexts
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Rohrdantz, Christian; Hund, Michael; Mayer, Thomas; Wälchli, Bernhard; Keim, Daniel A.; S. Bruckner, S. Miksch, and H. Pfister
This paper presents a novel Visual Analytics approach that helps linguistic researchers to explore the world's languages with respect to several important tasks: (1) The comparison of manually and automatically extracted language features across languages and within the context of language genealogy, (2) the exploration of interrelations among several of such features as well as their homogeneity and heterogeneity within subtrees of the language genealogy, and (3) the exploration of genealogical and areal influences on the features. We introduce the WORLD'S LANGUAGES EXPLORER, which provides the required functionalities in one single Visual Analytics environment. Contributions are made for different parts of the system: We introduce an extended Sunburst visualization whose so-called feature-rings allow for a cross-comparison of a large number of features at once, within the hierarchical context of the language genealogy. We suggest a mapping of homogeneity measures to all levels of the hierarchy. In addition, we suggest an integration of information from the areal data space into the hierarchical data space. With our approach we bring Visual Analytics research to a new application field, namely Historical Comparative Linguistics, and Linguistic and Areal Typology. Finally, we provide evidence of the good performance of our system in this area through two application case studies conducted by domain experts.
ConnectedCharts: Explicit Visualization of Relationships between Data Graphics
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Viau, Christophe; McGuffin, Michael; S. Bruckner, S. Miksch, and H. Pfister
Multidimensional multivariate data can be visualized using many different well-known charts, such as bar charts, stacked bar charts, grouped bar charts, scatterplots, or pivot tables, or also using more advanced highdimensional techniques such as scatterplot matrices (SPLOMs) or parallel coordinate plots (PCPs). These many techniques have different advantages, and users may wish to use several charts or data graphics to understand a dataset from different perspectives. We present ConnectedCharts, a technique for displaying relationships between multiple charts. ConnectedCharts allow for hybrid combinations of bar charts, scatterplots, and parallel coordinates, with curves drawn to show the conceptual links between charts. The charts can be thought of as coordinated views, where linking is achieved not only through interactive brushing, but also with explicitly drawn curves that connect corresponding data tuples or axes. We present a formal description of a design space of many simple charts, and also identify different kinds of connections that can be displayed between related charts. Our prototype implementation demonstrates how the connections between multiple charts can make relationships clearer and can serve to document the history of a user's analytical process, leading to potential applications in visual analytics and dashboard design.

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