EuroVis13: Eurographics Conference on Visualization

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https://diglib.eg.org/handle/10.2312/13888

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Towards High-dimensional Data Analysis in Air Quality Research
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Engel, Daniel; Hummel, Mathias; Hoepel, Florian; Bein, Keith; Wexler, Anthony; Garth, Christoph; Hamann, Bernd; Hagen, Hans; B. Preim, P. Rheingans, and H. Theisel
Analysis of chemical constituents from mass spectrometry of aerosols involves non-negative matrix factorization, an approximation of high-dimensional data in lower-dimensional space. The associated optimization problem is non-convex, resulting in crude approximation errors that are not accessible to scientists. To address this shortcoming, we introduce a new methodology for user-guided error-aware data factorization that entails an assessment of the amount of information contributed by each dimension of the approximation, an effective combination of visualization techniques to highlight, filter, and analyze error features, as well as a novel means to interactively refine factorizations. A case study and the domain-expert feedback provided by the collaborating atmospheric scientists illustrate that our method effectively communicates errors of such numerical optimization results and facilitates the computation of high-quality data factorizations in a simple and intuitive manner.
AmniVis - A System for Qualitative Exploration of Near-Wall Hemodynamics in Cerebral Aneurysms
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Neugebauer, Mathias; Lawonn, Kai; Beuing, Oliver; Berg, Philipp; Janiga, Gabor; Preim, Bernhard; B. Preim, P. Rheingans, and H. Theisel
The qualitative exploration of near-wall hemodynamics in cerebral aneurysms provides important insights for risk assessment. For instance, a direct relation between complex flow patterns and aneurysm formation could be observed. Due to the high complexity of the underlying time-dependent flow data, the exploration is challenging, in particular for medical researchers not familiar with such data. We present the AmniVis-Explorer, a system that is designed for the preparation of a qualitative medical study. The provided features were developed in close collaboration with medical researchers involved in the study. This comprises methods for a purposeful selection of surface regions of interest and a novel approach to provide a 2D overview of flow patterns that are represented by streamlines at these regions. Furthermore, we present a specialized interface that supports binary classification of patterns and temporal exploration as well as methods for selection, highlighting and automatic 3D navigation to particular patterns. Based on eight representative datasets, we conducted informal interviews with two bordcertified radiologists and a flow expert to evaluate the system. It was confirmed that the AmniVis-Explorer allows for an easy selection, qualitative exploration and classification of near-wall flow patterns that are represented by streamlines.
Evaluation of Attention-Guiding Video Visualization
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Kurzhals, Kuno; Höferlin, Markus; Weiskopf, Daniel; B. Preim, P. Rheingans, and H. Theisel
We investigate four different variants of attention-guiding video visualization techniques that aim to help users distribute their attention equally among potential objects of interest: bounding box visualization, force-directed visualization, top-down visualization, grid visualization. Objects of interest are highlighted by rectangular shapes and then we concentrate on the manipulation of color, motion, and size. We conducted a controlled laboratory user study (n
Comparative Visualization of Tracer Uptake in In Vivo Small Animal PET/CT Imaging of the Carotid Arteries
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Diepenbrock, Stefan; Hermann, Sven; Schäfers, Michael; Kuhlmann, Michael; Hinrichs, Klaus; B. Preim, P. Rheingans, and H. Theisel
Cardiovascular diseases are the main cause of death in the western world. Medical research on atherosclerosis is therefore of great interest and a very active research topic. We present a visualization system that supports scientists in exploring plaque development and evaluating the applicability of PET tracers for early diagnosis of cardiovascular diseases. In our application case a cone shaped cuff has been implanted around the carotid artery of ApoE knockout mice, fed with a high cholesterol western type diet. As a result, vascular lesions develop upstream and downstream from the cuff. Tracer uptake induced by these lesions needs to be analyzed in order to evaluate the effectiveness of different PET tracers. We discuss the approach previously utilized to perform this kind of analysis, the problems arising from in vivo image acquisition (in contrast to ex vivo) and the design process of our application. In close cooperation with domain experts we have developed new visualization techniques that display PET activity in the vessel wall and surrounding tissue in a single image. We use the vessel wall detected in the CT image to perform a normalized circular projection which allows the user to judge PET signal distribution in relation to the deformed vessel. Based on this projection a quantitative analysis of a defined region adjacent to the vessel wall can be performed and compared to the artery without the cuff.
An Information-Theoretic Observation Channel for Volume Visualization
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Bramon, Roger; Ruiz, Marc; Bardera, Anton; Boada, Imma; Feixas, Miquel; Sbert, Mateu; B. Preim, P. Rheingans, and H. Theisel
Different quality metrics have been proposed in the literature to evaluate how well a visualization represents the underlying data. In this paper, we present a new information-theoretic framework that quantifies the information transfer between the source data set and the rendered image. This approach is based on the definition of an observation channel whose input and output are given by the intensity values of the volumetric data set and the pixel colors, respectively. From this channel, the mutual information, a measure of information transfer or correlation between the input and the output, is used as a metric to evaluate the visualization quality. The usefulness of the proposed observation channel is illustrated with three fundamental visualization applications: selection of informative viewpoints, transfer function design, and light positioning.
Visualizing Robustness of Critical Points for 2D Time-Varying Vector Fields
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Wang, Bei; Rosen, Paul; Skraba, Primoz; Bhatia, Harsh; Pascucci, Valerio; B. Preim, P. Rheingans, and H. Theisel
Analyzing critical points and their temporal evolutions plays a crucial role in understanding the behavior of vector fields. A key challenge is to quantify the stability of critical points: more stable points may represent more important phenomena or vice versa. The topological notion of robustness is a tool which allows us to quantify rigorously the stability of each critical point. Intuitively, the robustness of a critical point is the minimum amount of perturbation necessary to cancel it within a local neighborhood, measured under an appropriate metric. In this paper, we introduce a new analysis and visualization framework which enables interactive exploration of robustness of critical points for both stationary and time-varying 2D vector fields. This framework allows the end-users, for the first time, to investigate how the stability of a critical point evolves over time. We show that this depends heavily on the global properties of the vector field and that structural changes can correspond to interesting behavior. We demonstrate the practicality of our theories and techniques on several datasets involving combustion and oceanic eddy simulations and obtain some key insights regarding their stable and unstable features.
An Interactive Analysis and Exploration Tool for Epigenomic Data
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Younesy, Hamidreza; Nielsen, Cydney B.; Möller, Torsten; Alder, Olivia; Cullum, Rebecca; Lorincz, Matthew C.; Karimi, Mohammad M.; Jones, Steven J. M.; B. Preim, P. Rheingans, and H. Theisel
In this design study, we present an analysis and abstraction of the data and tasks related to the domain of epigenomics, and the design and implementation of an interactive tool to facilitate data analysis and visualization in this domain. Epigenomic data can be grouped into subsets either by k-means clustering or by querying for combinations of presence or absence of signal (on/off) in different epigenomic experiments. These steps can easily be interleaved and the comparison of different workflows is explicitly supported. We took special care to contain the exponential expansion of possible on/off combinations by creating a novel querying interface. An interactive heat map facilitates the exploration and comparison of different clusters. We validated our iterative design by working closely with two groups of biologists on different biological problems. Both groups quickly found new insight into their data as well as claimed that our tool would save them several hours or days of work over using existing tools.
Visualizing Large-scale Parallel Communication Traces Using a Particle Animation Technique
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Sigovan, Carmen M.; Muelder, Chris W.; Ma, Kwan-Liu; B. Preim, P. Rheingans, and H. Theisel
Large-scale scientific simulations require execution on parallel computing systems in order to yield useful results in a reasonable time frame. But parallel execution adds communication overhead. The impact that this overhead has on performance may be difficult to gauge, as parallel application behaviors are typically harder to understand than the sequential types. We introduce an animation-based interactive visualization technique for the analysis of communication patterns occurring in parallel application execution. Our method has the advantages of illustrating the dynamic communication patterns in the system as well as a static image of MPI (Message Passing Interface) utilization history. We also devise a data streaming mechanism that allows for the exploration of very large data sets. We demonstrate the effectiveness of our approach scaling up to 16 thousand processes using a series of trace data sets of ScaLAPACK matrix operations functions.
Scale-Stack Bar Charts
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Hlawatsch, Marcel; Sadlo, Filip; Burch, Michael; Weiskopf, Daniel; B. Preim, P. Rheingans, and H. Theisel
It is difficult to create appropriate bar charts for data that cover large value ranges. The usual approach for these cases employs a logarithmic scale, which, however, suffers from issues inherent to its non-linear mapping: for example, a quantitative comparison of different values is difficult. We present a new approach for bar charts that combines the advantages of linear and logarithmic scales, while avoiding their drawbacks. Our scale-stack bar charts use multiple scales to cover a large value range, while the linear mapping within each scale preserves the ability to visually compare quantitative ratios. Scale-stack bar charts can be used for the same applications as classic bar charts; in particular, they can readily handle stacked bar representations and negative values. Our visualization technique is demonstrated with results for three different application areas and is assessed by an expert review and a quantitative user study confirming advantages of our technique for quantitative comparisons.
Continuous Representation of Projected Attribute Spaces of Multifields over Any Spatial Sampling
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Molchanov, Vladimir; Fofonov, Alexey; Linsen, Lars; B. Preim, P. Rheingans, and H. Theisel
For the visual analysis of multidimensional data, dimension reduction methods are commonly used to project to a lower-dimensional visual space. In the context of multifields, i.e., volume data with a multidimensional attribute space, the spatial arrangement of the samples in the volumetric domain can be exploited to generate a Continuous Representation of the Projected Attribute Space (CoRPAS). Here, the sample locations in the volumetric domain may be arranged in a structured or unstructured way and may or may not be connected by a grid or a mesh. We propose an approach to generate CoRPAS for any sample arrangement using an isotropic density function. An interactive visual exploration system with three coordinated views of volume visualization, CoRPAS, and an interaction widget based on star coordinates is presented. The star-coordinates widget provides an intuitive means for the user to change the projection matrix. The coordinated views allow for feature selection in form of brushing and linking. The approach is applied to both synthetic data and data resulting from numerical simulations of physical phenomena. In particular, simulations based on Smoothed Particle Hydrodynamics are addressed, where the simulation kernel can be used to produce a CoRPAS that is consistent with the simulation. We also show how a logarithmic scaling of attribute values in CoRPAS is supported, which is of high practical relevance.
TAMRESH - Tensor Approximation Multiresolution Hierarchy for Interactive Volume Visualization
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Suter, Susanne K.; Makhynia, Maxim; Pajarola, Renato; B. Preim, P. Rheingans, and H. Theisel
Interactive visual analysis of large and complex volume datasets is an ongoing and challenging problem. We tackle this challenge in the context of state-of-the-art out-of-core multiresolution volume rendering by introducing a novel hierarchical tensor approximation (TA) volume visualization approach. The TA framework allows us (a) to use a rank-truncated basis for compact volume representation, (b) to visualize features at multiple scales, and (c) to visualize the data at multiple resolutions. In this paper, we exploit the special properties of the TA factor matrix bases and define a novel multiscale and multiresolution volume rendering hierarchy. Different from previous approaches, to represent one volume dataset we use but one set of global bases (TA factor matrices) to reconstruct at all resolution levels and feature scales. In particular, we propose a coupling of multiscalable feature visualization and multiresolution DVR through the properties of global TA bases. We demonstrate our novel TA multiresolution hierarchy based volume representation and visualization on a number of mCT volume datasets.
AOI Rivers for Visualizing Dynamic Eye Gaze Frequencies
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Burch, Michael; Kull, Andreas; Weiskopf, Daniel; B. Preim, P. Rheingans, and H. Theisel
It is difficult to explore and analyze eye gaze trajectories for commonly applied visual task solution strategies because such data shows complex spatio-temporal structure. In particular, the traditional eye gaze plots of scan paths fail for a large number of study participants since these plots lead to much visual clutter. To address this problem we introduce the AOI Rivers technique as a novel interactive visualization method for investigating timevarying fixation frequencies, transitions between areas of interest (AOIs), and the sequential order of gaze visits to AOIs in a visual stimulus of an eye tracking experiment. To this end, we extend the ThemeRiver technique by influents, effluents, and transitions similar to the concept of Sankey diagrams. The AOI Rivers visualization is complemented by linked spatial views of the data in the form of heatmaps, gaze plots, or display of the visual stimulus. The usefulness of our technique is demonstrated for gaze trajectory data recorded in a previously conducted eye tracking experiment.
Rule-based Visual Mappings - with a Case Study on Poetry Visualization
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Abdul-Rahman, Alfie; Lein, Julie; Coles, Katharine; Maguire, Eamonn; Meyer, Miriah; Wynne, Martin; Johnson, Chris R.; Trefethen, Anne; Chen, Min; B. Preim, P. Rheingans, and H. Theisel
In this paper, we present a user-centered design study on poetry visualization. We develop a rule-based solution to address the conflicting needs for maintaining the flexibility of visualizing a large set of poetic variables and for reducing the tedium and cognitive load in interacting with the visual mapping control panel. We adopt Munzner's nested design model to maintain high-level interactions with the end users in a closed loop. In addition, we examine three design options for alleviating the difficulty in visualizing poems latitudinally. We present several example uses of poetry visualization in scholarly research on poetry.
Selecting Semantically-Resonant Colors for Data Visualization
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Lin, Sharon; Fortuna, Julie; Kulkarni, Chinmay; Stone, Maureen; Heer, Jeffrey; B. Preim, P. Rheingans, and H. Theisel
We introduce an algorithm for automatic selection of semantically-resonant colors to represent data (e.g., using blue for data about ''oceans'', or pink for ''love''). Given a set of categorical values and a target color palette, our algorithm matches each data value with a unique color. Values are mapped to colors by collecting representative images, analyzing image color distributions to determine value-color affinity scores, and choosing an optimal assignment. Our affinity score balances the probability of a color with how well it discriminates among data values. A controlled study shows that expert-chosen semantically-resonant colors improve speed on chart reading tasks compared to a standard palette, and that our algorithm selects colors that lead to similar gains. A second study verifies that our algorithm effectively selects colors across a variety of data categories.
imMens: Real-time Visual Querying of Big Data
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Liu, Zhicheng; Jiang, Biye; Heer, Jeffrey; B. Preim, P. Rheingans, and H. Theisel
Data analysts must make sense of increasingly large data sets, sometimes with billions or more records.We present methods for interactive visualization of big data, following the principle that perceptual and interactive scalability should be limited by the chosen resolution of the visualized data, not the number of records. We first describe a design space of scalable visual summaries that use data reduction methods (such as binned aggregation or sampling) to visualize a variety of data types. We then contribute methods for interactive querying (e.g., brushing & linking) among binned plots through a combination of multivariate data tiles and parallel query processing. We implement our techniques in imMens, a browser-based visual analysis system that uses WebGL for data processing and rendering on the GPU. In benchmarks imMens sustains 50 frames-per-second brushing & linking among dozens of visualizations, with invariant performance on data sizes ranging from thousands to billions of records.
Constructing Isosurfaces with Sharp Edges and Corners using Cube Merging
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Bhattacharya, Arindam; Wenger, Rephael; B. Preim, P. Rheingans, and H. Theisel
A number of papers present algorithms to construct isosurfaces with sharp edges and corners from hermite data, i.e. the exact surface normals at the exact intersection of the surface and grid edges. We discuss some fundamental problems with the previous algorithms and describe a new approach, based on merging grid cubes near sharp edges, that produces significantly better results. Our algorithm requires only gradients at the grid vertices, not at each surface-edge intersection point. We also give a method for measuring the correctness of the resulting sharp edges and corners in the isosurface.
ExPlates: Spatializing Interactive Analysis to Scaffold Visual Exploration
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Javed, Waqas; Elmqvist, Niklas; B. Preim, P. Rheingans, and H. Theisel
Visual exploration involves using visual representations to investigate data where the goals of the process are unclear and poorly defined. However, this often places unduly high cognitive load on the user, particularly in terms of keeping track of multiple investigative branches, remembering earlier results, and correlating between different views. We propose a new methodology for automatically spatializing the individual steps in visual exploration onto a large visual canvas, allowing users to easily recall, reflect, and assess their progress. We also present a webbased implementation of our methodology called EXPLATESJS where users can manipulate multidimensional data in their browsers, automatically building visual queries as they explore the data.
Interactive Extraction and Tracking of Biomolecular Surfaces Features
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Krone, Michael; Reina, Guido; Schulz, Christoph; Kulschewski, Tobias; Pleiss, Jürgen; Ertl, Thomas; B. Preim, P. Rheingans, and H. Theisel
We present a coordinated-view application for the analysis of molecular surface features like cavities, channels and pockets. Our tool employs object-space ambient occlusion for the detection of such features and tracks them over time. It offers time-dependent graphs of metrics concerning those features and allows analyzing the temporal relationship of the features, i.e. when they (dis)appear, split or merge and which features participate in each of these events. The automated analysis process is performed in real time while the user interactively explores a dynamic data set. The system supports linking and brushing to allow for a user-guided visual analysis based on different aspects of the data. We demonstrate the effectiveness of our approach by applying it to data sets from biochemistry and report the insights that can be gained. We also evaluate the benefits of our method with respect to recent advancements in the field. The algorithmic pipeline leverages the computing power of modern GPUs, thus achieving interactive frame rates without any precomputation for fully dynamic data sets.
dPSO-Vis: Topology-based Visualization of Discrete Particle Swarm Optimization
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Volke, Sebastian; Middendorf, Martin; Hlawitschka, Mario; Kasten, Jens; Zeckzer, Dirk; Scheuermann, Gerik; B. Preim, P. Rheingans, and H. Theisel
Particle swarm optimization (PSO) is a metaheuristic that has been applied successfully to many continuous and combinatorial optimization problems, e.g., in the fields of economics, engineering, and natural sciences. In PSO, a swarm of particles moves within a search space in order to find an optimal solution. Unfortunately, it is hard to understand in detail why and how changes in the design of PSO algorithms affect the optimization behavior. Visualizing the particle states could provide substantially better insight into PSO algorithms. Though in case of combinatorial optimization problems, it often raises the problem of illustrating the states within the discrete search space that cannot be embedded spatially. We propose a visualization approach to depict the optimization problem topologically using a landscape metaphor. This visualization is augmented by an illustration of the time-dependent states of the particles. Thus, the user of dPSO-Vis is able to analyze the swarm's behavior within the search space. In principle, our method can be used for any optimization algorithm where a swarm of individuals searches within a discrete search space. Our approach is verified with a case study for the PSO algorithm HelixPSO that predicts the secondary structure of RNA molecules.
Maximum Entropy Summary Trees
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Karloff, Howard; Shirley, Kenneth E.; B. Preim, P. Rheingans, and H. Theisel
Given a very large, node-weighted, rooted tree on, say, n nodes, if one has only enough space to display a knode summary of the tree, what is the most informative way to draw the tree? We define a type of weighted tree that we call a summary tree of the original tree that results from aggregating nodes of the original tree subject to certain constraints. We suggest that the best choice of which summary tree to use (among those with a fixed number of nodes) is the one that maximizes the information-theoretic entropy of a natural probability distribution associated with the summary tree, and we provide a (pseudopolynomial-time) dynamic-programming algorithm to compute this maximum entropy summary tree, when the weights are integral. The result is an automated way to summarize large trees and retain as much information about them as possible, while using (and displaying) only a fraction of the original node set. We illustrate the computation and use of maximum entropy summary trees on five real data sets whose weighted tree representations vary widely in structure. We also provide an additive approximation algorithm and a greedy heuristic that are faster than the optimal algorithm, and generalize to trees with real-valued weights.

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