32-Issue 3

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https://diglib.eg.org/handle/10.2312/181

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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.
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.
Augmenting Visualization with Natural Language Translation of Interaction: A Usability Study
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Nafari, Maryam; Weaver, Chris; B. Preim, P. Rheingans, and H. Theisel
As visualization tools get more complicated, users often find it increasingly difficult to learn interaction sequences, recall past queries, and interpret visual states.We examine a query-to-question (Q2Q) supporting system that takes advantage of natural language generation (NLG) techniques to automatically translate and display query interactions as natural language questions. We focus on a symmetric pattern of multiple coordinated views, cross-filtered views, that involves only nominal/categorical data. We describe a study of the effects of pairing a visualization with a Q2Q interface on several aspects of usability. Q2Q produces considerable improvements in learnability, efficiency, and memorability of visualization in terms of speed and the length of interaction sequences that users follow, along with a modest decrease in error ratio. From a visual language perspective, we analyze how Q2Q speeds up users' comprehension of interaction, particularly when a visualization representation has deficiencies in illustrating hidden items or relationships.
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.
Complexity Plots
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Thiyagalingam, Jeyarajan; Walton, Simon; Duffy, Brian; Trefethen, Anne; Chen, Min; B. Preim, P. Rheingans, and H. Theisel
In this paper, we present a novel visualization technique for assisting the observation and analysis of algorithmic complexity. In comparison with conventional line graphs, this new technique is not sensitive to the units of measurement, allowing multivariate data series of different physical qualities (e.g., time, space and energy) to be juxtaposed together conveniently and consistently. It supports multivariate visualization as well as uncertainty visualization. It enables users to focus on algorithm categorization by complexity classes, while reducing visual impact caused by constants and algorithmic components that are insignificant to complexity analysis. It provides an effective means for observing the algorithmic complexity of programs with a mixture of algorithms and blackbox software through visualization. Through two case studies, we demonstrate the effectiveness of complexity plots in complexity analysis in research, education and application.
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.
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.
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.
EvalBench: A Software Library for Visualization Evaluation
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Aigner, Wolfgang; Hoffmann, Stephan; Rind, Alexander; B. Preim, P. Rheingans, and H. Theisel
It is generally acknowledged in visualization research that it is necessary to evaluate visualization artifacts in order to provide empirical evidence on their effectiveness and efficiency as well as their usability and utility. However, the difficulties of conducting such evaluations still remain an issue. Apart from the required know-how to appropriately design and conduct user studies, the necessary implementation effort for evaluation features in visualization software is a considerable obstacle. To mitigate this, we present EvalBench, an easy-to-use, flexible, and reusable software library for visualization evaluation written in Java. We describe its design choices and basic abstractions of our conceptual architecture and demonstrate its applicability by a number of case studies. EvalBench reduces implementation effort for evaluation features and makes conducting user studies easier. It can be used and integrated with third-party visualization prototypes that need to be evaluated via loose coupling. Eval- Bench supports both, quantitative and qualitative evaluation methods such as controlled experiments, interaction logging, laboratory questionnaires, heuristic evaluations, and insight diaries.
Evaluating Isosurfaces with Level-set-based Information Maps
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Wei, Tzu-Hsuan; Lee, Teng-Yok; Shen, Han-Wei; B. Preim, P. Rheingans, and H. Theisel
While isosurfaces have been widely used for scalar data visualization, it is often difficult to determine if the selected isosurfaces for visualization are sufficient to represent the entire scalar field. In this paper, we present an information-theoretic approach to evaluate the representativeness of a given isosurface set. Our basic idea is that given two isosurfaces that enclose a subvolume, if the intermediate isosurfaces in the subvolume can be generated by smoothly morphing from one isosurface to the other, no additional isosurfaces are needed since the geometry of the true isosurfaces within the subvolume can be easily inferred. To realize this idea, given a pair of isosurfaces, to determine if such a smooth condition in the enclosed region is satisfied, we use a level-set approach to generate the intermediate surfaces. On each intermediate surface, we sample the values from the scalar field and exam the distribution. If the entropy of the distribution is low, this intermediate surface is aligned well with a true isosurface in the scalar field. For the intermediate surfaces generated by the level-set method from the boundary isosurfaces, the distributions of scalar values from the level-set surfaces form a 2D distribution, called isosurface information map. This information map can be used as an indicator of the representativeness of the boundary isosurfaces for the data in the subregion, allowing a quantitative measurement of information representable by the input isosurfaces. Based on this information-theoretic approach, this paper presents an isosurface selection algorithm that can automatically select isosurfaces for more effective visualization of scalar fields.
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
Evolutionary Visual Exploration: Evaluation With Expert Users
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Boukhelifa, Nadia; Cancino, Waldo; Bezerianos, Anastasia; Lutton, Evelyne; B. Preim, P. Rheingans, and H. Theisel
We present an Evolutionary Visual Exploration (EVE) system that combines visual analytics with stochastic optimisation to aid the exploration of multidimensional datasets characterised by a large number of possible views or projections. Starting from dimensions whose values are automatically calculated by a PCA, an interactive evolutionary algorithm progressively builds (or evolves) non-trivial viewpoints in the form of linear and non-linear dimension combinations, to help users discover new interesting views and relationships in their data. The criteria for evolving new dimensions is not known a priori and are partially specified by the user via an interactive interface: (i) The user selects views with meaningful or interesting visual patterns and provides a satisfaction score. (ii) The system calibrates a fitness function (optimised by the evolutionary algorithm) to take into account the user input, and then calculates new views. Our method leverages automatic tools to detect interesting visual features and human interpretation to derive meaning, validate the findings and guide the exploration without having to grasp advanced statistical concepts. To validate our method, we built a prototype tool (EvoGraphDice) as an extension of an existing scatterplot matrix inspection tool, and conducted an observational study with five domain experts. Our results show that EvoGraphDice can help users quantify qualitative hypotheses and try out different scenarios to dynamically transform their data. Importantly, it allowed our experts to think laterally, better formulate their research questions and build new hypotheses for further investigation.
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.
Fingerprint Matrices: Uncovering the Dynamics of Social Networks in Prose Literature
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Oelke, Daniela; Kokkinakis, Dimitrios; Keim, Daniel A.; B. Preim, P. Rheingans, and H. Theisel
In prose literature often complex dynamics of interpersonal relationships can be observed between the different characters. Traditionally, node-link diagrams are used to depict the social network of a novel. However, static graphs can only visualize the overall social network structure but not the development of the networks over the course of the story, while dynamic graphs have the serious problem that there are many sudden changes between different portions of the overall social network. In this paper we explore means to show the relationships between the characters of a plot and at the same time their development over the course of a novel. Based on a careful exploration of the design space, we suggest a new visualization technique called Fingerprint Matrices. A case study exemplifies the usage of Fingerprint Matrices and shows that they are an effective means to analyze prose literature with respect to the development of relationships between the different characters.
Gestaltlines
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Brandes, Ulrik; Nick, Bobo; Rockstroh, Brigitte; Steffen, Astrid; B. Preim, P. Rheingans, and H. Theisel
We propose a general technique to visualize multivariate data sequences. It is based on a symbiotic combination of three powerful concepts from information visualization: sparklines, glyphs and gestalt theory. By visualizing several well-known data sets in new ways we first demonstrate how explicit consideration of gestalt principles can be used to leverage visual perception capabilities for the identification of patterns such as trends, periodicities, change points, or outliers. A more detailed case study with complex and noisy data from a psychological experiment then demonstrates how basic design ideas for gestaltlines can be applied in less controlled, and thus more realistic, situations. The case study is complemented with reports on feedback from domain experts and a user study, both indicating that gestaltlines can be a convenient and valid means to explore and communicate patterns in micro-visualizations.
HiFiVE: A Hilbert Space Embedding of Fiber Variability Estimates for Uncertainty Modeling and Visualization
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Schultz, Thomas; Schlaffke, Lara; Schölkopf, Bernhard; Schmidt-Wilcke, Tobias; B. Preim, P. Rheingans, and H. Theisel
Obtaining reproducible fiber direction estimates from diffusion MRI is crucial for successful fiber tracking. Modeling and visualizing the probability distribution of the inferred fiber directions is an important step in evaluating and comparing different acquisition schemes and fiber models. However, this distribution is usually strongly dominated by its main direction, which makes it difficult to examine when plotted naively. In this work, we propose a new visualization of the fiber probability distribution. It is based on embedding the probability measure into a particular reproducing kernel Hilbert space. This permits a decomposition into an embedded delta peak, representing the main direction, and a non-negative residual. They are then combined into a new glyph representation which visually enhances the residual, in order to highlight even subtle differences. Moreover, the magnitude of the delta peak component quantifies precision of the main fiber direction. We demonstrate that our new glyph provides a more detailed impression of the uncertainty than the current standard method, cones that contain 95% of the estimated directions. We use our new method to contribute to the validation of different ways of resampling the data (bootstrapping), and to visualize the differences between alternative acquisition schemes and models for high angular resolution diffusion imaging (HARDI).
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.
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.
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.
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.

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