EuroVis11: Eurographics/ IEEE Symposium on Visualization

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https://diglib.eg.org/handle/10.2312/394

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Fast Extraction of High-quality Crease Surfaces for Visual Analysis
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Barakat, Samer; Andrysco, N.; Tricoche, Xavier; H. Hauser, H. Pfister, and J. J. van Wijk
We present a novel algorithm for the efficient extraction and visualization of high-quality ridge and valley surfaces from numerical datasets. Despite their rapidly increasing popularity in visualization, these so-called crease surfaces remain challenging to compute owing to their strongly nonlinear and non-orientable nature, and their complex boundaries. In this context, existing meshing techniques require an extremely dense sampling that is computationally prohibitive. Our proposed solution intertwines sampling and meshing steps to yield an accurate approximation of the underlying surfaces while ensuring the geometric quality of the resulting mesh. Using the computation power of the GPU, we propose a fast, parallel method for sampling. Additionally, we present a new front propagation meshing strategy that leverages CPU multiprocessing. Results are shown for synthetic, medical and fluid dynamics datasets.
Evaluation of the Visibility of Vessel Movement Features in Trajectory Visualizations
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Willems, Niels; Wetering, Huub van de; Wijk, Jarke J. van; H. Hauser, H. Pfister, and J. J. van Wijk
There are many visualizations that show the trajectory of a moving object to obtain insights in its behavior. In this user study, we test the performance of three of these visualizations with respect to three movement features that occur in vessel behavior. Our goal is to compare the recently presented vessel density by Willems et al. [WvdWvW09] with well-known trajectory visualizations such as an animation of moving dots and the space-time cube. We test these visualizations with common maritime analysis tasks by investigating the ability of users to find stopping objects, fast moving objects, and estimate the busiest routes in vessel trajectories. We test the robustness of the visualizations towards scalability and the influence of complex trajectories using small-scale synthetic data sets. The performance is measured in terms of correctness and response time. The user test shows that each visualization type excels for correctness for a specific movement feature. Vessel density performs best for finding stopping objects, but does not perform significantly less than the remaining visualizations for the other features. Therefore, vessel density is a nice extension in the toolkit for analyzing trajectories of moving objects, in particular for vessel movements, since stops can be visualized better, and the performance for comparing lanes and finding fast movers is at a similar level as established trajectory visualizations.
ImPrEd: An Improved Force-Directed Algorithm that Prevents Nodes from Crossing Edges
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Simonetto, Paolo; Archambault, Daniel; Auber, David; Bourqui, Romain; H. Hauser, H. Pfister, and J. J. van Wijk
PrEd [Ber00] is a force-directed algorithm that improves the existing layout of a graph while preserving its edge crossing properties. The algorithm has a number of applications including: improving the layouts of planar graph drawing algorithms, interacting with a graph layout, and drawing Euler-like diagrams. The algorithm ensures that nodes do not cross edges during its execution. However, PrEd can be computationally expensive and overlyrestrictive in terms of node movement. In this paper, we introduce ImPrEd: an improved version of PrEd that overcomes some of its limitations and widens its range of applicability. ImPrEd also adds features such as flexible or crossable edges, allowing for greater control over the output. Flexible edges, in particular, can improve the distribution of graph elements and the angular resolution of the input graph. They can also be used to generate Euler diagrams with smooth boundaries. As flexible edges increase data set size, we experience an execution/drawing quality trade off. However, when flexible edges are not used, ImPrEd proves to be consistently faster than PrEd.
Visualizing the Positional and Geometrical Variability of Isosurfaces in Uncertain Scalar Fields
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Pfaffelmoser, Tobias; Reitinger, Matthias; Westermann, Rüdiger; H. Hauser, H. Pfister, and J. J. van Wijk
We present a novel approach for visualizing the positional and geometrical variability of isosurfaces in uncertain 3D scalar fields. Our approach extends recent work by Pöthkow and Hege [PH10] in that it accounts for correlations in the data to determine more reliable isosurface crossing probabilities. We introduce an incremental updatescheme that allows integrating the probability computation into front-to-back volume ray-casting efficiently. Our method accounts for homogeneous and anisotropic correlations, and it determines for each sampling interval along a ray the probability of crossing an isosurface for the first time. To visualize the positional and geometrical uncertainty even under viewing directions parallel to the surface normal, we propose a new color mapping scheme based on the approximate spatial deviation of possible surface points from the mean surface. The additional use of saturation enables to distinguish between areas of high and low statistical dependence. Experimental results confirm the effectiveness of our approach for the visualization of uncertainty related to position and shape of convex and concave isosurface structures.
Temporal Visualization of Boundary-based Geo-information Using Radial Projection
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Drocourt, Y.; Borgo, Rita; Scharrer, K.; Murray, T.; Bevan, S. I.; Chen, M.; H. Hauser, H. Pfister, and J. J. van Wijk
This work is concerned with a design study by an interdisciplinary team on visualizing a 10-year record of seasonal and inter-annual changes in frontal position (advance/retreat) of nearly 200 marine terminating glaciers in Greenland. Whilst the spatiotemporal nature of the raw data presents a challenge to develop a compact and intuitive visual design, the focus on coastal boundaries provides an opportunity for dimensional reduction. In this paper, we report the user-centered design process carried out by the team, and present several visual encoding schemes that have met the requirements including compactness, intuitiveness, and ability to depict temporal changes and spatial relations. In particular, we designed a family of radial visualization, where radial lines correspond to different coastal locations, and nested rings represent the evolution of the temporal dimension from inner to outer circles. We developed an algorithm for mapping glacier terminus positions from Cartesian coordinates to angular coordinates. Instead of a naive uniform mapping, the algorithm maintains consistent spatial perception of the visually-sensitive geographical references between their Cartesian and angular coordinates, and distributes other termini positions between primary locations based on coastal distance. This work has provided a useful solution to address the problem of inaccuracy in change evaluation based on pixel-based visualization [BPC*10].
Visual Recommendations for Network Navigation
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Crnovrsanin, Tarik; Liao, Isaac; Wuy, Yingcai; Ma, Kwan-Liu; H. Hauser, H. Pfister, and J. J. van Wijk
Understanding large, complex networks is important for many critical tasks, including decision making, process optimization, and threat detection. Existing network analysis tools often lack intuitive interfaces to support the exploration of large scale data. We present a visual recommendation system to help guide users during navigation of network data. Collaborative filtering, similarity metrics, and relative importance are used to generate recommendations of potentially significant nodes for users to explore. In addition, graph layout and node visibility are adjusted in real-time to accommodate recommendation display and to reduce visual clutter. Case studies are presented to show how our design can improve network exploration.
Piecewise Laplacian-based Projection for Interactive Data Exploration and Organization
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Paulovich, Fernando V.; Eler, D. M.; Poco, J.; Botha, Charl P.; Minghim, R.; Nonato, L. G.; H. Hauser, H. Pfister, and J. J. van Wijk
Multidimensional projection has emerged as an important visualization tool in applications involving the visual analysis of high-dimensional data. However, high precision projection methods are either computationally expensive or not flexible enough to enable feedback from user interaction into the projection process. A built-in mechanism that dynamically adapts the projection based on direct user intervention would make the technique more useful for a larger range of applications and data sets. In this paper we propose the Piecewise Laplacian-based Projection (PLP), a novel multidimensional projection technique, that, due to the local nature of its formulation, enables a versatile mechanism to interact with projected data and to allow interactive changes to alter the projection map dynamically, a capability unique of this technique. We exploit the flexibility provided by PLP in two interactive projection-based applications, one designed to organize pictures visually and another to build music playlists. These applications illustrate the usefulness of PLP in handling high-dimensional data in a flexible and highly visual way. We also compare PLP with the currently most promising projections in terms of precision and speed, showing that it performs very well also according to these quality criteria.
Efficient Parallel Vectors Feature Extraction from Higher-Order Data
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Pagot, Christian; Osmari, D.; Sadlo, F.; Weiskopf, Daniel; Ertl, Thomas; Comba, J.; H. Hauser, H. Pfister, and J. J. van Wijk
The parallel vectors (PV) operator is a feature extraction approach for defining line-type features such as creases (ridges and valleys) in scalar fields, as well as separation, attachment, and vortex core lines in vector fields. In this work, we extend PV feature extraction to higher-order data represented by piecewise analytical functions defined over grid cells. The extraction uses PV in two distinct stages. First, seed points on the feature lines are placed by evaluating the inclusion form of the PV criterion with reduced affine arithmetic. Second, a feature flow field is derived from the higher-order PV expression where the features can be extracted as streamlines starting at the seeds. Our approach allows for guaranteed bounds regarding accuracy with respect to existence, position, and topology of the features obtained. The method is suitable for parallel implementation and we present results obtained with our GPU-based prototype. We apply our method to higher-order data obtained from discontinuous Galerkin fluid simulations.
Automatic Registration of Multi-Projector Domes Using a Single Uncalibrated Camera
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Sajadi, Behzad; Majumder, Aditi; H. Hauser, H. Pfister, and J. J. van Wijk
In this paper we present a novel technique for easily calibrating multiple casually aligned projectors on spherical domes using a single uncalibrated camera. Using the prior knowledge of the display surface being a dome, we can estimate the camera intrinsic and extrinsic parameters and the projector to display surface correspondences automatically using a set of images. These images include the image of the dome itself and a projected pattern from each projector. Using these correspondences we can register images from the multiple projectors on the dome. Further, we can register displays which are not entirely visible in a single camera view using multiple pan and tilted views of an uncalibrated camera making our method suitable for displays of different size and resolution. We can register images from any arbitrary viewpoint making it appropriate for a single head-tracked user in a 3D visualization system. Also, we can use several cartographic mapping techniques to register images in a manner that is appropriate for multi-user visualization. Domes are known to produce a tremendous sense of immersion and presence in visualization systems. Yet, till date, there exists no easy way to register multiple projectors on a dome to create a high-resolution realistic visualizations. To the best of our knowledge, this is the first method that can achieve accurate geometric registration of multiple projectors on a dome simply and automatically using a single uncalibrated camera.
Exploring Collections of Tagged Text for Literary Scholarship
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Correll, Michael; Witmore, M.; Gleicher, M.; H. Hauser, H. Pfister, and J. J. van Wijk
Modern literary scholars must combine access to vast collections of text with the traditional close analysis of their field. In this paper, we discuss the design and development of tools to support this work. Based on analysis of the needs of literary scholars, we constructed a suite of visualization tools for the analysis of large collections of tagged text (i.e. text where one or more words have been annotated as belonging to a specific category). These tools unite the aspects of the scholars' work: large scale overview tools help to identify corpus-wide statistical patterns while fine scale analysis tools assist in finding specific details that support these observations. We designed visual tools that support and integrate these levels of analysis. The result is the first tool suite that can support the multilevel text analysis performed by scholars, combining standard visual elements with novel methods for selecting individual texts and identifying represenative passages in them.
Visual Reconstructability as a Quality Metric for Flow Visualization
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Jänicke, Heike; Weidner, Thomas; Chung, David; Laramee, Robert S.; Townsend, Peter; Chen, Min; H. Hauser, H. Pfister, and J. J. van Wijk
We present a novel approach for the evaluation of 2D flow visualizations based on the visual reconstructability of the input vector fields. According to this metric, a visualization has high quality if the underlying data can be reliably reconstructed from the image. This approach provides visualization creators with a cost-effective means to assess the quality of visualization results objectively. We present a vision-based reconstruction system for the three most commonly-used visual representations of vector fields, namely streamlines, arrow glyphs, and line integral convolution. To demonstrate the use of visual reconstructability as a quality metric, we consider a selection of vector fields obtained from numerical simulations, containing typical flow features. We apply the three types of visualization to each dataset, and compare the visualization results based on their visual reconstructability of the original vector field.
Perceptual Evaluation of Ghosted View Techniques for the Exploration of Vascular Structures and Embedded Flow
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Baer, Alexandra; Gasteiger, Rocco; Cunningham, Douglas; Preim, Bernhard; H. Hauser, H. Pfister, and J. J. van Wijk
This paper presents three controlled perceptual studies investigating the visualization of the cerebral aneurysm anatomy with embedded flow visualization. We evaluate and compare the common semitransparent visualization technique with a ghosted view and a ghosted view with depth enhancement technique. We analyze the techniques' ability to facilitate and support the shape and spatial representation of the aneurysm models as well as evaluating the smart visibility characteristics. The techniques are evaluated with respect to the participants accuracy, response time and their personal preferences. We used as stimuli 3D aneurysm models of five clinical datasets. There was overwhelming preference for the two ghosted view techniques over the semitransparent technique. Since smart visibility techniques are rarely evaluated, this paper may serve as orientation for further studies.
Illustrative Molecular Visualization with Continuous Abstraction
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Zwan, Matthew van der; Lueks, Wouter; Bekker, Henk; Isenberg, Tobias; H. Hauser, H. Pfister, and J. J. van Wijk
Molecular systems may be visualized with various degrees of structural abstraction, support of spatial perception, and 'illustrativeness.' In this work we propose and realize methods to create seamless transformations that allow us to affect and change each of these three parameters individually. The resulting transitions give viewers a dedicated control of abstraction in illustrative molecular visualization and, consequently, allow them to seamlessly explore the resulting abstraction space for obtaining a fundamental understanding of molecular systems.We show example visualizations created with our approach and report informal feedback on our technique from domain experts.
Interactive Exploration of Protein Cavities
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Krone, M.; Falk, M.; Rehm, S.; Pleiss, J.; Ertl, T.; H. Hauser, H. Pfister, and J. J. van Wijk
We present a novel application for the interactive exploration of cavities within proteins in dynamic data sets. Inside a protein, cavities can often be found close to the active center. Therefore, when analyzing a molecular dynamics simulation trajectory it is of great interest to find these cavities and determine if such a cavity opens up to the environment, making the binding site accessible to the surrounding substrate. Our user-driven approach enables expert users to select a certain cavity and track its evolution over time. The user is supported by different visualizations of the extracted cavity to facilitate the analysis. The boundary of the protein and its cavities is obtained by means of volume ray casting, where the volume is computed in real-time for each frame, therefore allowing the examination of time-dependent data sets. A fast, partial segmentation of the volume is applied to obtain the selected cavity and trace it over time. Domain experts found our method useful when they applied it exemplarily on two trajectories of lipases from Rhizomucor miehei and Candida antarctica. In both data sets cavities near the active center were easily identified and tracked over time until they reached the surface and formed an open substrate channel.
A Gradient-Based Comparison Measure for Visual analysis of Multifield Data
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Nagaraj, Suthambhara; Natarajan, Vijay; Nanjundiah, Ravi S.; H. Hauser, H. Pfister, and J. J. van Wijk
We introduce a multifield comparison measure for scalar fields that helps in studying relations between them. The comparison measure is insensitive to noise in the scalar fields and to noise in their gradients. Further, it can be computed robustly and efficiently. Results from the visual analysis of various data sets from climate science and combustion applications demonstrate the effective use of the measure.
Probabilistic Marching Cubes
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Pöthkow, Kai; Weber, Britta; Hege, Hans-Christian; H. Hauser, H. Pfister, and J. J. van Wijk
In this paper we revisit the computation and visualization of equivalents to isocontours in uncertain scalar fields. We model uncertainty by discrete random fields and, in contrast to previous methods, also take arbitrary spatial correlations into account. Starting with joint distributions of the random variables associated to the sample locations, we compute level crossing probabilities for cells of the sample grid. This corresponds to computing the probabilities that the well-known symmetry-reduced marching cubes cases occur in random field realizations. For Gaussian random fields, only marginal density functions that correspond to the vertices of the considered cell need to be integrated. We compute the integrals for each cell in the sample grid using a Monte Carlo method. The probabilistic ansatz does not suffer from degenerate cases that usually require case distinctions and solutions of ill-conditioned problems. Applications in 2D and 3D, both to synthetic and real data from ensemble simulations in climate research, illustrate the influence of spatial correlations on the spatial distribution of uncertain isocontours.
Structural Decomposition Trees
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Engel, Daniel; Rosenbaum, R.; Hamann, B.; Hagen, Hans; H. Hauser, H. Pfister, and J. J. van Wijk
Researchers and analysts in modern industrial and academic environments are faced with a daunting amount of multi-dimensional data. While there has been significant development in the areas of data mining and knowledge discovery, there is still the need for improved visualizations and generic solutions. The state-of-the-art in visual analytics and exploratory data visualization is to incorporate more profound analysis methods while focusing on fast interactive abilities. The common trend in these scenarios is to either visualize an abstraction of the data set or to better utilize screen-space. This paper presents a novel technique that combines clustering, dimension reduction and multi-dimensional data representation to form a multivariate data visualization that incorporates both detail and overview. This amalgamation counters the individual drawbacks of common projection and multi-dimensional data visualization techniques, namely ambiguity and clutter. A specific clustering criterion is used to decompose a multi-dimensional data set into a hierarchical tree structure. This decomposition is embedded in a novel Dimensional Anchor visualization through the use of a weighted linear dimension reduction technique. The resulting Structural Decomposition Tree (SDT) provides not only an insight of the data set's inherent structure, but also conveys detailed coordinate value information. Further, fast and intuitive interaction techniques are explored in order to guide the user in highlighting, brushing, and filtering of the data.
The Undistort Lens
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Brosz, John; Carpendale, Sheelagh; Nacenta, Miguel A.; H. Hauser, H. Pfister, and J. J. van Wijk
Detail-in-context lens techniques can be useful for exploring visualizations of data spaces that are too large or have too much detail to fit in regular displays. For example, by bending the space in the right way we can bring together details from two separate areas for easy comparison while roughly keeping the context that situates each area within the global space. While these techniques can be powerful tools, they also introduce distortions that need to be understood, and often the tools have to be disabled in order to have access to the undistorted data. We introduce the undistort lens, a complement to existing distortion-based techniques that provides a local and separate presentation of the original geometry without affecting any distortion-based lenses currently used in the presentation. The undistort lens is designed to allow interactive access to the underlying undistorted data within the context of the distorted space, and to enable a better understanding of the distortions. The paper describes the implementation of a generic back-mapping mechanism that enables the implementation of undistort lenses for arbitrary distortion based techniques, including those presented in the lens literature. We also provide a series of use-case scenarios that demonstrate the situations in which the technique can complement existing lenses.
Semantic-Preserving Word Clouds by Seam Carving
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Wu, Yingcai; Provan, Thomas; Wei, Furu; Liu, Shixia; Ma, Kwan-Liu; H. Hauser, H. Pfister, and J. J. van Wijk
Word clouds are proliferating on the Internet and have received much attention in visual analytics. Although word clouds can help users understand the major content of a document collection quickly, their ability to visually compare documents is limited. This paper introduces a new method to create semantic-preserving word clouds by leveraging tailored seam carving, a well-established content-aware image resizing operator. The method can optimize a word cloud layout by removing a left-to-right or top-to-bottom seam iteratively and gracefully from the layout. Each seam is a connected path of low energy regions determined by a Gaussian-based energy function. With seam carving, we can pack the word cloud compactly and effectively, while preserving its overall semantic structure. Furthermore, we design a set of interactive visualization techniques for the created word clouds to facilitate visual text analysis and comparison. Case studies are conducted to demonstrate the effectiveness and usefulness of our techniques.
Complete Tensor Field Topology on 2D Triangulated Manifolds embedded in 3D
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Auer, Cornelia; Hotz, Ingrid; H. Hauser, H. Pfister, and J. J. van Wijk
This paper is concerned with the extraction of the surface topology of tensor fields on 2D triangulated manifolds embedded in 3D. In scientific visualization topology is a meaningful instrument to get a hold on the structure of a given dataset. Due to the discontinuity of tensor fields on a piecewise planar domain, standard topology extraction methods result in an incomplete topological skeleton. In particular with regard to the high computational costs of the extraction this is not satisfactory. This paper provides a method for topology extraction of tensor fields that leads to complete results. The core idea is to include the locations of discontinuity into the topological analysis. For this purpose the model of continuous transition bridges is introduced, which allows to capture the entire topology on the discontinuous field. The proposed method is applied to piecewise linear three-dimensional tensor fields defined on the vertices of the triangulation and for piecewise constant two or three-dimensional tensor fields given per triangle, e.g. rate of strain tensors of piecewise linear flow fields.

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