EuroVis10: Eurographics/ IEEE Symposium on Visualization

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https://diglib.eg.org/handle/10.2312/395

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Isosurface Similarity Maps
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Bruckner, Stefan; Möller, Torsten; G. Melancon, T. Munzner, and D. Weiskopf
In this paper, we introduce the concept of isosurface similarity maps for the visualization of volume data. Isosurface similarity maps present structural information of a volume data set by depicting similarities between individual isosurfaces quantified by a robust information-theoretic measure. Unlike conventional histograms, they are not based on the frequency of isovalues and/or derivatives and therefore provide complementary information. We demonstrate that this new representation can be used to guide transfer function design and visualization parameter specification. Furthermore, we use isosurface similarity to develop an automatic parameter-free method for identifying representative isovalues. Using real-world data sets, we show that isosurface similarity maps can be a useful addition to conventional classification techniques.
A Salience-based Quality Metric for Visualization
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Jänicke, Heike; Chen, Min; G. Melancon, T. Munzner, and D. Weiskopf
Salience detection is a principle mechanism to facilitate visual attention. A good visualization guides the observer s attention to the relevant aspects of the representation. Hence, the distribution of salience over a visualization image is an essential measure of the quality of the visualization. We describe a method for computing such a metric for a visualization image in the context of a given dataset. We show how this technique can be used to analyze a visualization s salience, improve an existing visualization, and choose the best representation from a set of alternatives. The usefulness of this proposed metric is illustrated using examples from information visualization, volume visualization and flow visualization.
Non-iterative Second-order Approximation of Signed Distance Functions for Any Isosurface Representation
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Molchanov, Vladimir; Rosenthal, Paul; Linsen, Lars; G. Melancon, T. Munzner, and D. Weiskopf
Signed distance functions (SDF) to explicit or implicit surface representations are intensively used in various computer graphics and visualization algorithms. Among others, they are applied to optimize collision detection, are used to reconstruct data fields or surfaces, and, in particular, are an obligatory ingredient for most level set methods. Level set methods are common in scientific visualization to extract surfaces from scalar or vector fields. Usual approaches for the construction of an SDF to a surface are either based on iterative solutions of a special partial differential equation or on marching algorithms involving a polygonization of the surface. We propose a novel method for a non-iterative approximation of an SDF and its derivatives in a vicinity of a manifold. We use a second-order algebraic fitting scheme to ensure high accuracy of the approximation. The manifold is defined (explicitly or implicitly) as an isosurface of a given volumetric scalar field. The field may be given at a set of irregular and unstructured samples. Stability and reliability of the SDF generation is achieved by a proper scaling of weights for the Moving Least Squares approximation, accurate choice of neighbors, and appropriate handling of degenerate cases. We obtain the solution in an explicit form, such that no iterative solving is necessary, which makes our approach fast.
Estimation and Modeling of Actual Numerical Errors in Volume Rendering
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Kronander, Joel; Unger, Jonas; Möller, Torsten; Ynnerman, Anders; G. Melancon, T. Munzner, and D. Weiskopf
In this paper we study the comprehensive effects on volume rendered images due to numerical errors caused by the use of finite precision for data representation and processing. To estimate actual error behavior we conduct a thorough study using a volume renderer implemented with arbitrary floating-point precision. Based on the experimental data we then model the impact of floating-point pipeline precision, sampling frequency and fixedpoint input data quantization on the fidelity of rendered images. We introduce three models, an average model, which does not adapt to different data nor varying transfer functions, as well as two adaptive models that take the intricacies of a new data set and transfer function into account by adapting themselves given a few different images rendered. We also test and validate our models based on new data that was not used during our model building.
The Perception of Correlation in Scatterplots
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Rensink, Ronald A.; Baldridge, Gideon; G. Melancon, T. Munzner, and D. Weiskopf
Supporting Exploratory Analysis with the Select and Slice Table
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Shrinivasan, Yedendra B.; Wijk, Jarke J. van; G. Melancon, T. Munzner, and D. Weiskopf
In interactive visualization, selection techniques such as dynamic queries and brushing are used to specify and extract items of interest. In other words, users define areas of interest in data space that often have a clear semantic meaning. We call such areas Semantic Zones, and argue that support for their manipulation and reasoning with them is highly useful during exploratory analysis. An important use case is the use of these zones across different subsets of the data, for instance to study the population of semantic zones over time. To support this, we present the Select & Slice Table. Semantic zones are arranged along one axis of the table, and data subsets are arranged along the other axis of the table. Each cell contains a set of items of interest from a data subset that matches the selection specifications of a zone. Items in cells can be visualized in various ways, as a count, as an aggregation of a measure, or as a separate visualization, such that the table gives an overview of the relationship between zones and data subsets. Furthermore, users can reuse zones, combine zones, and compare and trace items of interest across different semantic zones and data subsets. We present two case studies to illustrate the support offered by the Select & Slice table during exploratory analysis of multivariate data.
Topological Landscape Ensembles for Visualization of Scalar-Valued Functions
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Harvey, William; Wang, Yusu; G. Melancon, T. Munzner, and D. Weiskopf
Visual representation techniques enable perception and exploration of scientific data. Following the topological landscapes metaphor ofWeber et al., we provide a new algorithm for visualizing scalar functions defined on simply connected domains of arbitrary dimension. For a potentially high dimensional scalar field, our algorithm produces a collection of, in some sense complete, two-dimensional terrain models whose contour trees and corresponding topological persistences are identical to those of the input scalar field. The algorithm exactly preserves the volume of each region corresponding to an arc in the contour tree. We also introduce an efficiently computable metric on terrain models we generate. Based on this metric, we develop a tool that can help the users to explore the space of possible terrain models.
A Maximum Enhancing Higher-Order Tensor Glyph
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Schultz, Thomas; Kindlmann, Gordon; G. Melancon, T. Munzner, and D. Weiskopf
Glyphs are a fundamental tool in tensor visualization, since they provide an intuitive geometric representation of the full tensor information. The Higher-Order Maximum Enhancing (HOME) glyph, a generalization of the second-order tensor ellipsoid, was recently shown to emphasize the orientational information in the tensor through a pointed shape around maxima. This paper states and formally proves several important properties of this novel glyph, presents its first three-dimensional implementation, and proposes a new coloring scheme that reflects peak direction and sharpness. Application to data from High Angular Resolution Diffusion Imaging (HARDI) shows that the method allows for interactive data exploration and confirms that the HOME glyph conveys fiber spread and crossings more effectively than the conventional polar plot.
Hardware-Assisted Projected Tetrahedra
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Maximo, André; Marroquim, Ricardo; Farias, Ricardo; G. Melancon, T. Munzner, and D. Weiskopf
We present a flexible and highly efficient hardware-assisted volume renderer grounded on the original Projected Tetrahedra (PT) algorithm. Unlike recent similar approaches, our method is exclusively based on the rasterization of simple geometric primitives and takes full advantage of graphics hardware. Both vertex and geometry shaders are used to compute the tetrahedral projection, while the volume ray integral is evaluated in a fragment shader; hence, volume rendering is performed entirely on the GPU within a single pass through the pipeline. We apply a CUDA-based visibility ordering achieving rendering and sorting performance of over 6 M Tet/s for unstructured datasets. Furthermore, as each tetrahedron is processed independently, we employ a data-parallel solution which is neither bound by GPU memory size nor does it rely on auxiliary volume information. In addition, iso-surfaces can be readily extracted during the rendering process, and time-varying data are handled without extra burden.
Toward a Lagrangian Vector Field Topology
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Fuchs, Raphael; Peikert, Ronny; Kemmler, Jan; Schindler, Benjamin; Waser, Juergen; Sadlo, Filip; Hauser, Helwig; G. Melancon, T. Munzner, and D. Weiskopf
In this paper we present an extended critical point concept which allows us to apply vector field topology in the case of unsteady flow.We propose a measure for unsteadiness which describes the rate of change of the velocities in a fluid element over time. This measure allows us to select particles for which topological properties remain intact inside a finite spatio-temporal neighborhood. One benefit of this approach is that the classification of critical points based on the eigenvalues of the Jacobian remains meaningful. In the steady case the proposed criterion reduces to the classical definition of critical points. As a first step we show that finding an optimal Galilean frame of reference can be obtained implicitly by analyzing the acceleration field. In a second step we show that this can be extended by switching to the Lagrangian frame of reference. This way the criterion can detect critical points moving along intricate trajectories. We analyze the behavior of the proposed criterion based on two analytical vector fields for which a correct solution is defined by their inherent symmetries and present results for numerical vector fields.
Reusable Visualizations and Animations for Surgery Planning
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Mühler, Konrad; Preim, Bernhard; G. Melancon, T. Munzner, and D. Weiskopf
For surgical planning, the exploration of 3D visualizations and 2D slice views is essential. However, the generation of visualizations which support the specific treatment decisions is very tedious. Therefore, the reuse of once designed visualizations for similar cases can strongly accelerate the process of surgical planning. We present a new technique that enables the easy reuse of both medical visualization types: 3D scenes and 2D slice views. We introduce the keystates as a concept to describe the state of a visualization in a general manner. They can be easily applied to new datasets to create similar visualizations. Keystates can be shared between surgeons of one specialization to reproduce and document the planning process for collaborative work. Furthermore, animations can support the surgeon on individual exploration and are also useful in collaborative environments, where complex issues must be presented in a short time. Therefore, we provide a framework, where animations can be visually designed by surgeons during their exploration process without any programming or authoring skills. We discuss several transitions between different visualizations and present an application from clinical routine.
Multi-layer Depth Peeling by Single-Pass Hardware Rasterisation for Faster Isosurface Raytracing on a GPU
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Liu, Baoquan; Clapworthy, Gordon J.; Dong, Feng; G. Melancon, T. Munzner, and D. Weiskopf
Empty-space skipping is an essential acceleration technique for volume rendering. Image-order empty-space skipping is not well suited to GPU implementation, since it must perform checks on, essentially, a per-sample basis, as in kd-tree traversal, which can lead to a great deal of divergent branching at runtime, which is very expensive in a modern GPU pipeline. In contrast, object-order empty-space skipping is extremely fast on a GPU and has negligible overheads compared with approaches without empty-space skipping, since it employs the hardware unit for rasterisation. However, previous object-order algorithms have been able to skip only exterior empty space and not the interior empty space that lies inside or between volume objects. In this paper, we address these issues by proposing a multi-layer depth-peeling approach that can obtain all of the depth layers of the tight-fitting bounding geometry of the isosurface by a single rasterising pass. The maximum count of layers peeled by our approach can be up to thousands, while maintaining 32-bit float-point accuracy, which was not possible previously. By raytracing only the valid ray segments between each consecutive pair of depth layers, we can skip both the interior and exterior empty space efficiently. In comparisons with 3 state-of-the-art GPU isosurface rendering algorithms, this technique achieved much faster rendering across a variety of data sets.
Illustrative White Matter Fiber Bundles
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Otten, Ron; Vilanova, Anna; Wetering, Huub van de; G. Melancon, T. Munzner, and D. Weiskopf
Diffusion Tensor Imaging (DTI) has made feasible the visualization of the fibrous structure of the brain white matter. In the last decades, several fiber-tracking methods have been developed to reconstruct the fiber tracts from DTI data. Usually these fiber tracts are shown individually based on some selection criteria like region of interest. However, if the white matter as a whole is being visualized clutter is generated by directly rendering the individual fiber tracts. Often users are actually interested in fiber bundles, anatomically meaningful entities that abstract from the fibers they contain. Several clustering techniques have been developed that try to group the fiber tracts in fiber bundles. However, even if clustering succeeds, the complex nature of white matter still makes it difficult to investigate. In this paper, we propose the use of illustration techniques to ease the exploration of white matter clusters. We create a technique to visualize an individual cluster as a whole. The amount of fibers visualized for the cluster is reduced to just a few hint lines, and silhouette and contours are used to improve the definition of the cluster borders. Multiple clusters can be easily visualized by a combination of the single cluster visualizations. Focus+context concepts are used to extend the multiple-cluster renderings. Exploded views ease the exploration of the focus cluster while keeping the context clusters in an abstract form. Real-time results are achieved by the GPU implementation of the presented techniques.
Coherent Culling and Shading for Large Molecular Dynamics Visualization
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Grottel, Sebastian; Reina, Guido; Dachsbacher, Carsten; Ertl, Thomas; G. Melancon, T. Munzner, and D. Weiskopf
Molecular dynamics simulations are a principal tool for studying molecular systems. Such simulations are used to investigate molecular structure, dynamics, and thermodynamical properties, as well as a replacement for, or complement to, costly and dangerous experiments. With the increasing availability of computational power the resulting data sets are becoming increasingly larger, and benchmarks indicate that the interactive visualization on desktop computers poses a challenge when rendering substantially more than millions of glyphs. Trading visual quality for rendering performance is a common approach when interactivity has to be guaranteed. In this paper we address both problems and present a method for high-quality visualization of massive molecular dynamics data sets. We employ several optimization strategies on different levels of granularity, such as data quantization, data caching in video memory, and a two-level occlusion culling strategy: coarse culling via hardware occlusion queries and a vertex-level culling using maximum depth mipmaps. To ensure optimal image quality we employ GPU raycasting and deferred shading with smooth normal vector generation. We demonstrate that our method allows us to interactively render data sets containing tens of millions of high-quality glyphs.
An Interactive Visual Analytics System for Bridge Management
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Wang, Xiaoyu; Dou, Wenwen; Chen, Shen-En; Ribarsky, William; Chang, Remco; G. Melancon, T. Munzner, and D. Weiskopf
Bridges deteriorate over their life cycles and require continuous maintenance to ensure their structural integrity, and in turn, the safety of the public. Maintaining bridges is a multi-faceted operation that requires both domain knowledge and analytics techniques over large data sources. Although most existing bridge management systems (BMS) are very efficient at data storage, they are not as effective at providing analytical capabilities or as flexible at supporting different inspection technologies. In this paper, we present a visual analytics system that extends the capability of current BMSs. Based on a nation-wide survey and our interviews with bridge managers, we designed our system to be customizable so that it can provide interactive exploration, information correlation, and domainoriented data analysis. When tested by bridge managers of the U.S. Department of Transportation, we validated that our system provides bridge managers with the necessary features for performing in-depth analysis of bridges from a variety of perspectives that are in accordance to their typical workflow.
Alleviating the Modifiable Areal Unit Problem within Probe-Based Geospatial Analyses
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Butkiewicz, Thomas; Meentemeyer, Ross K.; Shoemaker, Douglas A.; Chang, Remco; Wartell, Zachary; Ribarsky, William; G. Melancon, T. Munzner, and D. Weiskopf
We present a probe-based interface for the exploration of the results of a geospatial simulation of urban growth. Because our interface allows the user great freedom in how they choose to define regions-of-interest to examine and compare, the classic geospatial analytic issue known as the modifiable areal unit problem (MAUP) quickly arises. The user may delineate regions with unseen differences that can affect the fairness of the comparisons made between them. To alleviate this problem, our interface first alerts the user if it detects any potential unfairness between regions when they are selected for comparison. It then presents the dimensions with potential problematic outliers to the user for evaluation. Finally, it provides a number of semi-automated tools to assist the user in correcting their regions boundaries to minimize the inequalities they feel could significantly impact their comparisons.
Visualizing Summary Statistics and Uncertainty
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Potter, Kristin; Kniss, Joe; Riesenfeld, Richard; Johnson, Chris R.; G. Melancon, T. Munzner, and D. Weiskopf
The graphical depiction of uncertainty information is emerging as a problem of great importance. Scientific data sets are not considered complete without indications of error, accuracy, or levels of confidence. The visual portrayal of this information is a challenging task. This work takes inspiration from graphical data analysis to create visual representations that show not only the data value, but also important characteristics of the data including uncertainty. The canonical box plot is reexamined and a new hybrid summary plot is presented that incorporates a collection of descriptive statistics to highlight salient features of the data. Additionally, we present an extension of the summary plot to two dimensional distributions. Finally, a use-case of these new plots is presented, demonstrating their ability to present high-level overviews as well as detailed insight into the salient features of the underlying data distribution.
Evaluation of Cluster Identification Performance for Different PCP Variants
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Holten, Danny; Wijk, Jarke J. van; G. Melancon, T. Munzner, and D. Weiskopf
Parallel coordinate plots (PCPs) are a well-known visualization technique for viewing multivariate data. In the past, various visual modifications to PCPs have been proposed to facilitate tasks such as correlation and cluster identification, to reduce visual clutter, and to increase their information throughput. Most modifications pertain to the use of color and opacity, smooth curves, or the use of animation. Although many of these seem valid improvements, only few user studies have been performed to investigate this, especially with respect to cluster identification. We performed a user study to evaluate cluster identification performance with respect to response time and correctness of nine PCP variations, including standard PCPs. To generate the variations, we focused on covering existing techniques as well as possible while keeping testing feasible. This was done by adapting and merging techniques, which led to the following novel variations. The first is an effective way of embedding scatter plots into PCPs. The second is a technique for highlighting fuzzy clusters based on neighborhood density. The third is a spline-based drawing technique to reduce ambiguity. The last is a pair of animation schemes for PCP rotation. We present an overview of the tested PCP variations and the results of our study. The most important result is that a fair number of the seemingly valid improvements, with the exception of scatter plots embedded into PCPs, do not result in significant performance gains.
Accelerated Visualization of Dynamic Molecular Surfaces
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Lindow, Norbert; Baum, Daniel; Prohaska, Steffen; Hege, Hans-Christian; G. Melancon, T. Munzner, and D. Weiskopf
Molecular surfaces play an important role in studying the interactions between molecules. Visualizing the dynamic behavior of molecules is particularly interesting to gain insights into a molecular system. Only recently it has become possible to interactively visualize dynamic molecular surfaces using ray casting techniques. In this paper, we show how to further accelerate the construction and the rendering of the solvent excluded surface (SES) and the molecular skin surface (MSS). We propose several improvements to reduce the update times for displaying these molecular surfaces. First, we adopt a parallel approximate Voronoi diagram algorithm to compute the MSS. This accelerates the MSS computation by more than one order of magnitude on a single core. Second, we demonstrate that the contour-buildup algorithm is ideally suited for computing the SES due to its inherently parallel structure. For both parallel algorithms, we observe good scalability up to 8 cores and, thus, obtain interactive frame rates for molecular dynamics trajectories of up to twenty thousand atoms for the SES and up to a few thousand atoms for the MSS. Third, we reduce the rendering time for the SES using tight-fitting bounding quadrangles as rasterization primitives. These primitives also accelerate the rendering of the MSS. With these improvements, the interactive visualization of the MSS of dynamic trajectories of a few thousand atoms becomes for the first time possible. Nevertheless, the SES remains a few times faster than the MSS.
Topology-based Smoothing of 2D Scalar Fields with C1-Continuity
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Weinkauf, Tino; Gingold, Yotam; Sorkine, Olga; G. Melancon, T. Munzner, and D. Weiskopf
Data sets coming from simulations or sampling of real-world phenomena often contain noise that hinders their processing and analysis. Automatic filtering and denoising can be challenging: when the nature of the noise is unknown, it is difficult to distinguish between noise and actual data features; in addition, the filtering process itself may introduce artificial features into the data set that were not originally present. In this paper, we propose a smoothing method for 2D scalar fields that gives the user explicit control over the data features. We define features as critical points of the given scalar function, and the topological structure they induce (i.e., the Morse- Smale complex). Feature significance is rated according to topological persistence. Our method allows filtering out spurious features that arise due to noise by means of topological simplification, providing the user with a simple interface that defines the significance threshold, coupled with immediate visual feedback of the remaining data features. In contrast to previous work, our smoothing method guarantees a C1-continuous output scalar field with the exact specified features and topological structures.

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