EuroVis10: Eurographics/ IEEE Symposium on Visualization

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

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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.
Scalable Multi-view Registration for Multi-Projector Displays on Vertically Extruded Surfaces
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Sajadi, Behzad; Majumder, Aditi; G. Melancon, T. Munzner, and D. Weiskopf
Recent work have shown that it is possible to register multiple projectors on non-planar surfaces using a single uncalibrated camera instead of a calibrated stereo pair when dealing with a special class of non-planar surfaces, vertically extruded surfaces. However, this requires the camera view to contain the entire display surface. This is often an impossible scenario for large displays, especially common in visualization, edutainment, training and simulation applications. In this paper we present a new method that can achieve an accurate geometric registration even when the field-of-view of the uncalibrated camera can cover only a part of the vertically extruded display at a time. We pan and tilt the camera from a single point and employ a multi-view approach to register the projectors on the display. This allows the method to scale easily both in terms of camera resolution and display size. To the best of our knowledge, our method is the first to achieve a scalable multi-view geometric registration of large vertically extruded displays with a single uncalibrated camera. This method can also handle a different situation of having multiple similarly oriented cameras in different locations, if the camera focal length is known. Keywords: Registration, Calibration, Multi-Projector Displays, Tiled Displays
Topographic Map Visualization from Adaptively Compressed Textures
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Andujar, Carlos; G. Melancon, T. Munzner, and D. Weiskopf
Raster-based topographic maps are commonly used in geoinformation systems to overlay geographic entities on top of digital terrain models. Using compressed texture formats for encoding topographic maps allows reducing latency times while visualizing large geographic datasets. Topographic maps encompass high-frequency content with large uniform regions, making current compressed texture formats inappropriate for encoding them. In this paper we present a method for locally-adaptive compression of topographic maps. Key elements include a Hilbert scan to maximize spatial coherence, efficient encoding of homogeneous image regions through arbitrarily-sized texel runs, a cumulative run-length encoding supporting fast random-access, and a compression algorithm supporting lossless and lossy compression. Our scheme can be easily implemented on current programmable graphics hardware allowing real-time GPU decompression and rendering of bilinear-filtered topographic maps.
Understanding Interactive Legends: a Comparative Evaluation with Standard Widgets
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Riche, Nathalie Henry; Lee, Bongshin; Plaisant, Catherine; G. Melancon, T. Munzner, and D. Weiskopf
Interactive information visualization systems rely on widgets to allow users to interact with the data and modify the representation. We define interactive legends as a class of controls combining the visual representation of static legends and interaction mechanisms of widgets. As interactive legends start to appear in popular websites, we categorize their designs for common data types and evaluate their effectiveness compare to standard widgets. Results suggest that 1) interactive legends can lead to faster perception of the mapping between data values and visual encodings and 2) interaction time is affected differently depending on the data type. Additionally, our study indicates superiority both in terms of perception and interaction of ordinal controls over numerical ones. Numerical techniques are mostly used in today s systems. By providing solutions to allowing users to modify ranges interactively, we believe that interactive legends make it possible to increase the use of ordinal techniques for visual exploration.
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.
Streaming-Enabled Parallel Dataflow Architecture for Multicore Systems
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Vo, Huy T.; Osmari, Daniel K.; Summa, Brian; Comba, João L. D.; Pascucci, Valerio; Silva, Cláudio T.; G. Melancon, T. Munzner, and D. Weiskopf
We propose a new framework design for exploiting multi-core architectures in the context of visualization dataflow systems. Recent hardware advancements have greatly increased the levels of parallelism available with all indications showing this trend will continue in the future. Existing visualization dataflow systems have attempted to take advantage of these new resources, though they still have a number of limitations when deployed on shared memory multi-core architectures. Ideally, visualization systems should be built on top of a parallel dataflow scheme that can optimally utilize CPUs and assign resources adaptively to pipeline elements. We propose the design of a flexible dataflow architecture aimed at addressing many of the shortcomings of existing systems including a unified execution model for both demand-driven and event-driven models; a resource scheduler that can automatically make decisions on how to allocate computing resources; and support for more general streaming data structures which include unstructured elements. We have implemented our system on top of VTK with backward compatibility. In this paper, we provide evidence of performance improvements on a number of applications.
ProbExplorer: Uncertainty-guided Exploration and Editing of Probabilistic Medical Image Segmentation
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Saad, Ahmed; Möller, Torsten; Hamarneh, Ghassan; G. Melancon, T. Munzner, and D. Weiskopf
In this paper, we develop an interactive analysis and visualization tool for probabilistic segmentation results in medical imaging. We provide a systematic approach to analyze, interact and highlight regions of segmentation uncertainty. We introduce a set of visual analysis widgets integrating different approaches to analyze multivariate probabilistic field data with direct volume rendering. We demonstrate the user s ability to identify suspicious regions (e.g. tumors) and correct the misclassification results using a novel uncertainty-based segmentation editing technique. We evaluate our system and demonstrate its usefulness in the context of static and time-varying medical imaging datasets.
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.
Image-Based Edge Bundles: Simplified Visualization of Large Graphs
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Telea, Alexandru; Ersoy, Ozan; G. Melancon, T. Munzner, and D. Weiskopf
We present a new approach aimed at understanding the structure of connections in edge-bundling layouts. We combine the advantages of edge bundles with a bundle-centric simplified visual representation of a graph s structure. For this, we first compute a hierarchical edge clustering of a given graph layout which groups similar edges together. Next, we render clusters at a user-selected level of detail using a new image-based technique that combines distance-based splatting and shape skeletonization. The overall result displays a given graph as a small set of overlapping shaded edge bundles. Luminance, saturation, hue, and shading encode edge density, edge types, and edge similarity. Finally, we add brushing and a new type of semantic lens to help navigation where local structures overlap. We illustrate the proposed method on several real-world graph datasets.
Winding Roads: Routing edges into bundles
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Lambert, Antoine; Bourqui, Romain; Auber, David; G. Melancon, T. Munzner, and D. Weiskopf
Visualizing graphs containing many nodes and edges efficiently is quite challenging. Drawings of such graphs generally suffer from visual clutter induced by the large amount of edges and their crossings. Consequently, it is difficult to read the relationships between nodes and the high-level edge patterns that may exist in standard nodelink diagram representations. Edge bundling techniques have been proposed to help solve this issue, which rely on high quality edge rerouting. In this paper, we introduce an intuitive edge bundling technique which efficiently reduces edge clutter in graphs drawings. Our method is based on the use of a grid built using the original graph to compute the edge rerouting. In comparison with previously proposed edge bundling methods, our technique improves both the level of clutter reduction and the computation performance. The second contribution of this paper is a GPU-based rendering method which helps users perceive bundles densities while preserving edge color.
Space-in-Time and Time-in-Space Self-Organizing Maps for Exploring Spatiotemporal Patterns
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Andrienko, Gennady; Andrienko, Natalia; Bremm, Sebastian; Schreck, Tobias; Landesberger, Tatiana von; Bak, Peter; Keim, Daniel; G. Melancon, T. Munzner, and D. Weiskopf
Spatiotemporal data pose serious challenges to analysts in geographic and other domains. Owing to the complexity of the geospatial and temporal components, this kind of data cannot be analyzed by fully automatic methods but require the involvement of the human analyst s expertise. For a comprehensive analysis, the data need to be considered from two complementary perspectives: (1) as spatial distributions (situations) changing over time and (2) as profiles of local temporal variation distributed over space. In order to support the visual analysis of spatiotemporal data, we suggest a framework based on the "Self-Organizing Map" (SOM) method combined with a set of interactive visual tools supporting both analytic perspectives. SOM can be considered as a combination of clustering and dimensionality reduction. In the first perspective, SOM is applied to the spatial situations at different time moments or intervals. In the other perspective, SOM is applied to the local temporal evolution profiles. The integrated visual analytics environment includes interactive coordinated displays enabling various transformations of spatiotemporal data and post-processing of SOM results. The SOM matrix display offers an overview of the groupings of data objects and their two-dimensional arrangement by similarity. This view is linked to a cartographic map display, a time series graph, and a periodic pattern view. The linkage of these views supports the analysis of SOM results in both the spatial and temporal contexts. The variable SOM grid coloring serves as an instrument for linking the SOM with the corresponding items in the other displays. The framework has been validated on a large dataset with real city traffic data, where expected spatiotemporal patterns have been successfully uncovered. We also describe the use of the framework for discovery of previously unknown patterns in 41-years time series of 7 crime rate attributes in the states of the USA.
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.
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.
Effective Techniques to Visualize Filament-Surface Relationships
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Kuß, Anja; Gensel, Maria; Meyer, Björn; Dercksen, Vincent J.; Prohaska, Steffen; G. Melancon, T. Munzner, and D. Weiskopf
Combined visualizations of filamentous structures and surrounding volumetric objects are common in biological and medical applications. Often, the structures spatial relationships remain unclear to the viewer. In this paper, we discuss and evaluate techniques to emphasize spatial relationships. We concentrate on the visualization of transparent objects and intersecting lines. Among various techniques, participants of an exploratory user study preferred coloring of lines, marking of line-surface intersections by glyphs, and the combination of both. These techniques were additionally evaluated in a confirmatory study in which participants were asked to judge whether a filament runs through a transparent structure. We found that the evaluated techniques significantly improve the participants performance in terms of the number of correct responses and response time. The best performance was found for the combination of line coloring and intersection glyph display.
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.
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.
Matrix Trees
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Andrysco, Nathan; Tricoche, Xavier; G. Melancon, T. Munzner, and D. Weiskopf
We propose a new data representation for octrees and kd-trees that improves upon memory size and algorithm speed of existing techniques. While pointerless approaches exploit the regular structure of the tree to facilitate efficient data access, their memory footprint becomes prohibitively large as the height of the tree increases. Pointerbased trees require memory consumption proportional to the number of tree nodes, thus exploiting the typical sparsity of large trees. Yet, their traversal is slowed by the need to follow explicit pointers across the different levels. Our solution is a pointerless approach that represents each tree level with its own matrix, as opposed to traditional pointerless trees that use only a single vector. This novel data organization allows us to fully exploit the tree s regular structure and improve the performance of tree operations. By using a sparse matrix data structure we obtain a representation that is suited for sparse and dense trees alike. In particular, it uses less total memory than pointer-based trees even when the data set is extremely sparse. We show how our approach is easily implemented on the GPU and illustrate its performance in typical visualization scenarios.
Pathline: A Tool For Comparative Functional Genomics
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Meyer, Miriah; Wong, Bang; Styczynski, Mark; Munzner, Tamara; Pfister, Hanspeter; G. Melancon, T. Munzner, and D. Weiskopf
Biologists pioneering the new field of comparative functional genomics attempt to infer the mechanisms of gene regulation by looking for similarities and differences of gene activity over time across multiple species. They use three kinds of data: functional data such as gene activity measurements, pathway data that represent a series of reactions within a cellular process, and phylogenetic relationship data that describe the relatedness of species. No existing visualization tool can visually encode the biologically interesting relationships between multiple pathways, multiple genes, and multiple species. We tackle the challenge of visualizing all aspects of this comparative functional genomics dataset with a new interactive tool called Pathline. In addition to the overall characterization of the problem and design of Pathline, our contributions include two new visual encoding techniques. One is a new method for linearizing metabolic pathways that provides appropriate topological information and supports the comparison of quantitative data along the pathway. The second is the curvemap view, a depiction of time series data for comparison of gene activity and metabolite levels across multiple species. Pathline was developed in close collaboration with a team of genomic scientists. We validate our approach with case studies of the biologists use of Pathline and report on how they use the tool to confirm existing findings and to discover new scientific insights.
A Multidirectional Occlusion Shading Model for Direct Volume Rendering
(The Eurographics Association and Blackwell Publishing Ltd., 2010) oltészová, Veronika; Patel, Daniel; Bruckner, Stefan; Viola, Ivan; G. Melancon, T. Munzner, and D. Weiskopf
In this paper, we present a novel technique which simulates directional light scattering for more realistic interactive visualization of volume data. Our method extends the recent directional occlusion shading model by enabling light source positioning with practically no performance penalty. Light transport is approximated using a tilted cone-shaped function which leaves elliptic footprints in the opacity buffer during slice-based volume rendering. We perform an incremental blurring operation on the opacity buffer for each slice in front-to-back order. This buffer is then used to define the degree of occlusion for the subsequent slice. Our method is capable of generating high-quality soft shadowing effects, allows interactive modification of all illumination and rendering parameters, and requires no pre-computation.

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