EuroVis09: Eurographics/ IEEE Symposium on Visualization

Permanent URI for this collection

https://diglib.eg.org/handle/10.2312/396

Interactive Visualization of Function Fields by Range-Space Segmentation

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Anderson, John C.

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Gosink, Luke J.

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Duchaineau, Mark A.

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Joy, Ken I.

Efficient and Adaptive Rendering of 2-D Continuous Scatterplots

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Bachthaler, Sven

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Weiskopf, Daniel

Lifted Domain Coloring

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Poelke, Konstantin

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Polthier, Konrad

Illuminated 3D Scatterplots

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Sanftmann, Harald

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Weiskopf, Daniel

Splatting the Lines in Parallel Coordinates

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Zhou, Hong

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Cui, Weiwei

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Qu, Huamin

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Wu, Yingcai

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Yuan, Xiaoru

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Zhuo, Wei

iPCA: An Interactive System for PCA-based Visual Analytics

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Jeong, Dong Hyun

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Ziemkiewicz, Caroline

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Fisher, Brian

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Ribarsky, William

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Chang, Remco

Instant Volume Visualization using Maximum Intensity Difference Accumulation

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Bruckner, Stefan

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Gröller, M. Eduard

Bivariate Transfer Functions on Unstructured Grids

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Song, Yuyan

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Chen, Wei

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Maciejewski, Ross

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Gaither, Kelly P.

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Ebert, David S.

Direct Visualization of Deformation in Volumes

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Busking, Stef

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Botha, Charl P.

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Post, Frits H.

Semi-Automatic Time-Series Transfer Functions via Temporal Clustering and Sequencing

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Woodring, Jonathan

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Shen, Han-Wei

The Gödel Engine - An Interactive Approach to Visualization in General Relativity

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Grave, Frank

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Müller, Thomas

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Dachsbacher, Carsten

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Wunner, Günter

Visualisation of Sensor Data from Animal Movement

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Grundy, Edward

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Jones, Mark W.

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Laramee, Robert S.

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Wilson, Rory P.

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Shepard, Emily L. C.

MultiClusterTree: Interactive Visual Exploration of Hierarchical Clusters in Multidimensional Multivariate Data

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Long, Tran Van

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Linsen, Lars

Selecting Good Views of High-dimensional Data using Class Consistency

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Sips, Mike

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Neubert, Boris

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Lewis, John P.

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Hanrahan, Pat

Accelerating Volume Raycasting using Proxy Spheres

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Liu, Baoquan

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Clapworthy, Gordon J.

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Dong, Feng

A Directional Occlusion Shading Model for Interactive Direct Volume Rendering

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Schott, Mathias

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Pegoraro, Vincent

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Hansen, Charles

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Boulanger, Kévin

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Bouatouch, Kadi

Fused Multi-Volume DVR using Binary Space Partitioning

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Lindholm, Stefan

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Ljung, Patric

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Hadwiger, Markus

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Ynnerman, Anders

Hierarchical Vortex Regions in Swirling Flow

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Petz, Christoph

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Kasten, Jens

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Prohaska, Steffen

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Hege, Hans-Christian

Volume Deformations in Grid-Less Flow Simulations

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Obermaier, Harald

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Hering-Bertram, Martin

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Kuhnert, Jörg

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Hagen, Hans

Smooth Stream Surfaces of Fourth Order Precision

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Schneider, Dominic

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Wiebel, Alexander

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Scheuermann, Gerik

Combining Map Displays and 3D Visualizations for the Analysis of Scalar Data on Cerebral Aneurysm Surfaces

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Neugebauer, Mathias

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Gasteiger, Rocco

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Beuing, Oliver

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Diehl, Volker

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Skalej, Martin

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Preim, Bernhard

Context-aware Volume Modeling of Skeletal Muscles

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Yan, Zhicheng

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Chen, Wei

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Lu, Aidong

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Ebert, David S.

Visual Analysis of Brain Activity from fMRI Data

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Janoos, Firdaus

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Nouanesengsy, Boonthanome

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Machiraju, Raghu

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Shen, Han Wei

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Sammet, Steffen

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Knopp, Michael

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Mórocz, István Á.

Comparing Parameter Manipulation with Mouse, Pen, and Slider User Interfaces

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Swindells, Colin

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Tory, Melanie

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Dreezer, Rebecca

Preconceptions and Individual Differences in Understanding Visual Metaphors

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Ziemkiewicz, Caroline

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Kosara, Robert

Extended Excentric Labeling

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Bertini, Enrico

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Rigamonti, Maurizio

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Lalanne, Denis

Visualization of Vessel Movements

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Willems, Niels

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Wetering, Huub van de

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Wijk, Jarke J. van

SDViz: A Context-Preserving Interactive Visualization System for Technical Diagrams

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Woo, Insoo

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Kim, SungYe

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Maciejewski, Ross

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Ebert, David S.

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Ropp, Timothy D.

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Thomas, Krystal

A Visualization Based Approach for Digital Signature Authentication

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Xu, Songhua

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Yang, Wenxia

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Lau, Francis C.M.

Visualizing the Evolution of Compound Digraphs with TimeArcTrees

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Greilich, Martin

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Burch, Michael

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Diehl, Stephan

Fully Automatic Visualisation of Overlapping Sets

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Simonetto, Paolo

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Auber, David

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Archambault, Daniel

Visualization Techniques for Schedule Comparison

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Huang, Dandan

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Tory, Melanie

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Staub-French, Sheryl

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Pottinger, Rachel

High-Quality Volumetric Reconstruction on Optimal Lattices for Computed Tomography

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Finkbeiner, Bernhard

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Alim, Usman R.

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Ville, Dimitri Van De

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Möller, Torsten

Quasi-interpolation on the Body Centered Cubic Lattice

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Entezari, Alireza

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Mirzargar, Mahsa

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Kalantari, Leila

Enclosing Surfaces for Point Clusters Using 3D Discrete Voronoi Diagrams

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Rosenthal, Paul

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Linsen, Lars

Scalable, Versatile and Simple Constrained Graph Layout

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Dwyer, Tim

Force-Directed Edge Bundling for Graph Visualization

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Holten, Danny

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Wijk, Jarke J. van

On Visualization and Reconstruction from Non-Uniform Point Sets using B-splines

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Vuçini, Erald

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Möller, Torsten

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Gröller, M. Eduard

Collaborative Brushing and Linking for Co-located Visual Analytics of Document Collections

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Isenberg, Petra

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Fisher, Danyel

DocuBurst: Visualizing Document Content using Language Structure

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Collins, Christopher

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Carpendale, Sheelagh

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Penn, Gerald

The Chinese Room: Visualization and Interaction to Understand and Correct Ambiguous Machine Translation

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Albrecht, Joshua

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Hwa, Rebecca

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Marai, G. Elisabeta

Browse

Now showing 1 - 41 of 41

Interactive Visualization of Function Fields by Range-Space Segmentation
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Anderson, John C.; Gosink, Luke J.; Duchaineau, Mark A.; Joy, Ken I.; H.-C. Hege, I. Hotz, and T. Munzner
We present a dimension reduction and feature extraction method for the visualization and analysis of function field data. Function fields are a class of high-dimensional, multi-variate data in which data samples are onedimensional scalar functions. Our approach focuses upon the creation of high-dimensional range-space segmentations, from which we can generate meaningful visualizations and extract separating surfaces between features. We demonstrate our approach on high-dimensional spectral imagery, and particulate pollution data from air quality simulations.
Efficient and Adaptive Rendering of 2-D Continuous Scatterplots
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Bachthaler, Sven; Weiskopf, Daniel; H.-C. Hege, I. Hotz, and T. Munzner
We extend the rendering technique for continuous scatterplots to allow for a broad class of interpolation methods within the spatial grid instead of only linear interpolation. To do this, we propose an approach that projects the image of a cell from the spatial domain to the scatterplot domain. We approximate this image using either the convex hull or an axis-aligned rectangle that forms a tight fit of the projected points. In both cases, the approach relies on subdivision in the spatial domain to control the approximation error introduced in the scatterplot domain. Acceleration of this algorithm in homogeneous regions of the spatial domain is achieved using an octree hierarchy. The algorithm is scalable and adaptive since it allows us to balance computation time and scatterplot quality. We evaluate and discuss the results with respect to accuracy and computational speed. Our methods are applied to examples of 2-D transfer function design.
Lifted Domain Coloring
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Poelke, Konstantin; Polthier, Konrad; H.-C. Hege, I. Hotz, and T. Munzner
Complex-valued functions are fundamental objects in complex analysis, algebra, differential geometry and in many other areas such as numerical mathematics and physics. Visualizing complex functions is a non-trivial task since maps between two-dimensional spaces are involved whose graph would be an unhandy submanifold in four-dimensional space. The present paper improves the technique of domain coloring in several aspects: First, we lift domain coloring from the complex plane to branched Riemann surfaces, which are essentially the correct domain for most complex functions. Second, we extend domain coloring to the visualization of general 2-valued maps on surfaces. As an application of such general maps we visualize the Gauss map of surfaces as domain colored plots and establish a link to current surface parametrization techniques and texture maps. Third, we adjust the color pattern in domain and in image space to produce higher quality domain colorings. The new color schemes specifically enhance the display of singularities, symmetries and path integrals, and give better qualitative measures of the complex map.
Illuminated 3D Scatterplots
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Sanftmann, Harald; Weiskopf, Daniel; H.-C. Hege, I. Hotz, and T. Munzner
In contrast to 2D scatterplots, the existing 3D variants have the advantage of showing one additional data dimension, but suffer from inadequate spatial and shape perception and therefore are not well suited to display structures of the underlying data. We improve shape perception by applying a new illumination technique to the pointcloud representation of 3D scatterplots. Points are classified as locally linear, planar, and volumetric structures according to the eigenvalues of the inverse distance-weighted covariance matrix at each data element. Based on this classification, different lighting models are applied: codimension-2 illumination, surface illumination, and emissive volumetric illumination. Our technique lends itself to efficient GPU point rendering and can be combined with existing methods like semi-transparent rendering, halos, and depth or attribute based color coding. The user can interactively navigate in the dataset and manipulate the classification and other visualization parameters. We demonstrate our visualization technique by showing examples of multi-dimensional data and of generic pointcloud data.
Splatting the Lines in Parallel Coordinates
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Zhou, Hong; Cui, Weiwei; Qu, Huamin; Wu, Yingcai; Yuan, Xiaoru; Zhuo, Wei; H.-C. Hege, I. Hotz, and T. Munzner
coordinates. Our framework consists of two major components: a polyline splatter for cluster detection and a segment splatter for clutter reduction. The cluster detection is performed by splatting the lines one by one into the parallel coordinates plots, and for each splatted line we enhance its neighboring lines and suppress irrelevant ones. To reduce visual clutter caused by line crossings and overlappings in the clustered results, we provide a segment splatter which represents each polyline by one segment and splats these segments with different speeds, colors, and lengths from the leftmost axis to the rightmost axis. Users can interactively control both the polyline splatting and the segment splatting processes to emphasize the features they are interested in. The experimental results demonstrate that our framework can effectively reveal some hidden patterns in parallel coordinates.
iPCA: An Interactive System for PCA-based Visual Analytics
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Jeong, Dong Hyun; Ziemkiewicz, Caroline; Fisher, Brian; Ribarsky, William; Chang, Remco; H.-C. Hege, I. Hotz, and T. Munzner
Principle Component Analysis (PCA) is a widely used mathematical technique in many fields for factor and trend analysis, dimension reduction, etc. However, it is often considered to be a black box operation whose results are difficult to interpret and sometimes counter-intuitive to the user. In order to assist the user in better understanding and utilizing PCA, we have developed a system that visualizes the results of principal component analysis using multiple coordinated views and a rich set of user interactions. Our design philosophy is to support analysis of multivariate datasets through extensive interaction with the PCA output. To demonstrate the usefulness of our system, we performed a comparative user study with a known commercial system, SAS/INSIGHT s Interactive Data Exploration. Participants in our study solved a number of high-level analysis tasks with each interface and rated the systems on ease of learning and usefulness. Based on the participants accuracy, speed, and qualitative feedback, we observe that our system helps users to better understand relationships between the data and the calculated eigenspace, which allows the participants to more accurately analyze the data. User feedback suggests that the interactivity and transparency of our system are the key strengths of our approach.
Instant Volume Visualization using Maximum Intensity Difference Accumulation
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Bruckner, Stefan; Gröller, M. Eduard; H.-C. Hege, I. Hotz, and T. Munzner
It has long been recognized that transfer function setup for Direct Volume Rendering (DVR) is crucial to its usability. However, the task of finding an appropriate transfer function is complex and time-consuming even for experts. Thus, in many practical applications simpler techniques which do not rely on complex transfer functions are employed. One common example is Maximum Intensity Projection (MIP) which depicts the maximum value along each viewing ray. In this paper, we introduce Maximum Intensity Difference Accumulation (MIDA), a new approach which combines the advantages of DVR and MIP. Like MIP, MIDA exploits common data characteristics and hence does not require complex transfer functions to generate good visualization results. It does, however, feature occlusion and shape cues similar to DVR. Furthermore, we show that MIDA in addition to being a useful technique in its own right can be used to smoothly transition between DVR and MIP in an intuitive manner. MIDA can be easily implemented using volume raycasting and achieves real-time performance on current graphics hardware.
Bivariate Transfer Functions on Unstructured Grids
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Song, Yuyan; Chen, Wei; Maciejewski, Ross; Gaither, Kelly P.; Ebert, David S.; H.-C. Hege, I. Hotz, and T. Munzner
Multi-dimensional transfer functions are commonly used in rectilinear volume renderings to effectively portray materials, material boundaries and even subtle variations along boundaries. However, most unstructured grid rendering algorithms only employ one-dimensional transfer functions. This paper proposes a novel pre-integrated Projected Tetrahedra (PT) rendering technique that applies bivariate transfer functions on unstructured grids. For each type of bivariate transfer function, an analytical form that pre-integrates the contribution of a ray segment in one tetrahedron is derived, and can be precomputed as a lookup table to compute the color and opacity in a projected tetrahedron on-the-fly. Further, we show how to approximate the integral using the pre-integration method for faster unstructured grid rendering. We demonstrate the advantages of our approach with a variety of examples and comparisons with one-dimensional transfer functions.
Direct Visualization of Deformation in Volumes
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Busking, Stef; Botha, Charl P.; Post, Frits H.; H.-C. Hege, I. Hotz, and T. Munzner
Deformation is a topic of interest in many disciplines. In particular in medical research, deformations of surfaces and even entire volumetric structures are of interest. Clear visualization of such deformations can lead to important insight into growth processes and progression of disease. We present new techniques for direct focus+context visualization of deformation fields representing transformations between pairs of volumetric datasets. Typically, such fields are computed by performing a non-rigid registration between two data volumes. Our visualization is based on direct volume rendering and uses the GPU to compute and interactively visualize features of these deformation fields in real-time. We integrate visualization of the deformation field with visualization of the scalar volume affected by the deformations. Furthermore, we present a novel use of texturing in volume rendered visualizations to show additional properties of the vector field on surfaces in the volume.
Semi-Automatic Time-Series Transfer Functions via Temporal Clustering and Sequencing
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Woodring, Jonathan; Shen, Han-Wei; H.-C. Hege, I. Hotz, and T. Munzner
When creating transfer functions for time-varying data, it is not clear what range of values to use for classification, as data value ranges and distributions change over time. In order to generate time-varying transfer functions, we search the data for classes that have similar behavior over time, assuming that data points that behave similarly belong to the same feature. We utilize a method we call temporal clustering and sequencing to find dynamic features in value space and create a corresponding transfer function. First, clustering finds groups of data points that have the same value space activity over time. Then, sequencing derives a progression of clusters over time, creating chains that follow value distribution changes. Finally, the cluster sequences are used to create transfer functions, as sequences describe the value range distributions over time in a data set.
The Gödel Engine - An Interactive Approach to Visualization in General Relativity
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Grave, Frank; Müller, Thomas; Dachsbacher, Carsten; Wunner, Günter; H.-C. Hege, I. Hotz, and T. Munzner
We present a methodical new approach to visualize the aspects of general relativity from a self-centered perspective. We focus on the visualization of the Gödel universe, which is an exact solution to Einstein s field equations of general relativity. This model provides astounding features such as the existence of an optical horizon and the possibility of time travel. Although we know that our universe is not of Gödel type, we can using this solution to Einstein s equations visualize and understand the effects resulting from the theory of relativity, which itself has been verified on the large scale in numerous experiments over the last century. We derive the analytical solution to the geodesic equations of Gödel s universe for special initial conditions. Along with programmable graphics hardware we achieve a tremendous speedup for the visualization of general relativity. This enables us to interactively explore the physical aspects and optical effects of Gödel s universe. We also demonstrate how the analytical solution enables dynamic lighting with local illumination models. Our implementation is tailored for Gödel s universe and five orders of magnitude faster than previous approaches. It can be adapted to manifolds for which an analytical expression of the propagation of light is available.
Visualisation of Sensor Data from Animal Movement
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Grundy, Edward; Jones, Mark W.; Laramee, Robert S.; Wilson, Rory P.; Shepard, Emily L. C.; H.-C. Hege, I. Hotz, and T. Munzner
A new area of biological research is identifying and grouping patterns of behaviour in wild animals by analysing data obtained through the attachment of tri-axial accelerometers. As these recording devices become smaller and less expensive their use has increased. Currently acceleration data are visualised as 2D time series plots, and analyses are based on summary statistics and the application of Fourier transforms. We develop alternate visualisations of this data so as to analyse, explore and present new patterns of animal behaviour. Our visualisations include interactive spherical scatterplots, spherical histograms, clustering methods, and feature-based state diagrams of the data. We study the application of these visualisation methods to accelerometry data from animal movement. The reaction of biologists to these visualisations is also reported.
MultiClusterTree: Interactive Visual Exploration of Hierarchical Clusters in Multidimensional Multivariate Data
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Long, Tran Van; Linsen, Lars; H.-C. Hege, I. Hotz, and T. Munzner
Visual analytics of multidimensional multivariate data is a challenging task because of the difficulty in understanding metrics in attribute spaces with more than three dimensions. Frequently, the analysis goal is not to look into individual records but to understand the distribution of the records at large and to find clusters of records with similar attribute values. A large number of (typically hierarchical) clustering algorithms have been developed to group individual records to clusters of statistical significance. However, only few visualization techniques exist for further exploring and understanding the clustering results. We propose visualization and interaction methods for analyzing individual clusters as well as cluster distribution within and across levels in the cluster hierarchy. We also provide a clustering method that operates on density rather than individual records. To not restrict our search for clusters, we compute density in the given multidimensional multivariate space. Clusters are formed by areas of high density. We present an approach that automatically computes a hierarchical tree of high density clusters. To visually represent the cluster hierarchy, we present a 2D radial layout that supports an intuitive understanding of the distribution structure of the multidimensional multivariate data set. Individual clusters can be explored interactively using parallel coordinates when being selected in the cluster tree. Furthermore, we integrate circular parallel coordinates into the radial hierarchical cluster tree layout, which allows for the analysis of the overall cluster distribution. This visual representation supports the comprehension of the relations between clusters and the original attributes. The combination of the 2D radial layout and the circular parallel coordinates is used to overcome the overplotting problem of parallel coordinates when looking into data sets with many records. We apply an automatic coloring scheme based on the 2D radial layout of the hierarchical cluster tree encoding hue, saturation, and value of the HSV color space. The colors support linking the 2D radial layout to other views such as the standard parallel coordinates or, in case data is obtained from multidimensional spatial data, the distribution in object space.
Selecting Good Views of High-dimensional Data using Class Consistency
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Sips, Mike; Neubert, Boris; Lewis, John P.; Hanrahan, Pat; H.-C. Hege, I. Hotz, and T. Munzner
Abstract Many visualization techniques involve mapping high-dimensional data spaces to lower-dimensional views. Unfortunately, mapping a high-dimensional data space into a scatterplot involves a loss of information; or, even worse, it can give a misleading picture of valuable structure in higher dimensions. In this paper, we propose class consistency as a measure of the quality of the mapping. Class consistency enforces the constraint that classes of n D data are shown clearly in 2 D scatterplots. We propose two quantitative measures of class consistency, one based on the distance to the class s center of gravity, and another based on the entropies of the spatial distributions of classes. We performed an experiment where users choose good views, and show that class consistency has good precision and recall. We also evaluate both consistency measures over a range of data sets and show that these measures are efficient and robust.
Accelerating Volume Raycasting using Proxy Spheres
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Liu, Baoquan; Clapworthy, Gordon J.; Dong, Feng; H.-C. Hege, I. Hotz, and T. Munzner
In this paper, we propose an efficient solution that addresses the performance problems of current single-pass GPU raycasting algorithms. Our paper provides more control over the rendering process by introducing tighter ray segments for raycasting, while at the same time avoiding the introduction of any new rendering artefacts. We achieve this by dynamically generating, on the GPU, a coarsely fitted proxy geometry, composed of spheres, for the active blocks. The spheres are then rasterised into two z-buffers by a single rendering pass. The resulting two z-buffers are used as the first-hit and last-hit points for the subsequent raycaster. With this approach, only the valid ray segments between the two z-buffers need to be sampled during raycasting. This also provides more coherent parallelism on the GPU due to more consistent ray length and avoidance of the overheads and dynamic branching of performing checks on a per-sample basis during the raycasting pass. Our technique is ideal for dynamic data exploration in which both the transfer function and view parameters need to be changed frequently at runtime. The rendering results of our algorithm are identical to the general cube-based proxy geometry algorithm, but the performance can be up to 15.7 times faster. Furthermore, the approach can be adopted by any existing raycasting system in a straightforward way.
A Directional Occlusion Shading Model for Interactive Direct Volume Rendering
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Schott, Mathias; Pegoraro, Vincent; Hansen, Charles; Boulanger, Kévin; Bouatouch, Kadi; H.-C. Hege, I. Hotz, and T. Munzner
Volumetric rendering is widely used to examine 3D scalar fields from CT/MRI scanners and numerical simulation datasets. One key aspect of volumetric rendering is the ability to provide perceptual cues to aid in understanding structure contained in the data. While shading models that reproduce natural lighting conditions have been shown to better convey depth information and spatial relationships, they traditionally require considerable (pre)computation. In this paper, a shading model for interactive direct volume rendering is proposed that provides perceptual cues similar to those of ambient occlusion, for both solid and transparent surface-like features. An image space occlusion factor is derived from the radiative transport equation based on a specialized phase function. The method does not rely on any precomputation and thus allows for interactive explorations of volumetric data sets via on-the-fly editing of the shading model parameters or (multi-dimensional) transfer functions while modifications to the volume via clipping planes are incorporated into the resulting occlusion-based shading.
Fused Multi-Volume DVR using Binary Space Partitioning
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Lindholm, Stefan; Ljung, Patric; Hadwiger, Markus; Ynnerman, Anders; H.-C. Hege, I. Hotz, and T. Munzner
Multiple-volume visualization is a growing field in medical imaging providing simultaneous exploration of volumes acquired from varying modalities. However, high complexity results in an increased strain on performance compared to single volume rendering as scenes may consist of volumes with arbitrary orientations and rendering is performed with varying sample densities. Expensive image order techniques such as depth peeling have previously been used to perform the necessary calculations. In this work we present a view-independent region based scene description for multi-volume pipelines. Using Binary Space Partitioning we are able to create a simple interface providing all required information for advanced multi-volume renderings while introducing a minimal overhead for scenes with few volumes. The modularity of our solution is demonstrated by the use of visual development and performance is documented with benchmarks and real-time simulations.
Hierarchical Vortex Regions in Swirling Flow
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Petz, Christoph; Kasten, Jens; Prohaska, Steffen; Hege, Hans-Christian; H.-C. Hege, I. Hotz, and T. Munzner
We propose a new criterion to characterize hierarchical two-dimensional vortex regions induced by swirling motion. Central to the definition are closed loops that intersect the flow field at a constant angle. The union of loops belonging to the same area of swirling motion defines a vortex region. These regions are disjunct but may be nested, thus introducing a spatial hierarchy of vortex regions. We present a parameter free algorithm for the identification of these regions. Since they are not restricted to star- or convex-shaped geometries, we are able to identify also intricate regions, e.g., of elongated vortices. Computing an integrated value for each loop and mapping these values to a vortex region, introduces new ways for visualizing or filtering the vortex regions. Exemplary, an application based on the Rankine vortex model is presented. We apply our method to several CFD datasets and compare our results to existing approaches.
Volume Deformations in Grid-Less Flow Simulations
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Obermaier, Harald; Hering-Bertram, Martin; Kuhnert, Jörg; Hagen, Hans; H.-C. Hege, I. Hotz, and T. Munzner
Abstract This paper presents a novel method for the extraction and visualization of volume deformations in grid-less point based flow simulations. Our primary goals are the segmentation of different paths through a mixing device and the visualization of ellipsoidal particle deformations. The main challenges are the numerically efficient processing of deformation tensors and the robust integration of stream- and streaklines at boundaries of the dataset such that closed segments are obtained. Our results show two- and three-dimensional particle deformations as well as the segmentation of volumes in stationary fields and areas in time-dependent datasets taking consistent paths through a mixing device.
Smooth Stream Surfaces of Fourth Order Precision
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Schneider, Dominic; Wiebel, Alexander; Scheuermann, Gerik; H.-C. Hege, I. Hotz, and T. Munzner
We introduce a novel technique for the construction of smooth stream surfaces of 4th order precision. While common stream surface techniques use linear interpolation for generating seed points for new streamlines in the refinement phase, we use Hermite interpolation. The derivatives needed for Hermite interpolation are obtained by integration along the streamlines. This yields stream surfaces of 4th order precision. Additionally, we analyse the accuracy of the well known Hultquist approach and our new algorithm and proof that Hultquist s method is exact for linear vector fields. We compare both methods using the well known distance based and a novel error based refinement strategy. Our resulting surface is C1-continuous, enabling improved rendering among other benefits.
Combining Map Displays and 3D Visualizations for the Analysis of Scalar Data on Cerebral Aneurysm Surfaces
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Neugebauer, Mathias; Gasteiger, Rocco; Beuing, Oliver; Diehl, Volker; Skalej, Martin; Preim, Bernhard; H.-C. Hege, I. Hotz, and T. Munzner
Cerebral aneurysms result from a congenital or evolved weakness of stabilizing parts of the vessel wall and potentially lead to rupture and a life-threatening bleeding. Current medical research concentrates on the integration of blood flow simulation results for risk assessment of cerebral aneurysms. Scalar flow characteristics close to the aneurysm surface, such as wall shear stress, form an important part of the simulation results. Aneurysms exhibit variable surface shapes with only few landmarks. Therefore, the exploration and mental correlation of different surface regions is a difficult task. In this paper, we present an approach for the intuitive and interactive overview visualization of near wall flow data that is mapped onto the surface of a 3D model of a cerebral aneurysm. We combine a multi-perspective 2D projection map with a standard 3D visualization and present techniques to facilitate the correlation between a 3D model and a related 2D map. An informal evaluation with 4 experienced radiologists has shown that the map-based overview actually improves the surface exploration. Furthermore, different color schemes were discussed and, as a result, an appropriate color scheme for the visual analysis of the wall shear stress is presented.
Context-aware Volume Modeling of Skeletal Muscles
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Yan, Zhicheng; Chen, Wei; Lu, Aidong; Ebert, David S.; H.-C. Hege, I. Hotz, and T. Munzner
This paper presents an interactive volume modeling method that constructs skeletal muscles from an existing volumetric dataset. Our approach provides users with an intuitive modeling interface and produces compelling results that conform to the characteristic anatomy in the input volume. The algorithmic core of our method is an intuitive anatomy classification approach, suited to accommodate spatial constraints on the muscle volume. The presented work is useful in illustrative visualization, volumetric information fusion and volume illustration that involve muscle modeling, where the spatial context should be faithfully preserved.
Visual Analysis of Brain Activity from fMRI Data
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Janoos, Firdaus; Nouanesengsy, Boonthanome; Machiraju, Raghu; Shen, Han Wei; Sammet, Steffen; Knopp, Michael; Mórocz, István Á.; H.-C. Hege, I. Hotz, and T. Munzner
Classically, analysis of the time-varying data acquired during fMRI experiments is done using static activation maps obtained by testing voxels for the presence of significant activity using statistical methods. The models used in these analysis methods have a number of parameters, which profoundly impact the detection of active brain areas. Also, it is hard to study the temporal dependencies and cascading effects of brain activation from these static maps. In this paper, we propose a methodology to visually analyze the time dimension of brain function with a minimum amount of processing, allowing neurologists to verify the correctness of the analysis results, and develop a better understanding of temporal characteristics of the functional behaviour. The system allows studying time-series data through specific volumes-of-interest in the brain-cortex, the selection of which is guided by a hierarchical clustering algorithm performed in the wavelet domain. We also demonstrate the utility of this tool by presenting results on a real data-set.
Comparing Parameter Manipulation with Mouse, Pen, and Slider User Interfaces
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Swindells, Colin; Tory, Melanie; Dreezer, Rebecca; H.-C. Hege, I. Hotz, and T. Munzner
Visual fixation on one s tool(s) takes much attention away from one s primary task. Following the belief that the best tools disappear and become invisible to the user, we present a study comparing visual fixations (eye gaze within locations on a graphical display) and performance for mouse, pen, and physical slider user interfaces. Participants conducted a controlled, yet representative, color matching task that required user interaction representative of many data exploration tasks such as parameter exploration of medical or fuel cell data. We demonstrate that users may spend up to 95% fewer visual fixations on physical sliders versus standard mouse and pen tools without any loss in performance for a generalized visual performance task.
Preconceptions and Individual Differences in Understanding Visual Metaphors
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Ziemkiewicz, Caroline; Kosara, Robert; H.-C. Hege, I. Hotz, and T. Munzner
Understanding information visualization is more than a matter of reading a series of data values; it is also a matter of incorporating a visual structure into one s own thinking about a problem. We have proposed visual metaphors as a framework for understanding high-level visual structure and its effect on visualization use. Although there is some evidence that visual metaphors can affect visualization use, the nature of this effect is still ambiguous. We propose that a user s preconceived metaphors for data and other individual differences play an important role in her ability to think in a variety of visual metaphors, and subsequently in her ability to use a visualization. We test this hypothesis by conducting a study in which a participant s preconceptions and thinking style were compared with the degree to which she is affected by conflicting metaphors in a visualization and its task questions. The results show that metaphor compatibility has a significant effect on accuracy, but that factors such as spatial ability and personality can lessen this effect. We also find a complex influence of self-reported metaphor preference on performance. These findings shed light on how people use visual metaphors to understand a visualization.
Extended Excentric Labeling
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Bertini, Enrico; Rigamonti, Maurizio; Lalanne, Denis; H.-C. Hege, I. Hotz, and T. Munzner
The paper presents an extension to the Excentric Labeling, a labeling technique to dynamically show labels around a movable lens. Each labels refers to one object within the lens and is connected to it through a line. The original implementation has several known limitations and potential improvements that we address in this work, like: high density areas, uneven density distributions, and summary statistics. We describe the implemented extensions and present a think-aloud user study. The study shows that users can naturally understand and easily operate the majority of the implemented function but label scrolling, which requires additional research. From the study we also gained unanticipated requirements and interesting directions for further research.
Visualization of Vessel Movements
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Willems, Niels; Wetering, Huub van de; Wijk, Jarke J. van; H.-C. Hege, I. Hotz, and T. Munzner
We propose a geographical visualization to support operators of coastal surveillance systems and decision making analysts to get insights in vessel movements. For a possibly unknown area, they want to know where significant maritime areas, like highways and anchoring zones, are located. We show these features as an overlay on a map. As source data we use AIS data: Many vessels are currently equipped with advanced GPS devices that frequently sample the state of the vessels and broadcast them. Our visualization is based on density fields that are derived from convolution of the dynamic vessel positions with a kernel. The density fields are shown as illuminated height maps. Combination of two fields, with a large and small kernel provides overview and detail. A large kernel provides an overview of area usage revealing vessel highways. Details of speed variations of individual vessels are shown with a small kernel, highlighting anchoring zones where multiple vessels stop. Besides for maritime applications we expect that this approach is useful for the visualization of moving object data in general.
SDViz: A Context-Preserving Interactive Visualization System for Technical Diagrams
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Woo, Insoo; Kim, SungYe; Maciejewski, Ross; Ebert, David S.; Ropp, Timothy D.; Thomas, Krystal; H.-C. Hege, I. Hotz, and T. Munzner
When performing daily maintenance and repair tasks, technicians require access to a variety of technical diagrams. As technicians trace components and diagrams from page-to-page, within and across manuals, the contextual information of the components they are analyzing can easily be lost. To overcome these issues, we have developed a Schematic Diagram Visualization System (SDViz) designed for maintaining and highlighting contextual information in technical documents, such as schematic and wiring diagrams. Our system incorporates various features to aid in the navigation and diagnosis of faults, as well as maintaining contextual information when tracing components/connections through multiple diagrams. System features include highlighting relationships between components and connectors, diagram annotation tools, the animation of flow through the system, a novel contextual blending method, and a variety of traditional focus+context visualization techniques. We have evaluated the usefulness of our system through a qualitative user study in which subjects utilized our system in diagnosing faults during a standard aircraft maintenance exercise.
A Visualization Based Approach for Digital Signature Authentication
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Xu, Songhua; Yang, Wenxia; Lau, Francis C.M.; H.-C. Hege, I. Hotz, and T. Munzner
We propose a visualization based approach for digital signature authentication. Using our method, the speed and pressure aspects of a digital signature process can be clearly and intuitively conveyed to the user for digital signature authentication. Our design takes into account both the expressiveness and aesthetics of the derived visual patterns. With the visual aid provided by our method, digital signatures can be authenticated with better accuracy than using existing methods even novices can examine the authenticity of a digital signature in most situations using our method. To validate the effectiveness of our method, we conducted a comprehensive user study which confirms positively the advantages of our approach. Our method can be employed as a new security enhancement measure for a range of business and legal applications in reality which involve digital signature authorization and authentication.
Visualizing the Evolution of Compound Digraphs with TimeArcTrees
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Greilich, Martin; Burch, Michael; Diehl, Stephan; H.-C. Hege, I. Hotz, and T. Munzner
Compound digraphs are a widely used model in computer science. In many application domains these models evolve over time. Only few approaches to visualize such dynamic compound digraphs exist and mostly use animation to show the dynamics. In this paper we present a new visualization tool called TimeArcTrees that visualizes weighted, dynamic compound digraphs by drawing a sequence of node-link diagrams in a single view. Compactness is achieved by aligning the nodes of a graph vertically. Edge crossings are reduced by drawing upward and downward edges separately as colored arcs. Horizontal alignment of the instances of the same node in different graphs facilitates comparison of the graphs in the sequence. Many interaction techniques allow to explore the given graphs. Smooth animation supports the user to better track the transitions between views and to preserve his or her mental map. We illustrate the usefulness of the tool by looking at the particular problem of how shortest paths evolve over time. To this end, we applied the system to an evolving graph representing the German Autobahn and its traffic jams.
Fully Automatic Visualisation of Overlapping Sets
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Simonetto, Paolo; Auber, David; Archambault, Daniel; H.-C. Hege, I. Hotz, and T. Munzner
Visualisation of taxonomies and sets has recently become an active area of research. Many application fields now require more than a strict classification of elements into a hierarchy tree. Euler diagrams, one of the most natural ways of depicting intersecting sets, may provide a solution to these problems. In this paper, we present an approach for the automatic generation of Euler-like diagrams. This algorithm differs from previous approaches in that it has no undrawable instances of input, allowing it to be used in systems where the output is always required. We also improve the readability of Euler diagrams through the use of Bézier curves and transparent coloured textures. Our approach has been implemented using the Tulip platform. Both the source and executable program used to generate the results are freely available.
Visualization Techniques for Schedule Comparison
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Huang, Dandan; Tory, Melanie; Staub-French, Sheryl; Pottinger, Rachel; H.-C. Hege, I. Hotz, and T. Munzner
Project schedules are effectively represented by Gantt charts, but comparing multiple versions of a schedule is difficult. To compare versions with current methods, users must search and navigate through multiple large documents, making it difficult to identify differences. We present two novel visualization techniques to support the comparison of Gantt charts. First, we encode two Gantt charts in one view by overlapping them to show differences. Second, we designed an interactive visual technique, the TbarView , that allows users to compare multiple schedules within one single view. We evaluated the overlap and TbarView techniques via a user study. The study results showed that our design provided a quick overview of the variances among two or more schedules, and the techniques also improved efficiency by minimizing view switching. Our visual techniques for schedule comparison could be combined with other resource analysis tools to help project teams identify and resolve errors and problems in project schedules.
High-Quality Volumetric Reconstruction on Optimal Lattices for Computed Tomography
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Finkbeiner, Bernhard; Alim, Usman R.; Ville, Dimitri Van De; Möller, Torsten; H.-C. Hege, I. Hotz, and T. Munzner
Within the context of emission tomography, we study volumetric reconstruction methods based on the Expectation Maximization (EM) algorithm. We show, for the first time, the equivalence of the standard implementation of the EM-based reconstruction with an implementation based on hardware-accelerated volume rendering for nearest- neighbor (NN) interpolation. This equivalence suggests that higher-order kernels should be used with caution and do not necessarily lead to better performance. We also show that the EM algorithm can easily be adapted for different lattices, the body-centered cubic (BCC) one in particular. For validation purposes, we use the 3D version of the Shepp-Logan synthetic phantom, for which we derive closed-form analytical expressions of the projection data. The experimental results show the theoretically-predicted optimality of NN interpolation in combination with the EM algorithm, for both the noiseless and the noisy case. Moreover, reconstruction on the BCC lattice leads to superior accuracy, more compact data representation, and better noise reduction compared to the Cartesian one. Finally, we show the usefulness of the proposed method for optical projection tomography of a mouse embryo.
Quasi-interpolation on the Body Centered Cubic Lattice
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Entezari, Alireza; Mirzargar, Mahsa; Kalantari, Leila; H.-C. Hege, I. Hotz, and T. Munzner
This paper introduces a quasi-interpolation method for reconstruction of data sampled on the Body Centered Cubic (BCC) lattice. The reconstructions based on this quasi-interpolation achieve the optimal approximation order offered by the shifts of the quintic box spline on the BCC lattice. We also present a local FIR filter that is used to filter the data for quasi-interpolation. We document the improved quality and fidelity of reconstructions after employing the introduced quasi-interpolation method. Finally the resulting quasi-interpolation on the BCC sampled data are compared to the corresponding quasi-interpolation method on the Cartesian sampled data.
Enclosing Surfaces for Point Clusters Using 3D Discrete Voronoi Diagrams
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Rosenthal, Paul; Linsen, Lars; H.-C. Hege, I. Hotz, and T. Munzner
Point clusters occur in both spatial and non-spatial data. In the former context they may represent segmented particle data, in the latter context they may represent clusters in scatterplots. In order to visualize such point clusters, enclosing surfaces lead to much better comprehension than pure point renderings. We propose a flexible system for the generation of enclosing surfaces for 3D point clusters. We developed a GPUbased 3D discrete Voronoi diagram computation that supports all surface extractions. Our system provides three different types of enclosing surfaces. By generating a discrete distance field to the point cluster and extracting an isosurface from the field, an enclosing surface with any distance to the point cluster can be generated. As a second type of enclosing surfaces, a hull of the point cluster is extracted. The generation of the hull uses a projection of the discrete Voronoi diagram of the point cluster to an isosurface to generate a polygonal surface. Generated hulls of non-convex clusters are also non-convex. The third type of enclosing surfaces can be created by computing a distance field to the hull and extracting an isosurface from the distance field. This method exhibits reduced bumpiness and can extract surfaces arbitrarily close to the point cluster without losing connectedness. We apply our methods to the visualization of multidimensional spatial and non-spatial data. Multidimensional clusters are extracted and projected into a 3D visual space, where the point clusters are visualized. The respective clusters can also be visualized in object space when dealing with multidimensional particle data.
Scalable, Versatile and Simple Constrained Graph Layout
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Dwyer, Tim; H.-C. Hege, I. Hotz, and T. Munzner
We describe a new technique for graph layout subject to constraints. Compared to previous techniques the proposed method is much faster and scalable to much larger graphs. For a graph with n nodes, m edges and c constraints it computes incremental layout in time O(nlogn+m+c) per iteration. Also, it supports a much more powerful class of constraint: inequalities or equalities over the Euclidean distance between nodes.We demonstrate the power of this technique by application to a number of diagramming conventions which previous constrained graph layout methods could not support. Further, the constraint-satisfaction method inspired by recent work in position-based dynamics is far simpler to implement than previous methods.
Force-Directed Edge Bundling for Graph Visualization
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Holten, Danny; Wijk, Jarke J. van; H.-C. Hege, I. Hotz, and T. Munzner
Abstract Graphs depicted as node-link diagrams are widely used to show relationships between entities. However, nodelink diagrams comprised of a large number of nodes and edges often suffer from visual clutter. The use of edge bundling remedies this and reveals high-level edge patterns. Previous methods require the graph to contain a hierarchy for this, or they construct a control mesh to guide the edge bundling process, which often results in bundles that show considerable variation in curvature along the overall bundle direction. We present a new edge bundling method that uses a self-organizing approach to bundling in which edges are modeled as flexible springs that can attract each other. In contrast to previous methods, no hierarchy is used and no control mesh. The resulting bundled graphs show significant clutter reduction and clearly visible high-level edge patterns. Curvature variation is furthermore minimized, resulting in smooth bundles that are easy to follow. Finally, we present a rendering technique that can be used to emphasize the bundling.
On Visualization and Reconstruction from Non-Uniform Point Sets using B-splines
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Vuçini, Erald; Möller, Torsten; Gröller, M. Eduard; H.-C. Hege, I. Hotz, and T. Munzner
In this paper we present a novel framework for the visualization and reconstruction from non-uniform point sets. We adopt a variational method for the reconstruction of 3D non-uniform data to a uniform grid of chosen resolution. We will extend this reconstruction to an efficient multi-resolution uniform representation of the underlying data. Our multi-resolution representation includes a traditional bottom-up approach and a novel top-down hierarchy for adaptive hierarchical reconstruction. Using a hybrid regularization functional we can improve the reconstruction results. Finally, we discuss further application scenarios and show rendering results to emphasize the effectiveness and quality of our proposed framework. By means of qualitative results and error comparisons we demonstrate superiority of our method compared to competing methods.
Collaborative Brushing and Linking for Co-located Visual Analytics of Document Collections
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Isenberg, Petra; Fisher, Danyel; H.-C. Hege, I. Hotz, and T. Munzner
Many real-world analysis tasks can benefit from the combined efforts of a group of people. Past research has shown that to design visualizations for collaborative visual analytics tasks, we need to support both individual as well as joint analysis activities. We present Cambiera, a tabletop visual analytics tool that supports individual and collaborative information foraging activities in large text document collections. We define collaborative brushing and linking as an awareness mechanism that enables analysts to follow their own hypotheses during collaborative sessions while still remaining aware of the group's activities. With Cambiera, users are able to collaboratively search through documents, maintaining awareness of each others' work and building on each others' findings.
DocuBurst: Visualizing Document Content using Language Structure
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Collins, Christopher; Carpendale, Sheelagh; Penn, Gerald; H.-C. Hege, I. Hotz, and T. Munzner
Textual data is at the forefront of information management problems today. One response has been the development of visualizations of text data. These visualizations, commonly based on simple attributes such as relative word frequency, have become increasingly popular tools. We extend this direction, presenting the first visualization of document content which combines word frequency with the human-created structure in lexical databases to create a visualization that also reflects semantic content. DocuBurst is a radial, space-filling layout of hyponymy (the IS-A relation), overlaid with occurrence counts of words in a document of interest to provide visual summaries at varying levels of granularity. Interactive document analysis is supported with geometric and semantic zoom, selectable focus on individual words, and linked access to source text.
The Chinese Room: Visualization and Interaction to Understand and Correct Ambiguous Machine Translation
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Albrecht, Joshua; Hwa, Rebecca; Marai, G. Elisabeta; H.-C. Hege, I. Hotz, and T. Munzner
We present The Chinese Room, a visualization interface that allows users to explore and interact with a multitude of linguistic resources in order to decode and correct poor machine translations. The target users of The Chinese Room are not bilingual and are not familiar with machine translation technologies. We investigate the ability of our system to assist such users in decoding and correcting faulty machine translations. We found that by collaborating with our application, end-users can overcome many difficult translation errors and disambiguate translated passages that were otherwise baffling. We also examine the utility of our system to machine translation researchers. Anecdotal evidence suggests that The Chinese Room can help such researchers develop better machine translation systems.

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