EuroVis10: Eurographics/ IEEE Symposium on Visualization

Permanent URI for this collection

https://diglib7.eg.org/handle/10.2312/395

Isosurface Similarity Maps

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Bruckner, Stefan

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Möller, Torsten

An Exploratory Technique for Coherent Visualization of Time-varying Volume Data

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Tikhonova, Anna

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Correa, Carlos D.

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Ma, Kwan-Liu

Evaluation of Cluster Identification Performance for Different PCP Variants

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Holten, Danny

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Wijk, Jarke J. van

Visualizing Summary Statistics and Uncertainty

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Potter, Kristin

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Kniss, Joe

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Riesenfeld, Richard

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Johnson, Chris R.

Supporting Exploratory Analysis with the Select and Slice Table

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Shrinivasan, Yedendra B.

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Wijk, Jarke J. van

Brushing Moments in Interactive Visual Analysis

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Kehrer, Johannes

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Filzmoser, Peter

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Hauser, Helwig

SmallWorlds: Visualizing Social Recommendations

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Gretarsson, Brynjar

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O'Donovan, John

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Bostandjiev, Svetlin

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Hall, Christopher

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Höllerer, Tobias

Image-Based Edge Bundles: Simplified Visualization of Large Graphs

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Telea, Alexandru

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Ersoy, Ozan

Winding Roads: Routing edges into bundles

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Lambert, Antoine

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Bourqui, Romain

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Auber, David

GraphDice: A System for Exploring Multivariate Social Networks

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Bezerianos, Anastasia

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Chevalier, Fanny

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Dragicevic, Pierre

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Elmqvist, Niklas

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Fekete, Jean-Daniel

Out-of-Core Simplification and Crack-Free LOD Volume Rendering for Irregular Grids

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Du, Zhiyan

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Chiang, Yi-Jen

Estimation and Modeling of Actual Numerical Errors in Volume Rendering

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Kronander, Joel

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Unger, Jonas

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Möller, Torsten

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Ynnerman, Anders

A Multidirectional Occlusion Shading Model for Direct Volume Rendering

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oltészová, Veronika

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Patel, Daniel

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Bruckner, Stefan

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Viola, Ivan

Hardware-Assisted Projected Tetrahedra

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Maximo, André

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Marroquim, Ricardo

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Farias, Ricardo

Space-in-Time and Time-in-Space Self-Organizing Maps for Exploring Spatiotemporal Patterns

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Andrienko, Gennady

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Andrienko, Natalia

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Bremm, Sebastian

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Schreck, Tobias

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Landesberger, Tatiana von

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Bak, Peter

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Keim, Daniel

Alleviating the Modifiable Areal Unit Problem within Probe-Based Geospatial Analyses

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Butkiewicz, Thomas

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Meentemeyer, Ross K.

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Shoemaker, Douglas A.

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Chang, Remco

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Wartell, Zachary

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Ribarsky, William

Real-Time Temporal-Coherent Color Contrast Enhancement for Dichromats

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Machado, Gustavo Mello

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Oliveira, Manuel M.

Accelerated Visualization of Dynamic Molecular Surfaces

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Lindow, Norbert

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Baum, Daniel

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Prohaska, Steffen

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Hege, Hans-Christian

Coherent Culling and Shading for Large Molecular Dynamics Visualization

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Grottel, Sebastian

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Reina, Guido

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Dachsbacher, Carsten

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Ertl, Thomas

Matrix Trees

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Andrysco, Nathan

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Tricoche, Xavier

Dynamic Multi-View Exploration of Shape Spaces

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Busking, Stef

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Botha, Charl P.

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Post, Frits H.

HyperMoVal: Interactive Visual Validation of Regression Models for Real-Time Simulation

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Piringer, Harald

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Berger, Wolfgang

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Krasser, Jürgen

Topological Landscape Ensembles for Visualization of Scalar-Valued Functions

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Harvey, William

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Wang, Yusu

Effective Techniques to Visualize Filament-Surface Relationships

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Kuß, Anja

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Gensel, Maria

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Meyer, Björn

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Dercksen, Vincent J.

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Prohaska, Steffen

Illustrative White Matter Fiber Bundles

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Otten, Ron

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Vilanova, Anna

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Wetering, Huub van de

DTI in Context: Illustrating Brain Fiber Tracts In Situ

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Svetachov, Pjotr

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Everts, Maarten H.

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Isenberg, Tobias

An Interactive Visual Analytics System for Bridge Management

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Wang, Xiaoyu

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Dou, Wenwen

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Chen, Shen-En

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Ribarsky, William

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Chang, Remco

Pathline: A Tool For Comparative Functional Genomics

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Meyer, Miriah

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Wong, Bang

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Styczynski, Mark

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Munzner, Tamara

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Pfister, Hanspeter

Video Visualization for Snooker Skill Training

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Höferlin, Markus

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Grundy, Edward

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Borgo, Rita

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Weiskopf, Daniel

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Chen, Min

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Griffiths, Iwan W.

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Griffiths, W.

Scalable Multi-view Registration for Multi-Projector Displays on Vertically Extruded Surfaces

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Sajadi, Behzad

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Majumder, Aditi

Streaming-Enabled Parallel Dataflow Architecture for Multicore Systems

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Vo, Huy T.

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Osmari, Daniel K.

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Summa, Brian

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Comba, João L. D.

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Pascucci, Valerio

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Silva, Cláudio T.

Topographic Map Visualization from Adaptively Compressed Textures

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Andujar, Carlos

Visual Support for Interactive Post-Interventional Assessment of Radiofrequency Ablation Therapy

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Rieder, Christian

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Weihusen, Andreas

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Schumann, Christian

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Zidowitz, Stephan

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Peitgen, Heinz-Otto

Reusable Visualizations and Animations for Surgery Planning

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Mühler, Konrad

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Preim, Bernhard

ProbExplorer: Uncertainty-guided Exploration and Editing of Probabilistic Medical Image Segmentation

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Saad, Ahmed

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Möller, Torsten

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Hamarneh, Ghassan

An Evaluation of Glyph Perception for Real Symmetric Traceless Tensor Properties

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Jankun-Kelly, T. J.

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Lanka, Yagneshwara

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II, J. Edward Swan

Visual Analysis of Multi-Joint Kinematic Data

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Krekel, Peter R.

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Valstar, Edward R.

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Groot, Jurriaan de

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Post, Frits H.

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Nelissen, Rob G. H. H.

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Botha, Charl P.

Topology Aware Stream Surfaces

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Schneider, Dominic

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Reich, Wieland

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Wiebel, Alexander

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Scheuermann, Gerik

A Maximum Enhancing Higher-Order Tensor Glyph

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Schultz, Thomas

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Kindlmann, Gordon

Toward a Lagrangian Vector Field Topology

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Fuchs, Raphael

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Peikert, Ronny

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Kemmler, Jan

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Schindler, Benjamin

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Waser, Juergen

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Sadlo, Filip

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Hauser, Helwig

The Readability of Path-Preserving Clusterings of Graphs

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Archambault, Daniel

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Purchase, Helen C.

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Pinaud, Bruno

The Perception of Correlation in Scatterplots

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Rensink, Ronald A.

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Baldridge, Gideon

A Salience-based Quality Metric for Visualization

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Jänicke, Heike

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Chen, Min

Understanding Interactive Legends: a Comparative Evaluation with Standard Widgets

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Riche, Nathalie Henry

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Lee, Bongshin

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Plaisant, Catherine

Topology-based Smoothing of 2D Scalar Fields with C1-Continuity

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Weinkauf, Tino

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Gingold, Yotam

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Sorkine, Olga

Multi-layer Depth Peeling by Single-Pass Hardware Rasterisation for Faster Isosurface Raytracing on a GPU

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Liu, Baoquan

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Clapworthy, Gordon J.

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Dong, Feng

Visualization and Analysis-Oriented Reconstruction of Material Interfaces

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Meredith, Jeremy

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Childs, Hank

Non-iterative Second-order Approximation of Signed Distance Functions for Any Isosurface Representation

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Molchanov, Vladimir

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Rosenthal, Paul

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Linsen, Lars

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Now showing 1 - 48 of 48

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.
An Exploratory Technique for Coherent Visualization of Time-varying Volume Data
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Tikhonova, Anna; Correa, Carlos D.; Ma, Kwan-Liu; G. Melancon, T. Munzner, and D. Weiskopf
The selection of an appropriate global transfer function is essential for visualizing time-varying simulation data. This is especially challenging when the global data range is not known in advance, as is often the case in remote and in-situ visualization settings. Since the data range may vary dramatically as the simulation progresses, volume rendering using local transfer functions may not be coherent for all time steps. We present an exploratory technique that enables coherent classification of time-varying volume data. Unlike previous approaches, which require pre-processing of all time steps, our approach lets the user explore the transfer function space without accessing the original 3D data. This is useful for interactive visualization, and absolutely essential for in-situ visualization, where the entire simulation data range is not known in advance. Our approach generates a compact representation of each time step at rendering time in the form of ray attenuation functions, which are used for subsequent operations on the opacity and color mappings. The presented approach offers interactive exploration of time-varying simulation data that alleviates the cost associated with reloading and caching large data sets.
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.
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.
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.
Brushing Moments in Interactive Visual Analysis
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Kehrer, Johannes; Filzmoser, Peter; Hauser, Helwig; G. Melancon, T. Munzner, and D. Weiskopf
We present a systematic study of opportunities for the interactive visual analysis of multi-dimensional scientific data that is based on the integration of statistical aggregations along selected independent data dimensions in a framework of coordinated multiple views (with linking and brushing). Traditional and robust estimates of the four statistical moments (mean, variance, skewness, and kurtosis) as well as measures of outlyingness are integrated in an iterative visual analysis process. Brushing particular statistics, the analyst can investigate data characteristics such as trends and outliers. We present a categorization of beneficial combinations of attributes in 2D scatterplots: (a) kth vs. (k+1)th statistical moment of a traditional or robust estimate, (b) traditional vs. robust version of the same moment, (c) two different robust estimates of the same moment. We propose selected view transformations to iteratively construct this multitude of informative views as well as to enhance the depiction of the statistical properties in scatterplots and quantile plots. In the framework, we interrelate the original distributional data and the aggregated statistics, which allows the analyst to work with both data representations simultaneously. We demonstrate our approach in the context of two visual analysis scenarios of multi-run climate simulations.
SmallWorlds: Visualizing Social Recommendations
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Gretarsson, Brynjar; O'Donovan, John; Bostandjiev, Svetlin; Hall, Christopher; Höllerer, Tobias; G. Melancon, T. Munzner, and D. Weiskopf
We present SmallWorlds, a visual interactive graph-based interface that allows users to specify, refine and build item-preference profiles in a variety of domains. The interface facilitates expressions of taste through simple graph interactions and these preferences are used to compute personalized, fully transparent item recommendations for a target user. Predictions are based on a collaborative analysis of preference data from a user s direct peer group on a social network. We find that in addition to receiving transparent and accurate item recommendations, users also learn a wealth of information about the preferences of their peers through interaction with our visualization. Such information is not easily discoverable in traditional text based interfaces. A detailed analysis of our design choices for visual layout, interaction and prediction techniques is presented. Our evaluations discuss results from a user study in which SmallWorlds was deployed as an interactive recommender system on Facebook.
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.
GraphDice: A System for Exploring Multivariate Social Networks
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Bezerianos, Anastasia; Chevalier, Fanny; Dragicevic, Pierre; Elmqvist, Niklas; Fekete, Jean-Daniel; G. Melancon, T. Munzner, and D. Weiskopf
Social networks collected by historians or sociologists typically have a large number of actors and edge attributes. Applying social network analysis (SNA) algorithms to these networks produces additional attributes such as degree, centrality, and clustering coefficients. Understanding the effects of this plethora of attributes is one of the main challenges of multivariate SNA. We present the design of GraphDice, a multivariate network visualization system for exploring the attribute space of edges and actors. GraphDice builds upon the ScatterDice system for its main multidimensional navigation paradigm, and extends it with novel mechanisms to support network exploration in general and SNA tasks in particular. Novel mechanisms include visualization of attributes of interval type and projection of numerical edge attributes to node attributes. We show how these extensions to the original ScatterDice system allow to support complex visual analysis tasks on networks with hundreds of actors and up to 30 attributes, while providing a simple and consistent interface for interacting with network data.
Out-of-Core Simplification and Crack-Free LOD Volume Rendering for Irregular Grids
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Du, Zhiyan; Chiang, Yi-Jen; G. Melancon, T. Munzner, and D. Weiskopf
We propose a novel out-of-core simplification and level-of-detail (LOD) volume rendering algorithm for large irregular grids represented as tetrahedral meshes. One important feature of our algorithm is that it creates a space decomposition as required by I/O-efficient simplification and volume rendering, and simplifies both the internal and boundary portions of the sub-volumes progressively by edge collapses using the (extended) quadric error metric, while ensuring any selected LOD mesh to be crack-free (i.e., any neighboring sub-volumes in the LOD have consistent boundaries, and all the cells in the LOD do not have negative volumes), with all computations performed I/O-efficiently. This has been an elusive goal for out-of-core progressive meshes and LOD visualization, and our novel solution achieves this goal with a theoretical guarantee to be crack-free for tetrahedral meshes. As for selecting a desirable LOD mesh for volume rendering, our technique supports selective refinement LODs (where different places can have different error bounds), in addition to the basic uniform LODs (where the error bound is the same in all places). The proposed scalar-value range and view-dependent selection queries for selective refinement are especially effective in producing images of the highest quality with a much faster rendering speed. The experiments demonstrate the efficacy of our new technique.
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.
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.
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.
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.
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.
Real-Time Temporal-Coherent Color Contrast Enhancement for Dichromats
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Machado, Gustavo Mello; Oliveira, Manuel M.; G. Melancon, T. Munzner, and D. Weiskopf
We present an automatic image-recoloring technique for enhancing color contrast for dichromats whose computational cost varies linearly with the number of input pixels. Our approach can be efficiently implemented on GPUs, and we show that for typical image sizes it is up to two orders of magnitude faster than the current stateof- the-art technique. Unlike previous approaches, ours preserve temporal coherence and, therefore, is suitable for video recoloring. We demonstrate the effectiveness of our technique by integrating it into a visualization system and showing, for the first time, real-time high-quality recolored visualizations for dichromats.
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.
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.
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.
Dynamic Multi-View Exploration of Shape Spaces
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Busking, Stef; Botha, Charl P.; Post, Frits H.; G. Melancon, T. Munzner, and D. Weiskopf
Statistical shape modeling is a widely used technique for the representation and analysis of the shapes and shape variations present in a population. A statistical shape model models the distribution in a high dimensional shape space, where each shape is represented by a single point. We present a design study on the intuitive exploration and visualization of shape spaces and shape models. Our approach focuses on the dual-space nature of these spaces. The high-dimensional shape space represents the population, whereas object space represents the shape of the 3D object associated with a point in shape space. A 3D object view provides local details for a single shape. The high dimensional points in shape space are visualized using a 2D scatter plot projection, the axes of which can be manipulated interactively. This results in a dynamic scatter plot, with the further extension that each point is visualized as a small version of the object shape that it represents. We further enhance the population-object duality with a new type of view aimed at shape comparison. This new shape evolution view visualizes shape variability along a single trajectory in shape space, and serves as a link between the two spaces described above. Our three-view exploration concept strongly emphasizes linked interaction between all spaces. Moving the cursor over the scatter plot or evolution views, shapes are dynamically interpolated and shown in the object view. Conversely, camera manipulation in the object view affects the object visualizations in the other views. We present a GPU-accelerated implementation, and show the effectiveness of the three-view approach using a number of realworld cases. In these, we demonstrate how this multi-view approach can be used to visually explore important aspects of a statistical shape model, including specificity, compactness and reconstruction error.
HyperMoVal: Interactive Visual Validation of Regression Models for Real-Time Simulation
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Piringer, Harald; Berger, Wolfgang; Krasser, Jürgen; G. Melancon, T. Munzner, and D. Weiskopf
Abstract During the development of car engines, regression models that are based on machine learning techniques are increasingly important for tasks which require a prediction of results in real-time. While the validation of a model is a key part of its identification process, existing computation- or visualization-based techniques do not adequately support all aspects of model validation. The main contribution of this paper is an interactive approach called HyperMoVal that is designed to support multiple tasks related to model validation: 1) comparing known and predicted results, 2) analyzing regions with a bad fit, 3) assessing the physical plausibility of models also outside regions covered by validation data, and 4) comparing multiple models. The key idea is to visually relate one or more n-dimensional scalar functions to known validation data within a combined visualization. HyperMoVal lays out multiple 2D and 3D sub-projections of the n-dimensional function space around a focal point.We describe how linking HyperMoVal to other views further extends the possibilities for model validation. Based on this integration, we discuss steps towards supporting the entire workflow of identifying regression models. An evaluation illustrates a typical workflow in the application context of car-engine design and reports general feedback of domain experts and users of our approach. These results indicate that our approach significantly accelerates the identification of regression models and increases the confidence in the overall engineering process.
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.
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.
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.
DTI in Context: Illustrating Brain Fiber Tracts In Situ
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Svetachov, Pjotr; Everts, Maarten H.; Isenberg, Tobias; G. Melancon, T. Munzner, and D. Weiskopf
We present an interactive illustrative visualization method inspired by traditional pen-and-ink illustration styles. Specifically, we explore how to provide context around DTI fiber tracts in the form of surfaces of the brain, the skull, or other objects such as tumors. These contextual surfaces are derived from either segmentation data or generated using interactive iso-surface extraction and are rendered with a flexible, slice-based hatching technique, controlled with ambient occlusion. This technique allows us to produce a consistent and frame-coherent appearance with precise control over the lines. In addition, we provide context through cutting planes onto which we render gray matter with stippling. Together, our methods not only facilitate the interactive exploration and illustration of brain fibers within their anatomical context but also allow us to produce high-quality images for print reproduction. We provide evidence for the success of our approach with an informal evaluation with domain experts.
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.
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.
Video Visualization for Snooker Skill Training
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Höferlin, Markus; Grundy, Edward; Borgo, Rita; Weiskopf, Daniel; Chen, Min; Griffiths, Iwan W.; Griffiths, W.; G. Melancon, T. Munzner, and D. Weiskopf
We present a feasibility study on using video visualization to aid snooker skill training. By involving the coaches and players in the loop of intelligent reasoning, our approach addresses the difficulties of automated semantic reasoning, while benefiting from mature video processing techniques. This work was conducted in conjunction with a snooker club and a sports scientist. In particular, we utilized the principal design of the VideoPerpetuoGram (VPG) to convey spatiotemporal information to the viewers through static visualization, removing the burden of repeated video viewing. We extended the VPG design to accommodate the need for depicting multiple video streams and respective temporal attribute fields, including silhouette extrusion, spatial attributes, and non-spatial attributes. Our results and evaluation have shown that video visualization can provide snooker coaching with visually quantifiable and comparable summary records, and is thus a cost-effective means for assessing skill levels and monitoring progress objectively and consistently.
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
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.
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.
Visual Support for Interactive Post-Interventional Assessment of Radiofrequency Ablation Therapy
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Rieder, Christian; Weihusen, Andreas; Schumann, Christian; Zidowitz, Stephan; Peitgen, Heinz-Otto; G. Melancon, T. Munzner, and D. Weiskopf
Percutaneous radiofrequency (RF) ablation is a minimally invasive, image-guided therapy for the treatment of liver tumors. The assessment of the ablation area (coagulation) is performed to verify the treatment success as an essential part of the therapy. Traditionally, pre- and post-interventional CT images are used to visually compare the shape, size, and position of tumor and coagulation. In this work, we present a novel visualization as well as a navigation tool, the so-called tumor map. The tumor map is a pseudo-cylindrical mapping of the tumor surface onto a 2D image. It is used for a combined visualization of all ablation zones of the tumor to allow a reliable therapy assessment. Additionally, the tumor map serves as an interactive tool for intuitive navigation within the 3D volume rendering of the tumor vicinity as well as with familiar 2D viewers.
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.
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 Evaluation of Glyph Perception for Real Symmetric Traceless Tensor Properties
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Jankun-Kelly, T. J.; Lanka, Yagneshwara; II, J. Edward Swan; G. Melancon, T. Munzner, and D. Weiskopf
A perceptual study of four tensor glyphs for symmetric, real, traceless tensors was performed. Each glyph encodes three properties of the system: Orientation, uniaxiality (alignment along the direction of orientation), and biaxiality (alignment along a vector orthogonal to the orientation). Thirty users over two studies were asked to identify these three properties for each glyph type under a variety of permutations in order to evaluate the effectiveness of visually communicating the properties; response time was also measured. We discuss the significant differences found between the methods as guidance to the use of these glyphs for traceless tensor visualization.
Visual Analysis of Multi-Joint Kinematic Data
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Krekel, Peter R.; Valstar, Edward R.; Groot, Jurriaan de; Post, Frits H.; Nelissen, Rob G. H. H.; Botha, Charl P.; G. Melancon, T. Munzner, and D. Weiskopf
Kinematics is the analysis of motions without regarding forces or inertial effects, with the purpose of understanding joint behaviour. Kinematic data of linked joints, for example the upper extremity, i.e. the shoulder and arm joints, contains many related degrees of freedom that complicate numerical analysis. Visualisation techniques enhance the analysis process, thus improving the effectiveness of kinematic experiments. This paper describes a new visualisation system specifically designed for the analysis of multi-joint kinematic data of the upper extremity. The challenge inherent in the data is that the upper extremity is comprised of five cooperating joints with a total of fifteen degrees of freedom. The range of motion may be affected by subtle deficiencies of individual joints that are difficult to pinpoint. To highlight these subtleties our approach combines interactive filtering and multiple visualisation techniques. Our system is further differentiated by the fact that it integrates simultaneous acquisition and visual analysis of biokinematic data. Also, to facilitate complex queries, we have designed a visual query interface with visualisation and interaction elements that are based on the domain-specific anatomical representation of the data. The combination of these techniques form an effective approach specifically tailored for the investigation and comparison of large collections of kinematic data. This claim is supported by an evaluation experiment where the technique was used to inspect the kinematics of the left and right arm of a patient with a healed proximal humerus fracture, i.e. a healed shoulder fracture.
Topology Aware Stream Surfaces
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Schneider, Dominic; Reich, Wieland; Wiebel, Alexander; Scheuermann, Gerik; G. Melancon, T. Munzner, and D. Weiskopf
We present an algorithm that allows stream surfaces to recognize and adapt to vector field topology. Standard stream surface algorithms either refine the surface uncontrolled near critical points which slows down the computation considerably and may lead to a poor surface approximation. Alternatively, the concerned region is omitted from the stream surface by severing it into two parts thus generating an incomplete stream surface. Our algorithm utilizes topological information to provide a fast, accurate, and complete triangulation of the stream surface near critical points. The required topological information is calculated in a preprocessing step. We compare our algorithm against the standard approach both visually and in performance.
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.
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.
The Readability of Path-Preserving Clusterings of Graphs
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Archambault, Daniel; Purchase, Helen C.; Pinaud, Bruno; G. Melancon, T. Munzner, and D. Weiskopf
Graph visualization systems often exploit opaque metanodes to reduce visual clutter and improve the readability of large graphs. This filtering can be done in a path-preserving way based on attribute values associated with the nodes of the graph. Despite extensive use of these representations, as far as we know, no formal experimentation exists to evaluate if they improve the readability of graphs. In this paper, we present the results of a user study that formally evaluates how such representations affect the readability of graphs. We also explore the effect of graph size and connectivity in terms of this primary research question. Overall, for our tasks, we did not find a significant difference when this clustering is used. However, if the graph is highly connected, these clusterings can improve performance. Also, if the graph is large enough and can be simplified into a few metanodes, benefits in performance on global tasks are realized. Under these same conditions, however, performance of local attribute tasks may be reduced.
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
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.
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.
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.
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.
Visualization and Analysis-Oriented Reconstruction of Material Interfaces
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Meredith, Jeremy; Childs, Hank; G. Melancon, T. Munzner, and D. Weiskopf
Reconstructing boundaries along material interfaces from volume fractions is a difficult problem, especially because the under-resolved nature of the input data allows for many correct interpretations. Worse, algorithms widely accepted as appropriate for simulation are inappropriate for visualization. In this paper, we describe a new algorithm that is specifically intended for reconstructing material interfaces for visualization and analysis requirements. The algorithm performs well with respect to memory footprint and execution time, has desirable properties in various accuracy metrics, and also produces smooth surfaces with few artifacts, even when faced with more than two materials per cell.
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.

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