EuroVisShort2014

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https://diglib.eg.org/handle/10.2312/7747

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Bilateral Depth Filtering for Enhanced Vessel Reformation
(The Eurographics Association, 2014) Kretschmer, Jan; Preim, Bernhard; Stamminger, Marc; N. Elmqvist and M. Hlawitschka and J. Kennedy
Curved Planar Reformation is a powerful visualization technique for the diagnosis of vascular diseases. It allowsan accurate centerline-driven investigation of vessel lumen while providing valuable anatomical context.Extended methods like Multipath Curved Planar Reformation, Centerline Reformation or Curved Surface Reformationprovide additional flexibility by condensing entire vascular systems into rotatable views. Unfortunately, allthese methods produce depth discontinuities because they operate in a projective fashion. While large discontinuitiesprovide valuable hints about distinct anatomical contexts, small discontinuities, which frequently arise, havedistracting effects on the visualization result and do not contribute significant information. In this paper we presenta bilateral filtering technique which allows to selectively remove depth discontinuities without affecting discontinuitiesthat carry information. The presented approach significantly improves the quality of vessel reformations,can be applied at interactive frame rates and is orthogonal to existing methods.
Characterization of Blood-Flow Patterns from Phase-Contrast MRI Velocity Fields
(The Eurographics Association, 2014) Pelt, Roy van; Fuster, Andrea; Claassen, Geert; Vilanova, Anna; N. Elmqvist and M. Hlawitschka and J. Kennedy
Hemodynamic information has proven valuable for analysis of cardiovascular diseases. Aberrant blood-flow patterns,for instance, often relate to disease progression. Magnetic resonance imaging enables blood-flow measurementsthat provide three-dimensional velocity fields during one heartbeat. However, visual analysis of these data ischallenging, because of the abundance and complexity of information. Explicit feature extraction can facilitate thepattern characterization, and hence support visualization techniques to effectively convey anomalous flow areas.In this work, we improve on existing pattern matching methods that characterize blood-flow patterns in volumetricimaging data. To this end, we propose a set of helical and vortical patterns that can be parameterized by a singlevariable. The characterization performance is validated on both synthetic and imaging blood-flow data. Moreover,we present a comprehensive visualization based on the pattern matching results, enabling semi-quantitativeassessment of the patterns in relation to the cardiovascular anatomy.
Coherent View-Dependent Streamlines for Understanding Blood Flow
(The Eurographics Association, 2014) Lawonn, Kai; Günther, Tobias; Preim, Bernhard; N. Elmqvist and M. Hlawitschka and J. Kennedy
The expressive visualization of (time-dependent) 3D blood flow along with the vessel wall is essential for understandingvascular diseases. However, the high complexity of the underlying flow data makes the explorationchallenging. For the biomedical research, it is necessary to provide methods that allow for rapid flow comprehension,ideally by emphasizing relevant flow characteristics. Therefore, we present a fast approach that visualizesstreamlines in a view-dependent way, while taking relevant flow features into consideration. For this, we adapt awell-established non-photorealistic rendering technique - suggestive contours - for surface meshes to streamlineillustrations. The advantages of our approach are confirmed in an informal user feedback with domain experts,who were able to comprehend the overall flow behavior faster.
Color and Uncertainty: It is not always Black and White
(The Eurographics Association, 2014) Tak, Susanne; Toet, Alexander; N. Elmqvist and M. Hlawitschka and J. Kennedy
To fully comprehend the meaning and impact of visualized data it is crucial that users are able to perceive andcomprehend the inherent uncertainty of the data in a correct and intuitive way. Data uncertainty is frequentlyvisualized through color mappings. Previous studies argued that color hue is not suitable for communicatinguncertainty because most hue scales lack an intrinsic perceptual order. In this paper we examine the use of hue forcommunicating data uncertainty in more detail. We investigated the potential of distinct color triples (rather thanthe entire spectrum of colors, as used in previously studies) to represent different levels of uncertainty.We identifiedseveral color triples that reliably map to an intuitive ordering of certainty. Bipolar color scales constructed fromthese color triples can be used to communicate uncertainty in visualizations, particularly to audiences of nonspecialists.A 'traffic light' configuration (with red and green at the endpoints and either yellow or orange in themiddle) communicates uncertainty most intuitively.
Comparing Three Designs of Macro-Glyphs for Poetry Visualization
(The Eurographics Association, 2014) Abdul-Rahman, Alfie; Maguire, Eamonn; Chen, Min; N. Elmqvist and M. Hlawitschka and J. Kennedy
Glyphs have been successfully used in poetry visualization for depicting the characteristics and positions of eachphonetic articulation in relation to the human vocal system. While existing glyph designs provide visual representationsfor detailed observation and external memorization of the dynamics throughout a poem, they are lesseffective for observing the relationship and variance between different lines in a poem and in comparing differentpoems. In this short paper, we present three designs of macro-glyphs for summarizing the spatio-temporal dynamicsat the level of poetic lines. In particular, we use statistics from a collection of poems to guide and optimize thedesigns. We report our comparative study on the effectiveness of these three designs.
The Design Space of Temporal Graph Visualisation
(The Eurographics Association, 2014) Kerracher, Natalie; Kennedy, Jessie; Chalmers, Kevin; N. Elmqvist and M. Hlawitschka and J. Kennedy
This paper presents our work in mapping the design space of techniques for temporal graph visualisation. Weidentify two independent dimensions upon which the techniques can be classified: graph structural encoding andtemporal encoding. Based on these dimensions, we create a matrix into which we organise existing techniques.We identify gaps in this design space which may prove interesting opportunities for the development of noveltechniques. We also consider additional dimensions upon which further useful classification could be made. Inorganising the disparate existing approaches from a wide range of domains, our classification will assist thosenew to the research area, and designers and evaluators developing systems for temporal graph data by raisingawareness of the range of possible approaches available, and highlighting possible directions for further research.
The Effect of Information Visualization Delivery on Narrative Construction and Development
(The Eurographics Association, 2014) Badawood, Donia; Wood, Jo; N. Elmqvist and M. Hlawitschka and J. Kennedy
We conducted a between-subject experiment with 32 participants to explore how two different models of informationvisualization delivery influence narratives constructed by audiences. The first model involves direct narrativeby a speaker using visualization software to tell a data story, while the second model involves constructing a storyby interactively exploring the visualization software. We used an open-ended questionnaire in a controlled laboratorysettings in which the primary goal was to collect a number of written data stories derived from the twomodels. The participants' data stories and answers were all analysed and coded using a number of themes, includinginsight types, and narrative structures. Our findings show that while the delivery model does not significantlyaffect how easy or difficult the participants found telling a data story to be, it does have an effect on the tendencyto identify and use outliers insights in the data story if they are not distracted from this by direct narration, and onthe narrative structure and depth of the data story. Our approach to data analysis and different storytelling axescan be usefully applied to other studies and comparisons of storytelling approaches.
Eliciting Multi-touch Selection Gestures for Interactive Data Graphics
(The Eurographics Association, 2014) Willett, Wesley; Lan, Qi; Isenberg, Petra; N. Elmqvist and M. Hlawitschka and J. Kennedy
We report the results of a study in which we elicited selection gestures for multi-touch data graphics. The selectionof data items is a common and extremely important form of interaction with data graphics, and serves as the basisfor many other data interaction techniques. However, interactive charting tools for multi-touch displays typicallyonly provide dedicated multi-touch gestures for single-point selection or zooming. Our study used gesture elicitationto explore a wider range of possible selection interactions for multi-touch data graphics. The results show a strongpreference for simple, one-handed selection gestures. They also show that users tend to interact with chart axes andmake figurative selection gestures outside the chart, rather than interact with the visual marks themselves. Finally,we found strong consensus around several unique selection gestures related to visual chart features.
Evaluation of Visualizations for Interface Analysis of SPH
(The Eurographics Association, 2014) Krone, Michael; Huber, Markus; Scharnowski, Katrin; Hirschler, Manuel; Kauker, Daniel; Reina, Guido; Nieken, Ulrich; Weiskopf, Daniel; Ertl, Thomas; N. Elmqvist and M. Hlawitschka and J. Kennedy
We present a GPU-accelerated visualization application that employs methods from computer graphics and visualizationto analyze SPH simulations from the field of material science. To this end, we extract the isosurfacethat separates the stable phases in a fluid mixture via the kernel function that was used by the simulation. Ourapplication enables the analysis of the separation process using interactive 3D renderings of the data and an additionalline chart that shows the computed surface area over time. This also allows us to validate the correctnessof the simulation method, since the surface area can be compared to the power law that describes the change inarea over time. Furthermore, we compare the isosurface that is based on the simulation kernel with an establishedmethod to extract smooth high-quality SPH surfaces. The comparison focuses on demonstrating the applicabilityfor data analysis in the context of material science, which is based on the resulting surface area and how wellthe two phases are separated with respect to the original particles. The evaluation was carried out together withexperts in material science.
Extracting Jacobi Structures in Reeb Spaces
(The Eurographics Association, 2014) Chattopadhyay, Amit; Carr, Hamish; Duke, David; Geng, Zhao; N. Elmqvist and M. Hlawitschka and J. Kennedy
Jacobi sets have been identified as significant in multi-field topological analysis, but are defined in the domain ofthe data rather than in the Reeb Space. This distinction is significant, as exploiting multi-field topology actuallydepends on the projection of the Jacobi set into the Reeb Space, and the details of its internal structure. Wetherefore introduce the Jacobi Structure of a Reeb Space which describes this, explain its relationships with boththe Jacobi Set and Fiber Analysis in mathematical topology, give an algorithm for computing the Jacobi Structurerecursively using a Multi-Dimensional Reeb Graph and illustrate it using an early implementation in VTK.
FluidDiagrams: Web-Based Information Visualisation using JavaScript and WebGL
(The Eurographics Association, 2014) Andrews, Keith; Wright, Benedict; N. Elmqvist and M. Hlawitschka and J. Kennedy
Much attention has been focused on the provision of information graphics and visualisations inside a web browser.Currently available infovis toolkits produce graphical output by either injecting SVG nodes into the DOM orusing the JavaScript Canvas 2D API. FluidDiagrams is a prototype information visualisation framework writtenin JavaScript which uses the WebGL 3D JavaScript API for its output, falling back to Canvas 2D as necessary,via the Three.js library. Six visualisations are currently implemented: bar chart and line chart, scatter plot andparallel coordinates for multidimensional data, and cone tree and hyperbolic for hierarchies.Anecdotally, visualisations using SVG nodes in the DOM for output can become rather sluggish when displayingmore than a few dozen items. Visualisations using Canvas 2D exhibit similarly slow performance. WebGLutilises hardware acceleration where available and promises much better performance for complex visualisations,potentially in the order of many thousands of items without becoming unresponsive.A comparison of parallel coordinates visualisations with 100 records in 20 dimensions compared three implementations:FluidDiagrams (WebGL), FluidDiagrams (Canvas 2D), and D3 (using SVG nodes). They achieved62, 6, and 10 frames per second respectively. The FluidDiagrams (WebGL) implementation was able to render1,000 records in 20 dimensions at 18 frames per second, compared to 1 and 6 respectively
Group-Level Graph Visualization Taxonomy
(The Eurographics Association, 2014) Saket, Bahador; Simonetto, Paolo; Kobourov, Stephen; N. Elmqvist and M. Hlawitschka and J. Kennedy
Task taxonomies for graph and network visualization focus on tasks commonly encountered when analyzing graphconnectivity and topology. However, in many application fields such as the social sciences (social networks),biology (protein interaction models), software engineering (program call graphs), connectivity and topology informationis intertwined with grouping and clustering information. Several recent visualization techniques, suchas BubbleSets, LineSets and GMap, make explicit use of grouping and clustering, but evaluating such visualizationshas been difficult due to the lack of standardized group-level tasks. With this in mind, our goal is to define anew set of tasks that assess group-level comprehension. We propose several types of group-level tasks and provideseveral examples of each type. Finally, we characterize some of the proposed tasks using a multi-level typology ofabstract visualization tasks. We believe that adding group-level tasks to the task taxonomy for graph visualizationwould make the taxonomy more useful for recent graph visualization techniques. It would help evaluators defineand categorize new tasks, and it would help generalize individual results collected in controlled experiments.
Interactive Design of Multidimensional Data Projection Layout
(The Eurographics Association, 2014) Molchanov, Vladimir; Linsen, Lars; N. Elmqvist and M. Hlawitschka and J. Kennedy
Projection methods support effective visualizations of multidimensional data. Linear projections are an importantsubclass, as they allow for interactive visual exploration of the data space and feature sensitivity analysis. Theuser interaction is usually based on an iterative modification of the projection matrix elements, for example, by theuse of a star coordinate widget. However, such interaction mechanisms become inefficient with increasing numberof dimensions. We propose to adapt the projection matrix by allowing the user to directly operate on the projectiondomain. The desired configuration of the projection layout is obtained by adjusting the positions of (freely chosen)control points. The update of the projection matrix is performed according to the interactive modifications bycomputing a least-square solution of a linear equation system. Changes can be tracked easily using animation. Weapply our method to classified multidimensional data and demonstrate that our approach allows for an intuitiveand effective design of projections with desired properties like improved class segregation or reduced clutter.
Interactive Visualisation of Automotive Warranty Data Using Novel Extensions of Chord Diagrams
(The Eurographics Association, 2014) Nicholas, Michael; Archambault, Daniel; Laramee, Robert S; N. Elmqvist and M. Hlawitschka and J. Kennedy
Descriptive and predictive analytics enable the automotive industry to be pro-active in its management of warrantyrepairs and the substantial unknown costs associated with future claims. Understanding what makes theircustomers most dissatisfied can assist manufacturers to take pro-active steps towards restoring satisfaction andincreasing the likelihood of customers making future purchases. Presented in this short work-in-progress paperare two techniques which enable the interactive visualisation of high-dimensional relationships within categoricaldata. Our Multi-Chord Diagram and Multi-Chord Glyph Diagram extend traditional Chord Diagrams, overcomingthe limitation of only depicting relationships between category pairs. We present these techniques in an application,addressing a real-world problem of visualising data relating to customer satisfaction following variouscombinations of automotive warranty repair. Although presented as a novel application for visualising customersatisfaction, we feel that the techniques described could also be applied to other scenarios involving the visualisationof variable high-dimensional relationships within categorical data.
Per-Fragment Image-based Flow Visualization using Interactive Surface Extraction from Unstructured Grids
(The Eurographics Association, 2014) Niebling, Florian; Becker, Martin; Schlegel, Thomas; N. Elmqvist and M. Hlawitschka and J. Kennedy
We present a method for image-based visualization of flow fields on unstructured grids. For interactive explorationof flow data from CFD simulations, we combine GPU-accelerated surface extraction methods and line integralconvolution (LIC) in a multi-pass algorithm. In contrast to other highly efficient methods, computation of streamlines is performed directly on the unstructured grid, where in previous methods the flow field had to be confinedto the extracted surface. The introduced algorithm is based on three passes: Surface extraction, rendering, andcomputation of stream lines to perform line integral convolution. Point location, a major performance factorin stream line computation on unstructured grids, can be greatly accelerated by reusing data from the surfaceextraction pass. This allows us to achieve interactive frame rates on current generation graphics hardware for thepost-processing of unstructured CFD datasets.
Redesigning the Sequence Logo with Glyph-based Approaches to Aid Interpretation
(The Eurographics Association, 2014) Maguire, Eamonn; Rocca-Serra, Philippe; Sansone, Susanna-Assunta; Chen, Min; N. Elmqvist and M. Hlawitschka and J. Kennedy
Sequence logos have been a prominent visualization tool in biological research since their inception two decadesago. Their primary use is in communicating conservation of biological sequences (protein, DNA or RNA), toindicate largest conservation at particular positions - namely places where only ever one or two possible residues(nucleotides or amino acids) are observed. Conservation is indicative of functional importance, as changes, beingselected against, reveal a loss of fitness for living organism or cells. Criticism of the sequence logo has longexisted, largely directed towards perception problems caused through use of letter height to indicate frequency.Here, we present a solution for use as a static image in publications or interactively on the web to address thereported flaws of the sequence logo. In addition to our improvements, we propose glyph based enhancements, tohighlight qualitatively relevant chemical insights resulting from residue substitution between sequences
Revisiting Perceptually Optimized Color Mapping for High-Dimensional Data Analysis
(The Eurographics Association, 2014) Mittelstädt, Sebastian; Bernard, Jürgen; Schreck, Tobias; Steiger, Martin; Kohlhammer, Jörn; Keim, Daniel A.; N. Elmqvist and M. Hlawitschka and J. Kennedy
Color is one of the most effective visual variables since it can be combined with other mappings and encodeinformation without using any additional space on the display. An important example where expressing additionalvisual dimensions is direly needed is the analysis of high-dimensional data. The property of perceptual linearity isdesirable in this application, because the user intuitively perceives clusters and relations among multi-dimensionaldata points. Many approaches use two-dimensional colormaps in their analysis, which are typically created byinterpolating in RGB, HSV or CIELAB color spaces. These approaches share the problem that the resulting colorsare either saturated and discriminative but not perceptual linear or vice versa. A solution that combines bothadvantages has been previously introduced by Kaski et al.; yet, this method is to date underutilized in InformationVisualization according to our literature analysis. The method maps high-dimensional data points into the CIELABcolor space by maintaining the relative perceived distances of data points and color discrimination. In this paper,we generalize and extend the method of Kaski et al. to provide perceptual uniform color mapping for visual analysisof high-dimensional data. Further, we evaluate the method and provide guidelines for different analysis tasks.
Studying Color Blending Perception for Data Visualization
(The Eurographics Association, 2014) Gama, Sandra; Gonçalves, Daniel; N. Elmqvist and M. Hlawitschka and J. Kennedy
Visualization is a powerful way to convey data, showing a great potential for joining and interrelating differentdata items. Nevertheless, when dealing with large amounts of data, visually merging different classes of informationposes several challenges. Color, however, due to its effectiveness for labeling and categorizing information,may be a solution to this shortcoming. Merging items with different colors may suggest mixing their original colors.This approach, while generating an immediately perceivable way to represent merged items, keeps contextthrough the association of the resulting color to its original provenience. We studied to which extent color blendingprovides users with the means to understand the provenience of data items by conducting a user study with73 subjects using CIE-LCh blending to ascertain (i) to which extent people are able to, given a particular color,understand its provenience, and (ii) the color model in which to perform color blending so that users find blendingintuitive. Results showed that people have difficulties in understanding blending of colors that are farther apart inthe color wheel and indicated that the CMYK model may show promise for representing blended colors.
Visibility-Driven Depth Determination of Surface Patches in Direct Volume Rendering
(The Eurographics Association, 2014) Stoppel, Sergej; Hege, Hans-Christian; Wiebel, Alexander; N. Elmqvist and M. Hlawitschka and J. Kennedy
This paper presents an algorithm called surfseek for selecting surfaces on the most visible features in directvolume rendering (DVR). The algorithm is based on a previously published technique (WYSIWYP) for picking 3Dlocations in DVR. The new algorithm projects a surface patch on the DVR image, consisting of multiple rays. Foreach ray the algorithm uses WYSIWYP or a variant of it to find the candidates for the most visible locations alongthe ray. Using these candidates the algorithm constructs a graph and computes a minimum cut on this graph.The minimum cut represents a visible and typically rather smooth surface. In the last step the selected surface isdisplayed. We provide examples for results using artificially generated and real-world data sets.
Visualizing Graphs as Maps with Contiguous Regions
(The Eurographics Association, 2014) Kobourov, Stephen; Pupyrev, Sergey; Simonetto, Paolo; N. Elmqvist and M. Hlawitschka and J. Kennedy
Relational datasets, which include clustering information, can be visualized with tools such as BubbleSets, Line-Sets, SOM, and GMap. The countries in SOM-based and GMap-based visualizations are fragmented, i.e., theyare represented by several disconnected regions. While BubbleSets and LineSets have contiguous regions, theseregions may overlap, even when the input clustering is non-overlapping. We describe two methods for creatingnon-fragmented and non-overlapping maps within the GMap framework. The first approach achieves contiguityby preserving the given embedding and creating a clustering based on geometric proximity. The second approachachieves contiguity by preserving the clustering information. The methods are quantitatively evaluated using embeddingand clustering metrics, and their usefulness is demonstrated with several real-world datasets and a fullyfunctionalonline system at gmap.cs.arizona.edu.

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