EuroVisShort2016

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https://diglib.eg.org/handle/10.2312/15272

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Cavity and Pore Segmentation in 3D Images with Ambient Occlusion
(The Eurographics Association, 2016) Baum, Daniel; Titschack, Jürgen; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
Many natural objects contain pores and cavities that are filled with the same material that also surrounds the object. When such objects are imaged using, for example, computed tomography, the pores and cavities cannot be distinguished from the surrounding material by considering gray values and texture properties of the image. In this case, morphological operations are often used to fill the inner region. This is efficient, if the pore and cavity structures are small compared to the overall size of the object and if the object's shape is mainly convex. If this is not the case, the segmentation might be very difficult and may result in a lot of noise. We propose the usage of ambient occlusion for the segmentation of pores and cavities. One nice property of ambient occlusion is that it generates smooth scalar fields. Due to this smoothness property, a segmentation based on those fields will result in smooth boundaries at the pore and cavity openings. This is often desired, particularly when dealing with natural objects.
Spiral Theme Plot
(The Eurographics Association, 2016) Jiang, Shenghui; Fang, Shiaofen; Grannis, Shaun; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
We introduce a new visualization method for temporal data, Spiral Theme Plot, by combining ThemeRiver method, spiral patterns, and scatter plot technique. Similar to ThemeRiver, data in different categories (themes) are visualized in different bands, but also in a spiral pattern. Themes are stacked along a spiral curve, which represent the time axis. Individual data points are plotted within the regions of the themes, with various visual features. In addition to showing the overall theme patterns over time, this approach also shows plotting patterns within the themes. Compared to ThemeRiver, Spiral Theme Plot can accommodate longer time axis, and more importantly, can provide periodic patterns that are typically not available in ThemeRiver.
Visualizing Time-Dependent Data Using Dynamic t-SNE
(The Eurographics Association, 2016) Rauber, Paulo E.; Falcão, Alexandre X.; Telea, Alexandru C.; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
Many interesting processes can be represented as time-dependent datasets. We define a time-dependent dataset as a sequence of datasets captured at particular time steps. In such a sequence, each dataset is composed of observations (high-dimensional real vectors), and each observation has a corresponding observation across time steps. Dimensionality reduction provides a scalable alternative to create visualizations (projections) that enable insight into the structure of such datasets. However, applying dimensionality reduction independently for each dataset in a sequence may introduce unnecessary variability in the resulting sequence of projections, which makes tracking the evolution of the data significantly more challenging. We show that this issue affects t-SNE, a widely used dimensionality reduction technique. In this context, we propose dynamic t-SNE, an adaptation of t-SNE that introduces a controllable trade-off between temporal coherence and projection reliability. Our evaluation in two time-dependent datasets shows that dynamic t-SNE eliminates unnecessary temporal variability and encourages smooth changes between projections.
Clarifying Hypotheses by Sketching Data
(The Eurographics Association, 2016) Marasoiu, Mariana; Blackwell, Alan F.; Sarkar, Advait; Spott, Martin; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
Discussions between data analysts and colleagues or clients with no statistical background are difficult, as the analyst often has to teach and explain their statistical and domain knowledge. We investigate work practices of data analysts who collaborate with non-experts, and report findings regarding types of analysis, collaboration and availability of data. Based on these, we have created a tool to enhance collaboration between data analysts and their clients in the initial stages of the analytical process. Sketching time series data allows analysts to discuss expectations for later analysis. We propose function composition rather than freehand sketching, in order to structure the analyst-client conversation by independently expressing expected features in the data. We evaluate the usability of our prototype through two small studies, and report on user feedback for future iterations.
Visualization for Understanding Uncertainty in Activation Volumes for Deep Brain Stimulation
(The Eurographics Association, 2016) Hollister, Brad E.; Duffley, Gordon; Butson, Chris; Johnson, Chris; Rosen, Paul; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
We have created the Neurostimulation Uncertainty Viewer (nuView or nView) tool for exploring data arising from deep brain stimulation (DBS). Simulated volume of tissue activated (VTA), using clinical electrode placements, are recorded along with patient outcomes in the Unified Parkinson's disease rating scale (UPDRS). The data is volumetric and sparse, with multi-value patient results for each activated voxel in the simulation. nView provides a collection of visual methods to explore the activated tissue to enhance understanding of electrode usage for improved therapy with DBS.
SpaceCuts: Making Room for Visualizations on Maps
(The Eurographics Association, 2016) Buchmüller, Juri; Jäckle, Dominik; Stoffel, Florian; Keim, Daniel A.; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
Visual map features like streets, rail tracks, or rivers do not provide enough space to visualize multiple attributes on them. Related approaches to solve space issues distort the map with lenses, apply distortion techniques to the map geometry, or employ three dimensional visualizations. All these techniques come at the cost of distortion or overlapping of relevant map features or they even produce overlap of visualized data. In this paper, we present SpaceCuts, a technique to generate additional space for data visualization on maps that does not distort the map and introduces only minimal overlap by cutting the map along a geographic structure and pulling the resulting areas apart. Besides introducing the basic technique, we discuss possible interactions, further extensions, application scenarios, and outline potential future research.
Space Bundling for Continuous Parallel Coordinates
(The Eurographics Association, 2016) Palmas, Gregorio; Weinkauf, Tino; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
Continuous Parallel Coordinates (CPC) are a visualization technique used to perform multivariate analysis of different scalar fields defined on the same domain. While classic Parallel Coordinates draws a line for each sample point, a CPC visualization uses a density-based representation. An interesting possibility for the classic method is to highlight higher-dimensional clusters using edge bundling, where each line becomes a spline bent towards the centroid of the cluster. This often leads to expressive, illustrative visualizations. Unfortunately, bundling lines is not possible for CPC, as they are not involved in this method. In this paper, we propose a deformation of the visualization space for Continuous Parallel Coordinates that leads to similar results as those obtained through classic edge bundling. We achieve this by performing a curved-profile transformation in image space. The approach lends itself to a computationally lightweight GPU implementation. Furthermore, we provide intuitive interactions with the bundled clusters. We show several examples of our technique applied to a commonly available data set.
Visualizing Flow Fields Using Fractal Dimensions
(The Eurographics Association, 2016) Shen, Han-Wei; Vasko, Ross; Wenger, Rephael; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
Streamlines are a popular way of visualizing flow in vector fields. A major challenge in flow field visualization is selecting the streamlines to view. Rendering too many streamlines clutters the visualization and makes features of the field difficult to identify. Rendering too few streamlines causes viewers to completely miss features of the flow field not rendered. The fractal dimension of a streamline represents its space-filling properties. To identify complex or interesting streamlines, we build a regular grid of scalar values which represent the fractal dimension of streamlines around each grid vertex. Vortices and turbulent regions are often associated with regions of high fractal dimension. We use this scalar grid both to filter streamlines by fractal dimension and to identify and visualize regions containing vortices and turbulence. We describe an interactive tool which allows for quick streamline selection and visualization of regions containing vortices and turbulence.
Classic Techniques in New Domains: An Alternative Recipe
(The Eurographics Association, 2016) Monroe, Megan; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
In this paper, we adapt the classic technique of depicting a process as a structured workflow to suit the standard recipe. Cooking can be thought of as a small data, big user task. A single recipe encompasses only a small amount of information, but is utilized across a large user base. Our goal was to understand and measure the benefits of tailoring the presentation of a recipe to suit a specific faction of users. As such, our more technical rendering was paired with a technically proficient user base, resulting in dramatic gains in both the speed and accuracy with which the information was interpreted. These benefits serve to motivate our continued work towards automatically translating recipes into a structured data format that can be easily reconfigured into this and other representations of the information to enable a more customized experience across a large and varied user base.
VarVis: Visualizing Anatomical Variation in Branching Structures
(The Eurographics Association, 2016) Smit, Noeska; Kraima, Annelot; Jansma, Daniel; deRuiter, Marco; Eisemann, Elmar; Vilanova, Anna; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
Anatomical variations are naturally-occurring deviations from typical human anatomy. While these variations are considered normal and non-pathological, they are still of interest in clinical practice for medical specialists such as radiologists and transplantation surgeons. The complex variations in branching structures, for instance in arteries or nerves, are currently visualized side-by-side in illustrations or expressed using plain text in medical publications. In this work, we present a novel way of visualizing anatomical variations in complex branching structures for educational purposes: VarVis. VarVis consists of several linked views that reveal global and local similarities and differences in the variations. We propose a novel graph representation to provide an overview of the topological changes. Our solution involves a topological similarity measure, which allows the user to select variations at a global level based on their degree of similarity. After a selection is made, local topological differences can be interactively explored using illustrations and topology graphs. We also incorporate additional information regarding the probability of the various cases. Our solution has several advantages over traditional approaches, which we demonstrate in an evaluation.
Towards Visual Mega-Analysis of Voxel-based Measurement in Brain Cohorts
(The Eurographics Association, 2016) Zhang, Guohao; Kochunov, Peter; Hong, Elliot; Carr, Hamish; Chen, Jian; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
We present a visualization prototype for comparative analysis of factional anisotropy (FA) distributions constructed from threedimensional (3D) brain diffusion tensor imaging (DTI) in brain cohorts. The prototype lets brain scientists examine metaanalysis (the pooled analysis of multiple smaller trials or multi-site studies) results for identifying differences in cohorts. Interactive side-by-side bar charts show multiple statistical results of FA comparisons in regions of interest (ROIs) defined by user-chosen atlas. An occlusion-free two-dimensional (2D) semantic merge tree further displays the global distribution of FA values. Two histograms on each tree arc reveal voxel-based FA distributions represented by that arc branch in cohorts. Interaction techniques support brushing-and-linking of local and global ROIs queries. ROIs can be defined from atlas or select through interaction. We report validation results in a case study and an interview.
Manifold Visualization via Short Walks
(The Eurographics Association, 2016) Zhao, Yang; Tasoulis, Sotirios; Roos, Teemu; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
Visualizing low-dimensional non-linear manifolds underlying high-dimensional data is a challenging data analysis problem. Different manifold visualization methods can be characterized by the associated definitions of proximity between highdimensional data points and score functions that lead to different low-dimensional embeddings, preserving different features in the data. The geodesic distance is a popular and well-justified metric. However, it is very hard to approximate reliably from finite samples especially between far apart points. In this paper, we propose a new method called Minimap. The basic idea is to approximate local geodesic distances by shortest paths along a neighborhood graph with an additional penalizing factor based on the number of steps in the path. Embedding the resulting metric by Sammon mapping further enhances the local structures at the expense of long distances that tend to be less reliable. Experiments on real-world benchmarks suggest that Minimap can robustly visualize manifold structures.
CompaRing: Reducing Costs of Visual Comparison
(The Eurographics Association, 2016) Tominski, Christian; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
Comparison is a frequent task when analyzing data. In visualization, comparison tasks are naturally carried out based on a visual representation of the data. Visual comparison allows us to gain insight where plain computations of numerical differences alone cannot grasp the complex interdependencies in the data. Yet, visual comparison also comes at a cost. There are costs when interpreting the visual representation and costs when interactively carrying out the comparison.We present techniques to reduce some of the costs associated with visual comparison. We address cognitive costs for comparing objects that are spread across a visual representation and interaction costs for selecting and navigating between objects to be compared. Our techniques are illustrated by the example of comparing geographic regions in choropleth maps.
Analytic Behavior and Trust Building in Visual Analytics
(The Eurographics Association, 2016) Sacha, Dominik; Boesecke, Ina; Fuchs, Johannes; Keim, Daniel A.; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
Visual Analytics (VA) is a collaborative process between human and computer, where analysts are performing numerous interactions and reasoning activities. This paper presents our current progress in developing a note taking environment (NTE) that can be plugged to any VA system. The NTE supports the analysis process on the one hand, and captures user interactions on the other hand. Our aim is to integrate human lower- (exploration) with higher- (verification) level analytic processes and to investigate those together related to further human factors, such as trust building. We conducted a user study to collect and investigate analytic provenance data. Our early results reveal that analysis strategies and trust building are very individual. However, we were able to identify significant correlations between trust levels and interactions of particular participants.
EuroVis Short Papers 2016: Frontmatter
(Eurographics Association, 2016) Enrico Bertini; Niklas Elmqvist; Thomas Wischgoll;
Error Estimates for Lagrangian Flow Field Representations
(The Eurographics Association, 2016) Hummel, Mathias; Bujack, Roxana; Joy, Kenneth I.; Garth, Christoph; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
Computing power outpaces I/O bandwidth in modern high performance computers, which leads to temporal sparsity in flow simulation data. Experiments show that Lagrangian flow representations (where pathlines are retrieved from short-time flow maps using interpolation and concatenation) outperform their Eulerian counterparts in advection tasks under these circumstances. Inspired by these results, we present the theoretical estimate of the Lagrangian error for individual pathlines, depending on the choice of temporal as well as spatial resolution. In-situ, this measure can be used to steer the output resolution and post-hoc, it can be used to visualize the uncertainty of the pathlines. To validate our theoretical bounds, we evaluate the measured and the estimated error for several example flow fields.
Fast 3D Thinning of Medical Image Data based on Local Neighborhood Lookups
(The Eurographics Association, 2016) Post, Tobias; Gillmann, Christina; Wischgoll, Thomas; Hagen, Hans; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
Three-dimensional thinning is an important task in medical image processing when performing quantitative analysis on structures, such as bones and vessels. For researchers of this domain a fast, robust and easy to access implementation is required. The Insight Segmentation and Registration Toolkit (ITK) is often used in medical image processing and visualization as it offers a wide range of ready to use algorithms. Unfortunately, its thinning implementation is computationally expensive and can introduce errors in the thinning process. This paper presents an implementation that is ready to use for thinning of medical image data. The implemented algorithm evaluates a moving local neighborhood window to find deletable voxels in the medical image. To reduce the computational effort, all possible combinations of a local neighborhood are stored in a precomputed lookup table. To show the effectiveness of this approach, the presented implementation is compared to the performance of the ITK library.
LMML: Initial Developments of an Integrated Environment for Forensic Data Visualization
(The Eurographics Association, 2016) Boussejra, Malik Olivier; Adachi, Noboru; Shojo, Hideki; Takahashi, Ryohei; Fujishiro, Issei; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
Fighting against crime is paramount to any society, maybe more today than ever before. Tools to fight and elucidate crime are rooted in forensic science. Through the autopsy of a body, we can answer a whole range of questions as to how death happened and come up with explanations and counter-measures so that the same dire circumstance does not happen again. Now, because the reports collecting the data are written manually, the recording of the data collected through traditional autopsy still is a cumbersome, time-consuming task. Our framework, based on a mark-up language (that we dubbed ''LMML'') to store, describe and arrange forensic data, aims at overcoming those issues. Our contribution is twofold: the design of the syntax and semantics of LMML, and the conception of an interface to create, edit, analyse or query files written in that language. Thus, this framework allows quicker, smoother input of forensic data, for better automation and visualization thereof, so that they can be used by medical examiners, investigators, as well as judicial courts.
Detecting and Visualizing Rip Current Using Optical Flow
(The Eurographics Association, 2016) Philip, Shweta; Pang, Alex; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
Rip current are fast moving and narrow currents that are strongest near the beach. They are dangerous not only for novice but also experienced swimmers. Once caught in the current, the flow of the water pulls the person away from the beach. Many people in panic try to swim against the current and end up drowning due to exhaustion since these currents are usually faster than the speed at which one can swim. They have led to the drowning deaths of more than 100 beachgoers each year in United States alone [USL16]. For a knowledgeable person, these rip-currents are fairly easy to spot. But they are a threat to most people who are unaware of rip-currents or who do not know how to identify them. In this paper, we discuss a novel approach that uses optical flow to detect rip currents and then visualize them in an intuitive manner.
Interactive Web-based Visualization for Accessibility Mapping of Transportation Networks
(The Eurographics Association, 2016) Schoedon, Alexander; Trapp, Matthias; Hollburg, Henning; Döllner, Jürgen; Enrico Bertini and Niklas Elmqvist and Thomas Wischgoll
Accessibility is a fundamental aspect in transportation, routing, and spare-time activity planning concerning traveling in modern cities. In this context, interactive web-based accessibility-map visualization techniques and systems are important tools for provisioning, exploration, analysis, and assessment of multi-modal and location-based travel time data and routing information. To enable their effective application, such interactive visualization techniques demands for flexible mappings with respect to user-adjustable parameters such as maximum travel times, the types of transportation used, or used color schemes. However, traditional approaches for web-based visualization of accessibility-maps do not allow this degree of parametrization without significant latencies introduced by required data processing and transmission between the routing server and the visualization client. This paper presents a novel web-based visualization technique that allows for efficient client-side mapping and rendering of accessibility data onto transportation networks using WebGL and the OpenGL transmission format. A performance evaluation and comparison shows the superior performance of the approach over alternative implementations.

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