Search Results

Now showing 1 - 10 of 21
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    Analysis of Vortex Merge Graphs
    (The Eurographics Association, 2012) Kasten, Jens; Zoufahl, Andre; Hege, Hans-Christian; Hotz, Ingrid; Michael Goesele and Thorsten Grosch and Holger Theisel and Klaus Toennies and Bernhard Preim
    We propose an analysis framework to investigate different flow quantities such as vorticity, λ<sub>2</sub> or the acceleration magnitude along vortex merge graphs and within their regions of influence. The explicit extraction of vortex merge graphs enables the application of statistical tools to investigate the vortex core lines themselves. The analysis tool provides common plots as scatter plots and parallel coordinates to explore the correlation of different quantities. An abstract representation of the vortex merge graph highlights birth, death and merges of vortices. Interactive picking of substructures supports a closer insepection of single vortices and their evolution. A further step integrates the regions of influence into the statistical analysis. Minima, maxima, median, mean and other percentiles of the measures along the vortex merge graph and its regions are visualized. The usability of the framework is demonstrated using a simulated flow data set of a mixing layer and a jet.
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    Synaptic Connectivity in Anatomically Realistic Neural Networks: Modeling and Visual Analysis
    (The Eurographics Association, 2012) Dercksen, Vincent J.; Egger, Robert; Hege, Hans-Christian; Oberlaender, Marcel; Timo Ropinski and Anders Ynnerman and Charl Botha and Jos Roerdink
    The structural organization of neural circuitry is an important determinant of brain function. Thus, knowing the brain's wiring (the connectome) is key to understanding how it works. For example, understanding how sensory information is translated into behavior requires a comprehensive view of the microcircuits performing this translation at the level of individual neurons and synapses. Obtaining a wiring diagram, however, is nontrivial due to size, complexity and accessibility of the involved brain regions. Even when such data were available, it were difficult to analyze. Here we describe how a network of around 0.5 million neurons and their synaptic connections, representing the vibrissal area of the rat primary somatosensory cortex, can be reconstructed. Furthermore, we present a framework for visual exploration of synaptic connectivity between (groups of) neurons within this model. It includes, first, the Cortical Column Connectivity Viewer (CCCV) that provides a hybrid abstract/spatial representation of the connections between neurons of different cell types and/or in different cortical columns. Second, it comprises a 3D view of cell type-specific synapse positions on selected morphologies. This framework is thus an effective tool to visually explore structural organization principles at the population, individual neuron and synapse levels.
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    3D Strokes on Visible Structures in Direct Volume Rendering
    (The Eurographics Association, 2013) Wiebel, Alexander; Preis, Philipp; Vos, Frans M.; Hege, Hans-Christian; Mario Hlawitschka and Tino Weinkauf
    In this paper we describe VisiTrace, a novel technique to draw 3D lines in direct volume rendered images. It allows to draw strokes in the 2D space of the screen to produce 3D lines that run on top or in the center of structures visible in the rendering. It is able to ignore structures that shortly occlude the structure that has been visible at the start of the stroke. For this purpose a shortest path algorithm finding the optimal curve in a specially designed graph is employed. We demonstrate the usefulness of the technique by applying it to image data from medicine and engineering, and show how it can be used to mark structures in the example data, and to automatically obtain good views toward these structures enabling faster navigation in the rendering.
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    Nonparametric Models for Uncertainty Visualization
    (The Eurographics Association and Blackwell Publishing Ltd., 2013) Pöthkow, Kai; Hege, Hans-Christian; B. Preim, P. Rheingans, and H. Theisel
    An uncertain (scalar, vector, tensor) field is usually perceived as a discrete random field with a priori unknown probability distributions. To compute derived probabilities, e.g. for the occurrence of certain features, an appropriate probabilistic model has to be selected. The majority of previous approaches in uncertainty visualization were restricted to Gaussian fields. In this paper we extend these approaches to nonparametric models, which are much more flexible, as they can represent various types of distributions, including multimodal and skewed ones. We present three examples of nonparametric representations: (a) empirical distributions, (b) histograms and (c) kernel density estimates (KDE). While the first is a direct representation of the ensemble data, the latter two use reconstructed probability density functions of continuous random variables. For KDE we propose an approach to compute valid consistent marginal distributions and to efficiently capture correlations using a principal component transformation. Furthermore, we use automatic bandwidth selection, obtaining a model for probabilistic local feature extraction. The methods are demonstrated by computing probabilities of level crossings, critical points and vortex cores in simulated biofluid dynamics and climate data.
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    Atomic Accessibility Radii for Molecular Dynamics Analysis
    (The Eurographics Association, 2018) Lindow, Norbert; Baum, Daniel; Hege, Hans-Christian; Jan Byska and Michael Krone and Björn Sommer
    In molecular structure analysis and visualization, the molecule's atoms are often modeled as hard spheres parametrized by their positions and radii. While the atom positions result from experiments or molecular simulations, for the radii typically values are taken from literature. Most often, van der Waals (vdW) radii are used, for which diverse values exist. As a consequence, different visualization and analysis tools use different atomic radii, and the analyses are less objective than often believed. Furthermore, for the geometric accessibility analysis of molecular structures, vdW radii are not well suited. The reason is that during the molecular dynamics simulation, depending on the force field and the kinetic energy in the system, non-bonded atoms can come so close to each other that their vdW spheres intersect. In this paper, we introduce a new kind of atomic radius, called 'atomic accessibility radius', that better characterizes the accessibility of an atom in a given molecular trajectory. The new radii reflect the movement possibilities of atoms in the simulated physical system. They are computed by solving a linear program that maximizes the radii of the atoms under the constraint that non-bonded spheres do not intersect in the considered molecular trajectory. Using this data-driven approach, the actual accessibility of atoms can be visualized more precisely.
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    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.
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    Probabilistic Local Features in Uncertain Vector Fields with Spatial Correlation
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Petz, Christoph; Pöthkow, Kai; Hege, Hans-Christian; S. Bruckner, S. Miksch, and H. Pfister
    In this paper methods for extraction of local features in crisp vector fields are extended to uncertain fields. While in a crisp field local features are either present or absent at some location, in an uncertain field they are present with some probability. We model sampled uncertain vector fields by discrete Gaussian random fields with empirically estimated spatial correlations. The variability of the random fields in a spatial neighborhood is characterized by marginal distributions. Probabilities for the presence of local features are formulated in terms of low-dimensional integrals over such marginal distributions. Specifically, we define probabilistic equivalents for critical points and vortex cores. The probabilities are computed by Monte Carlo integration. For identification of critical points and cores of swirling motion we employ the Poincaré index and the criterion by Sujudi and Haimes. In contrast to previous global methods we take a local perspective and directly extract features in divergence-free fields as well. The method is able to detect saddle points in a straight forward way and works on various grid types. It is demonstrated by applying it to simulated unsteady flows of biofluid and climate dynamics.
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    Exploring Uncertainty in Image Segmentation Ensembles
    (The Eurographics Association, 2018) Fröhler, Bernhard; Möller, Torsten; Weissenböck, Johannes; Hege, Hans-Christian; Kastner, Johann; Heinzl, Christoph; Anna Puig and Renata Raidou
    Finding the most accurate image segmentation involves analyzing results from different algorithms or parameterizations. In this work, we identify different types of uncertainty in this analysis that are represented by the results of probabilistic algorithms, by the local variability in the segmentation, and by the variability across the segmentation ensemble. We propose visualization techniques for the analysis of such types of uncertainties in segmentation ensembles. For a global analysis we provide overview visualizations in the image domain as well as in the label space. Our probability probing and scatter plot based techniques facilitate a local analysis. We evaluate our techniques using a case study on industrial computed tomography data.
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    Thin-Volume Visualization on Curved Domains
    (The Eurographics Association and John Wiley & Sons Ltd., 2021) Herter, Felix; Hege, Hans-Christian; Hadwiger, Markus; Lepper, Verena; Baum, Daniel; Borgo, Rita and Marai, G. Elisabeta and Landesberger, Tatiana von
    Thin, curved structures occur in many volumetric datasets. Their analysis using classical volume rendering is difficult because parts of such structures can bend away or hide behind occluding elements. This problem cannot be fully compensated by effective navigation alone, as structure-adapted navigation in the volume is cumbersome and only parts of the structure are visible in each view. We solve this problem by rendering a spatially transformed view of the volume so that an unobstructed visualization of the entire curved structure is obtained. As a result, simple and intuitive navigation becomes possible. The domain of the spatial transform is defined by a triangle mesh that is topologically equivalent to an open disc and that approximates the structure of interest. The rendering is based on ray-casting, in which the rays traverse the original volume. In order to carve out volumes of varying thicknesses, the lengths of the rays as well as the positions of the mesh vertices can be easily modified by interactive painting under view control. We describe a prototypical implementation and demonstrate the interactive visual inspection of complex structures from digital humanities, biology, medicine, and material sciences. The visual representation of the structure as a whole allows for easy inspection of interesting substructures in their original spatial context. Overall, we show that thin, curved structures in volumetric data can be excellently visualized using ray-casting-based volume rendering of transformed views defined by guiding surface meshes, supplemented by interactive, local modifications of ray lengths and vertex positions.
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    Conveying Archaeological Contexts to Museum Visitors: Case Study Pergamon Exhibition
    (The Eurographics Association, 2012) Klindt, Marco; Prohaska, Steffen; Baum, Daniel; Hege, Hans-Christian; David Arnold and Jaime Kaminski and Franco Niccolucci and Andre Stork
    Reconnecting the audience of an exhibition to the archaeological context of ancient artefacts and explaining their reception histories is a great challenge. Employing digital devices to support the understanding of connections between exhibits and their past, creates the additional challenge of developing a system that not only achieves comprehension but is also accessible to all museum visitors. We have devised a concept and an implementation of a kiosk application for conveying these contexts and evaluated the effectiveness in a special exhibition about the ancient city of Pergamon. We found that using postcards that are accessible through different navigation views as the central metaphor is an effective way for museum visitors to interact with and to spent time exploring contexts about exhibits.