Search Results

Now showing 1 - 8 of 8
  • Item
    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.
  • Item
    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.
  • Item
    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.
  • Item
    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.
  • Item
    Interactive Rendering of Materials and Biological Structures on Atomic and Nanoscopic Scale
    (The Eurographics Association and Blackwell Publishing Ltd., 2012) Lindow, Norbert; Baum, Daniel; Hege, Hans-Christian; S. Bruckner, S. Miksch, and H. Pfister
    The properties of both inorganic and organic materials and the function of biological structures can often only be understood by analyzing them simultaneously on atomic and nanoscopic, if not mesoscopic, scale. Here, the problem arises to render millions to billions of atoms. We propose a method by which it is possible to interactively visualize atomic data, bridging five orders of magnitude in length scale. For this, we propose a simple yet efficient GPU rendering method that enables interactive visualization of biological structures consisting of up to several billions of atoms. To be able to load all atomic data onto the GPU, we exploit the fact that biological structures often consist of recurring molecular substructures. We also exploit that these objects typically are rendered opaquely, so that only a fraction of the atoms is visible. The method is demonstrated on both biological structures as well as atom probe tomography data of an inorganic specimen. We conclude with a discussion about when during ascension from atomic to mesoscopic scale level-of-detail representations become necessary.
  • Item
    Vortex Merge Graphs in Two-dimensional Unsteady Flow Fields
    (The Eurographics Association, 2012) Kasten, Jens; Hotz, Ingrid; Noack, Bernd; Hege, Hans-Christian; Miriah Meyer and Tino Weinkaufs
    Among the various existing vortex definitions, there is one class that relies on extremal structures of derived scalar fields. These are, e.g., vorticity,λ<sub>2</sub>, or the acceleration magnitude. This paper proposes a method to identify and track extremal-based vortex structures in 2D time-dependent flows. It is based on combinatorial scalar field topology. In contrast to previous methods, merge events are explicitly handled and represented in the resulting graph. An abstract representation of this vortex merge graph serves as basis for the comparison of the different scalar identifiers. The method is applied to numerically simulated flows of a mixing layer and a planar jet.
  • Item
    Perceptually Linear Parameter Variations
    (The Eurographics Association and John Wiley and Sons Ltd., 2012) Lindow, Norbert; Baum, Daniel; Hege, Hans-Christian; P. Cignoni and T. Ertl
    Most visual analysis tasks require interactive adjustment of parameter values. In general, a linear variation of a parameter, using for instance a GUI slider, changes the visual result in a perceptually non-linear way. This hampers interactive adjustment of parameters, especially in regions where rapid perceptual changes occur. Selecting a good parameter value therefore remains a time-consuming and often difficult task. We propose a novel technique to build a non-linear function that maps a new parameter to the original parameter. By prefixing this function to the original parameter and using the new parameter as input, a linear relationship between input and visual feedback is obtained. To construct the non-linear function, we measure the variation of the visual result using image metrics. Given a suitable perceptual image metric, perceptually linear image variations are achieved. We demonstrate the practical utility of our approach by implementing two common image metrics, a perceptual and a non-perceptual one, and by applying the method to a few visual analysis tasks.
  • Item
    Advected Tangent Curves: A General Scheme for Characteristic Curves of Flow Fields
    (The Eurographics Association and John Wiley and Sons Ltd., 2012) Weinkauf, Tino; Hege, Hans-Christian; Theisel, Holger; P. Cignoni and T. Ertl
    We present the first general scheme to describe all four types of characteristic curves of flow fields - stream, path, streak, and time lines - as tangent curves of a derived vector field. Thus, all these lines can be obtained by a simple integration of an autonomous ODE system. Our approach draws on the principal ideas of the recently introduced tangent curve description of streak lines. We provide the first description of time lines as tangent curves of a derived vector field, which could previously only be constructed in a geometric manner. Furthermore, our scheme gives rise to new types of curves. In particular, we introduce advected stream lines as a parameterfree variant of the time line metaphor. With our novel mathematical description of characteristic curves, a large number of feature extraction and analysis tools becomes available for all types of characteristic curves, which were previously only available for stream and path lines. We will highlight some of these possible applications including the computation of time line curvature fields and the extraction of cores of swirling advected stream lines.