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Now showing 1 - 10 of 82
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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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    Freeform Shadow Boundary Editing
    (The Eurographics Association and Blackwell Publishing Ltd., 2013) Mattausch, Oliver; Igarashi, Takeo; Wimmer, Michael; I. Navazo, P. Poulin
    We present an algorithm for artistically modifying physically based shadows. With our tool, an artist can directly edit the shadow boundaries in the scene in an intuitive fashion similar to freeform curve editing. Our algorithm then makes these shadow edits consistent with respect to varying light directions and scene configurations, by creating a shadow mesh from the new silhouettes. The shadow mesh helps a modified shadow volume algorithm cast shadows that conform to the artistic shadow boundary edits, while providing plausible interaction with dynamic environments, including animation of both characters and light sources. Our algorithm provides significantly more fine-grained local and direct control than previous artistic light editing methods, which makes it simple to adjust the shadows in a scene to reach a particular effect, or to create interesting shadow shapes and shadow animations. All cases are handled with a single intuitive interface, be it soft shadows, or (self-)shadows on arbitrary receivers.
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    Interactive Comparative Visualization of Multimodal Brain Tumor Segmentation Data
    (The Eurographics Association, 2013) Lindemann, Florian; Laukamp, Kai; Jacobs, Andreas H.; Hinrichs, Klaus; Michael Bronstein and Jean Favre and Kai Hormann
    We present a visualization system for the analysis of multi-modal segmentation data of brain tumors. Our system is designed to allow researchers and doctors a further investigation of segmented tumor data beyond a quantitative assessment of size. This includes the efficient visual analysis of the shape and relative position of the different, often overlapping segmented data modalities, using high quality 3D renderings of the data. Furthermore, our system provides visualization methods to compare tumor segmentation volumes acquired at various points of time, which helps the user to explore changes in shape and size before and after treatment. We also employ two novel interactive diagrams which allow the user to quickly navigate and analyze overlapping tumor regions. All methods are assembled and linked in a multi-view framework.
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    Visualisation Strategies for Modelling and Simulation Using Geoscientific Data
    (The Eurographics Association, 2013) Rink, K.; Bilke, L.; O. Kolditz; O. Kolditz and K. Rink and G. Scheuermann
    We present a number of strategies to visualise a wide range of geoscientific data for the modelling of natural phenomena. Input data sets as well as simulation results of hydrological or thermal processes can be assessed and potential problems when incorporating data sets in a model can be detected and resolved. Algorithms for the demonstration of modelling case studies within specialised environments are presented and examples are given for a region in central Germany.
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    Multi-Perspective Detail+Overview Visualization for 3D Building Exploration
    (The Eurographics Association, 2013) Pasewaldt, Sebastian; Trapp, Matthias; Döllner, Jürgen; Silvester Czanner and Wen Tang
    Virtual 3D building models, as key elements of virtual 3D city models, are used in a growing number of application domains, such as geoanalysis, disaster management and architectural planning. Visualization systems for such building models often rely on perspective or orthogonal projections using a single viewpoint. Therefore, the exploration of a complete model requires a user to change the viewpoint multiple times and to memorize the content of each view to obtain a comprehensive mental model. Since this is usually a time-consuming task, which implies context switching, current visualization systems use multiple viewports to simultaneously depict an object from different perspectives. Our approach extends the idea of multiple viewports by combining two linked views for the interactive exploration of virtual 3D buildings model and their façades. In contrast to traditional approaches, we automatically generate a multi-perspective view that simultaneously depicts all façades of the building in one overview image. This facilitates the process of obtaining overviews and supports fast and direct navigation to various points-of-interest. We describe the concept and implementations of our Multiple-Center-of-Projection camera model for real-time multi-perspective image synthesis. Further, we provide insights into different interaction techniques for linked multi-perspective views and outline approaches of future work.
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    Robust Fitting on Poorly Sampled Data for Surface Light Field Rendering and Image Relighting
    (The Eurographics Association and Blackwell Publishing Ltd., 2013) Vanhoey, K.; Sauvage, B.; Génevaux, O.; Larue, F.; Dischler, J.‐M.; Holly Rushmeier and Oliver Deussen
    Two‐dimensional (2D) parametric colour functions are widely used in Image‐Based Rendering and Image Relighting. They make it possible to express the colour of a point depending on a continuous directional parameter: the viewing or the incident light direction. Producing such functions from acquired data is promising but difficult. Indeed, an intensive acquisition process resulting in dense and uniform sampling is not always possible. Conversely, a simpler acquisition process results in sparse, scattered and noisy data on which parametric functions can hardly be fitted without introducing artefacts. Within this context, we present two contributions. The first one is a robust least‐squares‐based method for fitting 2D parametric colour functions on sparse and scattered data. Our method works for any amount and distribution of acquired data, as well as for any function expressed as a linear combination of basis functions. We tested our fitting for both image‐based rendering (surface light fields) and image relighting using polynomials and spherical harmonics. The second one is a statistical analysis to measure the robustness of any fitting method. This measure assesses a trade‐off between precision of the fitting and stability with respect to input sampling conditions. This analysis along with visual results confirm that our fitting method is robust and reduces reconstruction artefacts for poorly sampled data while preserving the precision for a dense and uniform sampling.Generating surface light fields from real acquisition campaigns' data often leads to robustness issues that are due to irregular distribution and sparsity of the photographic sampling. Within this context, we present a robust least‐squares‐based method for fitting 2D parametric colour functions on sparse and scattered data. Moreover, we provide a statistical analysis to measure the robustness of such fitting approaches. The proposed method allows, on one hand, for high‐quality reconstructions in good sampling conditions and, on the other hand, for robust and predictable reconstructions in poor sampling conditions.
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    Shape Matching via Quotient Spaces
    (The Eurographics Association and Blackwell Publishing Ltd., 2013) Ovsjanikov, Maks; Mérigot, Quentin; Patraucean, Viorica; Guibas, Leonidas; Yaron Lipman and Hao Zhang
    We introduce a novel method for non-rigid shape matching, designed to address the symmetric ambiguity problem present when matching shapes with intrinsic symmetries. Unlike the majority of existing methods which try to overcome this ambiguity by sampling a set of landmark correspondences, we address this problem directly by performing shape matching in an appropriate quotient space, where the symmetry has been identified and factored out. This allows us to both simplify the shape matching problem by matching between subspaces, and to return multiple solutions with equally good dense correspondences. Remarkably, both symmetry detection and shape matching are done without establishing any landmark correspondences between either points or parts of the shapes. This allows us to avoid an expensive combinatorial search present in most intrinsic symmetry detection and shape matching methods. We compare our technique with state-of-the-art methods and show that superior performance can be achieved both when the symmetry on each shape is known and when it needs to be estimated.
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    Vessel Visualization using Curvicircular Feature Aggregation
    (The Eurographics Association and Blackwell Publishing Ltd., 2013) Mistelbauer, Gabriel; Morar, Anca; Varchola, Andrej; Schernthaner, Rüdiger; Baclija, Ivan; Köchl, Arnold; Kanitsar, Armin; Bruckner, Stefan; Gröller, Eduard; B. Preim, P. Rheingans, and H. Theisel
    Radiological investigations are common medical practice for the diagnosis of peripheral vascular diseases. Existing visualization methods such as Curved Planar Reformation (CPR) depict calcifications on vessel walls to determine if blood is still able to flow. While it is possible with conventional CPR methods to examine the whole vessel lumen by rotating around the centerline of a vessel, we propose Curvicircular Feature Aggregation (CFA), which aggregates these rotated images into a single view. By eliminating the need for rotation, vessels can be investigated by inspecting only one image. This method can be used as a guidance and visual analysis tool for treatment planning. We present applications of this technique in the medical domain and give feedback from radiologists.
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    Modeling Incremental Visualizations
    (The Eurographics Association, 2013) Angelini, Marco; Santucci, Giuseppe; M. Pohl and H. Schumann
    An increasing number of applications call for the incremental/iterative drawing of a visualization. That is an obvious requirement when dealing with continuously changing data, like the emerging field of data streams or scientific visualizations that have the burden of rendering complex and evolving physical phenomena. This paper postulates that the same need is rising in the field of Visual Analytics and cloud based applications and, in order to provide a support for such processes, it presents a formal model for characterizing the iterative drawing of a visualization, describing the practical issues and outlining the main parameters that can be used to drive and evaluate the whole process. The proposed model is general enough to capture all of the above presented scenarios. Two examples are presented, showing the role that such a model can play in designing iterative visualizations.
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    Simulation of Time-of-Flight Sensors using Global Illumination
    (The Eurographics Association, 2013) Meister, Stephan; Nair, Rahul; Kondermann, Daniel; Michael Bronstein and Jean Favre and Kai Hormann
    Time-of-Flight (ToF) cameras use specialized sensors and modulated infrared light to simultaneously obtain depth, amplitude and intensity images. Depth images from such cameras suffer from various errors which exhibit a more complex behavior than traditional intensity images. Of these errors, the phenomenon of multi-reflection or multipath interference poses the biggest challenge to researchers. It is caused by indirect light paths between camera and light source and is therefore dependent on scene geometry. While simulated data can be used for ground truth evaluation and whitebox testing, current simulators do not model multipath effects. The method we present is capable of simulating all scene-dependant effects by taking global illumination into consideration. This is accomplished by modifying a bidirectional path tracing algorithm such that it takes the time-dependent propagation of modulated light in a scene into consideration. Furthermore, by combination of the proposed method with a previous hardware simulator we are capable of reproducing all effects in ToF cameras. The system was validated both on test targets with known real Time of Flight camera responses as well as qualitatively on a more complex room scene. The simulator as well as the source code is available at http://hci.iwr.uni-heidelberg.de/Benchmarks/.