Search Results

Now showing 1 - 10 of 14
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    Skeleton Graph Generation for Feature Shape Description
    (The Eurographics Association, 2000) Reinders, Freek; Jacobson, Melvin E.D.; Post, Frits H.; W. de Leeuw and R. van Liere
    An essential step in feature extraction is the calculation of attribute sets describing the characteristics of a feature. Often, attribute sets include the position, size, and orientation of the feature. These attributes are very important, but they do not provide a good approximation of the shape of a feature. For better shape description, a more sophisticated method is needed. This paper describes a method that extracts a binary skeleton of a feature, and transforms it into a graphical representation: the skeleton-graph. This graph represents the original skeleton with controlled precision, and contains the essential topology and geometry of the skeleton. In addition, distance information is used to generate a simplified reconstruction of the original 3D feature shape, which can also be used as an iconic object for visualization.
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    Spring-Based Manipulation Tools for Virtual Environments
    (The Eurographics Association, 2001) Koutek, Michal; Post, Frits H.; B. Froehlich and J. Deisinger and H.-J. Bullinger
    In this paper we present new tools for user interaction with virtual worlds, to bring more natural behavior into the manipulation of objects in virtual environments. We present some principles of physically realistic behavior of virtual objects and a set of user input techniques suitable for semi-immersive VR devices such as the Responsive Workbench. We introduce springs, spring-forks and spring-probes as new tools for assisting direct manipulation of objects in VEs. In this paper we focus on controlling rotational motions.
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    Dynamics in Interaction on the Responsive Workbench
    (The Eurographics Association, 2000) Koutek, Michal; Post, Frits H.; J. D. Mulder and R. van Liere
    In this paper we present a different view of user interaction with virtual worlds. We start from the question: how can we bring more natural object behavior into virtual environments? Currently, objects in VR applications often behave in a very un-natural way. Incorporation of physical laws in the virtual environment, together with monitoring natural user actions and behavior is desirable.We present some principles of physically more realistic behavior of virtual objects and a set of user input techniques suitable for semi-immersive VR devices such as the Responsive Workbench. We introduce springs as a new tool for assisting direct manipulation of objects in VEs.
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    Selective Visualization of Vector Fields
    (Blackwell Science Ltd and the Eurographics Association, 1994) van Walsum, Theo; Post, Frits H.
    In this paper, we present an approach to selective vector field visualization. This selective visualization approach consists of three stages: selectdon creation, selection processing and selective visualization mapping. It is described how selected regions, called selections, can be represented and created, how selections can be processed and how they can be used in the visualization mapping. Combination of these techniques with a standard visualization pipeline improves the visualization process and offers new facilities for visualization. Examples of selective visualization of fluid flow datasets are provided.
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    Virtual Spring Manipulators for Particle Steering in Molecular Dynamics on the ResponsiveWorkbench
    (The Eurographics Association, 2002) Koutek, Michal; Hees, Jeroen van; Post, Frits H.; Bakker, A.F.; S. Mueller and W. Stuerzlinger
    In this paper we present new virtual spring manipulator-based tools for steering particles in molecular dynamics simulations in virtual environments. We briefly overview the MolDRIVE system, our visualization and computational steering environment for molecular dynamics real-time simulations, which is the platform for our particle steering implementation. Our study concentrates on visual feedback tools. We compare a basic virtual particle steering method with two other methods using a spring manipulator. The first just creates a visual feedback of a flexible connection between the user s interaction device and the steered particle, while the second technique creates a visual illusion of force feedback. The user can, through the spring manipulator, exert a force on the manipulated particle in the MD simulation. All presented particle steering tools are intuitive and easy to use.
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    Interactive Previewing for Transfer Function Specification in Volume Rendering
    (The Eurographics Association, 2002) Botha, Charl P.; Post, Frits H.; D. Ebert and P. Brunet and I. Navazo
    This paper presents a new technique for supplying meaningful visual feedback during direct volume rendering transfer function specification. The technique uses meta-data calculated during a pre-processing step to generate interactively an approximate volume rendering that is voxel-registered with a single user-selected slice. Because of the registration, this preview can easily be alpha-blended with a grey-scale image of the data that is being volume rendered. In this way, the user gets real-time visual feedback on her transfer function specification with regards to both the expected composited optical properties and the "fidelity" (how closely the rendering matches the original data) of the resulting rendering.
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    Vortex Tracking and Visualisation in a Flow Past a Tapered Cylinder
    (Blackwell Publishers, Inc and the Eurographics Association, 2002) Reinders, Freek; Sadarjoen, I. Ari; Vrolijk, Benjamin; Post, Frits H.
    In this paper we explore a novel combined application of two of our existing visualisation techniques to thetracking of 3D vortex tubes in an unsteady flow. The applied techniques are the winding-angle vortex extractiontechnique based on streamline geometry, and the attribute-based feature tracking technique. We have applied theseto the well-known case of an unsteady 3D flow past a tapered cylinder.First, 2D vortices are detected in a number of horizontal slices for each time step, by means of the winding-anglevortex extraction method. For each 2D vortex a number of attributes are calculated and stored. These vorticesare visualised by a special type of ellipse icons, showing the position, shape and rotational direction and speed ineach slice.Next, for each time step, 3D vortex tubes are constructed from the 2D vortices by applying the feature trackingprocedure in a spatial dimension to connect the corresponding vortices in adjacent slices. The result is a graphattribute set with the 2D vortex attributes in the nodes and the spatial correspondences as edges.Finally, the 3D vortex tubes are tracked in time using the same tracking procedure, for finding the correspondingtubes in successive time steps. The result is a description of the evolution of the 3D vortices. An interactive, time-dependentvisualisation is generated using the temporal correspondences of each vortex tube. This analysis revealsa number of interesting patterns.ACM CSS: I.3.8 Computer Graphics-Applications
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    Feature Extraction and Visualisation of Flow Fields
    (Eurographics Association, 2002) Post, Frits H.; Vrolijk, Benjamin; Hauser, Helwig; Laramee, Robert S.; Doleisch, Helmut
    Flow visualisation has already been a very attractive part of visualisation research for a long time. Usually very large data sets need to be processed, which often consist of multivariate data with a large number of sample locations, often arranged in multiple time steps. Recently, the steadily increasing performance of computers again has become a driving factor for a new boom in flow visualisation, especially in techniques based on feature extraction, vector field clustering, and topology extraction. In this state-of-the-art report, an attempt was made to (1) provide a useful categorisation of FlowVis solutions, (2) give an overview of existing solutions, and (3) focus on recent work, especially in the field of feature extraction. In separate sections we describe (a) direct visualisation techniques such as hedgehog plots, (b) visualisation using integral objects, such as streamlines, (c) texture-based techniques, including spot noise and line integral convolution, and (d) techniques based on extraction of features or flow topology.
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    Deformable Surface Techniques for Field Visualization
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Sadarjoen, I.; Post, Frits H.
    Surface extraction from data fields is often used in scientific visualization, as surfaces can represent meaningful information and they are well suited for display. This paper describes a general method for localized surface extraction from scalar and vector fields. An initial polygonal surface is placed within the field, and the shape of the surface is adapted to the field by iterative displacement of surface nodes according to a displacement criterion. To achieve a good approximation of a smooth surface, the polygon mesh can be locally refined during iteration. The type of surface extracted depends on the displacement criterion, which can be any function of the available field variables. Techniques for displacement and mesh refinement are discussed in detail. The results we show are generation of a local isosurface and extraction of a vortex tube. Finally, we will draw conclusions and discuss some issues for further development.
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    Experiments on the Accuracy of Feature Extraction
    (The Eurographics Association, 1998) Reinders, Freek; Spoelder, Hans J.W.; Post, Frits H.; Bartz, Dirk
    Feature extraction is an approach to visualization that ex- tracts important regions or objects of interest algorithmically from large data sets. In our feature extraction process, high-level attributes are cal- culated for the features, thus resulting in averaged quantitative measures. The usability of these measures depends on their robustness with noise and their dependency on parameters like the density of the grid that is used. In this paper experiments are described to investigate the accuracy and robustness of the feature extraction method. Synthetic data is gener- ated with prede ned features, this data is used in the feature extraction procedure, and the obtained attributes of the feature are compared to the input attributes. This has been done for several grid resolutions, for di erent noise levels, and with di erent feature extraction parameters. We present the results of the experiments, and also derive a number of guidelines for setting the extraction parameters.