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Item 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. StuerzlingerIn 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.Item 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. NavazoThis 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.Item 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-ApplicationsItem Feature Extraction and Visualisation of Flow Fields(Eurographics Association, 2002) Post, Frits H.; Vrolijk, Benjamin; Hauser, Helwig; Laramee, Robert S.; Doleisch, HelmutFlow 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.