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State-of-the-Art Report Feature Extraction and Visualization of Flow Fields

State-of-the-Art Report Feature Extraction and Visualization of Flow Fields. Helwig Hauser, R obert S. Laramee, Helmut Doleisch VRVis Research Center Austria www.VRVis.at {hauser,laramee,doleisch}@VRVis.at. Frits H. Post and Benjamin Vrolijk Delft University of Technology The Netherlands

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State-of-the-Art Report Feature Extraction and Visualization of Flow Fields

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  1. State-of-the-Art ReportFeature Extraction and Visualization of Flow Fields • Helwig Hauser, Robert S. Laramee, Helmut Doleisch • VRVis Research Center • Austria • www.VRVis.at • {hauser,laramee,doleisch}@VRVis.at • Frits H. Post and Benjamin Vrolijk • Delft University of Technology • The Netherlands • visualisation.tudelft.nl • {F.H.Post,B.Vrolijk}@its.tudelft.nl • Part 1: Visualization of Flow Fields • Part 2:Feature-Based FlowViz Feature Extraction and Visualization of Flow Fields

  2. Flow Visualization STAR Overview Part 1: Visualization of Flow Fields • Introduction to Flow Visualization (FlowViz) • Direct FlowViz • Texture-Based FlowViz • Geometric FlowViz Part 2: Feature-Based FlowViz Feature Extraction and Visualization of Flow Fields

  3. The FlowViz Job Goal: communicating FlowViz data: • data representing fluid/gas flow, i.e. vector field data (magnitude + direction) • not just scalar data • visualization is a very high bandwidth channel User Goals: • obtain overview of vector field • present characteristics • identify and investigate details and features Feature Extraction and Visualization of Flow Fields

  4. Computational vs. Experimental and Empirical FlowVis Computational FlowVis -using computers for FlowVis • data resulting from flow simulation, measurements, or flow modelling, e.g.,computational fluid dynamics (CFD) • computer-generated images and animations, often mimicking experimental FlowVis Visualization of actual fluids, e.g. water and air • dye injection • interferometry • Schlieren/shadows • flow topology graphs • etc. Feature Extraction and Visualization of Flow Fields

  5. FlowVis Data vs. Data Acquisition Data from Simulation: FOR EACH cell in (irregular) grid: • compute flow direction • compute flow magnitude (explicitly or implicitly) • compute pressure (à la Navier-Stokes equations) • further attributes Data from measurements: FOR EACH location of a (regular) grid: • flow direction (reconstructed) • measure flow magnitude Data from modelling: • Vector Field represented by analytic function • Flow direction and magnitude a function of location (and time) Feature Extraction and Visualization of Flow Fields

  6. FlowViz Data Characterized by Many Dimensions Spatial dimensions: • 2D (planar flow, simplified or synthetic) • 2.5D (boundary flow, flow on surface) • 3D (real-world flow) Temporal dimension: • steady flow -1 time step (or instantaneous flow) • time-dependent flow -multiple time steps (turbulent, real-world) • caution is advised in the context of animation Data dimensions: • velocity • temperature • pressure • and many more... Feature Extraction and Visualization of Flow Fields

  7. Direct vs. Geometric vs. Feature-Based FlowViz Overview, 1st impression more detailed view focus on features Feature Extraction and Visualization of Flow Fields

  8. FlowViz Fundamentals Flow Data from simulation: vector field represented as samples: vp,t (+ reconstruction) v(p,t) = dp/dt; p,v  Rn, tR Flow Integration • over Grids: Cartesian, curvi-linear, unstructured • integration techniques: Euler and Runge-Kutta • point location (which cell p lies in) and neighbor searching • flow reconstruction within a cell (à la interpolation) • computation of derived data p(s) = p0 +  v(p(),+t0)d [instantaneous] pE(t+t)=p(t)+tv(p(t),t) [time-dependent] Feature Extraction and Visualization of Flow Fields

  9. Direct Flow Visualization Direct Mapping of Flow Attributes to Visualization Space Advantages: • simplicity • less computation time • intuitive Disadvantages: • does not always clearly show flow properties and features, e.g., flow orientation Feature Extraction and Visualization of Flow Fields

  10. Direct FlowViz: Color Coded Slicing Color Coding in 2D, instantaneous: mapping flow attribute(s) to hue multiple slices for vortex visualization (missing color coded boundary) slicing probe for vortex visualization (Schulz et al) Feature Extraction and Visualization of Flow Fields

  11. Direct FlowViz: Arrow/Hedgehog plots in 2D and 3D, instantaneous Feature Extraction and Visualization of Flow Fields

  12. Direct FlowViz: Contours in 2D and isosurfaces in 3D Contours in a slice Isosurface (and color coding) in 3D Feature Extraction and Visualization of Flow Fields

  13. Direct FlowViz: Volume Rendering combined with color coding the curvilinear bluntfin data set (Westermann) Feature Extraction and Visualization of Flow Fields

  14. Direct FlowViz: Hybrid Solutions -arrow plots and color coding in 2D, steady and unsteady Feature Extraction and Visualization of Flow Fields

  15. Texture-Based Flow Visualization Computing textures that provide a dense coverage/visualization of a vector field Advantages: • detailed view of vector field • clearer perception of characteristics • contains elements of direct + geometric FlowViz Disadvantages: • computation time • 2.5D, 3D Feature Extraction and Visualization of Flow Fields

  16. Texture-Based FlowViz: Spot Noise (Van Wijk) and LIC (Cabral and Leedom) in 2D, instantaneous Feature Extraction and Visualization of Flow Fields

  17. Texture-Based FlowViz: Spot Noise in 2D, instantaneous, with color coding (de Leeuw) Good for visualizing detail. Feature Extraction and Visualization of Flow Fields

  18. Texture-Based FlowViz: Spot Noise and LIC in 2D, time-dependent (Van Wijk) Feature Extraction and Visualization of Flow Fields

  19. Texture-Based FlowViz: Time-Dependent Texture Advection in 2D Unsteady FlowViz of the Gulf of Mexico (Jobard et al) Feature Extraction and Visualization of Flow Fields

  20. Texture-Based FlowViz: LIC on Surfaces, unsteady A comparison of 3 LIC techniques (left) UFLIC, (middle) ELIC, and (right) PLIC (Verma et. al.) Feature Extraction and Visualization of Flow Fields

  21. Texture-Based FlowViz: LIC in 3D, instantaneous (Interrante and Grosch) Feature Extraction and Visualization of Flow Fields

  22. Geometric Flow Visualization The computation of objects whose shape is directly related to underlying geometry Advantages: • intuitive • clearer perception of characteristics Disadvantages: • placement • 3D Feature Extraction and Visualization of Flow Fields

  23. Geometric FlowViz: Some Terminology Stream vs. Path vs Streak vs Time lines Streamline • everywhere tangent to flow at instantaneous time,t0 (blue/aqua) Pathline • path traced by a particle over time,t (red/maroon) Streakline • line traced by continuous injection at location,x0 (light green) Timeline • temporal evolution of initial line,l0 (yellow) Feature Extraction and Visualization of Flow Fields

  24. Geometric FlowViz: Streamlines and Streamlets in 2D, steady-state Feature Extraction and Visualization of Flow Fields

  25. Geometric FlowViz: Pathlines and Streamlets in 2D, unsteady (Van Wijk) Feature Extraction and Visualization of Flow Fields

  26. Geometric FlowViz: Timelines in 2D (Van Wijk) and 3D (B. Girod) (unsteady) Feature Extraction and Visualization of Flow Fields

  27. Geometric FlowViz: Seeding in 2D (B. Jobard) and 3D (Schulz et al) Image-based, topology-based, and interactive seeding strategies Feature Extraction and Visualization of Flow Fields

  28. Geometric FlowViz: Streamribbons and Streamtubes, 3D, steady-state Feature Extraction and Visualization of Flow Fields

  29. Geometric FlowViz: Perceptual Issues in 3D, steady-state Illuminated Streamlines (Zoeckler) StreamRunner (Laramee) Feature Extraction and Visualization of Flow Fields

  30. Geometric FlowViz: Streaklines in 2D (Jobard et al) and 3D (B. Girod) Feature Extraction and Visualization of Flow Fields

  31. Geometric FlowViz: StreamBalls (Brill et al), StreamSurfaces (Hultquist), StreamArrows (Loeffelmann et al), 3D, steady-state Feature Extraction and Visualization of Flow Fields

  32. Geometric FlowViz: Flow Volumes (Crawfis), steady and unsteady A subset of 3D flow domain specified by initial 2D patch Feature Extraction and Visualization of Flow Fields

  33. Some Open Issues in FlowViz • Unsteady FlowViz on Surfaces -esp. Texture-based, unstructured • Steady-State FlowViz in 3D -perceptual issues, seeding strategies • Unsteady FlowViz in 3D -computation time • Lot’s of work to (still) be done. Feature Extraction and Visualization of Flow Fields

  34. Acknowledgements: Part 1 • Thanks to (1) the KPlus (www.kplus.at) -Austrian governmental research program, and (3) AVL (www.avl.com) for financial support • For more information see: www.VRVis.at or email laramee@VRVis.at • Now for Part 2! Feature Extraction and Visualization of Flow Fields

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