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

2. Laramee@VRVis.at 2 Feature Extraction and Visualization of Flow Fields 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

3. Laramee@VRVis.at 3 Feature Extraction and Visualization of Flow Fields 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

4. Laramee@VRVis.at 4 Feature Extraction and Visualization of Flow Fields 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.

5. Laramee@VRVis.at 5 Feature Extraction and Visualization of Flow Fields 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)

6. Laramee@VRVis.at 6 Feature Extraction and Visualization of Flow Fields 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...

7. Laramee@VRVis.at 7 Feature Extraction and Visualization of Flow Fields Direct vs. Geometric vs. Feature-Based FlowViz focus on featuresmore detailed viewOverview, 1st impression

8. Laramee@VRVis.at 8 Feature Extraction and Visualization of Flow Fields FlowViz Fundamentals Flow Data from simulation: vector field represented as samples: v p,t (+ reconstruction) v(p,t) = dp/dt; p,v  R n, 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) = p 0 +  v(p(  ),  +t 0 ) d  [instantaneous] p E (t+  t) = p(t) +  t v(p(t),t) [time-dependent]

9. Laramee@VRVis.at 9 Feature Extraction and Visualization of Flow Fields 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

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

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

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

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

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

15. Laramee@VRVis.at 15 Feature Extraction and Visualization of Flow Fields 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

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

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

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

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

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

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

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

23. Laramee@VRVis.at 23 Feature Extraction and Visualization of Flow Fields Geometric FlowViz: Some Terminology Stream vs. Path vs Streak vs Time lines Streamline  everywhere tangent to flow at instantaneous time, t 0 (blue/aqua) Pathline  path traced by a particle over time, t (red/maroon) Streakline  line traced by continuous injection at location, x 0 (light green) Timeline  temporal evolution of initial line, l 0 (yellow)

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

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

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

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

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

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

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

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

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

33. Laramee@VRVis.at 33 Feature Extraction and Visualization of Flow Fields 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.

34. Laramee@VRVis.at 34 Feature Extraction and Visualization of Flow Fields 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!