[Paraview] Arrow Glyphs imapping velocity vectors in, turbulent flow

[Richard Strelitz]

Brian and Don and anyone else interested,
  I am not sure whether this has been published in this form, although 
the idea has been bruited about in other contexts.  It is certainly 
something that I have been working on in my sputtering and lackadaisical 
fashion.
  The gist is that the placement of glyphs and indeed any other visual 
object should be dictated not by a computational geometry but by some 
measure of importance and value.  In other words, equal spaced glyphs 
and contours are not only lazy but also misleading.
  What I would recommend is that glyphs be placed such that they lie in 
the center of a region that contains a user-specified amount of 
"stuff".  For the vis scientist, this means doing a voronoi tesselation 
based on the "stuff" field.  For the flow buff, the obvious choice of 
"stuff" is variance, with a close second to flux. 
  Procedure (I would say flowchart, but the pun police are everywhere 
and I have a reputation to project)
   1) select regions devoid of discontinuities
   2) within that region
          for every original sample point, compute the distance weighted 
variance to nearby points
           (clever people would use multi pole methods here) computing 
Sij for i>j only.  The fun of 
           course is to find a compelling version of the distance 
between 2 vectors as a single scalar.
           For incompressible flow, the dot product works.  Otherwise, 
you have more options in
           blending magnitude changes with changes in direction. 
  3) do voronoi tesselation on S, or smoothed version thereof
  4) place glyph at center of polygon
I can root about in my files and look for slides from last year's DoECGF 
forum if there is call for pictures.

  Alternatively you can compute a LIC texture and then decimate at a 
user specified interval.  This is easy but morally unsatisfying.  And, 
unless you have taken the trouble to build in Jean Favre's 
implementation of LIC (PVLEA), 
<//http://www.cscs.ch/~jfavre/Projects/vtkLEA/vtklea.htm 
<http://www.cscs.ch/%7Ejfavre/Projects/vtkLEA/vtklea.htm>//>/ , /this is 
more work for you and the computer than can possibly  be justified.

Richard Strelitz, Visualization Team
 Advanced Computing Lab (CCS-1), LANL


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