arclength-parametrization of streamlines

[alext at win.tue.nl]

  Hi Thomas,

  In reply to your question about parametrization of streamline-tracing by
other parameters than travelled distance:

  I had a similar problem, i.e. I wanted to trace streamlines whose length
was controlled by other parameters than the maximum distance/travelled time
provided by vtkStreamLine. Two solutions emerged:

  1) (easy but not fully general): compute a derived vector field from your
     original one, trace streamlines in this field, and use the maximum
     travelled time stopping criterion. In your case, you could normalize
     your original vectorfield such that all vectors have the same length. 
     Then you can use the maximum travelled time as travelled distance,
     since the velocity of the traced 'particles' is the same everywhere.
     This method is however limited to the derivation of a new vector field
     from the original one and using the maximul travelled time as stopping
     criterion.

   2) (more difficult but more general): subclass the baseclass of
      vtkStreamLine, that is vtkStreamer, and override the 
      Execute() method. This method is the core of the streamline
      tracing process. If you override it, you can set into the new version
      of the method any stopping criterion you want, based on any data.
      I used this method, for example, to create a new version of
      vtkStreamLine which traces streamlines based on a user-given
      boolean expression involving AND/OR/comparison operators on
      the vtkScalars and vtkVectors data of the input-data. This means
      I can trace streamlines based on more complex criteria than just
      the comparison of the maximum travelled time. However, for this you
      have to know a bit of VTK's subclassing policy to derive a new class
      form vtkStreamer....

  Hope this helps,

  Alex

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  Alexandru C. Telea   	      | Technische Universiteit Eindhoven
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> 
> Dear users,
> 
> has anyone come arcoss a way to create stream lines that all have the
> same length? 
> 
> So far, I only figured out that all the streamlines created as
> vtkStreamLine(s) are parametrized by the distance a particle travels
> during a given time.
> 
> Instead, what I'd need is a possibility to set the arclength of each
> line.
> 
> Any help appreciated!
> 
> Thomas Brandner
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