[vtkusers] How to generate streamlines on surfaces?

[Petru Pau]

(Oops! I've just noticed that the first message in the thread was sent to
vtkusers at public.kitware.com - I hope it's the same list.)

> were the triangles restricted to two dimensions? I suspect that if you
> define a triangle via 6 values (as opposed to 9) then it will lie on
> the surface... 

Thanks for the message, Tom. I've also thought of this - but we really need
to work with three-dimensional surfaces.

In this case, it seems that the only available solution is to implement 
my own algorithm.
This task is somehow made easy by the fact that, if the vectors defined 
in the points of
a cell are parallel to the cell plane, then the streamline that starts 
in that cell lies
entirely inside the cell. See the first attached image.

However, I do not know how to persuade the integration process to end at 
the
border of the cell. See the second attached image: The end of the 
streamline
is close to an edge, but not quite on the edge. Since it does not touch, 
I cannot get
(easily) a point on that edge, which should be the seed point for the
streamline on the adjacent face...

Petru

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