[vtkusers] Cutting a 2D dataset with a vtkImplicitDataSet

[Paul Cochrane]

David,

I've got another (and very similar) problem you might be able to help me out
with.  I'm now trying to clip (instead of cut) a 2D data set with a contour
generated from another 2D data set.  I'll explain what I'm trying to do, and
what I've done to try and get vtk to do it, and hopefully you, or someone
else, may be able to give me some pointers.

What I've got is a 2D bubble rising up through a fluid.  The surface of the
bubble is defined by the zero value contour of one data set of scalars.
This is the easy part, I can just generate the contour using
vtkContourFilter.  I now want to clip a data set that holds the vector field
of the fluid with the contour, so that the vector field that is defined
inside the bubble (sounds odd, I know, having a vector field of a fluid in a
bubble when the fluid is outside, but anyway...  I think it's something to
do with this level set method that is being used to do the simulations) is
removed, and so I can display just the vector field outside the region of
the bubbles, which makes a lot more sense to visualise what's going on.

I've tried many ways of doing this, for instance:
- use the contour as input to vtkImplicitDataSet and pass this as the
  implicit function into vtkClipDataSet.  This doesn't produce anything on
  the output.
- use vtkClipPolyData on the arrow glyphs generated from the initial vector
  field, with the contour as imput to vtkImplicitDataSet.  Again, no output.
- use a vtkProbeFilter between the contour and the vtkImplicitDataSet to do
  something similar to what you advised me to do before.  This seemed to
  produce the right kind of output when one prints the object, but the
  vktImplicitDataSet complained about not the right data set on input.
- use vtkClipDataSet on the scalar data input with the value I would use for
  the contour, and try and use that data set to clip the vector data set.
  Again, couldn't get that to go.
- combine the two grids together (the vector and scalar) so that I can pass
  the new grid into vtkClipDataSet and use the scalar value in the grid to
  clip the vector part on output.  Again, couldn't get any output, or what
  did come out seemed like it was corrupted.  The grid that came out of the
  clip had bounds at around 1e299, but the names and dimensions etc of the
  vector and scalar arrays within the grid looked fine.
- I've also tried vtkExtractGeometry without success

I can't think of much else to try.  Any ideas as to what I'm doing wrong?
Or any ideas as to how to solve this problem?  At the end of the day, I just
want to be able to visualise the vector field outside the bubbles, but just
the vector field (I know I can make a bubble in 3D using the
RotationalExtrusionFilter to cover up the arrows, but that's just a bit of a
hack, and not what we want to see.

Anyway, any help with this would be greatly appreciated.

Many thanks in advance,

Paul

-- 
Paul Cochrane
Computational Scientist/Software Developer
Earth Systems Science Computational Centre
Rm 703, SMI Building
University of Queensland
Brisbane
Queensland 4072
Australia

E: cochrane at esscc.uq.edu.au
P: +61 7 3346 4109
F: +61 7 3365 7347