[vtkusers] Selecting points from unstructured grid

[Robert McCall]

My data consists of half a dozen files of unstructured grid data (which is
just 3-D point data with an associated scalar value). I am trying to extract
some 3-D sub-volumes of this data for closer examination. I have tried using
vtkExtractUnstructuredGrid to just grab the data I want, using the Extent
Clipping, but it removes the entire set of data if any part of it is outside
of the extent volume. I just want to select individual points/cells. I see a
similar behavior if I use vtkGeometryFilter.

I think that I could cut the data set with a plane (i.e. vtkCutter), but
that this would produce a sampled/interpolated result. I could probably do
the same thing with vtkProbe. However, I just want to see the points in the
specified volume. I suspect that I could use a vtkProgrammableFilter for
this, but it seems like a simple enough task that I must just be overlooking
the obvious. Can anyone help enlighten the clueless? 

Robert McCall
NOMOS Corporation