[vtkusers] incorrect pointid returned by vtkPointPicker

[Christopher M. Navarro]

After looking through the archives, I think I know what is wrong but I am 
unsure how to correct the returned point id.  I use vtkGlyph3D with 
GeneratePointIdsOn(), however after running through the glyph filter where 
I have a non-uniform height for each glyph based on the vector components, 
I send it to vtkClipPolyData to cut the cylinder glyphs in half so I can 
use height as a comparison.  Otherwise the bottom halfs are not aligned.  
This works except that when I get the pointId and try to reference the 
vector data to get the z scaling value, the pointId is wrong.  If I remove 
the vtkClipPolyData then the pointId returned is correct.  Is there some 
way that I can get around this changing of point id's by the clipper or 
adjust for the clipping?  Thanks for any help.

-chris