[vtkusers] probe cells of vtkPlaneSource output

[John Harris]

Hello

I have an unstructured grid that has velocity values associated at each 
node.  A vtkPlaneSource slices this mesh and the velocity values that it 
encounters are then color coded onto teh screen.

The output of vtkPlaneSource is just a square block of quad cells. Is there 
a way to probe each of these cells and find out if the velocity value it 
encountered was from the mesh or not? (I know a simple way to do this would 
be just to check if it has a non-zero velocity, if it does then that cell 
definately lies on top of the mesh. The problem is that values from the mesh 
can also be zero, and for these cases we dont know if they're from the mesh 
or not)

Let me know if you need clarification,

Thank you kindly for any suggestions,

JH