[vtkusers] Converting vtkPolyData to vtkUnstructuredGrid for Exodus Export

[Karl Merkley]

I have a vtkPolyData that I want to write out using the  
vtkExodusIIWriter which requires an unstructtured grid as input.    
What is the best way to convert from the vtkPolyData to a  
vtkUnstructuredGrid?

    Thanks,
         Karl