[vtkusers] Can't use vtkStructuredGridToPolyDataFilter.Why?

[hp.shen]

Hi, all
 
I want to use vtkStructuredGridToPolyDataFilter to convert
structuredgrid data to PolyData in tcl.
Where it doesn't work. The error says:
"invalid command name "vtkStructuredGridToPolyDataFilter"."
So may I missed some package , but I don't know which one.
Could you help me.
 
Thanks
Peace
 
===========codes:
.
vtkStructuredGrid sgrid
  sgrid SetDimensions $M $N 1
  sgrid SetPoints points
  [sgrid GetPointData] SetScalars faceColors
 
vtkStructuredGridToPolyDataFilter s2p
    s2p SetInput sgrid
.
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