[vtkusers] How to obtain surface normals of 3D object as input to new vtk code?

[Vidya Raghavan]

Dear VTK Users,

I need the surface normals of a 3D object for some filtering code that I 
will be writing in Tcl. I could display the normals using glyphs, but how do 
I actually get the normals' values as input to the code that I need?
The code that I have below is to create a .vtp data file and displaying the 
3d object from the.vtp file. I will really appreciate your help.
Thanks,
-vidya
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foreach tissue {1} {

   # write the models to file
    selectTissue ThresholdBetween $tissue $tissue
    writer SetFileName model$tissue.vtk
    writer Write

    #create readers, mappers, and actors
    vtkXMLPolyDataReader reader$tissue
       reader$tissue SetFileName model$tissue.vtk


    vtkPolyDataMapper mapper$tissue
       mapper$tissue SetInput [reader$tissue GetOutput]

   vtkProperty prop$tissue
      prop$tissue SetDiffuseColor [math Random] [math Random] [math Random]
prop$tissue SetSpecularPower 50
      prop$tissue SetSpecular .5
      prop$tissue SetDiffuse .8

    vtkActor actor$tissue
       actor$tissue SetMapper mapper$tissue
       actor$tissue SetProperty prop$tissue

       ren AddActor actor$tissue
  ren AddActor hhogActor
}

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