[vtkusers] How to orient faces of a polydata?

[Majid Mohammad sadeghi]

Dear All,
I am exrtuding a 2D polygon using vtkLinearExtrusionFilter, the resulting polydata has misoriented faces on the mesh, meaning that for a closed mesh, faces inside and outside direction is mixed up. (for example when I open the data with meshlab and look at the normals, some are pointing in and some outwards)

How is it possible to orient order of each triangle vertices in a mesh so that there is a consistancy betwwen all faces?
Thanks for the help.
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