[vtkusers] testing the normal direction for a PolyData

[David Netherway]

Hello,

After using vtkPolyDataNormals to ensure that the normals of a polydata are
consitent I wish to test whether they are facing inwards or outwards.
Toggling FlipNormals, if necessary, will then give me orientation I want.
What I need is a method SetNormalsInward or SetNormalsOutward. Please let me
know if such methods exist or there is a methodology for doing this.

I envisage getting the closest triangle to a particular point  that I know
is on the surface interior to an unknown triangle, and then checking whether
the normal is in the view direction.

Comments on a good method would be welcome.

Thanks, David