[vtkusers] confused UnstructredGrid normals!

[Louis Desjardins]

Hi there,

I have an unstructured grid that I convert to a surface mesh via the 
following pipeline:

vtkUnstructuredGrid
vtkGeometryFilter
vtkDecimatePro
vtkStripper
vtkPolyDataNormals

If I don't add vtkPolyDataNormals to the pipeline, then the normals dont 
seem to be computed for vtkPolyDataMapper.
After adding this to the pipeline it appears that the normals are available 
for vtkPolyDataMapper, however they are a little screwd up... My mesh 
intersects with a plane and for some reason when I cull the frontface 
polygons of the mesh, many still appear in front the plane where they should 
be in face hidden behind the plane.. in other words, it appears to be 
confused :S  (and yes depthtesting and depthmask is also enalbed)

This must be something to do with the orientation of the normals; does 
anyone know why my normals might appear screwd up, or why the front facing 
polygons are not always front facing?

Thank you kindly for your help!

LD

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