vtk Filters causing point doubling and mangling normal values

Question

Using VTK version 5.1, I'm having some issues with some models not displaying correctly in OpenGL.

The process for getting the models into VTK is a bit roundabout, but gets there and is fairly simple. Each model is a manifold mesh comprised of only quads and tris.

Blender models->custom export format containing points, point normals, and polygons Custom export format->Custom C++ parser->vtkPolyData

vtkPolydata->vtkTriangleFilter->vtkStripper->vtkPolyDataNormals->final product

As our final product was showing irregular and missing normals when it was rendered, I had VTK write the object to a plaintext file, which I then parsed back into Blender using python.

Initial results were that the mesh was correct and matched the original model, however, when I used the Blender "select non-manifold" option, about 15% of the model showed to be nonmanifold. A bit of reading around online suggested the "remove doubles" as a solution, which did in fact solve the issue of making the mesh closed, but the normals were still irregular.

So, I guess I'm hoping there are some additional options/functions/filters I can use to ensure the models are properly read and/or processed through the filters.

Answer 1

This was solved by requesting that Blender perform a triangulization of the mesh prior to the export operation.

The mangling was due to Blender performing implicit triangulization of quads, resulting in faces which were stored as 4 non-coplanar points. By forcing explicit triangulation in advance, I was able to successfully perform the export and maintain model integrity/manifold-ness. The holes that were being experienced were due to the implicit triangulation not being copied by the exporter and thus causing loss of data.