Incorrect contouring on quadratic tetrahedrons.
This issue was created automatically from an original Mantis Issue. Further discussion may take place here.
When a VTK_QUADRATIC_TETRA is contoured, visual artifacts can appear depending on the orientation of the data relative to the internal decomposition. A quadratic tetra is decomposed inside of vtkQuadraticTetra.cxx into 8 linear tetras: 4 for the corners and 4 that make a central octahedron. The 4 central linear tetras share a diagonal of the octahedron. Values interpolated along this diagonal get interpolated as if the linear tetra was independent of the quadratic tetra.
Data that is the central tetra region perpendicular to the diagonal is interpolated correctly.
Attached is a tarball with 2 small test unstructured grid data sets, images from those sets, and an image showing the effect in a fluid simulation.