It was brought to our attention by @user27182 in https://gitlab.kitware.com/vtk/vtk/-/issues/19639 that the point ordering implied by the parametric coordinates of vtkWedge, and utilized by its shape functions for interpolation/derivation, did not match what the vtk-book was showing
VTK-Book:
Parametric Coordinates
Because of this issue, many things were wrong:
- Face winding of wedges was inwards not outwards
- Tetrahedralization of wedges was producing tets with negative volume
- several readers/and sources in VTK were generating wedges with the point ordering
Additionally, even though the VTK-book was showing the correct point ordering for vtkQuadraticWedges, vtkBiQuadraticWedges and vtkQuadraticLinearWedges which was matching their parametric coordinates, again several things were wrong because they were assuming the point ordering of vtkWedge shown in the VTK-book instead of the actual one:
- Face winding of quadratic wedges was inwards not outwards
- Tetrahedralization of quadratic wedges was producing tets with negative volume
- Contouring/Clipping was using linear wedges with negative volumes
- several readers/and sources in VTK were generating quadratic wedges with the point ordering
All that is being addressed in this MR https://gitlab.kitware.com/vtk/vtk/-/merge_requests/12988.
If backwards compatibility for vtkUnstructuredGridReader or vtkXMLUnstructuredGridReader is need for vtkWedges, please let us know.