Looks like there is a discrepancy in the FreeCAD source code.
Code statements
FreeCAD has this code for repairing mesh:
void MeshTopoAlgorithm::RemoveDegeneratedFacet(unsigned long index)
{
// coincident corners (either topological or geometrical)
for (int i=0; i<3; i++) {
// ...
// isolate the face and remove it
rFace._aulNeighbours[0] = ULONG_MAX;
rFace._aulNeighbours[1] = ULONG_MAX;
rFace._aulNeighbours[2] = ULONG_MAX;
_rclMesh.DeleteFacet(index); // *** Facet is isolated before deleting
return;
// ...
}
// We have a facet of the form
// P0 +----+------+P2
// P1
for (int j=0; j<3; j++) {
// ...
else
_rclMesh.DeleteFacet(index); // *** Facet is NOT isolated before deleting
return;
// ...
}
}
Difference
The above statements contain two calls to this method MeshKernel::DeleteFacet with this difference:
- The first call isolates the facet before calling delete method
- The second call doesn't isolate the facet before calling delete method
Note
It should be noted that the delete method itself depends upon neighborhood data to re-adjust neighbors, so by isolating a facet, we are basically throwing away its neighborhood data. Hence, its neighborhood cannot be re-adjusted:
bool MeshKernel::DeleteFacet (const MeshFacetIterator &rclIter)
{
// ...
// *** The following loop depends upon the neighborhood data.
// *** So if facet is isolated before calling this method,
// *** the following loop is skipped and the neighborhood cannot be re-adjusted.
// *** Am I right?
// invalidate neighbour indices of the neighbour facet to this facet
for (i = 0; i < 3; i++) {
ulNFacet = rclIter._clIter->_aulNeighbours[i];
if (ulNFacet != ULONG_MAX) {
for (j = 0; j < 3; j++) {
if (_aclFacetArray[ulNFacet]._aulNeighbours[j] == ulInd) {
_aclFacetArray[ulNFacet]._aulNeighbours[j] = ULONG_MAX;
break;
}
}
}
}
// ...
}
Question
Why does the above difference exist when deleting facets? Is there any specific reason for it?
