[vtk-developers] vtkPolyData->IsEdge fix

[Rasmus Reinhold Paulsen]

I am currently trying to get a deeper understanding of the way VTK handles
topology. I found a strange "feature" in vtkPolyData->IsEdge. Apparently I
am not the first:

Luca, January 2003:

1) vtkPolyData::IsEdge(vtkIdType, vtkIdType) returns 1 if two points are
on the same cell, and 0 otherwise. Quite a handy method indeed, but its
name can be misleading if you work with n-sided polygons (n>3), since to
me polygon edges are cell boundary edges. I think a caveat in IsEdge
documentation would be perfect.

Luca proposes a fix:

inline int vtkPolyData::IsEdge(int p1, int p2)
{
  unsigned short int ncells;
  int npts;
  int i, j;
  vtkIdType *cells, *pts;

  this->GetPointCells(p1,ncells,cells);
  for (i=0; i<ncells; i++)
  {
    this->GetCellPoints(cells[i],npts,pts);
    for (j=0; j<npts; j++)
    {
      if (p1==pts[j])
        if ((pts[(j-1)%npts]==p2)||(pts[(j+1)%npts]==p2))
          return 1;
    }
  }

  return 0;
}


Is there a reason for the current IsEdge behavior or should the above fix
be applied?


Regards
Rasmus