CGAL exception with UnitTet mesh when calling all_intersected_entities() or any_intersected_entities()

[Neilen Marais]

Running

from dolfin import *

mesh = UnitTetrahedron()
mesh.all_intersected_entities(Point(0,0,0))

results in

/tmp/python-1850ZRE.py in <module>()
      1 from dolfin import *
      2
      3 mesh = UnitTetrahedron()
----> 4 mesh.all_intersected_entities(Point(0,0,0))

StandardError: CGAL ERROR: assertion violation!
Expr: m_primitives.size() > 1
File: /usr/include/CGAL/AABB_tree.h
Line: 470

This is running a devlopment version, revision 5840, bzr+ssh://bazaar.launchpad.net/%2Bbranch/dolfin/ on 64bit Ubuntu 10.10

[Andre Massing (massing)]

Thanks for the bug report.
I mark that bug as invalid/won't fix since that is expected behavior in the sense that because of a limited precision for the standard geometry kernel, there are case where such exceptions do occur, especially if you take an subentity of an element (here a point which is a vertex of the cell)
 A current workaround is to not use the intersection related member functions in the Mesh class but to initiate a separate IntersectionOperator which gives a more fine-grained control over the geometric kernel. Either use "ExactPredicates" in the constructor or reset it via the reset_kernel member function (in IntersectionOperator class). One may discuss whether and how this might be controlled from within the mesh class, suggestion are very welcome!