CGAL users discussion list

[Juan Carlos Lopez Alfonso <>]

Hi There:

I have this concrete example:

p1x = 0.00000000000000000;

p1y = 0.20000000000000001;

p1z = 0.00000000000000000;

p2x = 0.20000000000000001;

p2y = 0.20000000000000001;

p2z = 0.20000000000000001;

p3x = 0.40000000000000002;

p3y = 0.80000000000000004;

p3z = 1.00000000000000000;

p4x = 0.20000000000000001;

p4y = 0.40000000000000002;

p4z = 0.40000000000000002;

Jacobian = (p2x - p1x) * (p3y - p1y) * (p4z - p1z) + (p3x - p1x) * (p4y - p1y) * (p2z - p1z) + (p4x - p1x) * (p2y - p1y) * (p3z - p1z) - (p4x - p1x) * (p3y - p1y) * (p2z - p1z) - (p3x - p1x) * (p2y - p1y) * (p4z - p1z) - (p2x - p1x) * (p4y - p1y) * (p3z - p1z);

for this case, the jacobian is equal to 0 and for this reason these 4 points are coplanar.

However, in CGAL this test (if (CGAL::orientation(p1, p2, p3, p4) == CGAL::COPLANAR)) is not satisfied for the same 4 points. My questions are the follows:

- How is possible that in CGAL these points are not coplanar? because these points are coplanar.

- In order that I can't remove points, How Can I say to CGAL when computes the triangualtion that these points are coplanar?

- I will use the resultant triangulation in other software where the jacobian is computed and I can't use the CGAL library. Is possible to change the CGAL test of coplanar points when the triangulation is computed?

Sorry for my several questions, but I need to solve this problem.

Thank you in advance and waiting suggestions

Juan Cralos