CGAL::orthogonal_vector

Vector_3<Kernel>	orthogonal_vector ( Plane_3<Kernel> p)
		computes an orthogonal vector of the plane p, which is directed to the positive side of this plane.
Vector_3<Kernel>	orthogonal_vector ( Point_3<Kernel> p, Point_3<Kernel> q, Point_3<Kernel> r)
		computes an orthogonal vector of the plane defined by p, q and r, which is directed to the positive side of this plane.