CGAL::orientation

Orientation	orientation ( Point_2<Kernel> p, Point_2<Kernel> q, Point_2<Kernel> r)
		returns LEFT_TURN, if $$r lies to the left of the oriented line $$l defined by $$p and $$q, returns RIGHT_TURN if $$r lies to the right of $$l, and returns COLLINEAR if $$r lies on $$l.
Orientation	orientation ( Point_3<Kernel> p, Point_3<Kernel> q, Point_3<Kernel> r, Point_3<Kernel> s)
		returns POSITIVE, if $$s lies on the positive side of the oriented plane $$h defined by $$p, $$q, and $$r, returns NEGATIVE if $$s lies on the negative side of $$h, and returns COPLANAR if $$s lies on $$h.

See Also