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

CGAL::collinear
CGAL::left_turn
CGAL::right_turn