CGAL::centroid

Point_2<Kernel>	centroid ( Point_2<Kernel> p, Point_2<Kernel> q, Point_2<Kernel> r)
		compute the centroid of the points $$p, $$q, and $$r.
Point_2<Kernel>	centroid ( Point_2<Kernel> p, Point_2<Kernel> q, Point_2<Kernel> r, Point_2<Kernel> s)
		compute the centroid of the points $$p, $$q, $$r, and $$s.
Point_3<Kernel>	centroid ( Point_3<Kernel> p, Point_3<Kernel> q, Point_3<Kernel> r)
		compute the centroid of the points $$p, $$q, and $$r.
Point_3<Kernel>	centroid ( Point_3<Kernel> p, Point_3<Kernel> q, Point_3<Kernel> r, Point_3<Kernel> s)
		compute the centroid of the points $$p, $$q, $$r, and $$s.