etl::hermite<Vector> curve(segment.p1,segment.p2,segment.t1,segment.t2);
etl::derivative< etl::hermite<Vector> > deriv(curve);
etl::hermite<Vector> curve(segment.p1,segment.p2,segment.t1,segment.t2);
etl::derivative< etl::hermite<Vector> > deriv(curve);