YLScsDrawing.Geometry.Vector.IsCCW C# (CSharp) Method

        public static bool IsCCW(PointF pt1, PointF pt2, PointF pt3)
        {
            Vector V21 = new Vector(pt2, pt1);
            Vector v23 = new Vector(pt2, pt3);
            return V21.CrossProduct(v23) > 0;  // sin(angle pt2 pt1 pt3) < 0, 180<angle pt2 pt1 pt3 <360
        }