//ger radian angle of vector A and B
public static double GetAngleOf2Vectors(Pt A, Pt B)
{
double length_A = get_vector_length(A);
double length_B = get_vector_length(B);
double cos_sita = A.Dot(B) / (length_A * length_B);
double sita = Math.Acos(cos_sita);
//degree in 0^180
//sita = sita * 180.0 / PI;
return sita;
}
public static int Ccw(Pt a, Pt b, Pt c)
{
b -= a;
c -= a;
if (b.Cross(c) > 0) return 1; //counter clockwise
if (b.Cross(c) < 0) return -1; //clockwise
if (b.Dot(c) < 0) return 2; //c--a--b on line
if (b.Norm() < c.Norm()) return -2; //a--b--c on line
return 0;
}