def get_orientation(o, a, b):
    """
    Given three 2D points o, a and b, by using the cross product of oa and ob
    :return: positive if o->a->b is in counter-clockwise order; negative if o->a->b is in clockwise order; zero if
    the three points are colinear
    """
    return (a[0] - o[0]) * (b[1] - a[1]) - (a[1] - o[1]) * (b[0] - a[0])