get radius function

def calculate_radius(point1, point2, timedelta = 1.0):
    if point1 is None:
        p1 = np.array([0.0,0.0])
    else:
        p1 = np.array(point1)
    p2 = np.array(point2)
    dist = np.linalg.norm(p2-p1)
    radius = (dist/timedelta)
    return int(radius)