import math


def get_radian_angle_btwn_vecs(vec1_x, vec1_y, vec2_x, vec2_y):
    """Compute the angle between two vectors (vec1, vec2) in radians.

    :param vec1_x: the x-coordinate of vec1
    :param vec1_y: the y-coordinate of vec1
    :param vec2_x: the x-coordinate of vec2
    :param vec2_y: the y-coordinate of vec2
    :return: the angle between vec1 and vec2
    """
    test = (vec1_x * vec2_x + vec1_y * vec2_y) / math.sqrt(vec1_x ** 2 + vec1_y ** 2) / math.sqrt(
        vec2_x ** 2 + vec2_y ** 2)
    if test > 1:
        test = 1
    if test < -1:
        test = -1
    rad = math.acos(test)

    return rad