import math


def get_angle(knot1, knot2):
    """
    Calculates the global angle between the x-axis and a line being defined by the knots
    :param knot1: start knot of the line
    :param knot2: end knot of the line
    :return: angle in radian
    """
    dx = knot2.x_-knot1.x_
    dy = knot2.y_-knot1.y_
    return math.atan2(dy, dx)