Python-opencv calculates the angle of two straight lines or line segments

method one

Calculated through the slope relationship, the formula is as follows:
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Be careful not to appear vertical when calculating the slope. Python calculations will report an error, but it should be possible to calculate infinite. Let’s leave it here for now. I will explain it later when I have time. reason.

#openpose求角度
def GetAngle(line1, line2):
    """
    计算两条线段之间的夹角，若已知两直线斜率：m1,m2
     angle = atan(abs((m2 - m1) / (1 + (m2 * m1)))
    :param line1:
    :param line2:
    :return:
    """
    dx1 = line1[0][0] - line1[1][0]
    dy1 = line1[0][1] - line1[1][1]
    dx2 = line2[0][0] - line2[1][0]
    dy2 = line2[0][1] - line2[1][1]

    #求斜率
    m1=dy1/dx1
    m2=dy2/dx2
    insideAngle=math.atan(abs((m2-m1)/(1+(m1*m2))))

    angle=insideAngle/math.pi*180
    if angle>-370 and angle<370:
        angle=int(angle)

    return angle

Method Two:

#openpose求角度
def GetAngle(line1, line2):
    """
    计算两条线段之间的夹角
    :param line1:
    :param line2:
    :return:
    """
    dx1 = line1[0][0] - line1[1][0]
    dy1 = line1[0][1] - line1[1][1]
    dx2 = line2[0][0] - line2[1][0]
    dy2 = line2[0][1] - line2[1][1]
    angle1 = math.atan2(dy1, dx1)
    angle1 = int(angle1 * 180 / math.pi)
    # print(angle1)
    angle2 = math.atan2(dy2, dx2)
    angle2 = int(angle2 * 180 / math.pi)
    # print(angle2)
    if angle1 * angle2 >= 0:
        insideAngle = abs(angle1 - angle2)
    else:
        insideAngle = abs(angle1) + abs(angle2)
        if insideAngle > 180:
            insideAngle = 360 - insideAngle
    insideAngle = insideAngle % 180
    return insideAngle

Method three

Calculate the angle of three points through the cosine theorem:
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If the three sides are a, b, c, then as shown in the figure, in △ABC:

Prerequisite for use: Do not have 0 in the denominator.

Implementation: form a triangle through three points, first calculate the length of each side, and then use the cosine formula to solve the angle

def DIST(p1,p2):
    '''
    func:求两点间距离
    @para p1,p2:点坐标(x1,y1),(x2,y2)
    @para return:距离
    '''
    return math.sqrt((p1[0]-p2[0])*(p1[0]-p2[0])+(p1[1]-p2[1])*(p1[1]-p2[1]))


# #openpose求角度
def GetAngle(p1,p2,p3):
    """
    若已知3点,求以中间点为原点的夹角
    :param p1,p2,p3:点坐标(x,y)
    :param return: 角度
    """
    #余弦定理求夹角
    A=DIST(p1,p2)
    B=DIST(p2,p3)
    C=DIST(p1,p3)

    angle=math.acos((A*A+B*B-C*C)/(2*A*B))
    return angle/math.pi*180