圆弧检测

[yingma111]

def isOnArc(p: tuple, center: tuple, tanMat: np.ndarray, T: float) -> bool:
    """
    验证给定点p是否是以center为中心的圆上的点\n
    :param p:
    :param center:
    :param tanMat:
    :param T:
    :return:
    """
    px = p[0]
    py = p[1]
    cx = center[0]
    cy = center[1]
    tan = tanMat[py][px]
    C = py - tan * px
    dist = abs(tan * cx - cy + C) / math.sqrt(1 + tan * tan)
    return dist < T

请问， dist = abs(tan cx - cy + C) / math.sqrt(1 + tan tan)，能解释一下意义吗？