__init__.py 文件源码

def dihedral_angle(a, b, c, d):
    """
    Calculate the dihedral angle between 4 vectors,
    representing 4 connected points. The angle is in range [-180, 180].

    @param a: the four points that define the dihedral angle
    @type a: array

    @return: angle in [-180, 180]
    """

    v = b - c
    m = numpy.cross((a - b), v)
    m /= norm(m)
    n = numpy.cross((d - c), v)
    n /= norm(n)

    c = numpy.dot(m, n)
    s = numpy.dot(numpy.cross(n, m), v) / norm(v)

    angle = math.degrees(math.atan2(s, c))        

    if angle > 0:
        return numpy.fmod(angle + 180, 360) - 180
    else:
        return numpy.fmod(angle - 180, 360) + 180