def SGpolar(SGData):
    """
    Determine identity of polar axes if any
    """
    POL = '', 'x', 'y', 'x y', 'z', 'x z', 'y z', 'xyz', '111'
    NP = [1, 2, 4]
    NPZ = [0, 1]
    for M, T in SGData['SGOps']:
        for i in range(3):
            if M[i][i] <= 0.0:
                NP[i] = 0
        if M[0][2] > 0:
            NPZ[0] = 8
        if M[1][2] > 0:
            NPZ[1] = 0
    NPol = (NP[0] + NP[1] + NP[2] + NPZ[0] * NPZ[1]) * (1 - int(SGData[
        'SGInv']))
    return POL[NPol]
