'Returns a 2-tuple of the units value and the units name,
and will automatically determines whether to return the linear
or angular units.'

@property
def units(self):

    if (self.projected or self.local):
        return capi.linear_units(self.ptr, byref(c_char_p()))
    elif self.geographic:
        return capi.angular_units(self.ptr, byref(c_char_p()))
    else:
        return (None, None)
