_read_channel(cha_element, _ns)[source]

Returns either a Channel object or None.

It should return None if and only if it did not manage to successfully create a Channel object which can only happen if one of the coordinates is not set. All the others are optional. If either the location or channel code is not set it raises but that is fine as that would deviate too much from the StationXML standard to be worthwhile to recover from.