[fdsn-wg2-data] StationXML location code

[Sleeman, Reinoud (KNMI)]

Dear WG-II members,

A recent discussion initiated by IRIS DMC on the representation of
empty location ID's in the FDSN StationXML format is taking place
mainly via the mailing list 'webservices at iris.washington.edu':
http://www.iris.washington.edu/pipermail/webservices/
Part of the initial discussion also took part within the FDSN WG2 mailing
list and via bi-lateral mail exchange between datacenters.

Core issue in the discussion is the need for a clear and umabigious
definition of how to  represent the "empty" SEED location ID in StationXML,
which in SEED is encoded using two spaces. Chad Trabant phrased it as:

" There now exists another fdsnws-station implementation that returns
   StationXML with the locationCode attribute set to an empty string
   when the SEED value is empty. The justification is that this follows
   the SEED rules of trimming the padding spaces from the values.

   Unfortunately this means there are now flavors of StationXML that are
   incompatible in the core channel name identifiers. In other words,
   two StationXML documents for the same SEED channel appear, without
   extra field translation, to be different channels.
"

Clearly we must NOT allow multiple flavors of StationXML. As chair of
Working Group II "Data Format and Data Centers " I like to enforce a decision
on this issue based on the various views and input by a number of contributors.
Their opinion, based on common practice, theoretical considerations and specific
implementations are very valuable and urge for a common agreement at the same
time.

In my opinion there is a prevailing number of contributors pleading for the use
of an empty string in the locationCode in StationXML in case the corresponding
location ID in SEED contains two spaces. I do support this view.

The SEED manual is clear on the location code and this must be applied directly
onto the representation of the location ID in StationXML:

-  a location code is required; therefore "no location code" does not exist.
-  SEED defines only A-Z and digits 0-9 as allowable characters in location codes
-  by definition spaces are not allowed to represent a location code; therefore two
   spaces in the SEED location field represent an empty location code;

Thus a two space location-ID field in SEED represents an empty location code
and must be represented in StationXML as:

LocationCode=""

In StationXML, the 2 spaces in SEED are not only unneeded to represent an empty
location code, they are illegal within a location code. We should not perpetuate an
unwanted SEED feature into StationXML.

Unless there are any other arguments beyond those that have been
brought in in the above mailing lists -and within 2 weeks - I will close this
discussion with the above definition.

Best regards,
Reinoud