[IGS-DCWG-14] Re: Resupplied data

[Angelyn W. Moore]

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IGS-DCWG Mail      16 Jun 18:10:53 PDT 2003      Message Number 14
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Author: Angelyn Moore

Great topic!

First an easy answer for Michael:

 > Is there A SINGLE LIST of sites (four character code or whatever),
 > maintained by A SINGLE person/agency, pertaining to data that MUST be
 > archived at all global data centers?  And, by list I mean something
 > available anonymously through ftp|http which is also easily parsed
 > AND limited only to these sites.

ftp://igscb.jpl.nasa.gov/pub/station/globalstns

This is a list of Global sites.  It's dynamic.... since the definition
is dynamic.

OK, now for the tough stuff.

GSAC files or something similar immediately lept to my mind as well
for a way for GDCs to evaluate what they've got against what another
GDC has.  Actually we at the CB are using the file publish times in
the .dhf files for latency calculations already.  It's very handy
as long as the conversion to UTC has been done correctly :)
(I won't name names).

In fact, this morning I started a message saying the publish time
info could be augmented with file sizes or even checksums to provide
"positive identification" of a unique file.  But reviewing the .dhf
specification just now, I see that both are already included !

Besides GDCs using .dhf's for this purpose, ACs could use them to
decide if there were any file republishings later than the time they
acquired that data.  It would be simpler for ACs (yet slightly more
complicated for DCs) if there were a small file listing *only* files
which have been replaced since the initial publication.  This file
could replace email notification to the user community. It would be
made available in a machine-readable .dhf-like format, but one
could also easily automatically make a web page out of this information
for the occasional/nonautomatic user's benefit.  It becomes
the AC's responsibility to use dates, checksums, and/or sizes as
it sees fit.  Each GDC would have one and the user would check
this file at each DC from which it gets data.

DC people will know better than me whether it is reasonable to require
than all ODCs/station operators push data.  It certainly would make
recognition of republished data very straightforward, as Heinz and
Michael have observed.

If "push-only" is not implemented, one possibility is that ODCs
which do not push data to GDCs must offer a .dhf file.  The GDCs
then would need to parse it and decide if any data has been republished.

Perhaps files which are republished should be required to state in
a COMMENT in the header when they were replaced, and why.

There are my disjointed thoughts for the moment!

Best regards,
Angie
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Angelyn W. Moore, Ph.D.            Deputy Director, IGS Central Bureau
  JPL/Caltech                               Angelyn.W.Moore at jpl.nasa.gov
  4800 Oak Grove Dr. MS 238-540                   voice: +1 818 354 5434
  Pasadena CA 91109 USA  http://igscb.jpl.nasa.gov  fax: +1 818 393 6686