Hello Bruce,
Yes there is much overlap between CRS informaton and existing CF attributes
for grid mapping.
The only missing thing is identification of datum. Shape of the
sphere/spheroid is not sufficient, since the same spheroid is often used in
many datums with location shift. For example, EPSG:6277 (OSGB 1936 datum)
in WKT is following:
DATUM["OSGB_1936",
SPHEROID["Airy 1830",6377563.396,299.3249646,
AUTHORITY["EPSG","7001"]],
AUTHORITY["EPSG","6277"]]
All numeric parameters can be expressed by inverse_flattening and
semi_major_axis, but the two attributes indicates only spheroid (Airy 1830).
The name "OSGB_1936" is essential to distinguish the datum from (for
example) Irish ones.
You might know UKMO proposed to expand GRIB2 for UK National Grid recently.
I commented the same point, and the WMO discussion converged to add datum
name. So similar approach is suggested if we take conservative approach to
expand existing grid mapping attributes.
Best,
Eizi
----- Original Message -----
From: "Wright, Bruce" <bruce.wri...@metoffice.gov.uk>
To: "Bryan Lawrence" <bryan.lawre...@ncas.ac.uk>; <cf-metadata@cgd.ucar.edu>
Sent: Thursday, October 06, 2011 1:42 AM
Subject: Re: [CF-metadata] Question on WKT representation of CRS
(Bentley,Philip)
Hi Bryan,
I suspect it probably is becoming important for weather forecast output
now.
At the Met Office, we're now generating 2km post-processed forecast data
(from models running at up 1.5km resolution). At present, this is mainly
shared internally (and with a small number of 'expert' customers) using
bespoke data formats (which don't fully describe the CRS) . However, in
future I'd expect to be sharing these data more widely, ideally using
CF-netCDF (and GRIB2), and would feel more comfortable, it we could
fully characterise CRS in use, to ensure appropriate use in combination
with other data.
But to echo your last comment, a CRS WKT enhancement should be optional,
and not replace the current CF grid description information - we don't
want to break existing client software, just allow a fuller description
of the CRS where required.
Regards,
Bruce
--
Bruce Wright Expert IT Analyst (Data Management)
Met Office FitzRoy Road Exeter EX1 3PB United Kingdom
Tel: +44 (0)1392 886481 Fax: +44 (0)1392 885681
E-mail: bruce.wri...@metoffice.gov.uk http://www.metoffice.gov.uk
-----Original Message-----
From: cf-metadata-boun...@cgd.ucar.edu
[mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of Bryan Lawrence
Sent: 05 October 2011 12:52
To: cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] Question on WKT representation of CRS
(Bentley,Philip)
Hi Seth
I haven't read all the threads ... but I strongly agree with your last
paragraph!
I have had many conversations with folks who think that adding datums
will make data more usable to the impacts community, where datum errors
can move things by o(10)s of km ... and my protestation that no one
should interpret as physical any differences on those scales from a
(climate) model (even one run at o(km) resolution if such exists) ...
was simply ignored. The reality is exactly what you say, that level of
specificity is simply inappropriate.
I appreciate some of the arguments raised in the thread on storing
lat/lon coordinates, about the need for the use of one in a GIS workflow
- but frankly I think that's an issue about workflow metadata not source
data metadata. As Balaji and others said, there might not even be *one*
datum appropriate for GCM work ...
Of course observational data may well be different, and I'm not sure
about NWP ... especially mesoscale models. So by all means, facilitate
the provision of this information, but don't make it compulsory ... and
I think it would be with WKT?
Cheers
Bryan
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