I agree; I don't see a need for a 'null'
I think the currently available grid mapping types will be fit for the vertical datum purposes so far discussed
mark
________________________________
From: CF-metadata [cf-metadata-bounces at cgd.ucar.edu] on behalf of Jim Biard [jbiard at cicsnc.org]
Sent: 14 March 2014 19:12
To: CF metadata
Subject: Re: [CF-metadata] Vertical datums (again)
Jonathan,
I thought this was already defined. In the second paragraph of section 5.6, it says that if you aren?t specifying a projected coordinate system (or, I assume, a Cartesian coordinate system such as ECF), then use the name ?latitude_longitude?. I haven?t noticed anything we?ve talked about that would invalidate this usage. We are talking about adding vertical datum specifications and such as further attributes to the variable, but even latitude and longitude values can shift depending on the ellipsoid and/or geoid being used, so these should specified even when there is no projected coordinate system.
Is there something I?m missing?
Grace and peace,
Jim
<
http://www.cicsnc.org/>Visit us on
Facebook<
http://www.facebook.com/cicsnc> Jim Biard
Research Scholar
Cooperative Institute for Climate and Satellites NC<
http://cicsnc.org/>
North Carolina State University<
http://ncsu.edu/>
NOAA's National Climatic Data Center<
http://ncdc.noaa.gov/>
151 Patton Ave, Asheville, NC 28801
e: jbiard at cicsnc.org<mailto:jbiard at cicsnc.org>
o: +1 828 271 4900
On Mar 14, 2014, at 2:21 PM, Jonathan Gregory <j.m.gregory at reading.ac.uk<mailto:j.m.gregory at reading.ac.uk>> wrote:
Dear Jim
Given what you say, what would you suggest for the grid_mapping_name when the
grid_mapping supplies only the figure of the Earth and does not specify any
transformation of coordinate systems?
I agree that grid_mapping is itself an unsatisfactory name, which reflects
the purpose we had in mind when it was first introduced, subsequently
generalised. In the data model we can (and indeed we propose to) call it
something else. We could change its name in the convention but we'd have to
retain the old one too for backward compatibility, I'd argue, and I would
feel it's not worth the effort. It's more important to describe clearly what
it does in principle.
Best wishes and thanks
Jonathan
----- Forwarded message from Jim Biard <jbiard at cicsnc.org<mailto:jbiard at cicsnc.org>> -----
The contents of the grid_mapping variable are doing as much mapping when specifying a projected coordinate system as they are when specifying a geographic (i.e., lon/lat) coordinate system. It is telling you how to understand the spatial coordinate information, particularly in relation to any other choice of coordinate system. It has an unfortunate name, in that it leads us to think about it as ?the thing that tells me how I got from my X & Y coordinate variables to my lon & lat grids?. When you have both X/Y coordinates and lon/lat auxiliary coordinates, the grid_mapping variable is actually telling you how to understand both. There is really no such thing as a ?null mapping?.
_______________________________________________
CF-metadata mailing list
CF-metadata at cgd.ucar.edu<mailto:CF-metadata at cgd.ucar.edu>
http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/attachments/20140317/ed9374b4/attachment.html>
Received on Mon Mar 17 2014 - 10:31:32 GMT
