Tim,
I could not agree more. Indeed, I would go even further and permit a simple EPSG code as a suitable definition of the geodesy. EPSG:4326 is all you need to specify WGS ellipsoid, datum etc.
crs:epsg_code = 4326 ; //this would be the 99% case. This is how google openlayers, wms, google, bing and others handle the tricky subject of geodesy metadata.
WKT is also very handy, but harder to generate and parse. I suspect this is the 1% case.
http://spatialreference.org/ref/epsg/4326/
regards
Paul Kennedy
Technical Development Manager
Fugro Survey Pty Ltd
24 Geddes St, Balcatta
Western Australia 6021
ABN: 81 009 172 990
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Email : p.kennedy at fugro.com.au
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-----Original Message-----
From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Timothy Hume
Sent: Tuesday, 31 July 2012 9:34 AM
To: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] How to include EPSG codes or WKT information in a CF file [SEC=UNCLASSIFIED]
Hi Jonathan,
Thanks for the help. I can see that option 80 is probably better, but option 69 is a lot easier for software developers to bolt onto existing NetCDF files. Most of the people I talk to don't see why anyone is interested in anything other than latitudes and longitudes on a spherical Earth; all the stuff about shape of the Earth etc is irrelevant to their needs. The truth is, because most of the NWP data I use is on a rather coarse grid, the grid mapping information is not that important; two coordinate variables with the longitudes and latitudes is sufficient for most purposes.
Therefore, the path of least resistance is option 69 (with all its potential pit falls); I think option 80 will be too much, and a lot of data writers will simply decide to add no grid mapping information at all, a worse situation than option 69.
Cheers,
Tim Hume
Bureau of Meteorology
________________________________________
From: CF-metadata [cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Jonathan Gregory [j.m.gregory at reading.ac.uk]
Sent: Monday, 30 July 2012 7:10 PM
To: cf-metadata at cgd.ucar.edu
Subject: [CF-metadata] How to include EPSG codes or WKT information in a CF file [SEC=UNCLASSIFIED]
Dear Tim
There are two open CF trac tickets that relate to this issue, proposing to add new conventions to store OGC information in different ways in CF. Ticket
80
https://cf-pcmdi.llnl.gov/trac/ticket/80 proposes several new attributes which correspond to WKT elements that currently do not have grid_mapping equivalents. Ticket 69
https://cf-pcmdi.llnl.gov/trac/ticket/69 proposed to add an attribute to record the WKT information without translation. Personally I prefer the former because I am concerned about duplication and possible inconsistency of information, but please have a look at the tickets and form your own view, and add comments if you like. So the answer to your question is that there is not yet a CF standard way to do it, but there will be.
Best wishes
Jonathan
----- Forwarded message from Timothy Hume <T.Hume at bom.gov.au> -----
> Date: Mon, 30 Jul 2012 11:36:19 +1000
> From: Timothy Hume <T.Hume at bom.gov.au>
> To: "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
> Subject: [CF-metadata] How to include EPSG codes or WKT information in a CF
> file [SEC=UNCLASSIFIED]
>
> Hi,
>
> I am adding grid mapping information to my NetCDF files. My data are on a lon-lat grid on a spherical Earth. I can put in the standard CF attributes, grid_mapping_name etc, but also want to include the EPSG and WKT codes to help software applications that might want these. I have not been able to find out how this is done in NetCDF-CF, so am using this format:
> =
> int crs ;
> crs:grid_mapping_name = "latitude_longitude" ;
> crs:earth_radius = 6371007.0 ;
> crs:prime_meridian = 0.0 ;
> crs:epsg_code = 4047 ;
> crs:wkt = "GEOGCS[\"Unspecified datum based upon the
> GRS 1980 Authalic Sphere\",DATUM[\"Not_specified_based_on
> _GRS_1980_Authalic_Sphere\",SPHEROID[\"GRS 1980 Authalic
> Sphere\",6371007,0,AUTHORITY[\"EPSG\",\"7048\"]],AUTHORITY[\"EPSG\",\
> "6047\"]],PRIMEM[\"Greenwich\",0,AUTHORITY[\"EPSG\",\"8901\"]],UNIT[\"
> degree\",0.01745329251994328,AUTHORITY[\"EPSG\",\"9122\"]],AUTHORITY[\
> "EPSG\",\"4047\"]]" ;
>
> What do other people do when including this extra grid information?
>
> Cheers,
>
> Tim Hume
> Centre for Australian Weather and Climate Research Bureau of
> Meteorology Melbourne Australia
> _______________________________________________
> CF-metadata mailing list
> CF-metadata at cgd.ucar.edu
> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
----- End forwarded message -----
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Received on Mon Jul 30 2012 - 19:56:14 BST
