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 Ph : +61 (0)8 6477 4400 Direct: +61 (0)8 6477 4418 Fax : +61 (0)8 6477 4499 Mobile: +61 (0)439 518 265 Email : [email protected] Skype : p.kennedy.fugro.com -----Original Message----- From: CF-metadata [mailto:[email protected]] On Behalf Of Timothy Hume Sent: Tuesday, 31 July 2012 9:34 AM To: [email protected] 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 [[email protected]] On Behalf Of Jonathan Gregory [[email protected]] Sent: Monday, 30 July 2012 7:10 PM To: [email protected] 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 <[email protected]> ----- > Date: Mon, 30 Jul 2012 11:36:19 +1000 > From: Timothy Hume <[email protected]> > To: "[email protected]" <[email protected]> > 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 > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata ----- End forwarded message ----- _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
