On Mon, Oct 3, 2011 at 11:04 PM, <cf-metadata-request at cgd.ucar.edu> wrote:
> Message: 3
> Date: Mon, 3 Oct 2011 12:49:42 +0100
> From: "Bentley, Philip" <philip.bentley at metoffice.gov.uk>
> Subject: Re: [CF-metadata] Question on WKT representation of CRS
> To: "Ethan Davis" <edavis at unidata.ucar.edu>, ? ?"CF metadata"
> ? ? ? ?<cf-metadata at cgd.ucar.edu>
> Message-ID:
> ? ? ? ?<E51EDFEBF10BE44BB4BDAF5FC2F024B90363698A at EXXMAIL02.desktop.frd.metoffice.com>
>
> Content-Type: text/plain; ? ? ? charset="us-ascii"
>
> Hi Ethan,
>
> All good questions! I've provided some brief - and probably inadequate -
> responses inline.
>
(snip)
And just an added comment to the below ...
>
>> 4) One last question. The OGC CRS WKT specification is less
>> than two pages of EBNF (without a lot of explanation). How
>> far is the current CF grid mapping spec from complete
>> coverage of the CRS WKT? Prime meridian and some units?
>
> That I can't answer I'm afraid. As you know, there have been a number of
> posts to the CF mailing list over recent months where people have stated
> that having a WKT attribute would allow them to provide a more
> complete/accurate definition of the coordinate system(s) used in their
> netCDF files. I would hope that those same people would be able to
> provide those examples as support for a putative CF proposal regarding
> use of a WKT attribute.
>
> Regards,
> Phil
A particular need for added info is named datums, and the ability to
attach EPSG codes to them.
For example, even having patched GDAL to save as much CF-1 compliant
info about datums as possible, in WKT a relevant example is:
DATUM["Geocentric_Datum_of_Australia_1994",
SPHEROID["GRS 1980",6378137,298.2572221010042,
AUTHORITY["EPSG","7019"]],
TOWGS84[0,0,0,0,0,0,0],
AUTHORITY["EPSG","6283"]],
PRIMEM["Greenwich",0],
UNIT["degree",0.0174532925199433],
AUTHORITY["EPSG","4283"]],
whereas in CF-1 we can mainly only save the spheroid info:
albers_conical_equal_area#semi_major_axis=6.37814e+06
albers_conical_equal_area#inverse_flattening=298.257
but as I understand it, named datums also implicitly refer to a set of
control points which are needed for very accurate georeferenced
display or transformation (see e.g.
http://www.unidata.ucar.edu/mailing_lists/archives/netcdf-java/2011/msg00024.html).
cheers, Patrick.
Received on Mon Oct 03 2011 - 17:38:39 BST
