[gdal-dev] NetCDF and datum handling suggestion

[Patrick Sunter]

Hi Etienne and others interested in NetCDF driver,

I did some work on WMS display of NetCDF files generated by GDAL
today, and it gave me a chance to play around with & think about how
to handle the Datum issue as described at
http://trac.osgeo.org/gdal/wiki/NetCDF_Improvements#Datumissues .

Here's a first cut suggestion of how GDAL should behave when writing a
new NetCDF file using gdal_translate:
 * Keep saving the current datum info, with names e.g. WGS84, as part
of the WKT that GDAL saves in it's special "spatial_ref" attribute.
 * But _also_ save the actual spheroid parameters for the datum in use
in attributes CF-1 can read, e.g. semi_major_axis, semi_minor_axis,
and inverse_flattening.

Then on import, GDAL would look for its "spatial_ref" by default as
authoritative for datum info, but could use the CF-1 as a backup.

This would parallel the way projection parameters are handled in the
NetCDF driver, i.e. writing WKT in the 'spatial_ref' attribute, but
also writes duplicate CF-1 convention ones if possible to help with
display of the file in NetCDF tools and things like THREDDS.

Perhaps this could be a passable option to the driver whether you
write the duplicate CF-1 datum info or not, with default to on.

(That is, unless the CF conventions have plan to support named datums
coming up imminently?)

cheers, Patrick.