Dear Etienne
To summarise so far: the new parameters required are
horizontal_datum_name
towgs84 (an array of float or double, with 3,6 or 7 values)
prime_meridian_name
reference_ellipsoid_name
projected_coordinate_system_name
geographic_coordinate_system_name
> coordinate system names are indicative, but what would be their use in
> grid_mapping if they are not authoritative (other than allow to
> represent a WKT string in CF grid_mapping)?
I think that would be their only use. As far as CF is concerned, they would
be unstandardised descriptive names, like long_name. I understand from your
email and from
http://home.gdal.org/projects/opengis/wktproblems.html that
the names of datums are not effectively standardised, but I don't think it's
the job of CF to standardise them.
> We can try and see if adding missing parameters to the CF spec
> would resolve the need to have the entire WKT string.
> As it seems consensual that WKT would be optional then it seems
> reasonable to add the missing parts to the CF spec to map a WKT string
> to a grid_mapping definition.
Yes, I agree. Is the above sufficient for the moment? If so we could proceed
to propose it as a trac ticket.
> I have a trac username and enough information to propose fixes to the
> CF spec and docs. All is missing is the time to do it!
I sympathise. It will be useful when you can do it. If the changes to be made
are simply mistakes or ambiguities to be resolved in the document, they could
be proposed as defect tickets rather than modifications to the standard.
> I would also like to add the following information to CF: proj.4
> string as well as WKT representation for all the projections. Should
> this be added to a separate wiki or incorporated into the CF document?
Do you mean a table which gives the equivalences between the parameters as
specified by grid_mapping, WKT and proj.4 for each of the projections? That
would be a very useful resource, I expect. I would suggest that it should not
be part of the CF standard document, but on a wiki.
Best wishes
Jonathan
Received on Thu Jan 05 2012 - 01:15:52 GMT
