Ok you mean that we could add new projections easily to the CF
standard? That's great to know.
I'm not sure I understand your question - do you mean to ask if these
additions to CF would be sufficient to describe most WKT definitions
in pure CF metadata (without the WKT)?
By all means my suggestions are not extensive... I'd have to think
about it a bit more.
A thing that is very useful in WKT is AUTHORITY nodes (namely EPSG codes).
In the case of Datums define named datums and control points, to make
accurate datum shifts. It would be best to add TOWGS84 and perhaps
omething like datum_epsg to keep the datum's epsg code if precise
transformations are needed. For transformations with errors less
than 1km, TOWGS84 parameters (for a Bursa-Wolf transformation) may not
be adequate, see this page:
http://www.unidata.ucar.edu/mailing_lists/archives/netcdf-java/2011/msg00024.html
However, I don't want to start this debate all over, as it seems the
use of EPSG codes is not accepted here (on their own). It seems that
for many applications (especially at the scale most netcdf files are
used for), TOWGS84 parameters are sufficient. A named datum would be
nice, but there are quite a few different ways to identify datums (OGC
vs ESRI).
The following page lists many projections which are supported by
GDAL/OGR and their OGC WKT Name, some of which are not supported by
the CF standard.
That list is not exhaustive and probably not all are frequently used.
I can't say if they all can be represented with CF
metadata.
http://remotesensing.org/geotiff/proj_list/
e.g. the sinusoidal projection at
http://remotesensing.org/geotiff/proj_list/sinusoidal.html
I'll think about which projections we could add easily to the CF
standard (sinusoidal is the first that comes to mind).
Here is a small compilation of the compatabilities between WKT (as
GDAL sees it) and CF-1.5 projections, there are a few
problems/unknowns with some projections:
http://trac.osgeo.org/gdal/wiki/NetCDF_ProjectionTestingStatus
The following page lists WKT parameters:
http://www.geoapi.org/2.0/javadoc/org/opengis/referencing/doc-files/WKT.html
There are a few other parameters like VERT_CS, COMPD_CS and VERT_DATUM
that some users may need.
Regards, Etienne
On Fri, Nov 25, 2011 at 4:57 PM, Jonathan Gregory
<j.m.gregory at reading.ac.uk> wrote:
> Dear Etienne
>
> Thanks for your email. It's great that you can convert successfully between
> CF and WKT in both directions.
>
>> you are correct about the additions that would be needed to support
>> these files.
>
> Those extensions to CF appear to me to be comparatively minor, and we ought
> to be able to add them easily. Is it your impression that we would meet the
> needs of WKT users, given your CF<->WKT conversion, if we added them, or are
> there others that also need to be considered?
>
> Best wishes
>
> Jonathan
>
Received on Mon Dec 05 2011 - 18:03:23 GMT
