[gdal-dev] discussion on improvements to the NetCDF driver and CF-1 convention

Etienne Tourigny etiennesky at yahoo.com
Wed Aug 24 16:37:19 EDT 2011

Hi all,
I would like to start a discussion with those interested about fixing various issues in the NetCDF driver.

As it stands, it is not fully CF-1.0 compliant, and produces geographical grids that are not valid for other software.
Also, the infamous "up-side down" problem has been addressed for importing netcdfs, but needs to be addressed for exporting.

Related ticket: http://trac.osgeo.org/gdal/ticket/2129
I have been submitting patches for some time to fix the related issues.

I have identified a number of issues, of which the following have been fixed partially in my proposed patch.

1- conform to the cf-1.0 standard for geographical grids (creating lat and lon dimensions and variables)
2- make netcdf grids "bottom-up" by default, as all software out there uses that convention
3- fix problems related to floating-point / string conversions (also reported in issue #4200 )
4- fix metadata handling and duplication (as reported in issue #4204), and keep band (variable) metadata outside of the global metadata

Pending issues:

5- how to deal with netcdfs which have no datum? Can we assume WGS84?
These files are extremely common, and CF-1.0 has provisions for identifying the key variables, but no Proj/Wkt codes. 
6- fix proper export of projected CRS (this is not fully necessary though) with lat/lon values respecting CF-1.0
7- handle time axis properly (at least when creating a netcdf) - that would be great for import/export of netcdf

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