[gdal-dev] proposed changes to netcdf export behaviour (perhaps RFC)

[Etienne Tourigny]

Dear devs and users,

As part of ongoing improvements to the netcdf driver (mainly for the
proper export of projected CRS) Patrick Sunter and I have prepared a
document - that may serve as an RFC - to deal with proposed changes to
the netcdf driver export and import.

Most of these changes are necessary for proper CF compatible export of
files with projected CRS.
We have written and tested the proposed changes (except 4 in the list
below), and the RFC wiki contains links to the code repository.


The main changes we suggest are summarized as :

1) Changes to metadata items including update to CF-1.5

2) Change to a default south-up orientation for NetCDF data

3) Changes to improve SRS Interoperability between GDAL and NetCDF
CF-1 for Map Projected data
     3.1) When exporting to NetCDF map projections via GDAL, save
projection coordinate variables.
     3.2) Continue saving GDAL custom attribute tags in addition to
CRS definition, but add option not to save
     3.3) Add saving of reference Ellipsoid parameters in CF-1
compliant format used by dataset

4) Add support for different netcdf file types and compression (this
one has not been implemented yet)


We have also fixed a number of issues with specific projections, some
of which have been reported in trac and many which were found with a
new autotest.


As there are a few changes to export and import, I am consulting the
members of the list to know their opinion on

A) do the changes require an RFC vote?
     - We propose to add new -co and Config options.
     - change #2 can cause backwards-compatibility issues in certain
rare cases (see the wiki)

B) can we have help testing the changes, to help catch any issues that
haven't been caught by our testing so far?

C) comments and recommendations from devs and users


For reference:

The (long) RFC page is at:
http://trac.osgeo.org/gdal/wiki/NetCDF_exportUpdateChanges

The following ticket was created to discuss technical issues and store
files such as patches.
http://trac.osgeo.org/gdal/ticket/4294

Status of support of the various projections can be found at
http://trac.osgeo.org/gdal/wiki/NetCDF_ProjectionTestingStatus

For reference, the page containing long-term ideas for improving the
NetCDF driver is at
http://trac.osgeo.org/gdal/wiki/NetCDF_Improvements


Regards,
Etienne Tourigny