Netcdf 6195 assume longlat

[mdsumner]

Implements the wish of #6195 to assume a regular grid NetCDF in a reasonable longitude/latitude range adopts the OGC:CRS84 crs, when all prior attempts to find one have failed.

• when all other attempts have been tried, we check the bounds and give it longlat crs if within -180,360 -90,90
• new config option GDAL_NETCDF_ASSUME_LONGLAT default NO, set to YES to apply the crs
• new open option ASSUME_LONGLAT same as config option GDAL_NETCDF_ASSUME_LONGLAT

There is a python test on netcdf/trmm-nc2.nc that invokes the use of the setting (this file otherwise doesn't have a crs set).

What are related issues/pull requests?

#6195

Example

here on a remote file, provides a CRS OGC:CRS84 only if the config option is set

export GDAL_NETCDF_ASSUME_LONGLAT=YES
gdalinfo NETCDF:"/vsicurl/https://rsg.pml.ac.uk/thredds/fileServer/cci/v6.0-release/geographic/daily/chlor_a/2021/ESACCI-OC-L3S-CHLOR_A-MERGED-1D_DAILY_4km_GEO_PML_OCx-20210101-fv6.0.nc":chlor_a -nomd

examples to invoke option control and overrides

export GDAL_NETCDF_ASSUME_LONGLAT=NO
gdalinfo ../autotest/gdrivers/data/netcdf/trmm-nc2.nc -nomd
gdalinfo ../autotest/gdrivers/data/netcdf/trmm-nc2.nc -nomd -oo ASSUME_LONGLAT=YES

export GDAL_NETCDF_ASSUME_LONGLAT=YES
gdalinfo ../autotest/gdrivers/data/netcdf/trmm-nc2.nc -nomd
gdalinfo ../autotest/gdrivers/data/netcdf/trmm-nc2.nc -nomd -oo ASSUME_LONGLAT=NO

Note that this flollowing file doesn't benefit from the assumption, because its geotransform puts it (just) outside the required range. A possible offshot TODO for me for the VRT driver 'vrt://...?a_ullr', or we could expand the bounds allowed.

gdalinfo ../autotest/gdrivers/data/netcdf/longitude_latitude.nc 

Tasklist

• add open option as well as config option
• Add test case(s)
• Add documentation
• Review
• Adjust for comments
• All CI builds and checks have passed

[rouault]

squashed & merged