dataset attrs are ignored upon writing

[veenstrajelmer]

When writing a uds to a file, the provided attributes are overwritten by the conventions from xugrid. This might be desireable behaviour for the Conventions attribute (but I'd like to know more about this), but the other attrs should not be dropped in my view.

import xugrid as xu

uds = xu.data.adh_san_diego()
uds = uds.assign_attrs({'Conventions': 'CF-1.8 UGRID-1.0 Deltares-0.10', #TODO: add Deltares convention (was CF-1.8 UGRID-1.0)
                        'institution': 'Deltares',
                        'references': 'https://www.deltares.nl'})

file_out = 'test_conventions.nc'
uds.ugrid.to_netcdf(file_out)

uds2 = xu.open_dataset(file_out)
print(uds.attrs)
print(uds2.attrs)

Returns:

• {'Conventions': 'CF-1.8 UGRID-1.0 Deltares-0.10', 'institution': 'Deltares', 'references': 'https://www.deltares.nl'}
• {'Conventions': 'CF-1.8 UGRID-1.0'}

Also, should it not be CF-1.9? ocean_sigma_over_z_coordinate was only correct from then onwards

[Huite]

https://github.com/Deltares/xugrid/blob/262f759abf0667da2b2278fb208ced119a0a3c06/xugrid/ugrid/ugrid2d.py#L360C7-L360C83

This is rather cutting the corner, indeed!