Fix warning when CF-writing a Scene with SwathDefinition area

[ghiggi]

This PR fixes an annoying erroneous warning occurring when writing with the CFWriter a satpy Scene to disk.

[djhoese]

What is the end result of this change? Does/should a SwathDefinition get a grid mapping? Because it isn't a gridded dataset so does CF grid mapping data handle 2D lon/lat arrays as coordinates?

[ghiggi]

The end result of this PR is simply to just not raise a warning when the area is a SwathDefinition.
Regarding the other questions:

• Yes, CF conventions say that when you have 2D lon/lat arrays you could/should also add a CRS coordinate for the geographic coordinates and add the grid_mapping: <crs_coord_name> and a coordinate: longitude latitude attribute to the data variables.

• In the case you have projected data (and you also include the longitude/latitude as coordinates), you should/could attach two CRS coordinates to the dataset, and reference both with, for example, grid_mapping: "crsWGS84: longitude latitude goes_abi_1km x, y"

[djhoese]

Note that there are some failing tests in all PRs due to an update in NetCDF and how we handle compression (apparently). @pnuu and @sfinkens were looking into it.

[ghiggi]

@djhoese I kinda just rushed on this because I would really like to have this warning removed with the next satpy release (which I plan to use to run the production of the dataset I am working on) to avoid my production log file and terminals be overwhelmed by this logger warning.
I modified the code to keep almost the current behavior and just do not print the warning if the area is a SwathDefinition.

[mraspaud]

@ghiggi failing tests should now be fixed, feel free to merge main into your PR to fix CI

[ghiggi]

@mraspaud I further simplified the PR to just avoid issuing a warning when the area is a SwathDefinition.
I guess it's ready to be merged ... but let's wait the tests ... ;)

[codecov]

Codecov Report

Merging #2411 (be76c77) into main (a2b1d1c) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #2411   +/-   ##
=======================================
  Coverage   94.76%   94.76%           
=======================================
  Files         329      329           
  Lines       48879    48880    +1     
=======================================
+ Hits        46319    46320    +1     
  Misses       2560     2560           

Flag	Coverage Δ
behaviourtests	4.42% <0.00%> (-0.01%)	⬇️
unittests	95.39% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
satpy/writers/cf_writer.py	95.64% <100.00%> (+0.01%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[coveralls]

Coverage: 95.349% (+0.0001%) from 95.349% when pulling be76c77 on ghiggi:fix-crs-swath-warning into a2b1d1c on pytroll:main.