Only add longitude/latitude variables in cf_writer if they are not included already.

[ninahakansson]

Only add lon/lat variables if they are not included already.
Level1c4pps ended up with both lat/lon and latitude/longitude coordinates.

• Tests added
• Passes flake8 satpy

[coveralls]

Coverage increased (+0.02%) to 90.484% when pulling 344d78f on ninahakansson:fix_cf_writer_latlons into 5cf76e6 on pytroll:master.

[codecov]

Codecov Report

Merging #1357 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1357      +/-   ##
==========================================
+ Coverage   90.46%   90.48%   +0.01%     
==========================================
  Files         228      228              
  Lines       33211    33269      +58     
==========================================
+ Hits        30045    30103      +58     
  Misses       3166     3166              

Impacted Files	Coverage Δ
satpy/tests/writer_tests/test_cf.py	99.64% <100.00%> (+0.02%)	⬆️
satpy/writers/cf_writer.py	94.09% <100.00%> (+0.20%)	⬆️
satpy/tests/reader_tests/test_utils.py	100.00% <0.00%> (ø)
satpy/readers/ahi_gridded.py
satpy/tests/reader_tests/test_ahi_gridded.py
...tpy/tests/reader_tests/test_ahi_l1b_gridded_bin.py	99.34% <0.00%> (ø)
satpy/readers/ahi_l1b_gridded_bin.py	99.05% <0.00%> (ø)
satpy/readers/utils.py	90.17% <0.00%> (+0.17%)	⬆️

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[mraspaud]

To make this clearer, could we have if ('lat' in dataarray.coords and...?

[mraspaud]

@ninahakansson Thanks for adding this. Do you know where the lon and lat variants are coming from? afaik we use the full longitude and latitude names in satpy.

[ninahakansson]

The lat/lon is from level1c4pps and from PPS. So in one way they do not belong here I guess. We have the include_lonlats attribute that in level1c4pps is set to False to avoid adding lat/lons again. But in area2cf this attribute is ignored if the data is in Swath definition. This line:
if isinstance(dataarray.attrs['area'], SwathDefinition) or strict:
Changing the or => and would also solve my problem. But I am afraid that would break something for other users.

[mraspaud]

@ninahakansson changing or with and would change the meaning of this. strict means that we want to include lons/lats even if there is a valid grid mapping.

[mraspaud]

Good start. I'm missing a test that describe your use case, with the renaming of the coordinates. Maybe that would be testing the _collect_datasets function?

[mraspaud]

LGTM, thanks for fixing the lon/lat overwrite!

[mraspaud]

@sfinkens do you want to check this against pygac-fdr before I merge this?

[sfinkens]

No, go ahead! I'll see what the system tests will find.