Suppress PROJ4 warning about losing projection by using `to_cf()` instead of `to_dict()`

[pnuu]

This PR removes a warning when getting actual projection details that are needed for CF by using to_cf() instead of to_dict(). This is part of Satpy reader cleanup started in https://github.com/pytroll/satpy/pull/2689

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (e82bf47) 94.06% compared to head (c9b9787) 94.23%. Report is 82 commits behind head on main.

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[mraspaud]

How about using pyproj's crs.to_cf() as a first guess instead of catching the warning? Here's an example output:

In [27]: crs.to_cf()
Out[27]: 
{'crs_wkt': 'PROJCRS["unknown",BASEGEOGCRS["unknown",DATUM["Unknown based on WGS 84 ellipsoid",ELLIPSOID["WGS 84",6378137,298.257223563,LENGTHUNIT["metre",1],ID["EPSG",7030]]],PRIMEM["Greenwich",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8901]]],CONVERSION["unknown",METHOD["Polar Stereographic (variant B)",ID["EPSG",9829]],PARAMETER["Latitude of standard parallel",60,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8832]],PARAMETER["Longitude of origin",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8833]],PARAMETER["False easting",0,LENGTHUNIT["metre",1],ID["EPSG",8806]],PARAMETER["False northing",0,LENGTHUNIT["metre",1],ID["EPSG",8807]]],CS[Cartesian,2],AXIS["(E)",south,MERIDIAN[90,ANGLEUNIT["degree",0.0174532925199433,ID["EPSG",9122]]],ORDER[1],LENGTHUNIT["metre",1,ID["EPSG",9001]]],AXIS["(N)",south,MERIDIAN[180,ANGLEUNIT["degree",0.0174532925199433,ID["EPSG",9122]]],ORDER[2],LENGTHUNIT["metre",1,ID["EPSG",9001]]]]',
 'semi_major_axis': 6378137.0,
 'semi_minor_axis': 6356752.314245179,
 'inverse_flattening': 298.257223563,
 'reference_ellipsoid_name': 'WGS 84',
 'longitude_of_prime_meridian': 0.0,
 'prime_meridian_name': 'Greenwich',
 'geographic_crs_name': 'unknown',
 'horizontal_datum_name': 'Unknown based on WGS 84 ellipsoid',
 'projected_crs_name': 'unknown',
 'grid_mapping_name': 'polar_stereographic',
 'standard_parallel': 60.0,
 'straight_vertical_longitude_from_pole': 0.0,
 'false_easting': 0.0,
 'false_northing': 0.0}

[pnuu]

Oh, that's much better! I tried looking at the methods if any of them provided the needed information. I'll adjust in a bit.

[djhoese]

There is a utility context manager function in some utils module that does this. I use it in geometry.py and other places. I think i left this bit of the CF code because I was hoping we could use the CRS object directly.

[coveralls]

coverage: 93.819%. remained the same when pulling c9b97877229d4b8d121b93186d35cd37150152b1 on pnuu:suppress-to-dict-warning into 522691dc2a39bae6e35a6ba3469920d6f90e592a on pytroll:main.