Catch or fix pyproj UserWarning when loading an AreaDefinition from a netCDF/CF file

[TomLav]

What's the problem:

pyresample's load_cf_area() forwards a UserWarning from pyproj:
UserWarning: You will likely lose important projection information when converting to a PROJ string from another format.

Severity:

Low. It is annoying to get the warning, but we know where it comes from.

Where does it come from:
The warning is triggered because we call pyproj's CRS.to_dict():

pyresample/pyresample/utils/cf.py

Line 66 in c0025ed

crs_dict = crs.to_dict()

We use CRS.to_dict() to test the type of the projection, not to do any math / transformation with it.

Solutions:
Two solutions:

1. Keep using to_dict() but catch the UserWarning (as done elsewhere in pyresample);
2. Access the parameters in another, more CRS-friendly way, that will not trigger a warning.

[djhoese]

It looks like 2 main properties are looked at:

1. Is this a geostationary projection?
2. Get satellite height

For geostationary check, I added a helper method a while back to the AreaDefinition that covers this:

pyresample/pyresample/geometry.py

Lines 1565 to 1571 in c0025ed

	@property
	def is_geostationary(self):
	"""Whether this area is in a geostationary satellite projection or not."""
	coord_operation = self.crs.coordinate_operation
	if coord_operation is None:
	return False
	return 'geostationary' in coord_operation.method_name.lower()

Extracting that as a utility function would make sense.

For geostationary height there is already a utility function for that:

pyresample/pyresample/utils/proj4.py

Lines 94 to 98 in c0025ed

	def get_geostationary_height(geos_area_crs):
	"""Get the height parameter from a geostationary CRS."""
	params = geos_area_crs.coordinate_operation.params
	h_param = [p for p in params if 'satellite height' in p.name.lower()][0]
	return h_param.value