Enable solar zenith angle caching for the DayNightCompositor

[simonrp84]

At present, the DayNightCompositor does not use the new lat/lon cacheing feature, which slows down processing of this type of composite.
This PR switches the compositor to use the ready-made cache features in angles.py. It requires a small modification to the get_cos_sza in that file to deal with chunking of RGB composites.

• Tests added

[djhoese]

A couple changes...and what do you think about tests? Maybe add an RGB case to the existing angles tests?

[simonrp84]

Yeah, this probably needs some new tests (at least the new helper function). I don't have a huge amount of time right now but can try to add some next week.

[djhoese]

Ok, I think this is done. It didn't actually work the way you had it (something I didn't notice either). The test cases don't have dims defined so I add a default that assumes (y, x). I added tests with RGB with no dims and RGB with dims.

[pnuu]

LGTM

[pnuu]

The TestDayNightCompositor.test_daynight_area test fails with

self = {'name': 'dn_test', 'optional_prerequisites': [], 'prerequisites': []}
projectables = [<xarray.DataArray 'array-4105b65f4b41e351f1402df7e0f94aca' (bands: 3, y: 2, x: 2)>
dask.array<array, shape=(3, 2, 2),...
Attributes:
    test:        b
    start_time:  2018-01-01 18:00:00
    area:        <MagicMock id='139787571969568'>]
kwargs = {}
foreground_data = <xarray.DataArray 'array-4105b65f4b41e351f1402df7e0f94aca' (bands: 3, y: 2, x: 2)>
dask.array<array, shape=(3, 2, 2), ...x
Attributes:
    test:        a
    start_time:  2018-01-01 18:00:00
    area:        <MagicMock id='139787571969568'>
lim_low = 0.08715574274765814, lim_high = 0.03489949670250108
get_cos_sza = <function get_cos_sza at 0x7f22fdc6c790>

    def __call__(self, projectables, **kwargs):
        """Generate the composite."""
        projectables = self.match_data_arrays(projectables)
        # At least one composite is requested.
        foreground_data = projectables[0]
    
        lim_low = np.cos(np.deg2rad(self.lim_low))
        lim_high = np.cos(np.deg2rad(self.lim_high))
        try:
>           coszen = np.cos(np.deg2rad(projectables[2 if self.day_night == "day_night" else 1]))
E           IndexError: list index out of range

satpy/composites/__init__.py:632: IndexError

During handling of the above exception, another exception occurred:

self = <satpy.tests.test_composites.TestDayNightCompositor testMethod=test_daynight_area>

    def test_daynight_area(self):
        """Test compositor both day and night portions when SZA data is not provided."""
        from satpy.composites import DayNightCompositor
        comp = DayNightCompositor(name='dn_test', day_night="day_night")
>       res = comp((self.data_a, self.data_b))

satpy/tests/test_composites.py:351: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
satpy/composites/__init__.py:637: in __call__
    coszen = get_cos_sza(foreground_data)
satpy/modifiers/angles.py:369: in get_cos_sza
    lons, lats = _get_valid_lonlats(data_arr.attrs["area"], chunks)
satpy/modifiers/angles.py:142: in __call__
    arg_hash = _hash_args(*new_args, unhashable_types=self._uncacheable_arg_types)
satpy/modifiers/angles.py:258: in _hash_args
    arg_hash.update(json.dumps(tuple(hashable_args)).encode('utf8'))
/usr/share/miniconda3/envs/test-environment/lib/python3.9/json/__init__.py:231: in dumps
    return _default_encoder.encode(obj)
/usr/share/miniconda3/envs/test-environment/lib/python3.9/json/encoder.py:199: in encode
    chunks = self.iterencode(o, _one_shot=True)
/usr/share/miniconda3/envs/test-environment/lib/python3.9/json/encoder.py:257: in iterencode
    return _iterencode(o, 0)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <json.encoder.JSONEncoder object at 0x7f231941a700>
o = <MagicMock id='139787571969568'>

    def default(self, o):
        """Implement this method in a subclass such that it returns
        a serializable object for ``o``, or calls the base implementation
        (to raise a ``TypeError``).
    
        For example, to support arbitrary iterators, you could
        implement default like this::
    
            def default(self, o):
                try:
                    iterable = iter(o)
                except TypeError:
                    pass
                else:
                    return list(iterable)
                # Let the base class default method raise the TypeError
                return JSONEncoder.default(self, o)
    
        """
>       raise TypeError(f'Object of type {o.__class__.__name__} '
                        f'is not JSON serializable')
E       TypeError: Object of type MagicMock is not JSON serializable

[djhoese]

MOCKING!?!?!?!

Edit: ...I'll see what I can do.

[codecov]

Codecov Report

Merging #2105 (d503619) into main (56eb21b) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2105      +/-   ##
==========================================
+ Coverage   93.92%   93.95%   +0.02%     
==========================================
  Files         283      283              
  Lines       42715    42877     +162     
==========================================
+ Hits        40120    40285     +165     
+ Misses       2595     2592       -3     

Flag	Coverage Δ
behaviourtests	4.75% <6.45%> (+0.04%)	⬆️
unittests	94.51% <100.00%> (+0.02%)	⬆️

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

Impacted Files	Coverage Δ
satpy/composites/__init__.py	90.14% <100.00%> (+0.19%)	⬆️
satpy/modifiers/angles.py	99.14% <100.00%> (+0.05%)	⬆️
satpy/tests/test_composites.py	100.00% <100.00%> (ø)
satpy/tests/test_modifiers.py	100.00% <100.00%> (ø)
satpy/readers/fci_l2_nc.py	99.45% <0.00%> (-0.01%)	⬇️
satpy/tests/reader_tests/test_seviri_l1b_icare.py	100.00% <0.00%> (ø)
satpy/readers/fci_l1c_nc.py	98.05% <0.00%> (+0.02%)	⬆️
satpy/tests/test_yaml_reader.py	99.60% <0.00%> (+0.03%)	⬆️
satpy/readers/yaml_reader.py	97.27% <0.00%> (+0.44%)	⬆️

---

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[coveralls]

Coverage increased (+0.03%) to 94.45% when pulling d503619 on simonrp84:chunkify_daynightcomposite into 56eb21b on pytroll:main.

[djhoese]

Ok with Panu's approval and the simple fix I've made since then, I think this is good to go. Merging...

[simonrp84]

Thanks for your reviews / coding on this @pnuu and @djhoese !