Delete kdtree after saving cache

[pnuu]

This simple change (delete the kdtree after saving the cache) makes it possible to use dask.distributed with nearest resampling. The only requirement is that cache_dir needs to be used, so this will not be very useful for other than geostationary satellites.

• Tests added
• Tests passed
• Passes flake8 satpy

[coveralls]

Coverage increased (+0.001%) to 89.778% when pulling f2c4105 on pnuu:feature-cached-remove-kdtree into ab17a71 on pytroll:master.

[codecov]

Codecov Report

Merging #1227 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1227   +/-   ##
=======================================
  Coverage   89.77%   89.77%           
=======================================
  Files         202      202           
  Lines       30031    30034    +3     
=======================================
+ Hits        26961    26964    +3     
  Misses       3070     3070           

Impacted Files	Coverage Δ
satpy/resample.py	90.77% <100.00%> (+0.01%)	⬆️
satpy/tests/test_resample.py	98.84% <100.00%> (+<0.01%)	⬆️

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[mraspaud]

LGTM

[djhoese]

Awesome! Nice catch.

I'm looking at this code in pyresample and I'm a little confused why we set it to a instance attribute anyway. It gets used in the same function that it is created in. Oh maybe dask needs a reference to it to keep it in memory.

One quick question: doesn't this still require computing the indexes on a local threaded scheduler and then after things are cached we are allowed to go distributed? This means you'd have to switch schedulers between computations, doesn't it?

[pnuu]

The computations appear to happen automatically in the local thread when saving the cache, so doesn't need manual adjustment for the scheduler. At least with the currend Dask version 😬