Downscaling

[dnerini]

• add documentation
• add gallery example
• add test

RTD build:

• gallery: https://pysteps.readthedocs.io/en/downscaling/auto_examples/rainfarm_downscale.html#sphx-glr-auto-examples-rainfarm-downscale-py
• reference: https://pysteps.readthedocs.io/en/downscaling/pysteps_reference/downscaling.html

[codecov]

Codecov Report

Merging #173 into master will increase coverage by 0.22%.
The diff coverage is 86.41%.

@@            Coverage Diff             @@
##           master     #173      +/-   ##
==========================================
+ Coverage   74.15%   74.38%   +0.22%     
==========================================
  Files         106      110       +4     
  Lines        8686     8814     +128     
==========================================
+ Hits         6441     6556     +115     
- Misses       2245     2258      +13     

Impacted Files	Coverage Δ
pysteps/io/interface.py	94.73% <ø> (ø)
pysteps/tests/test_io_bom_rf3.py	100.00% <ø> (ø)
pysteps/tests/test_io_fmi_pgm.py	100.00% <ø> (ø)
pysteps/tests/test_io_knmi_hdf5.py	100.00% <ø> (ø)
pysteps/tests/test_io_mch_gif.py	100.00% <ø> (ø)
pysteps/tests/test_io_opera_hdf5.py	100.00% <ø> (ø)
pysteps/tests/test_io_saf_crri.py	86.04% <ø> (ø)
pysteps/visualization/precipfields.py	69.31% <ø> (ø)
pysteps/utils/images.py	67.12% <20.00%> (-1.90%)	⬇️
pysteps/io/exporters.py	43.86% <40.00%> (-0.37%)	⬇️
... and 12 more

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[dnerini]

@jleinonen , I realize now that your implementation of rainfarm includes spatial downscaling only, as opposed to the Rebora et al 2006 paper, which also includes temporal downscaling.

This is not a problem, I'm just wondering what's the best way to proceed.

We could try to complete the code with the temporal part, but this risks to take some time which unfortunately I don't have at the moment.

We could simply specify in the docstring that this implementation is a simplified version which deals with spatial downscaling only. Hopefully the code will be completed and extended at some point.

What's your take on this?

[dnerini]

This still misses some testing of the new module, but I'd say that we are anyway ready for a first round of review. Any feedback and suggestion for improvement is welcomed!

@jleinonen would also be great if you could have a quick look, thanks!

[RubenImhoff]

Hi @dnerini,

This is a great contribution! I also like the gallery, a very clear example of the method.

I added two comment strings in the script for the gallery and I had two questions about the variables in rainfarm.py. So nothing major at all. :)
Regarding the rainfarm.py script, is it an idea to add some comment lines and perhaps refer to the equation numbers in the paper of Rebora et al? That may increase the readability of the script a bit.

Other than that, good to go!

Thanks!