`gradient_search` fails when resampling Himawari data

[simonrp84]

`gradient_search` fails when resampling Himawari data

[mraspaud]

@simonrp84 thanks for reporting the issue.

It looks like pyresample complains that the source and destination areas are the same, which is actually true for some of the channels of the true color image I suppose, and probably not for others.
My first reaction here is why not use the native resampler instead? Are you after the bilinear interpolation gradient search provides?

[simonrp84]

No, this is just a simple example to prove the bug. I'm actually trying to use the true_color_with_night_ir composite, which is unable to use native as it has non-geos data included. It produces the same error.

[mraspaud]

I understand. I suppose one solution will be to make this a warning rather than an error...

[djhoese]

@mraspaud perhaps Satpy, if it doesn't already, should skip resampling data in these cases and instead do a .copy(deep=True) on the DataArray? Why don't we see this issue with the kdtree version?

[djhoese]

Wait...are we completely wasting time with all resamplers by asking to resample data to its same projection?!?!? No. I don't believe it.

[simonrp84]

Yeah, that was going to be my next question: If this is a warning rather than an error then what happens with the data? Sounds like it might still get 'resampled' even for the bands where there's no need...

[mraspaud]

So, looking at this I can see that in the case of the kdtree resampler, the resampling will take place even if source and target areas are identical. Native works around it by nature (sizes being the same, nothing is done). Gradient search atm raises an error. Working on a PR for the latter.