[bug #63171] Strange patterns on warped images

[Mohammad Akhlaghi]

Update of bug #63171 (project gnuastro):

                  Status:                    None => In Progress            
             Assigned to:                    None => pedram                 

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Follow-up Comment #5:

I just noticed that this problem also occurs on J-PLUS images. For example,
with the command below, you can download a single-exposure J-PLUS image and
see the effect after running Warp:


$ wget
http://archive.cefca.es/catalogues/vo/siap/jplus-dr2/reduced/get_fits?id=771824
-Om51-single-exposure.fits.fz

$ astwarp m51-single-exposure.fits.fz


So it seems to be more comman than we thought! Therefore more urgent to
find/fix the cause.

However, I did find a solution: to resample each exposure such that the pixel
scale is half (we have 2x2 times more pixels!). This feature becomes much
weaker as you use a higher sampling. In the case of J-PLUS, I resampled the
three exposures to double the sampling, and after stacking, I resampled it
back to the original resolution and these features were gone.

If sampling is the only problem, we may be able to fix it by having a finer
sampled grid. But I am still puzzled by the varying smoothing level!


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