[bug #63171] Strange patterns on warped images

[Pedram Ashofteh Ardakani]

Follow-up Comment #9, bug #63171 (project gnuastro):

I thought maybe we can spot some difference between Warp and SWarp. So I made
these two images:

+verbose+
$ astwarp img.fits --width 601,601 --widthinpix  \
          --center 20.53208198,0.9266444499     \
          --cdelt 0.390897/3600 -o img_warp.fits
$ swarp img.fits -SUBTRACT_BACK N -PIXELSCALE_TYPE MANUAL   \
        -PIXEL_SCALE 0.390897 -IMAGEOUT_NAME img_swarp.fits \
        -IMAGE_SIZE 601,601 -CENTER_TYPE MANUAL -CENTER
20.53208198,0.9266444499
-verbose-

Then took the difference:

+verbose+
$ astarithmetic img_warp.fits -h1 img_swarp.fits -h0 - \
                -o warp-vs-swarp.fits
-verbose-

I tried different scales (and limits) to spot the patterns, but it wasn't
visible ... Does it mean that both Warp and SWarp actually ARE producing the
SAME pattern but we can see it better in Warp?

(file #53831)

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Additional Item Attachment:

File name: warp-minus-swarp.jpg           Size:194 KB
    <https://file.savannah.gnu.org/file/warp-minus-swarp.jpg?file_id=53831>



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