[gnuastro-devel] [bug #55217] --align not working as expected in left-hand oriented WCS

[Mohammad Akhlaghi]

URL:
  <https://savannah.gnu.org/bugs/?55217>

                 Summary: --align not working as expected in left-hand
oriented WCS
                 Project: GNU Astronomy Utilities
            Submitted by: makhlaghi
            Submitted on: Thu 13 Dec 2018 01:52:58 AM UTC
                Category: Warp
                Severity: 3 - Normal
              Item Group: Output not reasonable
                  Status: Postponed
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any

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Details:

When the input WCS dataset is left-hand oriented (East is to the left of
North, what ever direction North has), then the `--align' operator doesn't
work as expected. 

This problem can be reproduced with a simple mock image:


$ echo "0 25 25 1 2 1 45 0.5 1 5"                    \
       | astmkprof --oversample=1 --mergedsize=49,49 \
                   --output=in.fits
$ astwarp in.fits --flip=0,1 --rotate=20
$ astwarp in_warped.fits --align


The output `in_warped_aligned.fits' will not be aligned with the standard
RA/Dec directions (North to the top and East to the left). 

However, apparently no information is lost, because after opening `in.fits'
and `in_warped_aligned.fits' in ds9 and matching them by their WCS, things
seem reasonable. So --align is apparently just failing in finding the wrong
rotation, it doesn't look like a lower-level problem (in mixing pixels for
example).




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