[gnuastro-devel] [bug #50073] ImageWarp 'rotate' does not correctly propagate WCS pixel scale information into header

[Lee Kelvin]

Follow-up Comment #3, bug #50073 (project gnuastro):

Hello, and thank you for quickly addressing this issue. I can confirm that
using the latest build of GNUAstro largely fixes this issue.

However, I still find that there remains a small offset still when matching
the input file with an output file by WCS in a FITS viewer such as DS9. I once
more make use of the file 'input.fits' attached to the original post. I also
once more use the command:


$ astimgwarp --rotate=360 input.fits


Following recent naming convention changes in GNUAstro, this now produces an
output file named 'input_rotated.fits', attached to this post.

The input file has a pixel scale of 9.416666295793E-05 degrees per pixel, as
encoded by the CD1_1 header keyword.

The output file has a pixel scale of 9.41666629579E-05 degrees per pixel, as
encoded by the CDELT1 header keyword. (Note that the WCS encoding has been
converted from the CD to the PC/CDELT formalism when running ImageWarp as
discussed in support thread #109223.)

You will notice that one significant figure (3) is missing from the output
pixel scale. All other WCS header keywords appear identical.

When I match the input and output files in DS9 and blink between them there
exists an offset of ~0.1 pixels, mostly shifting on the x-axis. I'm unsure if
the loss of this significant figure in the pixel scale is the cause for this
discrepancy. 

Correspondence with Mohammad Akhlaghi has shown that this issue is not
reproducible on his system. I therefore copy below the version numbers for the
mandatory dependencies currently installed on my machine, for your reference.

Regards, 
Lee Kelvin

OS: Ubuntu 15.04 vivid
GNU Astro: 0.2.61-ad122
libgsl0: 1.16+dfsg-2build1
libcfitsio3: 3.340-3
libwcs4: 4.24-1


(file #39518)
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Additional Item Attachment:

File name: input_rotated.fits             Size:8 KB


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