[gnuastro-devel] [sr #109223] Change default WCS formalism from PCi_j to CDi_j

[Mohammad Akhlaghi]

Update of sr #109223 (project gnuastro):

                Category:               ImageWarp => All Gnuastro           
                  Status:                    None => Need Info              

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Follow-up Comment #3:

Unfortunately SWARP doesn't provide the version number of WCSLIB that it is
using. (just as a side-note, in Gnuastro, version information is taken very
seriously and written to all output headers as described in the book
<https://www.gnu.org/software/gnuastro/manual/html_node/Output-headers.html>.)


So I guess the only way would be to either dig into its code or ask Emmanuel.
But from the formatting of the WCS related keywords, you can guess that SWARP
doesn't use WCSLIB's FITS keyword output. In Gnuastro we directly write
WCSLIB's produced headers into the FITS file. You can see that both the
ordering and the comments on the keywords differs between SWARP and WCSLIB
(Gnuastro's outputs). I think SWARP writes the keywords itsself directly from
the structure.

Maybe we can make a feature request to WSCLIB. Currently `wcshdo' does take
some flags for telling it how to print the header information. So we might be
able to convince Mark Calabretta to add another flag for writing the `CDi_j'
elements. 

I just changed the category of this issue to "All Gnuastro" because all
Gnuastro's programs ultimately use a single function to read and write FITS
files, thus this discussion applies to all of them that deal with FITS WCS
information (the bug #50073 and bug #50073 also applied to all Gnuastro's
programs).

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