[bug #64615] Fits program's --pixelareaonwcs only accurate on equator

[Mohammad Akhlaghi]

URL:
  <https://savannah.gnu.org/bugs/?64615>

                 Summary: Fits program's --pixelareaonwcs only accurate on
equator
                   Group: GNU Astronomy Utilities
               Submitter: makhlaghi
               Submitted: Fri 01 Sep 2023 08:08:01 PM BST
                Category: Warp
                Severity: 3 - Normal
              Item Group: Output not reasonable
                  Status: In Progress
                 Privacy: Public
             Assigned to: makhlaghi
             Open/Closed: Open
         Discussion Lock: Any


    _______________________________________________________

Follow-up Comments:


-------------------------------------------------------
Date: Fri 01 Sep 2023 08:08:01 PM BST By: Mohammad Akhlaghi <makhlaghi>
As of version 0.20.65, the recently added '--pixelareaonwcs' option of the
FITS program only reports correct values on the equator! As we go to higher or
lower declinations, the area of each pixel becomes artificially larger!

The problem can be reproduced with the commands below where we will produce
the same image, but once on a CRVAL2 (declination of reference point) of 0 and
once with a CRVAL2 of 50.


$ for d in 0 50; do \
    echo "1 2 2 4 0 0 0 0 1 1" \
         | astmkprof --oversample=1 --mergedsize=3,3 \
                     --mforflatpix --crval=180,$d \
                     -o ra180-dec$d.fits --quiet; \
    astfits ra180-dec$d.fits --pixelareaonwcs --quiet; \
    echo "Declination $d:"; \
    aststatistics ra180-dec"$d"_pixarea.fits --minimum --maximum; \
  done


The output is this (at declination of 50, the pixels are much larger!) While
in the TAN projection the reference point (center of this image) should have
the same pixel scale as CDELT (which is correct in the declination 0 scenario
here). 


Declination 0:
6.944444e-11 6.944444e-11
Declination 50:
1.064109e-10 1.091394e-10


I am working on the fix now.







    _______________________________________________________

Reply to this item at:

  <https://savannah.gnu.org/bugs/?64615>

_______________________________________________
Message sent via Savannah
https://savannah.gnu.org/