[task #16272] FITS image to display area change due to distortion

[Mohammad Akhlaghi]

URL:
  <https://savannah.gnu.org/task/?16272>

                 Summary: FITS image to display area change due to distortion
                 Project: GNU Astronomy Utilities
               Submitter: makhlaghi
               Submitted: Thu 06 Oct 2022 06:43:49 PM BST
         Should Start On: Thu 06 Oct 2022 12:00:00 AM BST
   Should be Finished on: Thu 06 Oct 2022 12:00:00 AM BST
                Category: Fits
                Priority: 5 - Normal
              Item Group: Enhancement
                  Status: Postponed
                 Privacy: Public
        Percent Complete: 0%
             Assigned to: pedram
             Open/Closed: Open
         Discussion Lock: Any
                  Effort: 0.00


    _______________________________________________________

Follow-up Comments:


-------------------------------------------------------
Date: Thu 06 Oct 2022 06:43:49 PM BST By: Mohammad Akhlaghi <makhlaghi>
Distortion (or even projection on large scales) causes different pixels to
have different sizes on the World Coordinate System. With DS9, we can see the
effect of the distortions on the coordinate system as lines, but we don't see
the changes in area on a per-pixel case. However, this is important to
understand when confronted with a new image with a new distortion (see bug
#63171).

Therefore it wold be good to have an option in the Fits program for this job,
that would be called like this:


$ astfits img.fits --pixareaonwcs --output=pixarea.fits


The output 'pixarea.fits' will have the same size and same WCS as the input,
however, the pixel values will show the area of that pixel on the WCS (for
example if the two CUNITi values are 'deg', it the pixel values will be in
units of deg^2; this can be multiplied by 3600x3600 to be in units of
arcsec^2, or divided by the pixel scale to show change in units of pixels).
The resulting grid should clearly show the distortion pattern.

Thanks to the features in the newly added warp.c and warp.h library, we
already have functions to calculate the WCS coordinates all the pixel edges.
We can then use the polygon area functions to calculate the area of the
polygon of each input pixel on the sphere (in the case of celestial
coordinates).







    _______________________________________________________

Reply to this item at:

  <https://savannah.gnu.org/task/?16272>

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