GNU Astronomy Utilities  Tasks: task #16222, Arithmetic operators to convert...
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task #16222: Arithmetic operators to convert areas for example mag/arcsec2 to counts/pix
Submitter:  Mohammad Akhlaghi <makhlaghi>  
Submitted:  Tue 28 Jun 2022 05:53:47 PM UTC  
Should Start On:  Mon 27 Jun 2022 11:00:00 PM UTC  Should be Finished on:  Mon 27 Jun 2022 11:00:00 PM UTC 
Category:  Arithmetic  Priority:  5  Normal 
Item Group:  Enhancement  Status:  Postponed 
Privacy:  Public  Percent Complete:  0% 
Assigned to:  None  Open/Closed:  Open 
Effort:  0.00 
( Jump to the original submission )
Mon 24 Apr 2023 07:59:11 PM UTC, comment #7: 
Mohammad Akhlaghi <makhlaghi> 
Sun 26 Mar 2023 08:21:26 AM UTC, comment #6: Okay, sir.

Bharat <bharat> 
Sat 25 Mar 2023 12:18:51 AM UTC, comment #5: I am very busy in the next few days, so how about confirming the equation in the Matrix chat room for comments from others? In the meantime go on with the rest of the steps beyond that function: even if the equation is wrong, the necessary steps before and after it will be the same ;).

Mohammad Akhlaghi <makhlaghi> 
Fri 24 Mar 2023 08:08:44 PM UTC, comment #4: Thanks Mohammad sir, this clears most of my doubts.
required code will going to update in lib/arithmetic.c, gnuastro/arithmetic.h and gnuastro/units.h

Bharat <bharat> 
Tue 21 Mar 2023 02:54:23 PM UTC, comment #3: Thanks for your interest in this task Bharat.

Mohammad Akhlaghi <makhlaghi> 
Sun 19 Mar 2023 06:16:53 PM UTC, comment #2: Hello Mohammad SirðŸ‘‹,

Bharat <bharat> 
Thu 09 Mar 2023 06:15:21 PM UTC, comment #1: Hello! I have reviewed the task and believe that I can make an attempt to solve the issue.

Bharat <bharat> 
Tue 28 Jun 2022 05:53:47 PM UTC, original submission:
It would be very useful to have operators for converting arcsec^2 to number of pixels, and viceversa. Based on an input WCS. We currently have the necessary operators to convert magnitudes to counts and viceversa, but we don't have any for converting common area units.

Mohammad Akhlaghi <makhlaghi> 
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20220628  makhlaghi  CarbonCopy    Added email is unavailable 
Thanks a lot Bharat, the commit looks good.
There is just one thing that worries me: the 'gal_wcs_pixel_scale' function which is called on every conversion. This function is computationally much more complex than the actual unit conversion. So if someone wants to convert thousands of values, 'gal_wcs_pixel_scale' will be called thousands of times.
A more robust way is to estimate the pixel scale once (before 'arithmetic_function_binary_flt' starts to parse the set of inputs), and pass the pixel scale to 'gal_units_arcsecsq_to_pixnum' instead of the WCS ;).
By the way, can you also implement the inverse operation?