taskGNU Astronomy Utilities - Tasks: task #16282, Include ICRS equatorial coordinate...


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task #16282: Include ICRS equatorial coordinate type

Submitter:  Mohammad Akhlaghi <makhlaghi>
Submitted:  Mon 24 Oct 2022 05:27:49 PM UTC
Should Start On:  Sun 23 Oct 2022 11:00:00 PM UTC Should be Finished on:  Sun 23 Oct 2022 11:00:00 PM UTC
Category:  Libraries Priority:  5 - Normal
Item Group:  Enhancement Status:  None
Privacy:  Public Percent Complete:  0%
Assigned to:  None Open/Closed:  Open
Effort:  0.00

Mon 24 Oct 2022 11:06:06 PM UTC, comment #1: 

A nice review of ICRS in relation to FK5 and J2000 is given in Feissel and Mignard 1998. In their Figure 1, they show the pole positions in relation to each other.

We should be able to use these pole positions to convert ICRS to 'eq-j2000' and from that, to all the other coordinate systems that are currently recognized.

Some other references:

Mohammad Akhlaghi <makhlaghi>
Group administrator
Mon 24 Oct 2022 05:27:49 PM UTC, original submission:  

As of Gnuastro 0.19, we still don't recognize the "International Celestial Reference System" or ICRS (which is the IAU approved coordinate system; unlike FK5; that we do support!).

This stems from the fact that in lib/wcs.c we have used NED for the conversion of coordinate system information and NED doesn't have ICRS!

We should find the conversions (possibly from the link above, or other places) and implement them in the WCS library because many surveys like SDSS, J-PLUS or J-PAS use this equatorial coordinate system.

You can reproduce the problem like below:

$ sdssurl=https://dr12.sdss.org/sas/dr12/boss/photoObj/frames
$ wget $sdssurl/301/3716/6/frame-r-003716-6-0117.fits.bz2 -Or.fits.bz2
$ bunzip2 r.fits.bz2
$ astfits r.fits -h0 --wcscoordsys=eq-j2000
astfits: gal_wcs_coordsys_identify: the 'ICRS' value for 'RADESYS' is not yet implemented! Please contact us at bug-gnuastro@gnu.org to implement it

Mohammad Akhlaghi <makhlaghi>
Group administrator


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