[gnuastro-devel] [task #14625] Option to write a keyword title

[Mohammad Akhlaghi]

URL:
  <http://savannah.gnu.org/task/?14625>

                 Summary: Option to write a keyword title
                 Project: GNU Astronomy Utilities
            Submitted by: makhlaghi
            Submitted on: Wed 06 Sep 2017 10:50:34 AM CEST
         Should Start On: Wed 06 Sep 2017 12:00:00 AM CEST
   Should be Finished on: Wed 06 Sep 2017 12:00:00 AM CEST
                Category: Fits
                Priority: 5 - Normal
              Item Group: Enhancement
                  Status: Postponed
                 Privacy: Public
        Percent Complete: 0%
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
                  Effort: 0.00

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Details:

The FITS standard recognizes blank keyword lines and also comment lines
(starting with `\'). These features help write the keywords in related groups
in an easy to read (by eye) format, for example this output of Gnuastro's Crop
program:


XTENSION= 'IMAGE   '           / IMAGE extension                              
 
BITPIX  =                  -32 / number of bits per data pixel                
 
NAXIS   =                    2 / number of data axes                          
 
NAXIS1  =                  251 / length of data axis 1                        
 
NAXIS2  =                  251 / length of data axis 2                        
 
PCOUNT  =                    0 / required keyword; must = 0                   
 
GCOUNT  =                    1 / required keyword; must = 1                   
 
BUNIT   = 'ELECTRONS/S'        / physical units                               
 
                                                                              
 
                      / WCS information                                       
 
WCSAXES =                    2 / Number of coordinate axes                    
 
CRPIX1  =               2003.5 / Pixel coordinate of reference point          
 
CRPIX2  =               -996.5 / Pixel coordinate of reference point          
 
PC1_1   =             -1.0E+00 / Coordinate transformation matrix element     
 
CDELT1  =  1.66666666666670E-05 / [deg] Coordinate increment at reference
point 
CDELT2  =  1.66666666666667E-05 / [deg] Coordinate increment at reference
point 
CUNIT1  = 'deg'                / Units of coordinate increment and value      
 
CUNIT2  = 'deg'                / Units of coordinate increment and value      
 
CTYPE1  = 'RA---TAN'           / Right ascension, gnomonic projection         
 
CTYPE2  = 'DEC--TAN'           / Declination, gnomonic projection             
 
CRVAL1  =            53.122751 / [deg] Coordinate value at reference point    
 
CRVAL2  =           -27.805089 / [deg] Coordinate value at reference point    
 
LONPOLE =                180.0 / [deg] Native longitude of celestial pole     
 
LATPOLE =           -27.805089 / [deg] Native latitude of celestial pole      
 
RADESYS = 'FK5'                / Equatorial coordinate system                 
 
EQUINOX =               2000.0 / [yr] Equinox of equatorial coordinates       
 
                                                                              
 
                      / Crop information                                      
 
ICF1_1  = '/path/to/input/image/in/computer/'                               
ICF1PIX = '2733:2983,2803:3053' / Range of pixels used for this output.       
 
                                                                              
 
                      / Versions and date                                     
 
DATE    = '2017-09-06T08:29:02' / file creation date (YYYY-MM-DDThh:mm:ss UT) 
 
CFITSIO = '3.41    '           / CFITSIO version.                             
 
WCSLIB  = '5.16    '           / WCSLIB version.                              
 
GSL     = '2.4     '           / GNU Scientific Library version.              
 
GNUASTRO= '0.3.57-ae2f'        / GNU Astronomy Utilities version.             
 
COMMIT  = 'v0-8-g91809f5'      / Git's commit description in running dir.     
 
END


With this task, I am suggesting an option (maybe named) `--keygrouptitle') to
allow the users to create such titles and subsequently write related keywords
in the FITS HDU together under it. 

The focus of FITS keywords is mainly for software reading them automatically
and that is indeed the major use case. But when they are nicely categorized in
such a fashion, people will be encouraged to look at them directly, with a
command like the one below, and get a good general feeling of the dataset's
meta-data.


$ astfits -p image.fits





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