[AstroPy] Question about multiple WCS in FITS file

[John Zuhone]

Hello,

I have created some FITS image files with multiple WCS systems in them, using the format of appending letters to the keywords like so (here is the output of fitsdump on the header):

# HDU 4 in fiducial_1to3_b1_hdf5_plt_cnt_0000_proj_z.fits:
XTENSION= 'IMAGE   '           / Image extension                                
BITPIX  =                  -64 / array data type                                
NAXIS   =                    2 / number of array dimensions                     
NAXIS1  =                 2048                                                  
NAXIS2  =                 2048                                                  
PCOUNT  =                    0 / number of parameters                           
GCOUNT  =                    1 / number of groups                               
EXTNAME = 'KT      '           / extension name                                 
BTYPE   = 'kT      '                                                            
BUNIT   = 'keV     '                                                            
WCSAXES =                    2                                                  
CRPIX1  =               1024.5                                                  
CRPIX2  =               1024.5                                                  
CDELT1  =     6.96261175585938                                                  
CDELT2  =     6.96261175585938                                                  
CUNIT1  = 'kpc     '                                                            
CUNIT2  = 'kpc     '                                                            
CTYPE1  = 'LINEAR  '                                                            
CTYPE2  = 'LINEAR  '                                                            
CRVAL1  =                  0.0                                                  
CRVAL2  =                  0.0                                                  
LATPOLE =                 90.0                                                  
WCSNAME = 'yt      '                                                            
WCSAXESA=                    2                                                  
CRPIX1A =               1024.5                                                  
CRPIX2A =               1024.5                                                  
CDELT1A = -0.00200479940122947                                                  
CDELT2A =  0.00200479940122947                                                  
CUNIT1A = 'deg     '                                                            
CUNIT2A = 'deg     '                                                            
CTYPE1A = 'RA---TAN'                                                            
CTYPE2A = 'DEC--TAN'                                                            
CRVAL1A =                 30.0                                                  
CRVAL2A =                 45.0                                                  
LONPOLEA=                180.0                                                  
LATPOLEA=                 45.0                                                  
WCSNAMEA= 'celestial'                                                           
RADESYSA= 'ICRS    '                                                            
TIME    =                  0.0                                                  

So far, so good. However, if I try to access these keywords in Python, I cannot get at them:

In [7]: im.header
Out[7]: 
XTENSION= 'IMAGE   '           / Image extension                                
BITPIX  =                  -64 / array data type                                
NAXIS   =                    2 / number of array dimensions                     
NAXIS1  =                 2048                                                  
NAXIS2  =                 2048                                                  
PCOUNT  =                    0 / number of parameters                           
GCOUNT  =                    1 / number of groups                               
EXTNAME = 'KT      '           / extension name                                 
BTYPE   = 'kT      '                                                            
BUNIT   = 'keV     '                                                            
WCSAXES =                    2                                                  
CRPIX1  =               1024.5                                                  
CRPIX2  =               1024.5                                                  
CDELT1  =      6.9626117558594                                                  
CDELT2  =      6.9626117558594                                                  
CUNIT1  = 'kpc     '                                                            
CUNIT2  = 'kpc     '                                                            
CTYPE1  = 'LINEAR  '                                                            
CTYPE2  = 'LINEAR  '                                                            
CRVAL1  =                  0.0                                                  
CRVAL2  =                  0.0                                                  
LATPOLE =                 90.0                                                  
WCSNAME = 'yt      '                                                            

Querying for them in dict-like fashion doesn’t work either. What am I missing that would allow AstroPy to see these?

Best,

John Z
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