Output of attempting to load CLASS-generated FITS spectrum into specutils

ipython_session.py

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Python 3.6.0 |Anaconda custom (x86_64)| (default, Dec 23 2016, 13:19:00)
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Using matplotlib backend: MacOSX

In [1]: import specutils
INFO:root:Successfully loaded reader "cubetest1".
INFO:root:Successfully loaded reader "tabular-fits".
INFO:root:Successfully loaded reader "wcs1d-fits".

In [3]: s1d = specutils.wcs_fits_reader.wcs1d_fits('test_L1455IRS1_DCN2-1.fits')
INFO:root:Spectrum file looks like wcs1d-fits
WARNING: Header block contains null bytes instead of spaces for padding, and is not FITS-compliant. Nulls may be replaced with spaces upon writing. [astropy.io.fits.header]
WARNING:astropy:Header block contains null bytes instead of spaces for padding, and is not FITS-compliant. Nulls may be replaced with spaces upon writing.
WARNING: FITSFixedWarning: 'celfix' made the change 'Linear transformation matrix is singular'. [astropy.wcs.wcs]
WARNING:astropy:FITSFixedWarning: 'celfix' made the change 'Linear transformation matrix is singular'.
---------------------------------------------------------------------------
SingularMatrixError                       Traceback (most recent call last)
<ipython-input-3-165e2b31c6c4> in <module>()
----> 1 s1d = specutils.wcs_fits_reader.wcs1d_fits('test_L1455IRS1_DCN2-1.fits')
      2

/Users/tsrice/anaconda3/lib/python3.6/site-packages/specutils-0.1.dev727-py3.6.egg/specutils/io/registers.py in wrapper(*args, **kwargs)
     32         @wraps(func)
     33         def wrapper(*args, **kwargs):
---> 34             return func(*args, **kwargs)
     35         return wrapper
     36     return decorator

/Users/tsrice/anaconda3/lib/python3.6/site-packages/specutils-0.1.dev727-py3.6.egg/specutils/io/default_loaders/wcs_fits_reader.py in wcs1d_fits(file_name, spectral_axis_unit, **kwargs)
     37     with fits.open(file_name, **kwargs) as hdulist:
     38         header = hdulist[0].header
---> 39         wcs = WCS(header)
     40
     41         if 'BUNIT' in header:

/Users/tsrice/anaconda3/lib/python3.6/site-packages/astropy/wcs/wcs.py in __init__(self, header, fobj, key, minerr, relax, naxis, keysel, colsel, fix, translate_units, _do_set)
    501
    502         if _do_set:
--> 503             self.wcs.set()
    504
    505         for fd in close_fds:

SingularMatrixError: ERROR 3 in wcsset() at line 2213 of file cextern/wcslib/C/wcs.c:
Linear transformation matrix is singular.
ERROR 3 in linset() at line 607 of file cextern/wcslib/C/lin.c:
PCi_ja matrix is singular.

In [5]: from astropy.io.fits import getdata

In [6]: data, header = getdata("test_L1455IRS1_DCN2-1.fits", header=True)
WARNING: Header block contains null bytes instead of spaces for padding, and is not FITS-compliant. Nulls may be replaced with spaces upon writing. [astropy.io.fits.header]
WARNING:astropy:Header block contains null bytes instead of spaces for padding, and is not FITS-compliant. Nulls may be replaced with spaces upon writing.

In [10]: data
Out[10]:
array([[[[-0.00654329,  0.01778164, -0.01153884, ..., -0.01729367,
           0.01069437, -0.01851475]]]])            

In [11]: data.shape
Out[11]: (1, 1, 1, 37275)
      
In [7]: header
Out[7]:
SIMPLE  =                    T         /
BITPIX  =                  -64
NAXIS   =                    4         /
NAXIS1  =                37275         /
NAXIS2  =                    1         /
NAXIS3  =                    1         /
NAXIS4  =                    1         /
BLOCKED =                    T         /
DATAMIN = -0.146224617958E+000         /
DATAMAX =  0.140489089489E+001         /
BUNIT   = 'K       '                   /
CTYPE1  = 'FREQ    '                   /
CRVAL1  =  0.000000000000E+000         / Offset frequency
CDELT1  =  0.488281250000E+005         / Frequency resolution
CRPIX1  =  0.176140019531E+005         /
CTYPE2  = 'RA---GLS'                   /
EQUINOX =  0.200000000000E+004         /
CRVAL2  =  0.519129166667E+002         /
CDELT2  =  0.000000000000E+000         /
CRPIX2  =  0.000000000000E+000         /
CTYPE3  = 'DEC--GLS'                   /
CRVAL3  =  0.302175000000E+002         /
CDELT3  =  0.000000000000E+000         /
CRPIX3  =  0.000000000000E+000         /
CTYPE4  = 'STOKES  '                   /
CRVAL4  =      1.0000000000000         /
CDELT4  =      0.0000000000000         /
CRPIX4  =      0.0000000000000         /
TELESCOP= '30ME1-LI-F0-'               /
OBJECT  = 'L1455IRS1   '               /
LINE    = 'DCN(2-1)    '               / Line name
RESTFREQ=  0.144828001000E+012         / Rest frequency
VELO-LSR=  0.500000000000E+004         / Velocity of reference channel
DELTAV  = -0.101073712111E+003         / Velocity spacing of channels
IMAGFREQ=  0.157326768103E+012         / Image frequency
TSYS    =  0.845444717407E+002         / System temperature
OBSTIME =  0.165860595703E+004         / Integration time
SCAN-NUM=  0.100000000000E+001         / Scan number
TAU-ATM =  0.288365986198E-001         / Atmospheric opacity
NPHASE  =                    1         / Number of frequency phases
DELTAF1 =  0.000000000000E+000         / Frequency offset Phase 1
PTIME1  =  0.498978763819E+000         / Duration of Phase 1
WEIGHT1 =  0.000000000000E+000         / Weight of Phase 1
GAINIMAG=  0.501190014184E-001         / Image sideband gain ratio
BEAMEFF =  0.930000007153E+000         / Beam efficiency
FORWEFF =  0.930000007153E+000         / Image sideband gain ratio
ORIGIN  = 'CLASS-Grenoble  '           /
DATE    = '2017-09-21T00:00:00.000'    / Date written
TIMESYS = 'UTC             '           /
DATE-OBS= '2014-12-26T18:48:39.588'    / Date observed
DATE-RED= '2017-09-21T00:00:00.000'    / Date reduced
ELEVATIO=  0.592332514636E+002         /  Telescope elevation
AZIMUTH =  0.000000000000E+000         /  Telescope azimuth
UT      = ' 18:48:39.588'              /  Universal time at start
LST     = ' 00:55:48.714'              /  Sideral time at start

Yeah, setting CDELT2, CDELT3, and CDELT4 to 1 allows the WCS object to be created.