[AstroPy] Problems constructing astropy.wcs.WCS object from multi-plane 2MASS images
Peter Erwin
erwin at mpe.mpg.de
Fri Jul 7 06:12:41 EDT 2017
Hi,
I'm having trouble constructing WCS objects from 2MASS galaxy images.
(My goal is to determine the pixel coordinates of the galaxy center in the
J-band images, given the RA and Dec from e.g. NED or HyperLeda.)
For single-filter images from the 2MASS Large Galaxy Atlas, the following
works just fine:
>>> imdata,hdr = fits.getdata(fits_filename, header=True)
>>> wcsObj = astropy.wcs.WCS(header=hdr)
But for galaxies not in the Large Galaxy Atlas, using the "datacube" JHK images (obtained via NED),
produces this error:
>>> imdata,hdr = fits.getdata(fits_filename, header=True)
>>> wcsObj = astropy.wcs.WCS(header=hdr)
WARNING: FITSFixedWarning: 'celfix' made the change 'Unrecognized projection code (-SI in CTYPE2)'. [astropy.wcs.wcs]
---------------------------------------------------------------------------
InconsistentAxisTypesError Traceback (most recent call last)
<ipython-input-123-a63c9d39ae30> in <module>()
----> 1 wcsObj = astropy.wcs.WCS(header=hdr)
/Library/Frameworks/Python.framework/Versions/3.6/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)
502
503 if _do_set:
--> 504 self.wcs.set()
505
506 for fd in close_fds:
InconsistentAxisTypesError: ERROR 4 in wcs_types() at line 2432 of file cextern/wcslib/C/wcs.c:
Unrecognized projection code (-SI in CTYPE2).
This is puzzling, because the headers for both the Large Galaxy Atlas images and the
JHK datacubes seem to be very similar; in particular, the CTYPE2 header keyword
is 'DEC--SIN' for both sorts of image.
Here's the header from a Large Galaxy Atlas image:
SIMPLE = T
BITPIX = -32
NAXIS = 2
NAXIS1 = 800
NAXIS2 = 800
BLOCKED = T / TAPE MAY BE BLOCKED IN MULTIPLES OF 2880
EXTEND = T / TAPE MAY HAVE STANDARD FITS EXTENSIONS
BSCALE = 1.
BZERO = 0.
ORIGIN = '2MASS ' / 2MASS Survey Camera
CTYPE1 = 'RA---SIN'
CTYPE2 = 'DEC--SIN'
CRPIX1 = 400.5
CRPIX2 = 400.5
CRVAL1 = 23.5757103
CRVAL2 = -29.41875076
CDELT1 = -0.0002777777845
CDELT2 = 0.0002777777845
CROTA2 = 0.
EQUINOX = 2000.
JMAGZP = 20.98749924 / V3 Photometric zero point calibration
COMMENTC= 'CAL updated by T.H. Jarrett, IPAC/Caltech'
SIGMA = 0.7034527063 / Background Residual RMS noise (dn)
COMMENT1= '2MASS mosaic image'
COMMENT2= 'created by T.H. Jarrett, IPAC/Caltech'
END
And here's the header for a typical JHK datacube (note that it actually
has *six* image planes: the first three are sky-subtracted J, H, and K, while
the second three are sky-and-star-subtracted J, H, and K):
SIMPLE = T
BITPIX = -32
NAXIS = 3
NAXIS1 = 301
NAXIS2 = 301
NAXIS3 = 6
BLOCKED = T / TAPE MAY BE BLOCKED IN MULTIPLES OF 2880
EXTEND = T / TAPE MAY HAVE STANDARD FITS EXTENSIONS
ORIGIN = '2MASS ' / 2MASS Survey Camera
TELESCOP= '2MASS ' / North=Mt.Hopkins,South=CTIO
GID = '002433 ' / 2MASS ID #
NNAME = 'NGC_3412' / NED Cat Name
SCANNO = '136 ' / Scan Number
COADDNO = '209 ' / Coadd Number
ORDATE = '971215n ' / Observation Ref Date (yymmdd)
UTDATE = '971215 ' / UT Date of Frame (IC) (yymmdd)
UT = '12:42:44.02' / Time of Frame (IC) (sxgsml)
DATE-OBS= '1997-12-15T12:42:44.02' / Observation Ref Date
EQUINOX = 2000. / Equinox
CTYPE1 = 'RA---SIN' / Orthographic Projection
CTYPE2 = 'DEC---SIN' / Orthographic Projection
CTYPE3 = 'JHKs cube' / 1=J,2=H,3=Ks; 4=J,5=H,6=Ks
RA = 162.7221375 / RA at Frame Center, J2000 (deg)
DEC = 13.4121418 / Dec at Frame Center, J2000 (deg)
CRVAL1 = 162.7221375 / RA at Frame Center, J2000 (deg)
CRVAL2 = 13.4121418 / Dec at Frame Center, J2000 (deg)
CRPIX1 = 151. / Axis 1 Reference Pixel
CRPIX2 = 151. / Axis 2 Reference Pixel
CROTA2 = 0.002134113805 / Image Twist E of N, J2000 (deg)
CDELT1 = -0.0002777777845 / Axis 1 Pixel Size (deg)
CDELT2 = 0.0002777777845 / Axis 2 Pixel Size (deg)
JSKYVAL = 53.5084343 / GALWORKS J Sky Measurement
JSKYSIG = 0.4580373764 / GALWORKS J Noise Measurement
HSKYVAL = 281.6602478 / GALWORKS H Sky Measurement
HSKYSIG = 0.8120117188 / GALWORKS H Noise Measurement
KSKYVAL = 260.6483765 / GALWORKS K Sky Measurement
KSKYSIG = 0.8488883972 / GALWORKS K Noise Measurement
CALID = ' V3-CALIBRATED' / Calibration ID
JSEESH = 1.052999973 / Seeing J shape parameter
HSEESH = 1.018000007 / Seeing H shape parameter
KSEESH = 1.034999967 / Seeing K shape parameter
JMAGZP = 21.0540 / Calibrated J zero point from CALMAN
HMAGZP = 20.6830 / Calibrated H zero point from CALMAN
KMAGZP = 20.0540 / Calibrated K zero point from CALMAN
AMASS_FC= 1.052941084 / Airmass (aprox) at this position
COMMENT > Planes 1, 2 and 3 represent the background
COMMENT > subtracted images of the J, H and Ks bands;
COMMENT > Planes 4,5,6 represent the background **and**
COMMENT > star subtracted images of the J, H and Ks bands
HISTORY > GALWORKS Version 3
HISTORY > image created by galworks, Tom Jarrett, IPAC/Caltech/JPL
END
Any suggestions?
cheers,
Peter
=============================================================
Peter Erwin Max-Planck-Insitute for Extraterrestrial
erwin at mpe.mpg.de Physics, Giessenbachstrasse
tel. +49 (0)176 2481 7713 85748 Garching, Germany
fax +49 (0)89 30000 3495 http://www.mpe.mpg.de/~erwin
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