[AstroPy] Need some help with wcs

Tue Jan 29 18:07:20 EST 2013

That looks like a valid header to me. WCSDIM is non-standard, but that
should not be a problem since it is not needed to interpret the
header.

The pyast package reads the header successfully, and can convert
between pixel and sky coords.

David

On 29 January 2013 10:49, Christian Ambros <ambrosc at ymail.com> wrote:
> Hi guys,
>
> I'm new to astropy but as I see the potential, I like to use it my Ph.d thesis.
> After I had fun with some of the tuts and their data I started out to use some of my own data and ran into some problems with wcs.
>
> After I opend up a fits with pyfits.open I tried to use wcs= pywcs.WCS(hdulist[0].header) to get the wcs data. I got the error mesg:    312                 # The header may have SIP or distortions, but no core
>     313                 # WCS.  That isn't an error -- we want a "default"
>
> A typical header of the images I want to work with looks like this:
>
> SIMPLE  =                    T / Fits standard
> BITPIX  =                  -32 / Bits per pixel
> NAXIS   =                    2 / Number of axes
> NAXIS1  =                 1023 / Axis length
> NAXIS2  =                 1023 / Axis length
> ORIGIN  = 'NOAO-IRAF FITS Image Kernel July 1999' / FITS file originator
> EXTEND  =                    F / File may contain extensions
> DATE    = '2000-08-24T17:53:06' / Date FITS file was generated
> IRAF-TLM= '18:52:47 (24/08/2000)' / Time of last modification
> TIMESYS = 'UTC     '           / P0S| time scale specification
> RADESYS = 'FK5     '           / P2S| WCS for this file
> EQUINOX =         2.000000E+03 / P0R| equinox
> OBSERVER= 'Reiprich / Englhauser' / P0R| observer(s)
> TELESCOP= 'Skinakas 1.3m'      / P0R| telescope
> INSTRUME= 'CH 360  '           / P0R| instrument name
> OBS_MODE= 'DIRECT MODE'        / RDF| observing mode
> FILTER  = 'R       '           / RDF| filter ID
> OBJECT  = 'R1825.3+30'         / P0R| name of object
> DATE-OBS= '2000-06-07T23:54:40' / P0R| time of obs start (UTC)
> EXPOSURE=         3.000000E+02 / JER| exposure time (s)
> DATE_CCD= '2000-06-08T00:00:20' / JER| end of CCD readout (UTC)
> AIRMASS1= '1.005   '           / JER| air mass at obs start
> AIRMASS2= '1.007   '           / JER| air mass at obs end
> BLANK   =                65535 / P0R| undefined integer values
> CTYPE1  = 'RA---TAN'           / P0R| (assumed) axis type for dim 1
> CTYPE2  = 'DEC--TAN'           / P0R| (assumed) axis type for dim 2
> CRPIX1  =                511.5 / P0R| 'pixel 1 from 0.5 to 1.5' convention
> CRPIX2  =         5.125000E+02 / P0R| 'pixel 1 from 0.5 to 1.5' convention
> CRVAL1  =         2.763750E+02 / P0R| (assumed) sky coord of 1st axis (deg)
> CRVAL2  =         3.045000E+01 / P0R| (assumed) sky coord of 2nd axis (deg)
> CDELT1  =    -1.3944444444E-04 / P0R| (assumed) X degrees per pixel
> CDELT2  =     1.3944444444E-04 / P0R| (assumed) Y degrees per pixel
> OBSGROUP= '07JUN00 '           / JER| group ID of observations
> OBSFNAME= 'DATA0134'           / JER| file ID of observation
> HISTORY   Changes by FIXQSRC:
> HISTORY     * add new keywords (everything except for SIMPLE,BITPIX,NAXIS.);
> HISTORY         filled by information from the observation log files
> HISTORY     * fix I2 bug of PMIS (negative pixel values)
> COMMENT   Keyword types:
> COMMENT     * P0R - reserved  in Paper 0
> COMMENT     * P0S - suggested in Paper 0
> COMMENT     * P2S - suggested in Paper 2
> COMMENT     * RDF - present in ROSAT RDF FITS files
> COMMENT     * JER - introduced by JER
> COMMENT   References:
> COMMENT     * Paper 0: NOST 100-2.0, FITS Definition, http://fits.gsfc.nasa.gov/
> COMMENT     * Paper 2: Paper II in http://fits.gsfc.nasa.gov/documents.html#WCS
> WCSDIM  =                    2
> CD1_1   =  -1.3944444444000E-4
> CD2_2   =  1.39444444440000E-4
> LTM1_1  =                   1.
> LTM2_2  =                   1.
> WAT0_001= 'system=image'
> WAT1_001= 'wtype=tan axtype=ra'
> WAT2_001= 'wtype=tan axtype=dec'
> ZEROCOR = 'Aug 21 19:55 Zero level correction image is Zerom'
> CCDSEC  = '[1:1024,1:1024]'
> CCDMEANT=            651373512
> CCDPROC = 'Aug 22  1:05 CCD processing done'
> FLATCOR = 'Aug 22  1:05 Flat field image is FlatRm with scale=40679.34'
> LTV1    =                  -1.
> NCOMBINE=                   11
>
> As it is written in the documantation the values i.e. CRPIX j, PC i j or CD i j, CDELT i,CTYPE i, CRVAL i, or CUNIT i have to be present. As you can see in the middle of the header they exist ok the WCSAXES value ist missing but there is WCSDIM instead.
> The error message says something about a 'default'. Do those values have to stand in a particular order at a particular position in the header?
> I ran verify() but with no negativ result.
>
> Is there, maybe, an example header to which I can refer to? If so I will write myself a tool to re-write the header of all of those 169 targets I have already in my databank. I would revise my header correcting program which update the header after camera output to get the 'right' header once and for all.
>
> Thanks in advance,
> Christian
> --
> "A little learning never caused anyone's head to explode!"
>
> "Ein wenig Lernen hat noch niemandens Kopf zum Explodieren gebracht!"
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