wcs_getA

This simply named script performs most of the critical WCS calibration work:

  • It collects the catalogs and DSS image needed for the job,
  • It runs a gui to allow the user to manually identify matched stars for calibration data,
  • It computes two independent linear XY transformation equations (referred to as WCS0),
  • It derives the standardard WCS parameters for use in a FITS header (referred to as WCS1)
    • The final product of wcs_getA will be an image named A.fits. If A.fits already exists, then this script will exit. 
    
% wcs_getA name.fits
    The image "name.fits" is the original CCD image we have begun to calibrate.

    The wcs_getA and wcs_getB scripts are mostly the same with one important exception: the way they gather the initial set of paired X,Y and Ra,Dec sets. In the getA case, we presumably have only a rough RA,DEC image position in the name.fits header. Hence, in order to find matching sets of X,Y and Ra,Dec values for stars in the CCD image field, we use the wcs_prep script to collect star catalogs (from USNO, SDSS, and 2MASS) and a DSS image matching the position of our CCD image. In the getB case, we use the a ds9 gui inspection (with A.fits) to gather a new (larger) set of input star pair sets and derive a new calibrated image (B.fits).



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