wcs_getB

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

  • It displays the A.fits image with all available catalog stars overplotted. A set of fitting star star sets is established.
  • 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)
    • Here is a typcial run: 
    
% wcs_getB name.fits
    In the example above, name.fits is the name of the original image we have begun to astrometrically calibrate. It should be noted that the A.fits images (from the wcs_getA script) must be present in the local working directory in order for wcs_getB to run. Also, if the product of wcs_getB, B.fits, is already present, then the script will stop execution.

    As discuused in the documentation on the wcs_getA script, the getA and getB tasks are different in really only only one significant way: the manner in which the sets of X,Y and Ra,Dec are gathered for fitting. As discussed in the getA case, we must use collected catalogs and manually specify a few good sets of cross-matched stars. In the the getB case, we assume that a fairly well-calibrated image, A.fits, is already present. All we need is some way to confirm that the A.fits solution is reasonable, and then use that solution to gather a large number of X,Y and Ra,Dec pairs using a catalog (e.g. STARS.cdfp). The wcs_getB performs this task using the ds9_rwcs script.



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