This script will collect the basic data files we'll need to perform a WCS calibration. The basic call to wcs_prep is shown below:
% wcs_prep n3664R.fits N Y USNO % wcs_prep n3664R.fits N Y allcats arg1 - name of input FITS image arg2 - Y/N for automatic ds9 display arg3 - Y/N for cleaning directory of files arg4 - USNO to use usno catalog onlyI show two examples above in order to demonstrate the use of argument 4. If arg4 is assigned the value of "USNO", then only the USNO B1.0 catalog is used to gather targets for calibration. This is is usually done for very small fields where few sources of any type will generally be available. If any other value is used for arg4 (like "OTHER" or "allcats") then a process ifs used to derive the "best" star targets from USNO, 2MASS and SDSS.
The initial job for wcs_prep is to determine properties of the image to be calibrated (arg1): X size, Y size, Ra, Dec, etc..., and it uses the script ccdrev to do this.
By far, the most extensive work in wcs_prep is preformed with the script skygrab. This workhorse script gathers all the calibration and support information need in a typical WCS calibration run. One can learn a lot about the Spring/Summer tasks of 2014 by following the skygrab link above.
The wcs_pre and skygrab codes are fairly well documented in these scocode pages, but they may be altered occasionally to provide new features. I try to maintain the webdocs here (but, you know).
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Here we see a DSS collected and displayed with wcs_prep. Our original FITS file was a CCD image of NGC4618. I used a local "Faint_Mag.Limit" to set a faint magnitude limit of R2=15 so that a resaonably small number of sources was collected. For now (Aug2015) each target is overplotted with a simple running integer value (which is the order number oin the list of objects in the main catalog file called "STARS.cdfp"). |