Usage notes for generating a multi-frequency VLA beam

Python scripts require:
    Numpy
    pyFITS
    pyrap

Setup:
    multiBeamGen.py has a few hardcoded values that need to be changed.
    cbBin : the full path to cassbeam executable
    c2fScript : the full path to the cass2fits.py script

Examples:

1. Generating a set of beam FITS files based on the freqneucies in a VLA measurement set:

    multiBeamGen.py -f 3C147-C-LO.MS -t vla-template.in -o vla_1330_1519 -p 512 --pixelsperbeam=64 -c

    -f : measurement set to determine the frequency information
    -t : cassBeam input file, see the cassbeam documentation
    -o : output filename prefix
    -p : number of pixels in the output file (it is actually +1, so 512 returns a 513 x 513 pixel image)
    --pixelsperbeam : pixels across the primary lobe for the lowest frequency

    generated files:
    [prefix]_xx_im.fits
    [prefix]_xx_re.fits
    [prefix]_xy_im.fits
    [prefix]_xy_re.fits
    [prefix]_yx_im.fits
    [prefix]_yx_re.fits
    [prefix]_yy_im.fits
    [prefix]_yy_re.fits

