[fitsbits] Spectral FITS -- encoding extraction area

[Walter Jaffe]

For encoding irregular extraction areas, I recommand NOT using
a list of polygon vertices, but rather an image, which is much
more general and intuitive.  So in one FITS file you could
include both your spectra and a "finding chart" image, say of
integer values=0,1,2,3.  Pixels where chart values=1 were included
in spectrum 1, etc.  A more complicated variation is where pixels are
included in spectra with various unequal weights.  Then I would
use a 3-d image with the weights for each spectra in one plane of
the image.