RE: fun with co-adding images on Disk Set 19

[<aah@nofs.navy.mil>]

Rob,
  Your technique of matching stars, then coadding, is what
most image processing packages do (such as the nice iraf
package immatch).
  One thing you need to watch for is that an incorrect
polar alignment not only causes drift on the CCD, but also
rotation.  I had to rotate as well as translate all of my
images that made up the M31 composite.  In addition, you
want partial-pixel alignment, which means you have to decide
what algorithm you want to use for interpolation.  I'd
recommend looking at how iraf does it (imshift is the
appropriate routine).  Personally, this is a lot of work
and I'd rather use a standard image processing package to
do such reductions than to roll my own.
Arne