[fitsbits] CRPIX clarification

[Mark Calabretta]

On Fri 2008/05/30 12:48:46 +1000, Mark Calabretta wrote
in a message to: Jonathan McDowell <jcm at head.cfa.harvard.edu>,
      Eric Greisen <egreisen at nrao.edu>
and copied to: fitsbits at nrao.edu

>consequently a centre.  As I explained previously, in terms of Fourier
>sampling theory what we call an "image" is actually a shah function.

See
  http://en.wikipedia.org/wiki/Dirac_comb
  http://mathworld.wolfram.com/ShahFunction.html