🚀 go-pugleaf

In article <DWELLS.92Nov5190043@fits.cv.nrao.edu>
dwells@fits.cv.nrao.edu (Don Wells) writes:
>Bob Hanisch distributed copies of a paper which he and I prepared in
>February 1988. This paper documented the conclusions reached during a
>WCS workshop held in Charlottesville in January 1988; it should be the
>starting point for a new round of discussions of WCS issues.

In looking over this paper I am left asking a question about the
CRPIX1 and CRPIX2 values at the point of tangency on the sky.

The question boils down to another question:  Are FITS images representing
binned data or sampled data?  How do you tell?

By binned data I mean that pixels are represented by adjacent rectangular
regions and that the value of the pixel represents some kind of integral
(i.e., of the surface brightness of the sky) of a pixel response function
which is nearly uniform over the entire rectangle.

By sampled data I mean that pixels are represented by point samples within
each rectangle, or more precisely, that the pixel response function can be
thought as being very much smaller than the inter-pixel spacing.

In sampled data it is reasonable to think of the "middle" of the pixel as
having an integral coordinate.  In binned data there is some variance of
convention, but many people consider that the "middle" of a pixel has
a half-integral location (e.g., the boundaries between pixels are integral).

There are some applications where the distinction between sampled and binned
data should be made in order to assure a more rigorously correct
interpretation.  In either case, it is important to tell the next user of
this data which convention of pixel numbering is used to specify the
CRPIX values.

For the sake of this WCS proposal, which convention is being used?
_______________________________________________________________________________
Steve Allen          | That was the equation!         |   sla@lick.ucsc.edu
UCO/Lick Observatory | Existence!...Survival must     | If the UC were opining,
Santa Cruz, CA 95064 | cancel out programming! -- Ruk | it wouldn't tell me.