🚀 go-pugleaf

In article <1992Nov6.221211.9536@stsci.edu> hanisch@stsci.edu writes:
>In article 1deo6pINNlj9@darkstar.UCSC.EDU, sla@umbra.UCSC.EDU (Steve Allen) writes:
>>
>>The question boils down to another question:  Are FITS images representing
>>binned data or sampled data?  How do you tell?
>
>This issue was discussed during the meeting in Boston, and it was agreed
>that the proposal has to be revised to indicate the conventions being
>used.  The consensus was that for FITS, pixel (1,1) is the pixel in the lower
>left-hand corner of an image and that for the purpose of the WCS, this
>pixel represents data from 0.5 to 1.5 in pixel coordinates.  This clarification
>will be added to the proposal.

It will be very important to add this clarification.

From my experience I infer that the astronomical community has
pretty much established that the first pixel in an array is the pixel with
the integer tag 1 which has floating point boundaries 0.5 and 1.5
(middle of pixel is integral).

This is significantly different from the common practice in computer graphics
(CG) where the first pixel in an array is the pixel with
the integer tag 0 which has floating point boundaries 0.0 and 1.0
(edges of pixel are integral).

If the astronomical community will be variant in this way it will be
essential to clearly document the definition of a pixel.  There will
undoubtedly be some astronomical programmers who cling to the more widely
used CG definitions of pixels, and interoperation of their software with
other software will be difficult if these underlying assumptions are not
made explicit in the documentation.
_______________________________________________________________________________
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.