[iaufwg] Voting result on the FITS Standard

[Steve Allen]

On Mon 2008-05-19T16:29:15 -0400, William Pence hath writ:
>    While integral pixel coordinate values coincide with the corresponding
>    array indices, pixel coordinates are defined at all points within the
>    image lattice and outside it (except along conventional axes, see
>    Sect. 8.5).

This is still a bit obscure, perhaps obscure enough that programmers
implementing from the text might introduce an "off by one-half" error.

Is there some strong reason for avoiding an explicit specification
something like this:

    In those cases where pixels can be interpreted as having an
    extent, integral values of pixel coordinates correspond to the
    centers of pixel bins.

>     CRPIXj - [floating-point, indexed, default: 0.0]
>         Pixel coordinate element of the reference point for axis j,
>         corresponding to $r_j$ in Eq. (8.1).  Note that the reference
>         point may lie outside the image and that the first pixel in the
>         image has pixel coordinates $(1.0, 1.0, \ldots)$.

Again, programmers in languages which natively use zero-indexed
arrays may interpret "first" differently than "zeroeth".
I myself prefer to use the word "initial".

Furthermore, I would separate the sentence into one about being
outside the image and another about the counting.

--
Steve Allen                 <sla at ucolick.org>                WGS-84 (GPS)
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