[fitsbits] Start of the 'INHERIT' Public Comment Period

Steve wrote:

The data reduction package developed at Lick would not accept
FITS files unless the PHDU contained these keywords:

NAXIS = 2
NAXIS1 = 0
NAXIS2 = 0

So that's what we put in the empty PHDU of our mosaic files. But as
we got close to the point of deploying the instrument producing these
files we found that we could not continue that practice, for the data
reduction package developed at NOAO would not accept such FITS files.
What it wanted was

NAXIS = 0

I note with gratitude that Pence's FITSIO toolkit allowed either
scenario without forcing the issue.

This is also a case in which there is a clear answer in the standard
- either form is legal, but the latter is preferred:

NAXIS Keyword - The value field shall contain a non-negative
integer no greater than 999, representing the number of axes in
the associated data array. A value of zero signifies that no data
follow the header in the HDU.
NAXISn Keywords - The value field of this indexed keyword shall
contain a non-negative integer, representing the number of
elements along axis n of a data array. The NAXISn must be present
for all values n = 1,...,NAXIS, and for no other values of n. A
value of zero for any of the NAXISn signifies that no data follow
the header in the HDU. If NAXIS is equal to 0, there should not
be any NAXISn keywords.
The IRAF support is incomplete, but the Lick behavior is simply
bizarre. It is gratifying that CFITSIO accepted either form, but
data providers are certainly well advised to test compliance with a
range of community software resources.

Note that precisely the same issue applies here as with INHERIT. A
Lick file might be copied with third party software that quite
reasonably would note that since there are no data records that NAXIS
should equal zero. The Lick software would then refuse to recognize
the copy. The original file is conforming FITS, however.

Rob