[fitsbits] Associating ancillary data with primary HDU

[Steve Allen]

On Fri 2014-05-09T16:24:42 -0400, William Thompson hath writ:
> The simplest and most obvious approach would be to store the actual data in the
> primary HDU, and then store the exposure times in an extension with the same
> dimensionality.  For example, if the primary HDU had
>
> SIMPLE  =                    T
> BITPIX  =                   16
> NAXIS   =                    2
> NAXIS1  =                 1024
> NAXIS2  =                 1024
> EXTEND  =                    T
>
> The extension would have
>
> XTENSION=              'IMAGE'
> BITPIX  =                  -32
> NAXIS   =                    2
> NAXIS1  =                 1024
> NAXIS2  =                 1024
> EXTNAME =            'XPOSURE'
>
> In essence, this is similar to the Green Bank Convention, but applied to the
> individual pixels in a data array rather than to rows in a binary table.

At a glance this seems like a reasonable convention.
In this case I would suggest that the XHDU have

BUNIT    = 's'
and I would probably dare to extend the notion of WCS by coining
not actually standard keywords like
BTYPE    = 'TIME'       / in keeping with the imminent WCS time paper
BNAME    = 'exposure time of each pixel'

--
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