[fitsbits] Question on angstrom and erg units in FITS standard

[Steve Allen]

On Tue 2014-11-04T18:10:39 +0100, Thomas Robitaille hath writ:
>   Deprecated in IAU Style Manual (McNally 1988) but still in use.
>
> My question is, are these units deprecated in the FITS standard too? Or
> is this one of the places where the FITS standard deviates from McNally
> 1988?
>
> In short, should FITS readers/writers treat 'angstrom' and 'erg' as
> deprecated?

Our instruments produce a lot of values with units like "degC",
"degF", and others with unapproved units for values which are intended
as engineering metadata as opposed to science metadata.  If we had
enough resources (of both human labor and compute power in the
devices) to characterize what those measurements mean and how they
affect the science data then we would recast them in SI units.

In the case of angstrom and erg the conversion is simple enough that
most hardware and software systems are probably able to recast them
as nm and J, but the FITS standard writers recognize that may never
happen for already-deployed instruments.

Deprecated is not forbidden.  The point of FITS is that the meaning of
the file should be clear to the reader.  In the cases of angstrom and
erg it is probably more important to put effort into documenting the
reference frame and laboratory conditions than it is to convert to nm
and J.

--
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