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

[William Thompson]

Certainly in our field Angstroms will never go away.

On 11/04/14 12:57, Steve Allen wrote:
> 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.
>
> --
> Steve Allen                 <sla at ucolick.org>                WGS-84 (GPS)
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-- 
William Thompson
NASA Goddard Space Flight Center
Code 671
Greenbelt, MD  20771
USA

301-286-2040
William.T.Thompson at nasa.gov