[fitsbits] FITS 'keyword dictionaries'

[Tom Kuiper]

On 04/03/2014 07:51 AM, Joe Hourcle wrote:
> I was thinking that much like the 'file' command in UNIX, it might be 
> worth making a list of values in use, so that if someone had some 
> random FITS file, they could run it through a program that would 
> attempt to identify the file, and possibly give a reference of where 
> to find more information about that particular instrument. 
I remember seeing something like that a few years ago when I was working 
on this issue but had forgotten.  As I recall, the suggestion was to 
provide a URL for a repository with the detailed information.  I had 
some concerns about that though.  For example, can we count on the 
website being maintained?  A complete FITS header, at least, will exist 
as long as the FITS file exists.

In the rest of your e-mail, Joe, you give wonderful examples of the 
varied (mis?)use of supposedly standard keywords.  My inclination is to 
create much more specific keywords.  The reason is that in radio 
astronomy, at least, technology is now leading towards hardware which is 
very adaptable to an observer's specific requirements.  The most 
egregious example I can think of is the CASPER hardware.  We now have 
ROACH-1 boards with KATADCs for radio astronomy at each of out three DSN 
stations.  Observers can bring their own firmware, so that the same 
hardware may be a spectrometer for one group, a spectro-polarimeter for 
another, a pulsar timing back-end for a third group, a pulsar search 
engine for the fourth, and so on.  Our new receivers are configurable 
too, so that they provide HV polarization or RL polarization as 
requested, and the IF outputs can be I/Q (in/quadrature phase) or 
USB/LSB pairs.  The software that I'm trying to write must capture the 
state of that equipment and write it to FITS headers so the analyst will 
later know exactly what happened to convert photons to bits.

If I go with a new keyword set (it seems almost unavoidable to me) then 
TELESCOP, INSTRUME, DETECTOR, and any others in common use could have 
some cleverly crafted values for traditional software.  I would hope 
that most analysts will use some software like ASAP that can be easily 
extended to handle the added keywords.  Observatory staff could help by 
making libraries available that provide such extensions.

Best regards,

Tom

p.s. I've added to distribution people who may not follow this mail list 
but are going to impacted almost immediately by what I doing.

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