[fitsbits] Output array type when BZERO is an integer {External} {External}

[Mark Taylor]

On Wed, 13 Mar 2024, Richard J. Mathar via fitsbits wrote:

> rs> Date: Tue, 12 Mar 2024 22:00:49 +0000
> rs> From: "Seaman, Robert Lewis - (rseaman)" <rseaman at arizona.edu>
> rs> To: "Dubois-Felsmann, Gregory P." <gpdf at ipac.caltech.edu>, "Barrett,
> rs>         Paul" <pebarrett at email.gwu.edu>
> rs> Cc: "fitsbits at listmgr.nrao.edu" <fitsbits at listmgr.nrao.edu>
> rs> Subject: Re: [fitsbits] Output array type when BZERO is an integer
> rs>         {External}
> rs> ...
> rs> As a matter of curiosity, do Rubin operations depend on 64-bit unsigned integers? What are example use cases for 64-bit integers (signed or unsigned) in the community?...
> rs> 
> 
> It's difficult to imagine that any data taken from a real
> instrument need 64 bits (20 decimal digits), i.e. more than 32 bits.
> ADC's in the MHz range can produce 16bit data (10 decimal digits). 
> We can measure temperatures to 0.01K or perhaps better.
> 
> The exception are time stamps, if "stamped" by computers
> that can resolve milliseconds reliably and set the origin
> at some arbitrary J2000-alike or MJD references. (But clock synchronization
> is not easy, so in reality only time differences matter to resolve
> GRBs etc...) See https://en.wikipedia.org/wiki/Year_2038_problem .
> Atomic clocks and frequency combs are high-resolution data.
> 
> Astronomers are the only group of physics to generate data in FITS 
> (photographers/artists use the fact at PNG, TIFF etc also can store metadata); 
> so that time stamp or 64bit representation has probably not surfaced
> anywhere.

64-bit integers are often used as source identifiers, e.g. SDSS ObjID
and Gaia source_id.  These don't often come in images/arrays but do
often come in tables.  I have come across TZEROn = 9223372036854775808
to represent unsigned 64-bit integers (SDSS DR15 I think).

--
Mark Taylor  Astronomical Programmer  Physics, Bristol University, UK
m.b.taylor at bristol.ac.uk          https://www.star.bristol.ac.uk/mbt/