[fitswcs] FITS WCS Time Paper

[Arnold Rots]

How would this be, then (also updating the reference):

---------------------------------------------
GPS time is currently defined by the Interface Specification document
``IS-GPS-200F, Revision F''
\footnote{http://www.gps.gov/technical/icwg/\#is-gps-200}.
Note that GPS time is aligned to a specific UTC(USNO) epoch, 19~s
behind TAI, with the fractional part matching UTC(USNO) to within a
microsecond.

GPS time is convenient, but precision timestamps want to know whether
the receiver has implemented the corrections to the satellite clocks
and ionosphere given by the contents of Subframe 1 as documented in
section 20.3.3.3 of IS-GPS-200.

GPS system time should not be used before its date of inception (1980-01-06).
---------------------------------------------


Btw, the typo you note appeared in an earlier version and had been
corrected already in V0.93 :-)

  - Arnold


patrick.wallace at stfc.ac.uk wrote:
[ Charset UTF-8 unsupported, converting... ]
> Steve Allen wrote:
> 
> > Thus the text specifically directs the reader to read the GPS
> > Interface Specification.
> 
> Yes, but hardly anyone will:  lay readers won't, and it is old
> hat to time experts.  Even I became inattentive by the time I
> reached p94 or so.
> 
> The point I was trying to make is that the paper can afford to be
> more helpful to readers.  It has already mentioned that GPS is
> more or less TAI-19s, and it can be said again here.  And the
> statement "GPS time is only required to match UTC to within a
> microsecond" would not be harmed by adding a preamble "The
> fractional part of" or something of the kind.  Moreover, the
> statement "That is to emphasize that GPS time is *not* de?ned in
> terms of TAI" seems redundant, given that UTC is itself defined in
> terms of TAI.  I would write this:
> 
>   GPS time is de?ned by the document "ICD-GPS-200, Revision C with
>   IRNs 1 through 5". Note that GPS time is aligned to a specific
>   UTC(USNO) epoch, 19s behind TAI, with the fractional part
>   matching UTC(USNO) to within a microsecond.
> 
> Incidentally the introduction to the appendix contains the typo:
> 
>   "there are a more subtle issues"
> 
> 
> Patrick Wallace
> ____________________________________________________________________
> Space Science & Technology Department???????    ???? +44-1235-531198
> STFC Rutherford Appleton Laboratory
> Harwell Oxford
> Didcot, Oxfordshire, OX11 0QX, UK       ??Patrick.Wallace at stfc.ac.uk
> ____________________________________________________________________
> 
> 
> 
> 
> 
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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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