On Thu, Apr 23, 2015 at 7:19 AM, Julien Demaria <Julien.Demaria at acri-st.fr>
wrote:
> I?m also not an expert on this:
>
> ?GPS, Global Positioning System time, is the atomic time scale implemented
> by the atomic clocks in the GPS ground control stations and the GPS
> satellites themselves. GPS time was zero at 0h 6-Jan-1980 and since it is
> not perturbed by leap seconds GPS is now ahead of UTC by 16 seconds.?
>
It seems to me then, that the "right" way is to express this time as:
time_unit since 1908-01-06T00:00:00Z
since that is technically exactly correct.
clients are likely to translate to year-month-day-hour-minute-second using
UTC, but maybe not. And as others have pointed out, most libs don't do leap
seconds anyway, so are using "GPS time" whether they specify it or not.
I guess what I am saying is that this isn't really a "how to encode it in
CF" question -- if you use that epoch, then it becomes entirely up to the
client what time it wants to translate to.
-Chris
> http://www.leapsecond.com/java/gpsclock.htm
>
> a more detailed explanation:
>
> https://confluence.qps.nl/display/KBE/UTC+to+GPS+Time+Correction
>
>
>
> Thanks in advance,
>
>
>
> Julien
>
>
>
> >Jonathan Gregory j.m.gregory at reading.ac.uk
>
> >Thu Apr 23 07:58:09 MDT 2015
>
> >
>
> >Dear Julien
>
> >
>
> >Could you explain what the difference is between GPS time and UTC (for a
> non-
>
> >expert such as me)?
>
> >
>
> >Thanks
>
> >
>
> >Jonathan
>
>
>
> *De :* Julien Demaria
> *Envoy? :* jeudi 23 avril 2015 14:51
> *? :* 'cf-metadata at cgd.ucar.edu'
> *Objet :* How to define time coordinate in GPS?
>
>
>
> Hi,
>
>
>
> I need to define a time coordinate variable which use the GPS time
> referential instead of UTC, but I did not found how to specify this.
>
> For the moment my variable look like this :
>
>
>
> int64 time_stamp(rows) ;
>
> time_stamp:standard_name = "time" ;
>
> time_stamp:units = "microseconds since
> 2000-01-01 00:00:00" ;
>
> time_stamp:_FillValue = -1L ;
>
>
>
> Thanks in advance,
>
>
>
> Julien
>
>
>
> _______________________________________________
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>
>
--
Christopher Barker, Ph.D.
Oceanographer
Emergency Response Division
NOAA/NOS/OR&R (206) 526-6959 voice
7600 Sand Point Way NE (206) 526-6329 fax
Seattle, WA 98115 (206) 526-6317 main reception
Chris.Barker at noaa.gov
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