Julien,
The units attribute cannot have "UTC" in it. UTC is implied. Other than
that, it looks great!
Jim
On 4/24/15 12:14 PM, Julien Demaria wrote:
>
> Hi,
>
> Thanks a lot for all your accurate answers!
>
> With all these information, for the moment we think the best way to
> represent our time in CF is to convert the time stamp of the units
> attribute from GPS to UTC.
>
> We cannot change it for the GPS beginning 1980-01-06 so we must
> transform the 2000-01-01 from GPS to UTC to be more CF compliant.
>
> We also specify GPS in the long name and in a new non standard
> time_reference attribute :
>
> int64 time_stamp(rows) ;
>
> time_stamp:standard_name = "time" ;
>
> time_stamp:units = "microseconds since 2000-01-01 00:00:*13*UTC" ;
>
> time_stamp:long_name = "Elapsed time since 01 Jan 2000 0h GPS" ;
>
> time_stamp:time_reference = "GPS"
>
> I think with this solution a CF compliant software (which not support
> leap second) should interpret time ?correctly?.
>
> Let me know if I missed something.
>
> Thanks,
>
> Julien
>
> *De :*Manning, Evan M (398B) [mailto:Evan.M.Manning at jpl.nasa.gov]
> *Envoy? :* vendredi 24 avril 2015 14:30
> *? :* Chris Barker; Julien Demaria
> *Cc :* Jonathan Gregory; cf-metadata at cgd.ucar.edu
> *Objet :* RE: [CF-metadata] How to define time coordinate in GPS?
>
> It's probably overkill but for Suomi NPP CrIS and ATMS we are planning
> to provide
>
> timestamps for each obs in both TAI and UTC.
>
> TAI is the true time dimension, but UTC gives users a correct UTC if
> that's what they want and should minimize the temptation for them to
> do TAI to UTC conversions using tools which don't understand leap seconds.
>
> -- Evan
>
> ------------------------------------------------------------------------
>
> *From:*Chris Barker [chris.barker at noaa.gov]
> *Sent:* Thursday, April 23, 2015 4:48 PM
> *To:* Julien Demaria
> *Cc:* Jonathan Gregory; cf-metadata at cgd.ucar.edu
> <mailto:cf-metadata at cgd.ucar.edu>
> *Subject:* Re: [CF-metadata] How to define time coordinate in GPS?
>
> On Thu, Apr 23, 2015 at 7:19 AM, Julien Demaria
> <Julien.Demaria at acri-st.fr <mailto: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 <http://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 <mailto: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 <mailto:Chris.Barker at noaa.gov>
>
>
>
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Received on Fri Apr 24 2015 - 11:07:15 BST
