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Re: [Orekit Developers] [Orekit Users] Fwd: IERS Message No. 353: Anticipated change to the IERS Bulletin A solution
Le 30/03/2018 à 11:27, MAISONOBE Luc a écrit :
>
> Do you think we could add an indicator in each EOPEntry showing
> what kind of ITRF it defines (2005, 2008, 2014, ...)? This
> entry would be set up by the EOPHistoryLoarder according to
> their own logic. EOP XX C04 would rely on the file name,
> Bulletin A and Bulletin B would rely on the file production
> date which should probably be set in a configuration file rather
> than hard-coded in Orekit, so users stuck with one version of
> Orekit can still get the correct switch.
>
> We could consider that FramesFactory.getITRF() is kept as is
> and continue to provide an ITRF with the current EOP without
> any tranform applied (let's call it raw ITRF). Users really
> concerned with accuracy could ask for a specific ITRF that
> would be based on a new TransformProvider. If for example they
> want ITRF-2014, the new TransformProvider would keep a reference
> to the raw ITRF and for each date inspect the EOPEntry used by
> the raw ITRF for this date and either return the same Transform
> as the raw ITRF would if the type is correct, or apply the
> required HelmertTransform if it happens that for this date
> the available EOPEntry is for example an ITRF-2008 entry.
>
> This would be more transparent for users. I don't see any
> backward incompatibility, it can cross changes in IERS
> products as the change we experience this week, and it can
> be updated when further changes arrive, even for users stuck
> with one version of Orekit: they would simply have to update
> the EOP loader configuration file to tell it how to flag the
> EOPEntry according to date.
I have implemented this and pushed it to the develop branch.
It adds a new configuration file itrf-versions.txt that should
change very rarely (only when IERS changes the reference system
of their EOP files). The default ITRF version if no configuration
is found (for example if users rename the EOP files and no match
is found) is to consider the EOP produce ITRF-2014.
The former getITRF(convention, simpleEOP) factory method is still
there and can be used if no specific version is needed and the
very rare version jumps in EOP can be tolerated. The new method
getITRF(itrfVersion, convention, simpleEOP) adds the Helmert
transformation on the fly if needed, depending on date, so it
should support crossing an EOP reference change.
best regards,
Luc
>
> best regards,
> Luc
>
>>
>> Best Regards,
>> Evan
>>
>>
>>
>> The difference is small, at a few millimeters level, but we are
>> going in the direction of very high accuracy, so we should deal
>> with this, even if only a few users are concerned.
>>
>> best regards,
>> Luc
>>
>>
>>
>>
>> Best Regards,
>> Evan
>>
>>
>>
>>
>> In any case, this is only important if you need a very high accuracy.
>>
>> best regards,
>> Luc
>>
>> -------- Message transféré --------
>> Sujet : IERS Message No. 353: Anticipated change to the IERS Bulletin A
>>
>> solution
>> Date : Wed, 28 Mar 2018 18:32:27 +0200 (CEST)
>> De : central_bureau@iers.org<mailto:central_bureau@iers.org>
>> <mailto:central_bureau@iers.org>
>> Pour : messages@iers.org<mailto:messages@iers.org>
>> <mailto:messages@iers.org>
>>
>> ***********************************************************************
>> *
>> IERS Message No. 353 March 28,
>> 2018
>> ***********************************************************************
>> *
>>
>>
>> Anticipated change to the IERS Bulletin A solution
>>
>>
>> Dear IERS users,
>>
>> As of Bulletin A Vol XXXI, No. 013, on 29 March, 2018, the IERS Rapid
>> Service/Prediction Center will transition the EOP solution to be
>> consistent with the 14 C04 for polar motion, UT1-UTC, and celestial
>> pole
>> offsets. This change will result in a jump of less than 0.1 mas in
>> polar
>> motion and 10 us in UT1-UTC. Small adjustments will be made to the
>> celestial pole offsets from approximately March 2017 to present in
>> order
>> to be more consistent with the 14 C04 solution. The only users who need
>>
>> to be concerned with this change are those who need EOP accuracy to be
>> better than 0.1 mas (~0.3 cm at the Earth's surface, ~1.2 cm at GPS
>> orbit.)
>>
>> A final notice of the anticipated change will be contained near the top
>>
>> of the IERS Bulletin A Vol XXXI, No. 013, on 29 March 2018, where notes
>>
>> to users are placed. Users are strongly encouraged to review this
>> message to confirm the change or to note if the change was not
>> implemented due to technical problems.
>>
>> Kind regards,
>> Nick Stamatakos
>> IERS Rapid Service Prediction Centre:
>> Production director and lead project scientist
>>
>>
>> ***********************************************************************
>> *
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>> ***********************************************************************
>> *