[PROJ] Dealing with epoch and transformations

[Even Rouault]

Le 23/08/2024 à 22:17, Even Rouault via PROJ a écrit :
>
> Javier,
>
> Regarding intra-ITRF transformations, the EPSG database lacks the ITRF 
> plate motion models. We do have them (up to ITRF2014) in the 
> data/ITRFxxxx files (cf the link to a previous thread of mine that 
> Jack Riley has quoted). I see we don't have yet the ITRF2020 ones. 
> They are at https://itrf.ign.fr/docs/solutions/itrf2020/ITRF2020-PMM.dat
>
I've created the ITRF2020 file in 
https://github.com/OSGeo/PROJ/pull/4235. I've double checked him, but 
triple checking could be useful for the plate motion part, as it is easy 
to get an extra or missing decimal, or getting a sign wrong when porting 
from the PDF to the file...
>
> For a fully automated solution what would be mostly missing in PROJ is 
> support for non-rectangular area of interest, as the rectangular model 
> could be very inadequate for parts of the world
>
> Even
>
> Le 23/08/2024 à 11:28, Javier Jimenez Shaw via PROJ a écrit :
>> Hi
>>
>> I am a bit confused with the epoch of coordinates. For instance, if I 
>> connect to this NTRIP service
>> https://support.swiftnav.com/support/solutions/articles/44002386941-configuring-your-receiver
>> it says explicitly that "Skylark Nx RTK uses ITRF2020 reference frame."
>> Does it mean that the coordinates that I measure today do have an 
>> epoch of 2024.x (today's epoch), or the epoch of those measurements 
>> is 2015.0 (the epoch of ITRF2020 
>> https://epsg.org/datum_1322/International-Terrestrial-Reference-Frame-2020.html)
>>
>> If I want to transform from that reference system (ITRF2020) to, 
>> let's say, ETRS89 or NAD83(2011), should I add an epoch? which one? 
>> where? what happens if I do not set any?
>>
>> I have the impression that I could convert from one epoch to another 
>> for the same CRS, something like this
>> PROJ_DATA=data ./bin/projinfo -s EPSG:9989 -t EPSG:9989 --s_epoch 
>> 2015.0 --t_epoch 2020.0 -o proj
>> Candidate operations found: 1
>> -------------------------------------
>> Operation No. 1:
>>
>> unknown id, Null geographic offset from ITRF2020 to ITRF2020, 0 m, World.
>>
>> PROJ string:
>> +proj=noop
>>
>> ... but it does not. Should it do a non noop transformation?
>>
>> Note: s_epoch and t_epoch were added in PROJ 9.4
>>
>> Thanks.
>>
>>
>> PS. ITRF2020 to CH1903+ is a complete ballpark :(
>> .___ ._ ..._ .. . ._.  .___ .. __ . _. . __.. ... .... ._ .__
>>
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