[PROJ] Dealing with epoch and transformations

[Even Rouault]

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

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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