[PROJ] Dealing with epoch and transformations

[Javier Jimenez Shaw]

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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