[PROJ] Transformations in ITRF2020

[Even Rouault]

Javier,

I believe that registering a concatenated operation for ITRF2020 -> 
ETRS89 = ITF2020->ETRF2020+ETRF2020->ETRS89 in the database should be 
enough for PROJ to infer the ITRF2020 -> CH1903+ pipeline

Even

Le 27/08/2024 à 19:29, Javier Jimenez Shaw via PROJ a écrit :
> Hi
>
> I am now facing transformations with ITRF2020 with time(yes, because 
> Skylark, but I guess more NTRIPs are going to do (or already doing) 
> the same)
>
> The point is when the destination CRS does not have a direct 
> transformation from ITRF2020 (or almost).
>
> For instance, EPSG:4150, CH1903+ (the geographic of LV95, in 
> Switzerland) is only connected to ETRS89. See that CH1903+ is in the 
> European tectonic plate, as ETRS89
>
> A direct transformation is completely ballpark
>
> echo 42 6 0 2024.6 | ./cs2cs EPSG:9989 EPSG:4150 -d 9 --3d
> 42.000000000 6.000000000 0.000000000 2024.6
>
> However, from ITRF2020 to ETRS89 there is some change due to the time 
> (the European plate moving at 2.5 cm/a since 2015):
> echo 42 6 0 2024.6 | ./cs2cs EPSG:9989 EPSG:4937 -d 9 --3d
> 41.999994981 5.999991317 -0.001861237 2024.6
>
> and from ETRS89 to CH1903+ due to the datum offset:
> echo 42 6 0 2024.6 | ./cs2cs EPSG:4937 EPSG:4150 -d 9 --3d
> 42.000742733 6.000670188 -60.682799297 2024.6
>
> Looking at the pipelines, the steps would be ITRF2020 -> ETRF2020 -> 
> ETRS89 -> CH1903+
> (btw, only since PROJ 9.4.1, when ETRF2020 was added)
>
> I understand that the only way to get the proper transformation is 
> chaining these two manually. Via ETRS89 ... because I know it. Right?
>
> Well, the future does not look so promising to me: in EPSG I only see 
> transformations from ITRF2020 to ETRF family, NAD83(2011) family and 
> NAD83(CSRS)v8. That is Europe, USA and Canada. That's all, folks.
>
> Thanks,
> .___ ._ ..._ .. . ._.  .___ .. __ . _. . __..  ... .... ._ .__
> Javier Jimenez Shaw
> Mercator str 42.
> Null-Island
>
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