[PROJ] Transformations in ITRF2020

[Lesparre, Jochem]

> Looking at the pipelines, the steps would be ITRF2020 -> ETRF2020 -> ETRS89 -> CH1903+

I am pretty sure Switzerland uses ETRF2000 as ETRS89 realisation, not ETRF2020. So, the correct transformation would be:

ITRF2020 -> ETRF2000 -> ETRS89 -> CH1903+

The difference between ETRF2000 and ETRF2020 is about 7 cm. ETRF2000 is recommended for use by national mapping agencies.

Jochem


From: PROJ <proj-bounces at lists.osgeo.org> On Behalf Of Javier Jimenez Shaw via PROJ
Sent: dinsdag 27 augustus 2024 19:30
To: proj <PROJ at lists.osgeo.org>
Subject: [PROJ] Transformations in ITRF2020

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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