[PROJ] ETRFxx to national ETRS89 realizations (e.g. ETRS89-NLD [AGRS2010], RGF93 v2/v2b, ETRS89-HUN [ETRF2000], etc.) (was Re: Time dependency in ETRFxx to ETRFyy coordinate transformations?)

[Xavier Collilieux]

Hello,

If the output epoch is changed, there should be an additional operation for time propagation, which is the application of a deformation model.
For countries like France, or any country on the stable part of the tectonic plate for plate-fixed frames, the deformation model is simply a null-velocity field. Adding this null operation would make clearer the assumption which is made. 
As soon as an epoch needs to be changed, a deformation model should be applied. And it makes sense in some cases, not to change the coordinates when the deformation is negligible.

Best regards,
Xavier

-----Message d'origine-----
De : PROJ <proj-bounces at lists.osgeo.org> De la part de Even Rouault via PROJ Envoyé : dimanche 21 juin 2026 23:07 À : proj <proj at lists.osgeo.org> Objet : [PROJ] ETRFxx to national ETRS89 realizations (e.g. ETRS89-NLD [AGRS2010], RGF93 v2/v2b, ETRS89-HUN [ETRF2000], etc.) (was Re: Time dependency in ETRFxx to ETRFyy coordinate transformations?)

Thinking more and looking at "ETRS89-NLD [AGRS2010] to ETRF2000 (1)", I see it is a noop transformation, so with no time dependency...  How does that fit with the fact that ETRF2000 is dynamic. I see that "ETRS89-NLD [AGRS2010]" uses DATUM["AGRS2010 (ETRF2000)") and has ANCHOREPOCH[2010.5]. So I'm thinking the output coordinate when applying "ETRS89-NLD [AGRS2010] to ETRF2000 (1)" is at coordinate epoch 2010.5, right?   Shouldn't the PROJ pipeline +proj=set +v_4=2010.5 ?

Same question for ETRS89-FRA [RGF93 v2] to ETRF2000 (1) and ETRS89-FRA
[RGF93 v2b] to ETRF2000 (1) with are both no-ops. Shouln't output coordinate epochs be respectively 2009 and 2019 per their anchor epoch ?

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