[PROJ] National CRS to ITRS

[Lesparre, Jochem]

Dear Even,

Sorry, I was using PROJ 8.2.1 as I didn’t expect the PROJ behaviour had changed since that version (see updated command results below).

We use the ETRF2000 realisation like most other NMAs, as this is recommended by EUREF for georeferencing, not ETRF2014! Therefore, ETRS89 should not be transformed to ETRF2014 with a null transformation. The correct transformation routes are:

  *   RD -> Amersfoort -> ETRF2000 -> ITRF2000 -> ITRF2014
  *   NAP -> ETRF2000 -> ITRF2000 -> ITRF2014

I expected this could be achieved by changing the Amersfoort-ETRS89 transformation to Amersfoort-ETRF2000 “instead” in EPSG. I don’t understand what advantage a transformation to the ETRS89 datum ensemble “in addition” to a transformation to the specific ETRF2000 realisation in EPSG would give.

In PROJ 9.1.1. RDNAP to ITRF2014:
echo 128410.0957 445806.4960 -0.4754 2023.00 | cs2cs epsg:7415 epsg:7912 -d 9
Gives:
52.000004918 5.000008844 43.0018 2023.00
This should be:
52.000005512 5.000008256 43.0197 2023.00
Like RDNAP via ETRF2000 to ITRF2014:
echo 128410.0957 445806.4960 -0.4754 2023.00 | cs2cs epsg:7415 epsg:7931 -d 9 | cs2cs epsg:7931 epsg:7912 -d 9

In PROJ 9.1.1. RDNAP to WGS84:
echo 128410.0957 445806.4960 -0.4754 2023.00 | cs2cs epsg:7415 epsg:4326 -d 9
Gives:
51.999999889 5.000000153 -0.4754 2023.00
This should be:
52.000000000 5.000000000 43.0000 2023.00
Like RDNAP via ETRF2000 to WGS84:
echo 128410.0957 445806.4960 -0.4754 2023.00 | cs2cs epsg:7415 epsg:7931 -d 9 | cs2cs epsg:7931 epsg:4326 -d 9

Kind regards, Jochem





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