[PROJ] National CRS to ITRS

[Lesparre, Jochem]

Dear list members,

I work at Dutch NMA responsible for the Dutch national CRS named RDNAP. We recommend the use of PROJ for coordinate transformations, as it uses our official transformation to ETRS89 from EPSG.

  *   Horizontal: https://epsg.org/transformation_9282/Amersfoort-to-ETRS89-9.html (and https://epsg.org/transformation_9281/Amersfoort-to-ETRS89-8.html)
  *   Vertical: https://epsg.org/transformation_9597/ETRS89-to-ETRS89-NAP-height-2.html (and https://epsg.org/transformation_9283/ETRS89-to-NAP-height-2.html)

However, I noticed that at the moment PROJ doesn't by default use the transformation we recommend for transformation to ITRF2014.

RDNAP to ETRF2000:
echo 128410.0957 445806.4960 -0.4754 2023.00 | cs2cs epsg:7415 epsg:7931 -d 9
The result is in accordance with our official transformation:
52.000000000 5.000000000 43.0000 2023.00

RDNAP to WGS84:
echo 128410.0957 445806.4960 -0.4754 2023.00 | cs2cs epsg:7415 epsg:4326 -d 9
The result is a null transformation in accordance with our recommendation:
52.000000000 5.000000000 43.0000 2023.00

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
The result is a time-dependant transformation in accordance with our recommendation:
52.000005512 5.000008256 43.0197 2023.00

RDNAP to ITRF2014:
echo 128410.0957 445806.4960 -0.4754 2023.00 | cs2cs epsg:7415 epsg:7912 -d 9
The result is a null transformation, which is not what we recommend:
52.000000000 5.000000000 43.0000 2023.00

I assume that the best way to fix this is to ask EPSG to link RDNAP to ETRF2000 instead of the ETRS89 datum ensemble. Would that indeed solve the problem in PROJ?

Kind regards, Jochem



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