[PROJ] National CRS to ITRS

[Even Rouault]

Jochem

> *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:
>
> 52.00000_0000_ 5.00000_0000_ 43.0_000_ 2023.00
>
You didn't mention which PROJ version you use. But starting with 9.1.0, 
here's the result I get:

$ echo 128410.0957 445806.4960 -0.4754 2023.00 | PROJ_NETWORK=ON 
PROJ_DEBUG=2 bin/cs2cs epsg:7415 epsg:7912 -d 9
[...]
Using coordinate operation Inverse of RD New + Amersfoort to ETRS89 (9) 
+ Inverse of ETRS89 to NAP height (2) + Null geographic offset from 
ETRS89 (geog3D) to ETRS89 (geog2D) + ETRS89 to ETRF2014 + Conversion 
from ETRF2014 (geog2D) to ETRF2014 (geocentric) + Inverse of ITRF2014 to 
ETRF2014 (2) + Conversion from ITRF2014 (geocentric) to ITRF2014 (geog3D)
[...]
52.000004918    5.000008844 43.001783708 2023.00

This is the first pipeline suggested by projinfo -s epsg:7415 -t epsg:7912:

unknown id, Inverse of RD New + Amersfoort to ETRS89 (9) + Inverse of 
ETRS89 to NAP height (2) + Null geographic offset from ETRS89 (geog3D) 
to ETRS89 (geog2D) + ETRS89 to ETRF2014 + Conversion from ETRF2014 
(geog2D) to ETRF2014 (geocentric) + Inverse of ITRF2014 to ETRF2014 (2) 
+ Conversion from ITRF2014 (geocentric) to ITRF2014 (geog3D), 0.102 m, 
Netherlands - onshore, including Waddenzee, Dutch Wadden Islands and 
12-mile offshore coastal zone., at least one grid missing

PROJ string:
+proj=pipeline
   +step +inv +proj=sterea +lat_0=52.1561605555556 +lon_0=5.38763888888889
         +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel
   +step +proj=hgridshift +grids=nl_nsgi_rdtrans2018.tif
   +step +proj=vgridshift +grids=nl_nsgi_nlgeo2018.tif +multiplier=1
   +step +proj=cart +ellps=GRS80
   +step +inv +proj=helmert +x=0 +y=0 +z=0 +rx=0.001785 +ry=0.011151 
+rz=-0.01617
         +s=0 +dx=0 +dy=0 +dz=0 +drx=8.5e-05 +dry=0.000531 +drz=-0.00077 
+ds=0
         +t_epoch=2010 +convention=position_vector
   +step +inv +proj=cart +ellps=GRS80
   +step +proj=unitconvert +xy_in=rad +xy_out=deg
   +step +proj=axisswap +order=2,1

So this kind of works, but using the ETRS89 -> ETRF2014 direct 
transformation, not through the ETRF2000 -> ETRF2014 one you expect, 
which is quite logical since NAP height is only linked to ETRS89.


> 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?
>
I wouldn't say "instead", but "in addition". There should likely be a 
ETRF2014 to NAP height transformation, and a Amersfoort to ETRF2014 one 
(that could be a concatenation of Amersfoort to ETRS89 (9) + ETRS89 -> 
ETRF2000 + ETRF2000 -> ETRF2014  or Amersfoort to ETRS89 (9) + ETRS89 -> 
ETRF2014 depending on your preference)
>
> Kind regards, Jochem
>
>
>
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