Fix issue with WGS 84 + EGM2008 -> Amersfoort + NAP height (master only)

[rouault]

Fixes https://lists.osgeo.org/pipermail/proj/2026-February/011959.html

Output of projinfo EPSG:4326+3855 EPSG:7415 --spatial-test intersects

9.7.1
+++++

Operation No. 1:

unknown id, Inverse of WGS 84 to EGM2008 height (1) +
            Inverse of ETRS89 to WGS 84 (1) +
            ETRS89 to NAP height (2) +
            Inverse of Amersfoort to ETRS89 (9) +
            RD New,
            1.114 m, Netherlands - onshore, including Waddenzee, Dutch Wadden Islands and 12-mile offshore coastal zone., at least one grid missing

PROJ string:
+proj=pipeline
  +step +proj=axisswap +order=2,1
  +step +proj=unitconvert +xy_in=deg +xy_out=rad
  +step +proj=vgridshift +grids=us_nga_egm08_25.tif +multiplier=1
  +step +inv +proj=vgridshift +grids=nl_nsgi_nlgeo2018.tif +multiplier=1
  +step +inv +proj=hgridshift +grids=nl_nsgi_rdtrans2018.tif
  +step +proj=sterea +lat_0=52.1561605555556 +lon_0=5.38763888888889 +k=0.9999079
        +x_0=155000 +y_0=463000 +ellps=bessel

master before this change
+++++++++++++++++++++++++

Operation No. 1:

unknown id, Inverse of WGS 84 to EGM2008 height (1) +
            Inverse of ETRS89-NLD [AGRS2010] to WGS 84 (1) +
            ETRS89-NLD [AGRS2010] to NAP height (2) +
            Inverse of Amersfoort to ETRS89-NLD [AGRS2010] (9) +
            RD New,
            1.123 m, Netherlands - onshore and offshore., at least one grid missing

PROJ string:
+proj=pipeline
  +step +proj=axisswap +order=2,1
  +step +proj=unitconvert +xy_in=deg +xy_out=rad
  +step +proj=vgridshift +grids=us_nga_egm08_25.tif +multiplier=1
  +step +inv +proj=vgridshift +grids=nl_nsgi_nlgeo2018.tif +multiplier=1
  +step +inv +proj=hgridshift +grids=nl_nsgi_rdtrans2018.tif
  +step +proj=sterea +lat_0=52.1561605555556 +lon_0=5.38763888888889 +k=0.9999079
        +x_0=155000 +y_0=463000 +ellps=bessel

    OPERATIONACCURACY[1.123],
    USAGE[
        SCOPE["unknown"],
        AREA["Netherlands - onshore and offshore."],
        BBOX[50.75,2.53,55.77,7.22]]]

Operation No. 3:

unknown id, Inverse of WGS 84 to EGM2008 height (1) +
            Inverse of Amersfoort to WGS 84 (4) +
            ETRS89-NLD [AGRS2010] to NAP height (2) using Amersfoort to ETRS89-NLD [AGRS2010] (9) +
            RD New,
            1.123 m, Netherlands - onshore, including Waddenzee, Dutch Wadden Islands and 12-mile offshore coastal zone., at least one grid missing

PROJ string:
+proj=pipeline
  +step +proj=axisswap +order=2,1
  +step +proj=unitconvert +xy_in=deg +xy_out=rad
  +step +proj=vgridshift +grids=us_nga_egm08_25.tif +multiplier=1
  +step +proj=cart +ellps=WGS84
  +step +inv +proj=helmert +x=565.4171 +y=50.3319 +z=465.5524
        +rx=0.398957388243134 +ry=-0.343987817378283 +rz=1.87740163998045
        +s=4.0725 +convention=coordinate_frame
  +step +inv +proj=cart +ellps=bessel
  +step +proj=push +v_1 +v_2
  +step +proj=hgridshift +grids=nl_nsgi_rdtrans2018.tif +omit_inv
  +step +inv +proj=vgridshift +grids=nl_nsgi_nlgeo2018.tif +multiplier=1
  +step +inv +proj=hgridshift +grids=nl_nsgi_rdtrans2018.tif +omit_fwd
  +step +proj=pop +v_1 +v_2
  +step +proj=sterea +lat_0=52.1561605555556 +lon_0=5.38763888888889 +k=0.9999079
        +x_0=155000 +y_0=463000 +ellps=bessel
    OPERATIONACCURACY[1.123],
    USAGE[
        SCOPE["unknown"],
        AREA["Netherlands - onshore, including Waddenzee, Dutch Wadden Islands and 12-mile offshore coastal zone."],
        BBOX[50.75,3.2,53.7,7.22]]]

Analysis

Due to the ETRS89 datum ensemble changes, PROJ synthetized a new operation (operation 3) that has the same accuracy than the "correct" (operation 1), and a smaller area of use, thus it was selected. However that choice was not super relevant compared to 1, because it relied on using Amersfoort CRS in 3D (with ellipsoidal height), through the Helmert transformation "Amersfoort to WGS 84 (4)"). Given that there's no entry in the database for a 3D Amersfoort CRS, this possibility should be discarded when there is an alternative that uses only known objects.