Skip to content

Latest commit

 

History

History
76 lines (56 loc) · 3.27 KB

set.rst

File metadata and controls

76 lines (56 loc) · 3.27 KB
Raw

Set coordinate value

7.0.0

Set component(s) of a coordinate to a fixed value.

Alias set
Domain 4D
Input type Any
Output type Any

This operations allows for components of coordinates to be set to a fixed value. This may be useful in pipeline<pipeline> when a step requires some component, typically an elevation or a date, to be set to a fixed value.

Example

In the ETRS89 to Dutch RD with NAP height transformation, the used ellipsoidal height for the Helmert transformation is not the NAP height, but the height is set to 0 m. This is an unconventional trick to get the same results as when the effect of the Helmert transformation is included in the horizontal NTv2 grid. For the forward transformation from ETRS89 to RD with NAP height, we need to set the ellipsoidal ETRS89 height for the Helmert transformation to the equivalent of 0 m NAP. This is 43 m for the centre of the Netherlands and this value can be used as an approximation elsewhere (the effect of this approximation is below 1 mm for the horizontal coordinates, in an area up to hundreds of km outside the Netherlands).

The +proj=set +v_3=0 close to the end of the pipeline is to make it usable in the reverse direction.

$ cct -t 0 -d 4 +proj=pipeline \
     +step +proj=unitconvert +xy_in=deg +xy_out=rad \
     +step +proj=axisswap +order=2,1 \
     +step +proj=vgridshift +grids=nlgeo2018.gtx \
     +step +proj=push +v_3 \
     +step +proj=set +v_3=43 \
     +step +proj=cart +ellps=GRS80 \
     +step +proj=helmert +x=-565.7346 +y=-50.4058 +z=-465.2895 +rx=-0.395023 +ry=0.330776 +rz=-1.876073 +s=-4.07242 +convention=coordinate_frame +exact \
     +step +proj=cart +inv +ellps=bessel \
     +step +proj=hgridshift +inv +grids=rdcorr2018.gsb,null \
     +step +proj=sterea +lat_0=52.156160556 +lon_0=5.387638889 +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel \
     +step +proj=set +v_3=0 \
     +step +proj=pop +v_3

Parameters

+v_1=value

Set the first coordinate component to the specified value

+v_2=value

Set the second coordinate component to the specified value

+v_3=value

Set the third coordinate component to the specified value

+v_4=value

Set the fourth coordinate component to the specified value