Horizontal grid shiftΒΆ

Change of horizontal datum by grid shift.

Input type

Geodetic coordinates.

Output type

Geodetic coordinates.

Options

+grids

Comma-separated list of grids to load.

The horizontal grid shift is done by offsetting the planar input coordinates by a specific amount determined by the loaded grids. The simplest use case of the horizontal grid shift is applying a single grid:

+hgridshift +grids=nzgr2kgrid0005.gsb

More than one grid can be loaded at the same time, for instance in case the dataset needs to be transformed spans several countries. In this example grids of the continental US, Alaska and Canada is loaded at the same time:

+hgridshift +grids=@conus,@alaska,@ntv2_0.gsb,@ntv_can.dat

The @ in the above example states that the grid is optional, in case the grid is not found in the PROJ search path. The list of grids is prioritized so that grids in the start of the list takes presedence over the grids in the back of the list.

PROJ supports CTable2, NTv1 and NTv2 files for horizontal grid corrections. Details about all three formats can be found in the GDAL documentation. GDAL reads and writes all three formats. Using GDAL for construction of new grids is recommended.