Move 'Coordinate operations' to top level of docs [skip ci]

1 files changed, 39 insertions, 0 deletions

diff --git a/docs/source/operations/transformations/hgridshift.rst b/docs/source/operations/transformations/hgridshift.rst
new file mode 100644
index 00000000..7f3c9895
--- /dev/null
+++ b/docs/source/operations/transformations/hgridshift.rst
@@ -0,0 +1,39 @@
+.. _hgridshift:
+
+================================================================================
+Horizontal grid shift
+================================================================================
+
+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.