Merge pull request #1138 from rouault/geogoffset

Add geographic offset transformation method.

1 files changed, 70 insertions, 0 deletions

diff --git a/docs/source/operations/transformations/geogoffset.rst b/docs/source/operations/transformations/geogoffset.rst
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+.. _geogoffset:
+
+================================================================================
+Geographic offsets
+================================================================================
+
+.. versionadded:: 6.0.0
+
+The Geographic offsets transformation adds an offset to the geographic longitude,
+latitude coordinates, and an offset to the ellipsoidal height.
+
++---------------------+----------------------------------------------------------+
+| **Alias**           | geogoffset                                               |
++---------------------+----------------------------------------------------------+
+| **Domain**          | 3D                                                       |
++---------------------+----------------------------------------------------------+
+| **Input type**      | Geodetic coordinates (horizontal), meters (vertical)     |
++---------------------+----------------------------------------------------------+
+| **output type**     | Geodetic coordinates (horizontal), meters (vertical)     |
++---------------------+----------------------------------------------------------+
+
+This method is normally only used when low accuracy is tolerated. It is documented
+as coordinate operation method code 9619 (for geographic 2D) and 9660 (for
+geographic 3D) in the EPSG dataset (:cite:`EPSGGuidanceNumber7Part2`)
+
+It can also be used to implement the method Geographic2D with Height Offsets
+(code 9618) by noting that the input vertical component is a gravity-related
+height and the output vertical component is the ellispoid height (dh being
+the geoid undulation).
+
+It can also be used to implement the method Vertical offset (code 9616)
+
+The reverse transformation simply consists in subtracting the offsets.
+
+This method is a conveniency wrapper for the more general :ref:`affine`.
+
+Examples
+###############################################################################
+
+Geographic offset from the old Greek geographic 2D CRS to the newer GGRS87 CRS::
+
+    proj=geogoffset dlon=0.28 dlat=-5.86
+
+Conversion from Tokyo + JSLD69 height to WGS 84::
+
+    proj=geogoffset dlon=-13.97 dlat=7.94 dh=26.9
+
+Conversion from Baltic 1977 height to Black Sea height::
+
+    proj=geogoffset dh=0.4
+
+
+Parameters
+################################################################################
+
+Optional
+-------------------------------------------------------------------------------
+
+.. option:: +dlon=<value>
+
+    Offset in longitude, expressed in arc-second, to add.
+
+.. option:: +dlat=<value>
+
+    Offset in latitude, expressed in arc-second, to add.
+
+.. option:: +dh=<value>
+
+    Offset in height, expressed in meter, to add.
+