geodetictiffgrids.rst: update with deformation model

1 files changed, 27 insertions, 8 deletions

diff --git a/docs/source/specifications/geodetictiffgrids.rst b/docs/source/specifications/geodetictiffgrids.rst
index 479d6ca9..307d8657 100644
--- a/docs/source/specifications/geodetictiffgrids.rst
+++ b/docs/source/specifications/geodetictiffgrids.rst
@@ -137,9 +137,9 @@ is an easy way to inspect such grid files:
 
     * SamplesPerPixel = 1 for vertical shift grids.
 
-   In the future, different values of SamplesPerPixel may be used to accommodate
-   for other needs. For example for deformation models, SamplesPerPixel = 3 to combine
-   horizontal and vertical adjustments.
+    * SamplesPerPixel = 3 for deformation models combining
+      horizontal and vertical adjustments.
+
    And even for the current identified needs of horizontal or vertical shifts,
    more samples may be present (to indicate for example uncertainties), but
    will be ignored by PROJ.
@@ -215,28 +215,32 @@ is an easy way to inspect such grid files:
     - ``HORIZONTAL_OFFSET``: implies the presence of at least two samples.
       The first sample must contain the latitude offset and the second
       sample must contain the longitude offset.
-      Corresponds to PROJ ``hgridshift`` method.
+      Corresponds to PROJ :ref:`hgridshift` method.
 
     - ``VERTICAL_OFFSET_GEOGRAPHIC_TO_VERTICAL``: implies the presence of at least one sample.
       The first sample must contain the vertical adjustment. Must be used when
       the source/interpolation CRS is a Geographic CRS and the target CRS a Vertical CRS.
-      Corresponds to PROJ ``vgridshift`` method.
+      Corresponds to PROJ  :ref:`vgridshift` method.
 
     - ``VERTICAL_OFFSET_VERTICAL_TO_VERTICAL``: implies the presence of at least one sample.
       The first sample must contain the vertical adjustment. Must be used when
       the source and target CRS are Vertical CRS.
-      Corresponds to PROJ ``vgridshift`` method.
+      Corresponds to PROJ :ref:`vgridshift` method.
 
     - ``GEOCENTRIC_TRANSLATION``: implies the presence of at least 3 samples.
       The first 3 samples must be respectively the geocentric adjustments along
       the X, Y and Z axis. Must be used when the source and target CRS are
       geocentric CRS. The interpolation CRS must be a geographic CRS.
-      Corresponds to PROJ ``xyzgridshift`` method.
+      Corresponds to PROJ :ref:`xyzgridshift` method.
 
     - ``VELOCITY``: implies the presence of at least 3 samples.
       The first 3 samples must be respectively the velocities along
       the E(ast), N(orth), U(p) axis in the local topocentric coordinate system.
-      Corresponds to PROJ ``deformation`` method.
+      Corresponds to PROJ :ref:`deformation` method.
+
+    - ``DEFORMATION_MODEL``: implies the presence of the ``DISPLACEMENT_TYPE``
+      and ``UNCERTAINTY_TYPE`` metadata items.
+      Corresponds to PROJ :ref:`defmodel` method.
 
     For example:
 
@@ -284,6 +288,11 @@ is an easy way to inspect such grid files:
       Sample values should be the velocity in a linear/time unit in a ENU local
       topocentric coordinate system.
 
+    + ``east_offset`` / ``north_offset`` / ``vertical_offset``: valid for
+      TYPE=DEFORMATION_MODEL.
+      For east_offset and north_offset, the unit might be degree or metre.
+      For vertical_offset, the unit must be metre.
+
     For example:
 
     .. code-block:: xml
@@ -337,6 +346,16 @@ is an easy way to inspect such grid files:
         <Item name="UNITTYPE" sample="0" role="unittype">arc-second</Item>
         <Item name="UNITTYPE" sample="1" role="unittype">arc-second</Item>
 
+  * For TYPE=DEFORMATION_MODEL, the type of the displacement must be specified
+    with a `Item` whose ``name`` is set to ``DISPLACEMENT_TYPE``.
+
+    The accepted values are: ``HORIZONTAL``, ``VERTICAL``, ``3D`` or ``NONE``
+
+  * For TYPE=DEFORMATION_MODEL, the type of the uncertainty must be specified
+    with a `Item` whose ``name`` is set to ``UNCERTAINTY_TYPE``.
+
+    The accepted values are: ``HORIZONTAL``, ``VERTICAL``, ``3D`` or ``NONE``
+
   * The ``target_crs_epsg_code`` metadata item should be present.
     For a horizontal shift grid, this is the EPSG
     code of the target geographic CRS. For a vertical shift grid, this is the