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+.. _defmodel:
+
+================================================================================
+Multi-component time-based deformation model
+================================================================================
+
+.. versionadded:: 7.1.0
+
++---------------------+--------------------------------------------------------------------+
+| **Alias** | defmodel |
++---------------------+--------------------------------------------------------------------+
+| **Input type** | Geodetic or projected coordinates (horizontal), meters (vertical), |
+| | decimalyear (temporal) |
++---------------------+--------------------------------------------------------------------+
+| **Output type** | Geodetic or projected coordinates (horizontal), meters (vertical), |
+| | decimalyear (temporal) |
++---------------------+--------------------------------------------------------------------+
+| **Domain** | 4D |
++---------------------+--------------------------------------------------------------------+
+| **Available forms** | Forward and inverse |
++---------------------+--------------------------------------------------------------------+
+
+The defmodel transformation can be used to represent most deformation models
+currently in use, in particular for areas subject to complex deformation, including
+large scale secular crustal deformation near plate boundaries and vertical deformation
+due to Glacial Isostatic Adjustment (GIA). These can often be represented by a constant
+velocity model. Additionally, many areas suffer episodic deformation events such as
+earthquakes and aseismic slow slip event.
+
+The transformation relies on a "master" JSON file, describing general metadata on
+the deformation model, its spatial and temporal extent, and listing spatial
+components whose values are stored in :ref:`Geodetic TIFF grids (GTG) <geodetictiffgrids>`.
+The valuation of each component is modulated by a time function (constant, step,
+reverse step, velocity, piecewise, exponential).
+
+All details on the content of this JSON file are given in the `Proposal for encoding
+of a Deformation Model <https://github.com/linz/deformation-model-format/blob/master/doc/JsonGeotiffDeformationModelFormat_20200501.pdf>`__
+
+If input coordinates are given in the geographic domain (resp. projected domain),
+the output will also be in the geographic domain (resp. projected domain).
+The domain should be the corresponding to the source_crs metadata of the model.
+
+This transformation is a generalization of the :ref:`Kinematic datum shifting utilizing a deformation model <deformation>` transformation.
+
+Parameters
+-------------------------------------------------------------------------------
+
+Required
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+.. option:: +model=<filename>
+
+ Filename to the JSON master file for the deformation model.
+
+
+Example
+-------------------------------------------------------------------------------
+
+Transforming a point with the LINZ NZGD2000 deformation model:
+
+::
+
+ echo 166.7133850980 -44.5105886020 293.3700 2007.689 | cct +proj=defmodel +model=nzgd2000-20180701.json