DOC: Add documentation for new Sensor Model framework

Documentation/Cookbook/rst/C++/DeveloperGuide.rst

@@ -8,6 +8,7 @@ Developer Guide
     Filters
     StreamingAndThreading
     Metadata
+    SensorModel
     FunctorImageFilter
     PersistentFilters
     WriteAnApplication

Documentation/Cookbook/rst/C++/SensorModel.rst

+Sensor model
+============
+
+The class ``otb::SensorTransformBase`` is the base class for sensor
+models. It inherits from ``otb::Transform``, which inherits from
+``itk::Transform``. It is templated over the data type, and input and
+output dimentions. All sensor model classes should inherit from it,
+and implement the methods:
+
+- ``SetMetadataModel`` that takes a ``boost::any`` object representing the model;
+
+- ``IsValidSensorModel`` that returns true if the model is correctly set;
+
+- ``TransformPoint`` that process the transformation.
+
+.. image:: /Art/C++/UmlSensorModel.png
+
+RPC sensor model
+----------------
+
+The structure ``otb::Projection::RPCParam`` is used to store the
+parameters of the RPC model. It is based on `GDAL's RPC structure
+<https://gdal.org/development/rfc/rfc22_rpc.html>`_.
+
+The RPC model is stored in the ``otb::ImageMetadata`` object, using
+the key ``MDGeom::RPC``. The classes ``otb::RPCTransformBase``,
+``otb::RPCForwardTransform`` and ``otb::RPCInverseTransform`` are used
+to perform forward and inverse transformation using this model.
+
+The abstract class ``otb::RPCTransformBase`` contains the
+implementation of the SetMetadataModel method, which receives the RPC
+description from the ``otb::ImageMetadata`` and instantiates an
+``otb::GDALRPCTransformer``.
+
+The classes ``otb::RPCForwardTransform`` and
+``otb::RPCInverseTransform`` each implement a version of the
+``TransformPoint`` method which uses the ``otb::GDALRPCTransformer``.