Remove-OSSIM.md

@@ -156,6 +156,68 @@ Here is a new workflow to replace the current function
    to store the metadata.  If the parsing returns successfully, the
    generated ImageMetadata is given to the *ImageCommon* that
    propagate through the pipeline.
+   
+### The new Sensor Model mechanism
+
+```mermaid 
+classDiagram
+  class Transform~TScalarType, NInputDimensions, NOutputDimensions~{
+  -TransformPoint(Point)* Point
+  }
+
+  class SensorModelBase~TScalarType, NInputDimensions, NOutputDimensions~{
+  -SetMetadataModel(boost_any)* bool
+  -IsValidSensorModel()* bool
+  }
+
+  class RPCTransformBase~TScalarType, NInputDimensions, NOutputDimensions~{
+  -SetMetadataModel(boost_any) bool
+  -IsValidSensorModel() bool
+  #Projection_RPCParam m_RPCParam
+  #GDALRPCTransformer m_Transformer
+  }
+
+  class RPCForwardTransform~TScalarType, NInputDimensions, NOutputDimensions~{
+  -TransformPoint(Point) Point
+  }
+
+  class RPCInverseTransform~TScalarType, NInputDimensions, NOutputDimensions~{
+  -TransformPoint(Point) Point
+  }
+
+  Transform <|-- SensorModelBase
+  SensorModelBase <|-- RPCTransformBase
+  RPCTransformBase <|-- RPCForwardTransform
+  RPCTransformBase <|-- RPCInverseTransform
+```
+
+The class ```SensorModelBase``` is the new 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.
+  
+#### RPC sensor model
+
+The RPC model is stored in the ```ImageMetadata``` object, using the
+key ```MDGeom::RPC```. The classes ```RPCTransformBase```,
+```RPCForwardTransform``` and ```RPCInverseTransform``` are used to
+perform forward and inverse transformation using this model.
+
+The abstract class ```RPCTransformBase``` contains the implementation
+of the ```SetMetadataModel``` method, which receives the RPC
+description from the ```ImageMetadata``` and instantiates a
+```GDALRPCTransformer```.
+
+The classes ```RPCForwardTransform``` and ```RPCInverseTransform```
+each implement there version of the ```TransformPoint``` method which
+uses the ```GDALRPCTransformer```.
   
 ## Justifications for the technical choices