Migration-guide-OTBv8.md

@@ -13,8 +13,13 @@ small portion of OSSIM was used anyway.
 
 The two main work for this version 8 have been:
 
-- A complete refactoring of the metadata management
-- A re-implementation of the sensor model framework.
+- A complete refactoring of the metadata management. We replaced OSSIM
+  by GDAL to access the metadata in the image files, and we developed
+  classes called `ImageMetadataInterfaces` (IMI) to parse the metadata
+  and organize them in an `ImageMetadata` object.
+- A re-implementation of the sensor model framework. We replaced
+  OSSIM's RPC model by GDAL's. We implemented our own SAR model. A
+  whole new SensorModel factory as developed.
 
 A new DEM Handler was also developed.
 
@@ -346,4 +351,4 @@ auto sensorModel = otb::SensorTransformFactory::GetInstance().CreateTransform
   <double, InputSpaceDimension, OutputSpaceDimension>(*imd, TransformDirection::FORWARD);
 if (sensorModel != nullptr)
   [...]
-```
+```
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