DOC: explain coordinate expected in vector data

Code/OBIA/otbLabelMapToVectorDataFilter.h

@@ -40,7 +40,11 @@ namespace otb {
    * "An algorithm for the rapid computation of boundaries of run-length
    * encoded regions", Francis K. H. Queck, in Pattern Recognition 33
    * (2000), p 1637-1649.
- *
+   * 
+   * Note : the output vector data contains index coordinates (not physical coordinates).
+   * For instance, a polygon around the pixel at index (0,0) would have the following
+   * points : [-0.5,-0.5] , [0.5,-0.5] , [0.5,0.5] , [-0.5,0.5]
+   *
    * \sa VectorDataSource
  * \ingroup GeoSpatialAnalysis
  */

Code/OBIA/otbVectorDataToLabelMapWithAttributesFilter.h

@@ -48,6 +48,12 @@ namespace otb
  * The first Label is set using SetInitialLabel (by default it is 0), and increases 1 by 1.
  * The vector data attributes are also assigned to the object in the label map.
  *
+ * When AutomaticSizeComputation=True, the spacing from the vector data object 
+ * is used. Then the size and origin are computed so that the image extent 
+ * covers exactly the vector data bounding region.
+ * 
+ * Note : the coordinates in the vector data are assumed to be physical coordinates.  
+ *
  * \sa LabelMapSource
  */