Update the base polygon description

Author: Soyka-zz

osi_common.proto

@@ -155,12 +155,18 @@ message BaseStationary
     /// The relative orientation of the landmark w.r.t its parent frame.
     optional Orientation3d orientation = 3;
 
-    /// The two dimensional (flat) contour of the object. E.g. the projection of the contour onto the street.
-    /// The polygon is closed by connecting the last with the first point. Therefore these two points are 
-    /// different and there are at least three points.
-    /// The polygon is defined counter-clockwise.
-    /// For ground truth data the polygon is defined in two dimensional world coordiantes.
-    /// For sensor data the polygon is defined in two dimensional sensor coordinates.
+    /// Usage as ground truth:
+    /// The two dimensional (flat) contour of the object. This is an extension of the concept of a 
+    /// bounding box as defined in Dimension3d. The contour is the projection of the object outline 
+    /// on the z-plane in the object frame (independent of its current position and orientation). 
+    /// Usage as sensor data:
+    /// The polygon describes the visible part of the object's contour.
+    /// General definitions:
+    /// The polygon is defined in the local object frame: x pointing forward and y to the left.      
+    /// As ground truth, the polygon is closed by connecting the last with the first point. Therefore  
+    /// these two points are different and there are at least three points.
+    /// As sensor data, the polygon is open.
+    /// The polygon is defined counter-clockwise.    
     repeated Vector2d base_polygon = 4;
 }
 
@@ -191,11 +197,17 @@ message BaseMoving
     /// Obviously, the orientation rate becomes global/absolute if the parent frame is not rotating.
     optional Orientation3d orientation_rate = 6;
 
-    /// The two dimensional (flat) contour of the object. E.g. the projection of the contour onto the street.
-    /// The polygon is closed by connecting the last with the first point. Therefore these two points are 
-    /// different and there are at least three points.
-    /// The polygon is defined counter-clockwise.
-    /// For ground truth data the polygon is defined in two dimensional world coordiantes.
-    /// For sensor data the polygon is defined in two dimensional sensor coordinates.
+    /// Usage as ground truth:
+    /// The two dimensional (flat) contour of the object. This is an extension of the concept of a 
+    /// bounding box as defined in Dimension3d. The contour is the projection of the object outline 
+    /// on the z-plane in the object frame (independent of its current position and orientation). 
+    /// Usage as sensor data:
+    /// The polygon describes the visible part of the object's contour.
+    /// General definitions:
+    /// The polygon is defined in the local object frame: x pointing forward and y to the left.      
+    /// As ground truth, the polygon is closed by connecting the last with the first point. Therefore  
+    /// these two points are different and there are at least three points.
+    /// As sensor data, the polygon is open.
+    /// The polygon is defined counter-clockwise.    
     repeated Vector2d base_polygon = 7;    
 }