Add a short paragraph about the semantic of edge's next_left_edge and next_right_edge...

git-svn-id: http://svn.osgeo.org/postgis/trunk@7184 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/topology/README b/topology/README
index b89b1b943aa827c869e35493c796894dfca5bbe1..4b8c0076bb59126241877554153bc3680319de7e 100644 (file)
--- a/topology/README
+++ b/topology/README
@@ -96,7 +96,14 @@ under you topology schema:
         * face_id integer PRIMARY KEY
         * mbr box2d ( can be NULL )
 
-Details on semantic are contained in the SQL/MM specification, which
+The next_*_edge of an edge is the edge you encounter next while going
+around the specified face (right or left) in counterclockwise order
+(so that the face is on your left). Note that due to this definition
+the edge being considered is traversed in reverse order when traversing
+its "right" face. The values are signed to indicate wheter the next edge
+will be traversed in its original or reversed orientation.
+
+More details on semantic are contained in the SQL/MM specification, which
 this implementation follows as for these views structure.
 
 ==Validating topology data