DrivingDistance (#19) - list of edges returned by DrivingDistance vs. Shortest Path Tree? (#369) - Message List

Hello, the output of Driving Distance is a list of vertices and edges. When using the function, I've found that the list of vertices effectively includes all nodes within the required distance. (see e.g. last page of this report in French - sorry !  http://www.cete-mediterranee.fr/tt13/www/imgarea/DemoOSM-Manuel_Utilisation.pdf)

However the associated list of edges is NOT the shortest path tree of the nodes, as I would expect (or hope).

The web doc (http://pgrouting.postlbs.org/wiki/DrivingDistance) states "There is one row for each crossed edge, and an additional one containing the terminal vertex. The columns of each row are:

• vertex_id: the identifier of source vertex of each edge. There is one more row after the last edge, which contains the vertex identifier of the target path.
• edge_id: the identifier of the edge crossed "

But this is not clear...

Could you explain this please? And if possible how I could get the shortest path tree with a certain distance to the origin ? Thanks in advance

Best regards, patrick Gendre CETE Med, Aix-en-Provence, France