Driving Distance documentation issues

[drnextgis]

1. Driving Distance calculation page (http://www.pgrouting.org/docs/1.x/dd.html) tells that output field "cost" is
   "the cost associated to the current edge. It is 0 for the row after the last edge. Thus, the path total cost can be computated using a sum of all rows in the cost column." But it seems to me that cost attribute contains the total cost of travel from the starting node to the vertex_id node, isn't it?

2. Also in this document tells that "vertex_id: the identifier of source vertex of each edge". But when I perform the following query in my database:

   SELECT _.*, gid, osm_id, source, target FROM driving_distance('SELECT gid AS id, source AS source, target AS target, length AS cost FROM network_part', 4260, 2000, false, false) AS _ INNER JOIN network_part ON _.edge_id = network_part.gid WHERE OSM_ID=84675642

   it returns:
   vertex_id | edge_id | cost | gid | osm_id | source | target
   -----------+---------+------------------+--------+----------+--------+--------
   3520 | 539658 | 881.303092499435 | 539658 | 84675642 | 3520 | 3521
   3521 | 539658 | 911.340955617547 | 539658 | 84675642 | 3520 | 3521
   (2 rows)

   As you can see vertex_id is not the same as source of edge.

3. What is edge_id? Here is part of my road network: http://gis-lab.info/share/DR/ifort/dd_graph2.png
   If I perform query described above I get edge_id value the same for both vertex_id=3520 and 3521. I had assumed that vertex_id describes id of last edge but it is not correct. Please provide any information about edge_id field and how it can be used.

[YenTheFirst]

I'm running into these same issues.

What I've discovered so far:
for cost, vertex_id, edge_id,
'cost' is lowest cost to reach 'vertex_id'.
the edges to actually reach 'vertex_id' aren't necessarily included in the output
'edge_id' seems to be an edge that has 'vertex_id' either as its source or target, but, the other target/source isn't necessarily within the maximum_cost, and the edge shouldn't be considered part of the shortest path tree.

as far as I can tell, edge_id is fairly useless, unless you just want a general sense of some edges that might be reachable.

I'll have to dig into the C to figure out why this is.

[dkastl]

Documentation should be OK for version 2.0
Removing the "2.0" tag and replace it with one for "1.x"

[woodbri]

Closing - Wont fix.