Why is pgrouting driving distance skipping edges?

Question

I have a road network where I do a driving distance operation through pgrouting. This is my SQL:

SELECT * FROM driving_distance('SELECT gid AS id,source,target, cost FROM elveg',676663,1000,false,false);

From this query I get a strange result: http://bildr.no/view/1373984

Black is my road network and green is the result from the above query. From the image you see that some edges are not included(not green) while edges which can only be connected through this not included edge in fact is included?

How can this be? Am I doing something totally wrong here?

Answer 1

You have created routing table with too big tolerances.

When you have linestring table and you create edge/vertex table for routing algorithm, you need to give tolerance. For example

        |  a-line
  ------o-------
c-line /
        |  -b-line
        |

In example both a and b line should intersect at "o" but something went wrong somewhere. So easy "fix" is use that "1m" tolerance, but it his example it would probably "eat" c-line away because its lenght is "1m"

third edit: now that i picture again, it just looks like you routing edge/vertex table is broken, try regerate it using sane tolarenace see for howto "http://pgrouting.org/docs/howto/topology.html#pgrouting"

This one seems to be good example howto do it http://pgrouting.org/docs/foss4g2008/index.html