Why is pgRouting shortest route function complaining about wrong source and target IDs?

Question

This question is somewhat linked to underdark post, but I think here it would more helpful: https://underdark.wordpress.com/2011/12/18/osm2po-part-2-pgrouting-on-osm-the-easy-way/#comment-2636

I installed everything to enable the pgrouting, after that I did the extraction from an OSM (modified by me in JOSM) file, to PostgreSQL using Osm2Po but after trying to route it through QuantumGis and the Routing Plugin I had the following issue:

“No se puede ejecutar la consulta. El mensanje de error de la base de datos fue: ERROR: Start vertex was not found.”

Thing is that after I checked I notice that in my “spatial” table I have:

• 7,347 Nodes which are never sources
• 6,966 Nodes which are never targets
• 6,369 Rows which are never sources nor targets (including above) (Note: I have 19,191 nodes)

So I would like to know if you know any reasons why this could had happened or how I couId fix it.

Aside of that I tried routing using existing targets and sources ids, but then I got routes which were not from nor to the nodes I had used… which like dont know why could had happened, but I guess is linked to wrong OSM to PostgreSql Translation.

Finally I tried routing with Osm2Po in the Localhost site and it do worked, so I dont know if the data is ok but some configuration is wrong.

EDIT:

• Problem is NOT the missing sources or targets node ( @Carsten ).
• Problem is using wrongs Source Id and Target Id, using the the Street Segments Id instead of the Vertex Id (I could see that double-checking the web routing process of Osm2Po)

BUT the question still remains: How can I find the right source and targets, what Osm2Po called findClosestVertexId?

Answer 1

One possible reason: Imagine a one way ending outside your area. The result is a source node, which is connected to your network and an orphaned target node, that cannot act as source anymore. But this is not an osm2po issue.

I assume it has sth. to with pgRoutings "directed"-parameter.

Answer 2

The problem was referencing wrong the corners. I was using QGIS to determine the source and target ID, what I did was click the segment from when I wanted to go, with the "Identify Spatial Objects" option, and copy the value from the field ID which IS WRONG.

After triple-checking I see that the right value to pick, after clicking "Identify Spatial Objects" is the one in the SOURCE Field of the street segment properties if you want to specify where does the route starts. And the TARGET Field of the street segment properties if you want to specify the ending poing of the route

Answer 3

If you're missing "source" and "target" information it won't work and you will get either errors as you wrote or wrong results.

In your case the network topology is wrong. Maybe you modified something accidentally when you modified the OSM data.

You can do simple checks like these for example:

• run osm2po on the original OSM data and then try routing
• load the network data in QGIS for example and check if your network looks OK

Probably your original data is not correct or not in the right format that osm2po expects (ie. wrong projection).