[GIS] Why is pgRouting shortest route function complaining about wrong source and target IDs

osm2popgrouting

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?

Best Answer

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.

Related Solutions

pgRouting – Troubleshoot Slow pgr_* Routing Functions with OSM Data

Problem with pgRouting performance seems to be that new pgr_astar and pgr_dijkstra use whole graph (which guarantees solution if there is one). Simple solution to get better performance is limit used graph to smaller area. It has it own problems like sometimes it may create graphs that cannot be solved

 (SELECT ST_Expand(ST_Extent(geom_way),0.1) as box  FROM hh_2po_4pgr as l1 WHERE l1.source =7 OR l1.target = 12)

Creates BBOX over source and target collection and expands it 0.1 degrees, then same query is used to limit graph size in pgr_ query

Dijkstra from 1.2s to ~65ms

SELECT  seq, id1 AS node, id2 AS edge, g.geom_way as the_geom
    FROM pgr_dijkstra(
            'SELECT id, source, target, cost FROM hh_2po_4pgr as r, 
            (SELECT ST_Expand(ST_Extent(geom_way),0.1) as box  FROM hh_2po_4pgr as l1    WHERE l1.source =7 OR l1.target = 12) as box
            WHERE r.geom_way && box.box',
            7, 12, false, false
    ) as r INNER JOIN hh_2po_4pgr as g ON r.id2 = g.id ;

A* from 2s to ~50ms

SELECT seq, id1 AS node, id2 AS edge, cost
    FROM pgr_astar(
           'SELECT id, source, target, cost, x1,y1,x2,y2 FROM hh_2po_4pgr as r, 
             (SELECT ST_Expand(ST_Extent(geom_way),0.1) as box  FROM hh_2po_4pgr as l1    WHERE l1.source =7 OR l1.target = 12) as box
            WHERE r.geom_way && box.box',
            7, 12, false, false
    );

osm2po was used to import data (finland-latest) into postgis table. gist index added to geom_way column and full vacuum analyze run for database. shared memory 1G . workmem 512M

[GIS] Doubts about how pgRouting topology is built and how flexible it is

I'm trying to give a brief reply to your questions:

The topology function assigns a source and a vertex ID for each road segment. To do this a vertex table is created, which contains all source and target IDs. You can use this vertex table, but it's not required.
If there is no shared node at an intersection, then the topology script will not connect these 2 roads.
You can use any network data you want.
You need to handle intermediate points yourself. PostGIS provides various functions to find nearest roads and split them, see ST_LineLocatePoint or ST_LineSubstring. pgRouting is a set of basic functions, which add routing or network analysis functionality.
Turn restrictions are complex. You should first start with something simple.
PostGIS and pgRouting topology functions are different. pgRouting cares about a valid "network".

You probably best start with the pgRouting workshop.

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