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I have the road networks from osm and I created topology.

I know that dijkstra algorithm works, because I calculated the shortest path from two point layers. Now I would like to calculate catchment area for my points (from first layer).

I checked, how works pgr_drivingDistance. The result is far from expected.

I tried these codes:

SELECT pgr_drivingDistance( 'select id, source, target, leng as cost from osm_roads'
, 221, 1000)
     FROM osm_roads_vertices_pgr

where 221 is number of nodes. This code executed for a very long time and I had to stop it.

CREATE TABLE distances AS (SELECT a.node AS id, a.agg_cost AS distance, b.the_geom
FROM pgr_drivingDistance(
    'SELECT gid AS id, source, target, leng as cost FROM public.osm_roads',
    221,
    1000
) a, osm_roads_vertices_pgr b WHERE a.node = b.id);

but in this case result had only one point (start point) and this is not true.

I attach two screenshots:

The first, result from PgAdmin.

enter image description here

The second from visualization in QGIS. enter image description here

What am I doing wrong? Do you have an idea, how can I iprove my code?

I'm using PostgreSQL 10 with PostGIS 2.5.2 and Pgrouting 2.6.2.

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  • 1
    your first query executes pgr_drivingDistance once for every row in osm_roads_vertices_pgr; it simply fetches the full table, but instead of selecting columns that function will be executed for each row. just omit the FROM osm_roads_vertices_pgr. as to your actual issue; without knowing your network, this is impossible to debug (it might just as well be the expected result, and it just needs an explanation as to why it is)
    – geozelot
    Commented Oct 23, 2019 at 13:30
  • I have just added two screenshots.
    – Michal De
    Commented Oct 23, 2019 at 13:54
  • 1
    what's the unit of leng, meter? What happens if you replace it with ST_Length(geom::GEOGRAPHY) AS cost?
    – geozelot
    Commented Oct 23, 2019 at 15:15
  • I have this message: "Only lon/lat coordinate systems are supported in geography." When I delete ":GEOGRAPHY", result is the same. Unit of leng is meter. Coordinates are also in meters (EPSG:2180).
    – Michal De
    Commented Oct 24, 2019 at 18:06

1 Answer 1

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I found the solution.

My roads network wasn't good splitted. Node 220 had not connection.

I had to use pgr_nodeNetwork.

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