Using pgr_drivingDistance for isochrones?

I have tried to calculate Isochrones in 500m walking distance along paths around planned subway stations with pgrouting.

For the setup I used an OSM-road.shp clipped to the borders of Vienna and a point shp. with the 14 stations which I want to analyse.

I worked my way through several tutorial since I am new to pgrouting for setting up a street-network and finding the closest nodes from the stations.

So far so good…but when I to calculate the isochrones with pgr_DrivingDistance the output shows very few results.

Either I set up the network wrong or I have been using the DrivingDistance function wrong. It seems like the function is not able to use every path.

How do I improve the query?

PostgreSQL 9.5.11 Pgrouting 2.4.1

CREATE OR REPLACE VIEW road_ext AS SELECT *, ST_StartPoint(geom), ST_EndPoint(geom) FROM road; CREATE TABLE node AS SELECT row_number() OVER (ORDER by foo.p)::integer AS id, foo.p AS geom FROM ( SELECT DISTINCT road_ext.ST_StartPoint AS p FROM road_ext UNION SELECT DISTINCT road_ext.ST_EndPoint AS p FROM road_ext ) foo GROUP BY foo.p; 

I had to change the geometry type since OSM provided multistring

ALTER TABLE road ALTER COLUMN geom TYPE geometry(LineString, 31256) USING ST_GeometryN(geom, 1); 

Setup network

CREATE TABLE network AS SELECT a.*, b.id as start_id, c.id as end_id FROM road_ext AS a JOIN node AS b ON a.ST_Startpoint = b.geom JOIN node AS c ON a.ST_EndPoint = c.geom; ALTER TABLE network add column len_km double precision ALTER TABLE network add column time_walking double precision UPDATE network set len_km = (ST_Length(geom))/1000 UPDATE network set time_walking = ((60/5::double precision)*len_km) 

Setup the point shp

ALTER TABLE ubahnpointsmgi ADD Column nearest_node integer --Node in clostest distance is enough accuracy CREATE TABLE temp AS SELECT DISTINCT ON (a.gid) a.gid, b.id AS start_id, ST_Distance(a.geom, b.geom) AS dist FROM ubahnpointsmgi a, node b ORDER BY a.gid, ST_Distance(a.geom, b.geom), b.id UPDATE ubahnpointsmgi SET nearest_node = (SELECT start_id FROM temp WHERE temp.gid = ubahnpointsmgi.gid) 

Calculating Line geometry

CREATE TABLE ISO_500 AS SELECT seq, cost, agg_cost, node, edge, l.geom FROM pgr_drivingDistance( 'SELECT gid as id, start_id as source, end_id as target, len_km as cost FROM network', 41217,0.5, false) AS foo JOIN network l ON l.gid = foo.edge 

Calculating Point geometry

CREATE TABLE ISO_500 AS SELECT seq, cost, node, edge, l.geom FROM pgr_drivingDistance( 'SELECT gid as id, start_id as source, end_id as target, len_km as cost FROM network', 41217,0.5, false) AS foo LEFT JOIN node l ON l.id = foo.node 

Output Table:
Output QGIS: