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Preprocessing
Install osmnx
pip install osmnx
Download the road network of a city to shapefile using osmnx:
import osmnx as ox
place ="Shenzhen, China"
G = ox.graph_from_place(place, network_type='drive')
ox.save_graph_shapefile(G, filename='shenzhen_network')
The process may take several mintues.
It will generate two shapefiles edges and nodes. The edges shapefile already contains the topology of the road network (the attribute from,to node).
The configuration for generating ubodt can be
<?xml version="1.0" encoding="utf-8"?>
<ubodt_config>
<input>
<network>
<file>edges.shp</file>
<id>osmid</id>
<source>from</source>
<target>to</target>
</network>
</input>
<parameters>
<delta>0.01</delta>
</parameters>
<output>
<file>ubodt.txt</file>
</output>
</ubodt_config>
OSM road network generally contains an attribute called one-way to indicate the direction of an edge. To consider this information, a reverse edge should be added to the road network wherever one-way is false.
This can be done easily in PostGIS database using the ST_Reverse function.
The following sql codes are provided as a reference.
--- Import shapefile into a table in PostGIS database (run in bash shell).
shp2pgsql network.shp network.original | psql -U USER_NAME -d DATABASE_NAME
--- This command import network.shp into PostGIS database as a table `network.original`, which means schema.tablename.
--- Create a new table to store the dual version (run in psql)
CREATE TABLE network.dual
(
gid serial NOT NULL,
geom geometry(LineString),
source integer,
target integer,
cost double precision,
original_id integer,
CONSTRAINT dual_pkey PRIMARY KEY (gid)
);
-- Insert original edge (run in psql)
INSERT INTO
network.dual (geom,source,target,cost,original_id)
SELECT ST_LineMerge(geom),source,target,distance,gid FROM network.original;
-- Insert reversed edge (run in psql)
INSERT INTO
network.dual (geom,source,target,cost,original_id)
SELECT ST_Reverse(ST_LineMerge(geom)),target, source, distance, gid FROM network.original where one_way=="false";
-- Export to a shapefile network_dual.shp (run in bash shell)
pgsql2shp -f network_dual.shp -h localhost -u USER_NAME -d DATABASE_NAME "SELECT gid::integer as id,source,target,geom from network.dual"
If you already have a road network file in GDAL supported formats, e.g., ESRI shp, GeoJSON or CSV without topology information (id, source and target fields). Spatial database PostGIS and its extension pgRouting can solve the problem: