3. Do graph analysis

A. Execute ST_GraphAnalysis

Weighted

We do the actual graph analysis on connected component 1 as follows:

EXECUTE ST_GraphAnalysis(routes_1.edges, 'weight', 'routes_1', 3);

Please see the Javadoc for ST_GraphAnalysis (pending) for an explanation of the parameters. The default output table prefix is output.

This produces a table routes.graph_analysis containing

• id The node id
• betweenness_centrality Betweenness centrality
• closeness_centrality Closeness centrality

Unweighted

We could just as easily consider the graph to be unweighted bidirectional:

EXECUTE ST_GraphAnalysis(routes_1.edges, 1, 'routes_1_unweighted', 3);

B. Recover the node geometries

It remains only to match the node ids with their geometries in routes.nodes (or in routes_1.nodes).

CREATE TABLE routes_1.graph_analysis AS SELECT a.the_geom, b.* FROM routes.nodes a, routes_1.graph_analysis b WHERE a.id=b.id;

For unweighted graphs:

CREATE TABLE routes_1_unweighted.graph_analysis AS SELECT a.the_geom, b.* FROM routes.nodes a, routes_1_unweighted.graph_analysis b WHERE a.id=b.id;

C. Clean up

Here we get rid of intermediate tables we no longer need:

DROP TABLE routes_1.nodes PURGE;
DROP TABLE routes_1_start.edges PURGE;
DROP TABLE routes_1_end.edges PURGE;
DROP TABLE routes_1.edges PURGE;
DROP TABLE routes_1_tmp.graph_analysis PURGE;