[pgrouting-users] best/fastest way to calculate thousands of trsp routes

[McDonaldR]

Hi List,

I'm running pgRouting 2.1 with PostGIS 2.2.2 on PostgreSQL 9.2.20.

I have 16,000 pupils going to 57 schools.  I have a network with turn restrictions.  I have a function (below) that loops through all the pupils and calculates a TRSP route and updates the pupil table with the route cost.  I have some questions too.


1.       It's going to take ~ 2 hours to process all the pupils.  Will it make things faster if I created, say, 4 functions that each processed a different set of pupils?  I have a multicore server and memory to spare. I have to run this for time and distance and also for all the pupils assigned an "optimally located" school. What's the best/fastest way to do this?

2.       I pre-processed the pupil data to assign each pupil the nearest node on the network. Some pupils in rural areas are a mile from the nearest node and are assigned the node at the end furthest from the school. How would I use the pgr_trsp with edges and edge position to create a position for each pupil at a point on the nearest edge?

CREATE OR REPLACE FUNCTION public.pupil_journeys()
  RETURNS character varying AS
$BODY$
DECLARE

  cur_pupil refcursor;
  v_pid integer;
  v_pnn integer;
  v_snn integer;
  v_cost double precision;
  v_sql varchar(1000);

BEGIN
  RAISE NOTICE 'Processing pupil journeys...';
  OPEN cur_pupil FOR EXECUTE format('SELECT pupilid, pupil_nn, school_nn FROM edn_pupilschoolroute WHERE pupil_NN IS NOT NULL');
  LOOP
  FETCH cur_pupil INTO v_pid, v_pnn, v_snn;
  EXIT WHEN NOT FOUND;
  SELECT SUM(cost) AS v_cost FROM pgr_trsp('
                SELECT ogc_fid AS id,
                  source::integer,
                  target::integer,
                  cost_len::double precision AS cost,
                  rcost_len::double precision AS reverse_cost
                FROM hw_roadlink'::text,
                v_pnn, --pupil_nn gets inserted here
                v_snn, --school_nn gets inserted here
                true,
                true,
                'select to_cost, teid as target_id, feid||coalesce('',''||via,'''') as via_path from hw_nt_restrictions'::text) INTO v_cost;
  -- insert route cost into pupil data table
  v_sql:='UPDATE edn_pupilschoolroute SET p_dist = ' || v_cost || ' WHERE pupil_nn = ' || v_pnn || ' AND school_nn = ' || v_snn || ' AND pupilid = ' || v_pid;
  EXECUTE v_sql;
  END LOOP;
  RETURN 'Well, that worked!';
  CLOSE cur_pupil;
END;
$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100;

Thanks in advance

Ross

Ross McDonald | GIS Data Coordinator | Angus Council | Angus House, Orchardbank Business Park, Sylvie Way, Forfar DD8 1AT | t: 01307 476419


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