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

[Stephen Woodbridge]

On 4/24/2017 4:55 AM, McDonaldR wrote:
> Thanks Steve
> 
> The function to get the source and target points on to the nearest
> edges gives a much better result than using nearest node.  Now I just
> need to work out how to get the geometry of the route from these
> projected points.

For the first and last edgeid in the result, use the linear referencing 
functions to split that edge and keep the part you need instead of the 
whole thing. the "pos" can be used as the split location on the edge.

-Steve

> Thanks very much for the help
> 
> Ross
> 
> -----Original Message----- From: Pgrouting-users
> [mailto:pgrouting-users-bounces at lists.osgeo.org] On Behalf Of Stephen
> Woodbridge Sent: 20 April 2017 16:50 To:
> pgrouting-users at lists.osgeo.org Subject: Re: [pgrouting-users]
> best/fastest way to calculate thousands of trsp routes
> 
> On 4/20/2017 6:49 AM, McDonaldR wrote:
>> 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?
> 
> Yes, this sounds reasonable.
> 
>> 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?
> 
> Here is a function that might be useful, or you might modify it for
> your specific needs. tol is maximum search distance in degrees, you
> can estimate this degrees = meters/111120.0. It returns the edge_id,
> pos on the that edge and these can be used to args to trsp.
> 
> -Steve W
> 
> create or replace function pointToEdgePos(edge_table text, lon
> float8, lat float8, tol float8, OUT edge_id integer, OUT pos float8) 
> returns record as $body$ -- ASSUMPTIONS -- * edge_table as columns
> "gid" and "geom" -- * edge_able.geom uses srid=4326 declare rr
> record; pct float8; pnt geometry; geom geometry;
> 
> begin -- create a point from lon, lat pnt :=
> st_setsrid(st_makepoint(lon,lat), 4326);
> 
> -- set the error condition edge_id := null; pos := -1.0;
> 
> -- find the closest edge within tol distance execute 'select * from '
> || _pgr_quote_ident(edge_table) || ' where st_dwithin(''' ||
> pnt::text || '''::geometry, geom, ' || tol || ') order by
> st_distance(''' || pnt::text || '''::geometry, geom) asc limit 1'
> into rr;
> 
> if rr.geom is not null then -- deal with MULTILINESTRINGS geom :=
> rr.geom; if geometrytype(geom)='MULTILINESTRING' THEN geom :=
> ST_GeometryN(geom, 1); end if;
> 
> -- project the point onto the linestring pos :=
> st_line_locate_point(geom, pnt); edge_id := rr.gid; end if;
> 
> end; $body$ language plpgsql stable;
> 
> 
>> 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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