🔞 🔹 🎃 我们在OpenStreetMap上进行路由（路由）。增加对单向道路的支持 👩🏽‍💻 😼 🥠

我们将继续一系列有关基于开放源PostgreSQL数据库和OpenStreetMap上的PgRouting扩展构建具有复杂要求的路由系统的文章。今天，我们将讨论如何增加对单向道路（行车路线）的支持。通常，缺少此支持是将PgRouting切换到其他路由“引擎”的主要原因。像往常一样，所有数据和结果都可以在我发布时添加的OSM Routing Tricks GitHub存储库中找到。

在OpenStreetMap上的330个地址的简短路由。

什么是单向路，为什么需要它们

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PgRouting

PgRouting pgr_TSP — Using Simulated Annealing approximation algorithm :

If using directed := true, the resulting non symmetric matrix must be converted to symmetric by fixing the non symmetric values according to your application needs.

, , . , . , , Travelling salesman problem: Asymmetric:

Solving an asymmetric TSP graph can be somewhat complex. The following is a 3×3 matrix containing all possible path weights between the nodes A, B and C. One option is to turn an asymmetric matrix of size N into a symmetric matrix of size 2N.

, , ( ) . , PgRouting, , . . — , . . , ( , ).

	A	B	C
A		1	2
B	6		3
C	5	4

	A	B	C	A'	B'	C'
A				-w	6	5
B				1	-w	4
C				2	3	-w
A'	-w	1	2
B'	6	-w	3
C'	5	4	-w

-w , ,

w=0 is not always low enough

- PgRouting. PgRouting , ( ) [] , PgRouting ( , , ).

CREATE OR REPLACE FUNCTION pgr_dijkstraSymmetrizeCostMatrix(matrix_cell_sql text,
    OUT start_vid BIGINT, OUT end_vid BIGINT, OUT agg_cost float)
RETURNS SETOF RECORD AS
$BODY$
DECLARE
    sql text;
    r record;
BEGIN
    sql := 'with edges as (' || matrix_cell_sql || ')
        select 3e9+start_vid as start_vid, end_vid as end_vid, agg_cost from edges
        union
        select end_vid, 3e9+start_vid, agg_cost from edges
        union
        select 3e9+start_vid, start_vid, 0 from edges
        union
        select start_vid, 3e9+start_vid, 0 from edges
        union
        select start_vid, end_vid, 1e6 from edges
        union
        select 3e9+start_vid, 3e9+end_vid, 1e6 from edges
        ';
    FOR r IN EXECUTE sql LOOP
        start_vid := r.start_vid;
        end_vid   := r.end_vid;
        agg_cost  := r.agg_cost;
        RETURN NEXT;
    END LOOP;
END;
$BODY$
LANGUAGE plpgsql VOLATILE STRICT;

, . , PgRouting , ,

An Infinity value was found on the Matrix

- ( pgr_dijkstraSymmetrizeCostMatrix() , , , , ):

CREATE OR REPLACE FUNCTION pgr_dijkstraValidateCostMatrix(matrix_cell_sql text,
    OUT start_vid BIGINT, OUT end_vid BIGINT, OUT agg_cost float)
RETURNS SETOF RECORD AS
$BODY$
DECLARE
    sql text;
    r record;
BEGIN
    sql := 'WITH RECURSIVE src AS (' || matrix_cell_sql || '),
    dst AS (
        select
            *
        from src where start_vid =
            (select
                start_vid
            from src
            group by start_vid
            order by count(*) desc
            limit 1)
        union
        select
            src.*
        from src, dst
        where src.start_vid=dst.end_vid
    )
    select * from dst';
    FOR r IN EXECUTE sql LOOP
        start_vid := r.start_vid;
        end_vid   := r.end_vid;
        agg_cost  := r.agg_cost;
        RETURN NEXT;
    END LOOP;
END;
$BODY$
LANGUAGE plpgsql VOLATILE STRICT;

PgRouting . , , , ( ).

, . load.sh PostgreSQL .

, , . , , . , ( ) . , (type='osm') (type='osmreverse') . , ( , , ). , (type='osm') — (type='osmreverse'). , :

    case when (type='osmreverse' and oneway) then 1000000 else length end as cost,
    case when type ilike 'osm%' then 1000000 else length end as reverse_cost,

length — . ( ), .

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