基於pgrouting的最短路徑規划

最近項目上有一個計算兩點最短路徑的需求，即就是類似於百度地圖的路徑規划問題，小編研究了一段時間，並參考了相關資料，基於postgresql+postgis+pgrouting實現了簡單的路徑規划，計算的結果是組成最短路徑的所有線路的集合，話不多說，直接上主要的存儲過程：

CREATE OR REPLACE FUNCTION public.pgr_shortest_road(
IN startx double precision,
IN starty double precision,
IN endx double precision,
IN endy double precision,
OUT road_name character varying,
OUT v_shpath character varying,
OUT cost double precision)
RETURNS SETOF record AS
$BODY$ 
declare 
v_startLine geometry;--離起點最近的線 
v_endLine geometry;--離終點最近的線 
v_startTarget integer;--距離起點最近線的終點 
v_endSource integer;--距離終點最近線的起點 
v_statpoint geometry;--在v_startLine上距離起點最近的點 
v_endpoint geometry;--在v_endLine上距離終點最近的點 
v_res geometry;--最短路徑分析結果 
v_perStart float;--v_statpoint在v_res上的百分比 
v_perEnd float;--v_endpoint在v_res上的百分比 
v_rec record; 
first_name varchar;
end_name varchar;
first_cost double precision;
end_cost double precision;
begin 
--查詢離起點最近的線 
execute 'select geom,target,name from china_road where 
ST_DWithin(geom,ST_Geometryfromtext(''point('|| startx ||' ' || starty||')''),0.01) 
order by ST_Distance(geom,ST_GeometryFromText(''point('|| startx ||' '|| starty ||')'')) limit 1' 
into v_startLine ,v_startTarget,first_name; 
--查詢離終點最近的線 
execute 'select geom,source,name from china_road
where ST_DWithin(geom,ST_Geometryfromtext(''point('|| endx || ' ' || endy ||')''),0.01) 
order by ST_Distance(geom,ST_GeometryFromText(''point('|| endx ||' ' || endy ||')'')) limit 1' 
into v_endLine,v_endSource,end_name; 
--如果沒找到最近的線，就返回null 
if (v_startLine is null) or (v_endLine is null) then 
return; 
end if ; 
select ST_ClosestPoint(v_startLine, ST_Geometryfromtext('point('|| startx ||' ' || starty ||')')) into v_statpoint; 
select ST_ClosestPoint(v_endLine, ST_GeometryFromText('point('|| endx ||' ' || endy ||')')) into v_endpoint; 

--計算距離起點最近線上的點在該線中的位置
select ST_Line_Locate_Point(st_linemerge(v_startLine), v_statpoint) into v_perStart;

select ST_Line_Locate_Point(st_linemerge(v_endLine), v_endpoint) into v_perEnd;

select ST_Distance_Sphere(v_statpoint,ST_PointN(ST_GeometryN(v_startLine,1), ST_NumPoints(ST_GeometryN(v_startLine,1)))) into first_cost;

select ST_Distance_Sphere(ST_PointN(ST_GeometryN(v_endLine,1),1),v_endpoint) into end_cost; 

if (ST_Intersects(st_geomfromtext('point('|| startx ||' '|| starty ||') '), v_startLine) and ST_Intersects(st_geomfromtext('point('|| endx ||' '|| endy ||') '), v_startLine)) then 
select ST_Distance_Sphere(v_statpoint, v_endpoint) into first_cost;

select ST_Line_Locate_Point(st_linemerge(v_startLine), v_endpoint) into v_perEnd;
for v_rec in 
select ST_Line_SubString(st_linemerge(v_startLine), v_perStart,v_perEnd) as point,COALESCE(end_name,'無名路') as name,end_cost as cost loop
v_shPath:= ST_AsGeoJSON(v_rec.point);
cost:= v_rec.cost;
road_name:= v_rec.name;
return next;
end loop;
return;
end if;
--最短路徑 
for v_rec in 
(select ST_Line_SubString(st_linemerge(v_startLine),v_perStart,1) as point,COALESCE(first_name,'無名路') as name,first_cost as cost
union all
SELECT st_linemerge(b.geom) as point,COALESCE(b.name,'無名路') as name,b.length as cost
FROM pgr_dijkstra(
'SELECT gid as id, source, target, length as cost FROM china_road
where st_intersects(geom,st_buffer(st_linefromtext(''linestring('||startx||' ' || starty ||','|| endx ||' ' || endy ||')''),0.05))', 
v_startTarget, v_endSource , false 
) a, china_road b 
WHERE a.edge = b.gid
union all
select ST_Line_SubString(st_linemerge(v_endLine),0,v_perEnd) as point,COALESCE(end_name,'無名路') as name,end_cost as cost)
loop
v_shPath:= ST_AsGeoJSON(v_rec.point);
cost:= v_rec.cost;
road_name:= v_rec.name;
return next;
end loop; 
end; 
$BODY$
LANGUAGE plpgsql VOLATILE STRICT;

 

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