使用PostGIS完成两点间的河流轨迹及流经长度的计算(推荐)

CREATE OR REPLACE FUNCTION “public”.”pgr_shortest_river”(IN “startx” float8, IN “starty” float8, IN “endx” float8, IN “endy” float8, OUT “river_name” varchar, OUT “v_shpath” varchar, OUT “cost” float8)
RETURNS SETOF “pg_catalog”.”record” AS $BODY$
declare
v_startLine geometry;–离起点最近的线
v_endLine geometry;–离终点最近的线
v_startTarget integer;–距离起点最近线的终点
v_endSource integer;–距离终点最近线的起点
v_statpoint geometry;–在v_startLine上距离起点最近的点
v_endpoint geometry;–在v_endLine上距离终点最近的点
v_res geometry;–最短路径分析结果
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
–查询离起点最近的线
execute ‘select (st_dump(geom)).geom as geom,target as target,name from singleriver 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;
raise notice ‘起点线段%’,v_startLine;
raise notice ‘起点位置%’,v_startTarget;
raise notice ‘河流名称%’,first_name;
–查询离终点最近的线
execute ‘select (st_dump(geom)).geom as geom,”source” as source,name from singleriver
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;
–如果没找到最近的线，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;

–计算距离起点最近线上的点在该线中的位置
select st_linelocatepoint(st_linemerge(v_startLine), v_statpoint) into v_perStart;

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

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

select st_distancesphere(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_distancesphere(v_statpoint, v_endpoint) into first_cost;

select st_linelocatepoint(st_linemerge(v_startLine), v_endpoint) into v_perEnd;
for v_rec in
select st_linesubstring(st_linemerge(v_startLine), v_perStart,v_perEnd) as point,COALESCE(end_name,’无名河流’) as name,end_cost as cost loop
v_shPath:=ST_AsGeoJSON(v_rec.point);
cost:=v_rec.cost;
river_name:=v_rec.name;
return next;
end loop;
return;
end if;
–最短路径
for v_rec in
(select st_linesubstring(st_linemerge(v_startLine),v_perStart,1) as point,COALESCE(first_name,’无名河流’) as name,first_cost as cost
union all
SELECT st_linemerge(b.geom) as point,COALESCE(b.name,’无名河流’) as name,st_length(geom, false) as cost
FROM pgr_dijkstra(
‘SELECT gid as id, source, target, st_length(geom, false) as cost FROM singleriver
where st_intersects(geom,st_buffer(st_linefromtext(”linestring(‘||startx||’ ‘ || starty ||’,’|| endx ||’ ‘ || endy ||’)”),0.05))’,
v_startTarget, v_endSource , false
) a, singleriver b
WHERE a.edge=b.gid
union all
select st_linesubstring(st_linemerge(v_endLine),0,v_perEnd) as point,COALESCE(end_name,’无名河流’) as name,end_cost as cost)
loop
v_shPath:=ST_AsGeoJSON(v_rec.point);
cost:=v_rec.cost;
river_name:=v_rec.name;
return next;
end loop;
end;
$BODY$
LANGUAGE plpgsql VOLATILE STRICT
COST 100
ROWS 1000