如何计算最近点到PostGIS中的线串？

问题描述：

我按照这个question来计算最近的道路（线串）的POI。我能够计算线串中的最近点，但是我无法找到从POI到线串上最近点（顶点）的距离。如何计算最近点到PostGIS中的线串？

这是我寻找最近POI的代码。

CREATE TABLE road(id serial PRIMARY KEY, the_geog geography(LINESTRING,4326)); 

CREATE TABLE poi(gid serial PRIMARY KEY, name varchar, city varchar, the_geog geography(POINT,4326))

值是：

INSERT INTO road (id, the_geog) VALUES (123, ST_GeographyFromText('SRID=4326;LINESTRING(85.280194 23.296728,85.281572 23.297479)'));

要计算最近点：

SELECT poi.name,poi.city,ST_AsTEXT(poi.the_geog), ST_Distance(road.the_geog, poi.the_geog)/1000.0 AS distance_km,ST_AsTEXT(road.the_geog::geometry) FROM road, poi WHERE road.id = 123 AND ST_DWithin(road.the_geog, poi.the_geog, 10000.0) ORDER BY ST_LineLocatePoint(road.the_geog::geometry, poi.the_geog::geometry), ST_Distance(road.the_geog, poi.the_geog);

如果线串是由这代表：[85.280194 23.296728,85.281572 23.297479]，我要像结果：

poi     vertex     distance_km 
85.280194 23.296728 85.280001 23.299876 3 
85.289673 23.291987 85.281572 23.297479 5

答

U SE ST_DumpPoints()提取线的顶点：

SELECT id,the_geog, (ST_dumppoints(road.the_geog::GEOMETRY)).geom AS vertex FROM road;

你要投地理学几何，否则st_dumppoints不起作用。

你的整个查询可能看起来像这样：

SELECT road.id AS road_id, 
     ST_Astext(poi.the_geog) AS poi, 
     ST_astext(road.vertex) AS vertex, 
     ST_AsText(road.the_geog) AS line, 
     ST_Distance(vertex, poi.the_geog) AS distance 
FROM (SELECT id,the_geog, (ST_dumppoints(road.the_geog::GEOMETRY)).geom AS vertex 
      FROM road 
    ) as road, 
     poi 
WHERE road.id = 123 
ORDER by ST_Distance(vertex, poi.the_geog);

如何计算最近点到PostGIS中的线串？

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