如何計算最近點到PostGIS中的線串？

Question

我按照這個question來計算最近的道路（線串）的POI。我能夠計算線串中的最近點，但是我無法找到從POI到線串上最近點（頂點）的距離。

這是我尋找最近POI的代碼。

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)')); 

要計算最近點：

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); 

如果線串是由這代表：[85.280194 23.296728,85.281572 23.297479]，我要像結果：

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

Answer 1

U SE ST_DumpPoints()提取線的頂點：

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

你要投地理學幾何，否則st_dumppoints不起作用。

你的整個查詢可能看起來像這樣：

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);