从 postgis 中的查询中插入表单

Question

我尝试通过查询在我的表geofield 中插入一个多边形。表geofield 定义如下：

CREATE TABLE geofield(id SERIAL PRIMARY KEY, field GEOMETRY);

insert into geofield(field) values (myfield)
SELECT
    'POLYGON(('||cast((select lat from coordinates where id=1)as varchar)||' '||
      cast((select lon from coordinates where id=1)as varchar)||','||
      cast((select lat from coordinates where id=2)as varchar)||' '||
      cast((select lon from coordinates where id=2)as varchar)||','||
      cast((select lat from coordinates where id=3)as varchar)||' '||
      cast((select lon from coordinates where id=3)as varchar)||','||
      cast((select lat from coordinates where id=4)as varchar)||' '||
      cast((select lon from coordinates where id=4)as varchar)||','||
      cast((select lat from coordinates where id=1)as varchar)||' '||
      cast((select lon from coordinates where id=1)as varchar)||'))') AS myfield;

SELECT 单独返回我：

POLYGON((46.744628268759314 6.569952920654968,46.74441692818192 6.570487107359068,46.74426116111054 6.570355867853787,46.74447250168793 6.569821681149689,46.744628268759314 6.569952920654968))

但它不起作用，我也尝试了 ST_GeomFromText 但结果相同。

Answer 1

我会避免使用文本连接，而是使用普通的PostGIS functions：

SELECT
    /* Make a polygon from the linestring */
    ST_MakePolygon(
        /* Close the polygon */
        ST_AddPoint(
            t.linestring,
            ST_StartPoint(t.linestring)
        )
    )
FROM (
    SELECT
        /* Aggregate into a linestring */
        ST_MakeLine(ST_MakePoint(c.lon, c.lat) ORDER BY c.id) AS linestring
    FROM coordinates AS c
) t
;

按照您的prior question，如果您愿意，可以直接从json 取回：

SELECT
    /* Make a polygon from the linestring */
    ST_MakePolygon(
        /* Close the polygon */
        ST_AddPoint(
            t.linestring,
            ST_StartPoint(t.linestring)
        )
    )
FROM (
    SELECT
        /* Aggregate into a linestring */
        ST_MakeLine(ST_MakePoint(c.lon, c.lat) ORDER BY c.id) AS linestring
    FROM
    (
        SELECT
            e.id,
            (e.element->>'lat')::numeric AS lat,
            (e.element->>'lon')::numeric AS lon
        FROM
            field AS f,
            json_array_elements(f.data->'vertices') WITH ORDINALITY AS e(element, id)
    ) AS c
) t
;

Answer 2

字符串是正确的 WKT 格式，所以这不是问题。问题是您的经度和纬度值颠倒了，INSERT 的语法是错误的。您还应该先将字符串转换为geometry：

INSERT INTO geofield(field)
    SELECT ST_GeomFromText(
        'POLYGON(('||cast((select lat from coordinates where id=1)as varchar)||' '||
          cast((select lon from coordinates where id=1)as varchar)||','||
          cast((select lat from coordinates where id=2)as varchar)||' '||
          cast((select lon from coordinates where id=2)as varchar)||','||
          cast((select lat from coordinates where id=3)as varchar)||' '||
          cast((select lon from coordinates where id=3)as varchar)||','||
          cast((select lat from coordinates where id=4)as varchar)||' '||
          cast((select lon from coordinates where id=4)as varchar)||','||
          cast((select lat from coordinates where id=1)as varchar)||' '||
          cast((select lon from coordinates where id=1)as varchar)||'))');

但这一切都非常浪费，不适合较大的多边形。只要你的多边形由一个环组成，你就可以这样做，这样会更快，更不容易出错：

INSERT INTO geofield(field)
    SELECT ST_GeomFromText('POLYGON((' || coords.c || ',' || coord1.c || '))', 4326)
    FROM
        ( SELECT string_agg(lon::text || ' ' || lat::text, ',' ORDER BY id) AS c
          FROM coordinates ) coords,
        ( SELECT lon::text || ' ' || lat::text AS c
          FROM coordinates
          WHERE id = 1 ) coord1;

第一个子查询将所有坐标串在一起，而第二个子查询只获取第一个坐标以关闭多边形。使用尽可能多的点。