postgresql - 从 PostGIS 点获取纬度/经度

Question

我有一个 PostGIS 表，其中包含 SRID 3857 数据的几何字段。我想将几何的质心作为纬度/经度坐标，但似乎无法正确转换值:

SELECT 
ST_X(ST_CENTROID(geometry)),
ST_Y(ST_CENTROID(geometry)),
ST_X(ST_TRANSFORM(ST_CENTROID(geometry),3857)) AS LONG, 
ST_Y(ST_CENTROID(ST_TRANSFORM(geometry,3857))) AS LAT
FROM my_table

=> -8220067.19453888107, 4997528.08142071683, -8220067.19453888107, 4997528.08142071683

Answer 1

您正在使用 3857 projection (伪墨卡托)不是以经/纬度为单位，而是以米为单位。

要获取经/纬度值，您需要使用 4326 projection :

db=# SELECT
ST_X(ST_Centroid(geometry)),
ST_Y(ST_Centroid(geometry)),
ST_X(ST_Centroid(ST_Transform(geometry, 4326))) AS long,
ST_Y(ST_Centroid(ST_Transform(geometry, 4326))) AS lat
FROM my_table;
       st_x        |       st_y       |       long        |       lat
-------------------+------------------+-------------------+------------------
 -8220067.19453888 | 4997528.08142072 | -73.8421199734375 | 40.8994922746749
(1 row)