描述

返回一个 POINT 它保证位于曲面(多边形、多重曲面和弯曲多边形)的内部。在PostGIS中，此功能也适用于线和点几何图形。

This method implements the OGC Simple Features Implementation Specification for SQL 1.1. S3.2.14.2//s3.2.18.2

This method implements the SQL/MM specification. SQL-MM 3：8.1.5、9.5.6。规范仅为曲面几何图形定义ST_PointOnSurface。PostGIS扩展了该功能，以支持所有常见的几何类型。其他数据库(Oracle、DB2、ArcSDE)似乎仅支持曲面的此功能。SQL Server 2008支持所有常见几何图形类型。

This function supports 3d and will not drop the z-index.

示例

SELECT ST_AsText(ST_PointOnSurface('POINT(0 5)'::geometry));
------------
 POINT(0 5)

SELECT ST_AsText(ST_PointOnSurface('LINESTRING(0 5, 0 10)'::geometry));
------------
 POINT(0 5)

SELECT ST_AsText(ST_PointOnSurface('POLYGON((0 0, 0 5, 5 5, 5 0, 0 0))'::geometry));
----------------
 POINT(2.5 2.5)

SELECT ST_AsEWKT(ST_PointOnSurface(ST_GeomFromEWKT('LINESTRING(0 5 1, 0 0 1, 0 10 2)')));
----------------
 POINT(0 0 1)

示例： ST_PointOnSurface的结果保证位于面内，而由计算的点 ST_Centroid 可能在外面。

SELECT ST_AsText(ST_PointOnSurface(geom)) AS pt_on_surf,
       ST_AsText(ST_Centroid(geom)) AS centroid
    FROM (SELECT 'POLYGON ((130 120, 120 190, 30 140, 50 20, 190 20,
                      170 100, 90 60, 90 130, 130 120))'::geometry AS geom) AS t;

   pt_on_surf    |                  centroid
-----------------+---------------------------------------------
 POINT(62.5 110) | POINT(100.18264840182648 85.11415525114155)

另请参阅

ST_Centroid , ST_MaximumInscribedCircle