描述

如果第N个几何图形是POLYHEDRALSURFACE或POLYHEDRALSURFACEM，则返回从1开始的第N个几何图形(面)。否则，返回NULL。这将返回与多面体曲面的ST_GeometryN相同的答案。使用ST_GeometryN更快。

可用性：2.0.0

This method implements the SQL/MM specification. SQL-MM 3：？

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

This function supports Polyhedral surfaces.

示例

--Extract the 2nd face of the polyhedral surface
SELECT ST_AsEWKT(ST_PatchN(geom, 2)) As geomewkt
FROM (
VALUES (ST_GeomFromEWKT('POLYHEDRALSURFACE( ((0 0 0, 0 0 1, 0 1 1, 0 1 0, 0 0 0)),
        ((0 0 0, 0 1 0, 1 1 0, 1 0 0, 0 0 0)), ((0 0 0, 1 0 0, 1 0 1, 0 0 1, 0 0 0)),
        ((1 1 0, 1 1 1, 1 0 1, 1 0 0, 1 1 0)),
        ((0 1 0, 0 1 1, 1 1 1, 1 1 0, 0 1 0)), ((0 0 1, 1 0 1, 1 1 1, 0 1 1, 0 0 1)) )')) ) As foo(geom);

              geomewkt
---+-----------------------------------------
 POLYGON((0 0 0,0 1 0,1 1 0,1 0 0,0 0 0))

另请参阅

ST_AsEWKT , ST_GeomFromEWKT , ST_Dump , ST_GeometryN , ST_NumGeometries