描述

如果此几何图形为空几何图形，则返回True。如果为真，则此几何图形表示空的几何图形集合、多边形、点等。

	SQL-MM将ST_IsEmpty(NULL)的结果定义为0，而PostGIS返回NULL。

This method implements the OGC Simple Features Implementation Specification for SQL 1.1. s2.1.1.1

This method implements the SQL/MM specification. SQL-MM 3：5.1.7

This method supports Circular Strings and Curves

	已更改：在以前版本的PostGIS ST_GeomFromText(‘GEOMETRYCOLLECTION(Empty)’)中允许2.0.0。现在，为了更好地符合SQL/MM标准，这在PostGIS 2.0.0中是非法的

示例

SELECT ST_IsEmpty(ST_GeomFromText('GEOMETRYCOLLECTION EMPTY'));
 st_isempty
------------
 t
(1 row)

 SELECT ST_IsEmpty(ST_GeomFromText('POLYGON EMPTY'));
 st_isempty
------------
 t
(1 row)

SELECT ST_IsEmpty(ST_GeomFromText('POLYGON((1 2, 3 4, 5 6, 1 2))'));

 st_isempty
------------
 f
(1 row)

 SELECT ST_IsEmpty(ST_GeomFromText('POLYGON((1 2, 3 4, 5 6, 1 2))')) = false;
 ?column?
----------
 t
(1 row)

 SELECT ST_IsEmpty(ST_GeomFromText('CIRCULARSTRING EMPTY'));
  st_isempty
------------
 t
(1 row)