描述

如果几何图形在给定距离内，则返回 true

对于几何图形：距离以几何图形的空间参考系统定义的单位指定。 为了使此函数有意义，源几何图形必须位于同一坐标系中（具有相同的 SRID）。

对于 地理：单位为米，距离测量默认使用 use_spheroid = true（使用椭球体）。为了更快的计算，可以使用 use_spheroid = false，在球面上进行测量。

此方法实现了 SQL 1.1 的 OGC 简单功能规范。

可用性：1.5.0 引入了对地理的支持

增强：2.1.0 提高了地理速度。 有关详细信息，请参阅使地理更快。

增强：2.1.0 引入了对弯曲几何形状的支持。

在版本1.3之前，通常会将ST_Expand与 && 和ST_Distance一起使用来测试距离，而在1.3.4之前的版本中，该函数使用了这种逻辑。从1.3.4版本开始，ST_DWithin使用更快速的短路距离函数。

示例

-- Find the nearest hospital to each school
-- that is within 3000 units of the school.
--  We do an ST_DWithin search to utilize indexes to limit our search list
--  that the non-indexable ST_Distance needs to process
-- If the units of the spatial reference is meters then units would be meters
SELECT DISTINCT ON (s.gid) s.gid, s.school_name, s.geom, h.hospital_name
  FROM schools s
    LEFT JOIN hospitals h ON ST_DWithin(s.geom, h.geom, 3000)
  ORDER BY s.gid, ST_Distance(s.geom, h.geom);

-- The schools with no close hospitals
-- Find all schools with no hospital within 3000 units
-- away from the school.  Units is in units of spatial ref (e.g. meters, feet, degrees)
SELECT s.gid, s.school_name
  FROM schools s
    LEFT JOIN hospitals h ON ST_DWithin(s.geom, h.geom, 3000)
  WHERE h.gid IS NULL;

-- Find broadcasting towers that receiver with limited range can receive.
-- Data is geometry in Spherical Mercator (SRID=3857), ranges are approximate.

-- Create geometry index that will check proximity limit of user to tower
CREATE INDEX ON broadcasting_towers using gist (geom);

-- Create geometry index that will check proximity limit of tower to user
CREATE INDEX ON broadcasting_towers using gist (ST_Expand(geom, sending_range));

-- Query towers that 4-kilometer receiver in Minsk Hackerspace can get
-- Note: two conditions, because shorter LEAST(b.sending_range, 4000) will not use index.
SELECT b.tower_id, b.geom
  FROM broadcasting_towers b
  WHERE ST_DWithin(b.geom, 'SRID=3857;POINT(3072163.4 7159374.1)', 4000)
    AND ST_DWithin(b.geom, 'SRID=3857;POINT(3072163.4 7159374.1)', b.sending_range);

        

相关信息

ST_Distance, ST_3DDWithin