ST_DWithin
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名称

ST_DWithin — 测试两个几何图形是否在给定距离内

大纲

boolean ST_DWithin(geometry g1, geometry g2, double precision distance_of_srid);

boolean ST_DWithin(geography gg1, geography gg2, double precision distance_meters, boolean use_spheroid = true);

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。

[注意]

将 ST_3DDWithin用于 3D 几何图形。
[注意]

此函数调用包括利用几何上可用的任何索引的边界框比较。

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

增强功能：2.1.0版本提升了地理（Geography）类型的速度。有关详细信息，请参阅Making Geography faster。

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

This self-contained geometry example keeps the compared shapes visible while also returning the boolean results.

Code
WITH sample AS (
  SELECT ST_Buffer('POINT(100 90)'::geometry, 50, 'quad_segs=2') AS coverage,
         ST_Point(120, 120) AS inside_pt,
         ST_Point(170, 90) AS outside_pt
)
SELECT ST_DWithin(coverage, inside_pt, 0) AS inside_now,
       ST_DWithin(coverage, outside_pt, 10) AS outside_within_10,
       coverage AS coverage_geom,
       inside_pt AS inside_geom,
       outside_pt AS outside_geom
FROM sample;
栅格输出
-[ RECORD 1 ]-----
inside_now        | t
outside_within_10 | f
coverage_geom     | POLYGON((150 90,135 55,100 40,65 55,50 90,65 125,100 140,135 125,150 90))
inside_geom       | POINT(120 120)
outside_geom      | POINT(170 90)
Figure
Geometry figure for visual-st-dwithin-01

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.

Code
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 are in units of spatial reference (for example meters, feet, or degrees).

Code
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 locations more than 3000 units away from their nearest hospital. Use NOT EXISTS so that a location is returned only when no nearby hospital exists.

Code
SELECT l.location_name
  FROM locations l
  WHERE NOT EXISTS (
    SELECT 1
    FROM hospitals h
    WHERE ST_DWithin(l.geom, h.geom, 3000)
  );

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

Code
CREATE INDEX ON broadcasting_towers USING gist (geom);
CREATE INDEX ON broadcasting_towers USING gist (ST_Expand(geom, sending_range));

Query towers that a 4-kilometer receiver in Minsk Hackerspace can get. Note: two conditions are required because the shorter LEAST(b.sending_range, 4000) will not use an index.

Code
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