Categories:

Geospatial functions

ST_BUFFER

Returns a GEOMETRY object that represents a MultiPolygon containing the points within a specified distance of the input GEOMETRY object. The returned object effectively represents a “buffer” around the input object.

您还可以通过指定负的距离值来“缩小”输入对象。

语法

ST_BUFFER( <geometry_expression> , <distance> )

实参

geometry_expression

实参必须是 GEOMETRY 类型的表达式。

distance

与 GEOMETRY 对象的距离。要“缩小”对象，可以指定负的距离值。

The units depend on the spatial reference system identifier (SRID) of the GEOMETRY object. For example, ESPG:4326 (https://epsg.io/4326) units are degrees, while ESPG:25855 (https://epsg.io/25833) units are meters.

返回

返回一个 GEOMETRY 对象。

使用说明

  • SRIDs are based on the EPSG standard (https://epsg.org/home.html) (v10.082). For example, the SRID 4326 corresponds to the authority EPSG with the code 4326.
  • ST_BUFFER 使用八个段来模拟四分之一圆。
  • If distance is a negative value, the returned object is smaller than the input object. You can use this to remove small irregularities from the shape.
  • 对于 LineStrings，端盖和联接样式始终是圆形。
  • LineStrings 始终在两侧缓冲。

示例

Before executing the examples, set the GEOMETRY_OUTPUT_FORMAT parameter to WKT:

ALTER SESSION SET GEOMETRY_OUTPUT_FORMAT='WKT';

以下示例返回一个围绕着点且半径为 1 的多边形：

SELECT ST_BUFFER(TO_GEOMETRY('POINT(0 0)'), 1) AS geom;
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| GEOM                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
%-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------%
| MULTIPOLYGON(((1 0,0.9807852804 -0.195090322,0.9238795325 -0.3826834324,0.8314696123 -0.555570233,0.7071067812 -0.7071067812,0.555570233 -0.8314696123,0.3826834324 -0.9238795325,0.195090322 -0.9807852804,6.123233996e-17 -1,-0.195090322 -0.9807852804,-0.3826834324 -0.9238795325,-0.555570233 -0.8314696123,-0.7071067812 -0.7071067812,-0.8314696123 -0.555570233,-0.9238795325 -0.3826834324,-0.9807852804 -0.195090322,-1 7.657137398e-16,-0.9807852804 0.195090322,-0.9238795325 0.3826834324,-0.8314696123 0.555570233,-0.7071067812 0.7071067812,-0.555570233 0.8314696123,-0.3826834324 0.9238795325,-0.195090322 0.9807852804,2.480838239e-15 1,0.195090322 0.9807852804,0.3826834324 0.9238795325,0.555570233 0.8314696123,0.7071067812 0.7071067812,0.8314696123 0.555570233,0.9238795325 0.3826834324,0.9807852804 0.195090322,1 0))) |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

The following example uses a negative value for distance to remove small irregularities (such as spikes) from the shape. The TO_GEOMETRY call passes in TRUE as the second argument, which allows the function to create a GEOMETRY object for an invalid shape.

SELECT ST_BUFFER(TO_GEOMETRY('SRID=2261;POLYGON((
  1540792.21541900 290472.63529214, 1547018.61770388 302537.02285369,
  1546965.96550151 302752.51514772, 1547018.61770388 302537.02285369,
  1549532.42729914 301257.07398027, 1543327.42218339 289322.60923536,
  1540792.21541900 290472.63529214))', True), -1e-08) AS geom;
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| GEOM                                                                                                                                                                                        |
%---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------%
| MULTIPOLYGON(((1543327.42218339 289322.609235373,1540792.21541901 290472.635292145,1547018.61770388 302537.022853677,1549532.42729913 301257.073980266,1543327.42218339 289322.609235373))) |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+