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.

You can also “shrink” the input object by specifying a negative value for the distance.

Syntax

ST_BUFFER( <geometry_expression> , <distance> )

Arguments

geometry_expression

The argument must be an expression of type GEOMETRY.

distance

The distance from the GEOMETRY object. To “shrink” the object, you can specify a negative value for the distance.

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

Returns

Returns a GEOMETRY object.

Usage notes

  • SRIDs are based on the EPSG standard (v10.082). For example, the SRID 4326 corresponds to the authority EPSG with the code 4326.
  • ST_BUFFER uses eight segments to approximate a quarter circle.
  • 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.
  • For LineStrings, the endcap and join styles are always round.
  • LineStrings are always buffered on both sides.

Examples

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

ALTER SESSION SET GEOMETRY_OUTPUT_FORMAT='WKT';

The following example returns a Polygon around a Point with a radius of one:

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))) |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+