ApsaraDB RDS:ST_Buffer

Syntax

geometry  ST_Buffer(geometry  g1, float radiusOfBuffer);
geometry  ST_Buffer(geometry  g1, float radiusOfBuffer, integer numSegQuarterCircle);
geometry  ST_Buffer(geometry  g1, float radiusOfBuffer, text bufferStyleParameters);
geography ST_Buffer(geography g1, float radiusOfBufferInMeters);
geography ST_Buffer(geography g1, float radiusOfBuffer, integer numSegQuarterCircle);
geography ST_Buffer(geography g1, float radiusOfBuffer, text bufferStyleParameters);

Parameters

Buffer style options

Pass these options as key-value pairs in the bufferStyleParameters argument (for example, 'quad_segs=4 endcap=flat').

• quad_segs=<integer> — Number of line segments used to approximate a quarter circle. Default: 8. A higher value produces a smoother curve.

• endcap=round|flat|square — End cap style for buffered lines. Default: round.

• join=round|mitre|bevel — Join style at line vertices. Default: round.

• mitre_limit=<float> — Maximum mitre ratio. Default: 5.0. Applies only when join=mitre.

• side=both|left|right — Which side of a LineString to buffer. left or right produces a single-sided buffer relative to the line direction. Has no effect on point or polygon objects.

Usage notes

Negative radius behavior

If you specify a polygon object and set the radius of the buffer to a negative value, the ST_Buffer function shrinks the polygon inward instead of expanding it.

Geography objects

For geography inputs, ST_Buffer internally projects the geography into a suitable planar SRS, computes the buffer, and reprojects the result back to WGS 84. The projection is chosen in this order of preference: Universal Transverse Mercator (UTM), Lambert Azimuthal Equal Area (LAEA), Universal Polar Stereographic (UPS), and Mercator (worst case).

Z coordinates

ST_Buffer ignores Z coordinates. Even for 3D input, the result is always a 2D geometry.

Radius searches

For proximity queries such as "find all points within 500 meters of this location," use ST_DWithin instead of ST_Buffer. ST_DWithin leverages spatial indexes directly, while ST_Buffer first generates a polygon and then performs a containment check, which bypasses index acceleration and is significantly slower.

Examples

Results returned with different values of quad_segs

SELECT ST_Buffer('POINT(0 0)'::geometry, 1),
       ST_Buffer('POINT(3 0)'::geometry, 1, 'quad_segs=2');

Results returned with different values of endcap

SELECT ST_Buffer('LINESTRING(0 0,0 3)'::geometry,  1, 'endcap=round'),
       ST_Buffer('LINESTRING(6 0,6 3)'::geometry,  1, 'endcap=flat'),
       ST_Buffer('LINESTRING(12 0,12 3)'::geometry, 1, 'endcap=square');

Results returned with different values of join

SELECT ST_Buffer('LINESTRING(0 0,3 0,3 3)'::geometry,  1.2, 'join=round'),
       ST_Buffer('LINESTRING(6 0,9 0,9 3)'::geometry,  1.2, 'join=mitre'),
       ST_Buffer('LINESTRING(12 0,15 0,15 3)'::geometry, 1.2, 'join=bevel');

Results returned with different values of mitre_limit

SELECT ST_Buffer('LINESTRING(0 0,3 0,3 3)'::geometry,  1.2, 'join=mitre mitre_limit=1.0'),
       ST_Buffer('LINESTRING(6 0,9 0,9 3)'::geometry,  1.2, 'join=mitre mitre_limit=0.5'),
       ST_Buffer('LINESTRING(12 0,15 0,15 3)'::geometry, 1.2, 'join=mitre mitre_limit=0.1');

Results returned with different values of side

SELECT ST_Buffer('LINESTRING(0 0,3 0,3 3,0 3)'::geometry,   1, 'side=both'),
       ST_Buffer('LINESTRING(6 0,9 0,9 3,6 3)'::geometry,   1, 'side=right'),
       ST_Buffer('LINESTRING(12 0,15 0,15 3,12 3)'::geometry, 1, 'side=left');