H2GIS

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ST_SideBuffer

Signature

GEOMETRY ST_SideBuffer(GEOMETRY geom, DOUBLE bufferSize);
GEOMETRY ST_SideBuffer(GEOMETRY geom, DOUBLE bufferSize, VARCHAR bufferStyle);

Description

Return a buffer at a given distance on only one side of each input lines of the geom.

The buffer size (bufferSize) is given in projection units.

The optional third parameter can either specify the number of segments used to approximate a quarter circle or a VARCHAR list of space-separated key=value pairs:

key=value Description Default value
quad_segs=# number of segments used to approximate a quarter circle 8
join=round|mitre|bevel join style round
mitre_limit=#.# mitre ratio limit (only affects mitered join style) 5

The end cap style for single-sided buffers is always ignored, and forced to the equivalent of ‘flat’ (Synonym of ‘butt’).

Examples

SELECT ST_SideBuffer('LINESTRING (1 1, 4 4)', 1) as THE_GEOM;
-- Answer: POLYGON ((4 4, 1 1, 0.2928932188134524 1.7071067811865475, 3.2928932188134525 4.707106781186548, 4 4))

SELECT ST_SideBuffer('LINESTRING (1 1, 4 4)', -1) as THE_GEOM;
-- Answer: POLYGON ((1 1, 4 4, 4.707106781186548 3.2928932188134525, 1.7071067811865475 0.2928932188134524, 1 1))

SELECT ST_SideBuffer('MULTILINESTRING ((1 1, 4 4), (1 4, 4 2))', 1) as THE_GEOM;
-- Answer: POLYGON ((1.951471862576143 3.365685424949238, 1 4, 1.5547001962252291 4.832050294337844, 2.6725821176689406 4.0867956800420355, 3.2928932188134525 4.707106781186548, 4 4, 3.5211102550927977 3.5211102550927977, 4.554700196225229 2.8320502943378436, 4 2, 2.8 2.8, 1 1, 0.2928932188134524 1.7071067811865475, 1.951471862576143 3.365685424949238))

SELECT ST_SideBuffer('LINESTRING (1 1, 4 4, 4 2)', 1, 'join=round') as THE_GEOM;
-- Answer: POLYGON ((4 2, 4 4, 1 1, 0.2928932188134524 1.7071067811865475, 3.2928932188134525 4.707106781186548, 3.444429766980398 4.831469612302545, 3.6173165676349104 4.923879532511287, 3.804909677983872 4.98078528040323, 4 5, 4.195090322016128 4.98078528040323, 4.38268343236509 4.923879532511287, 4.555570233019602 4.831469612302545, 4.707106781186548 4.707106781186548, 4.831469612302545 4.555570233019602, 4.923879532511287 4.38268343236509, 4.98078528040323 4.195090322016129, 5 4, 5 2, 4 2)) 

SELECT ST_SideBuffer('LINESTRING (1 1, 4 4, 4 2)', 1, 'join=mitre') as THE_GEOM;
-- Answer: POLYGON ((4 2, 4 4, 1 1, 0.2928932188134524 1.7071067811865475, 5 6.414213562373096, 5 2, 4 2))

SELECT ST_SideBuffer('LINESTRING (1 1, 4 4, 4 2)', 1, 'join=bevel') as THE_GEOM;
-- Answer: POLYGON ((4 2, 4 4, 1 1, 0.2928932188134524 1.7071067811865475, 3.2928932188134525 4.707106781186548, 5 4, 5 2, 4 2))

SELECT ST_SideBuffer('LINESTRING (1 1, 4 4, 4 2)', 1, 
                           'join=mitre mitre_limit=1') as THE_GEOM;
-- Answer: POLYGON ((4 2, 4 4, 1 1, 0.2928932188134524 1.7071067811865475, 3.8123572904470766 5.1601163554696505, 4.953009574283103 4.687642709552923, 5 2, 4 2))

SELECT ST_SideBuffer('LINESTRING (1 1, 4 4, 4 2)', 1, 
                           'join=mitre mitre_limit=2') as THE_GEOM;
-- Answer: POLYGON ((4 2, 4 4, 1 1, 0.2928932188134524 1.7071067811865475, 4.54859411340544 5.937549278574211, 4.982139616054918 5.757968851470936, 5 2, 4 2)) 

SELECT ST_SideBuffer('LINESTRING (1 1, 4 4, 4 2)', 1, 
                           'join=mitre mitre_limit=3') as THE_GEOM;
-- Answer: POLYGON ((4 2, 4 4, 1 1, 0.2928932188134524 1.7071067811865475, 5 6.414213562373096, 5 2, 4 2))

See also