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ST_RingSideBuffer

Signature

GEOMETRY ST_RingSideBuffer(GEOMETRY geom, DOUBLE bufferSize, 
                             INT numBuffer);
GEOMETRY ST_RingSideBuffer(GEOMETRY geom, DOUBLE bufferSize, 
                             INT numBuffer, VARCHAR endCapStyle);
GEOMETRY ST_RingSideBuffer(GEOMETRY geom, DOUBLE bufferSize, 
                             INT numBuffer, VARCHAR endCapStyle, 
                             BOOLEAN doDifference);

Description

Return a ring 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 number of rings is defined with numBuffer.

The optional fourth 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’).

The doDifference parameter is used to define if the user want to keep only difference between buffers. Default is true (doDifference=1).

This function does not work on GEOMETRYCOLLECTIONs.

Examples

SELECT ST_RINGSIDEBUFFER('LINESTRING (1 1, 4 4, 4 2)', 0.5, 3) as THE_GEOM;
-- Answer: MULTIPOLYGON (((4 2, 4 4, 1 1, 0.6464466094067263 1.3535533905932737, 3.646446609406726 4.353553390593274, 3.722214883490199 4.4157348061512725, 3.808658283817455 4.461939766255643, 3.902454838991936 4.490392640201615, 4 4.5, 4.097545161008064 4.490392640201615, 4.191341716182545 4.461939766255643, 4.2777851165098015 4.4157348061512725, 4.353553390593274 4.353553390593274, 4.4157348061512725 4.277785116509801, 4.461939766255643 4.191341716182545, 4.490392640201615 4.097545161008064, 4.5 4, 4.5 2, 4 2)), ((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, 4.5 2, 4.5 4, 4.490392640201615 4.097545161008064, 4.461939766255643 4.191341716182545, 4.4157348061512725 4.277785116509801, 4.353553390593274 4.353553390593274, 4.2777851165098015 4.4157348061512725, 4.191341716182545 4.461939766255643, 4.097545161008064 4.490392640201615, 4 4.5, 3.902454838991936 4.490392640201615, 3.808658283817455 4.461939766255643, 3.722214883490199 4.4157348061512725, 3.646446609406726 4.353553390593274, 0.6464466094067263 1.3535533905932737, 1 1)), ((0.2928932188134525 1.7071067811865475, -0.0606601717798214 2.0606601717798214, 2.9393398282201786 5.060660171779821, 3.1666446504705963 5.247204418453817, 3.4259748514523647 5.38581929876693, 3.707364516975807 5.471177920604846, 3.9999999999999996 5.5, 4.292635483024192 5.471177920604846, 4.574025148547634 5.38581929876693, 4.833355349529403 5.247204418453818, 5.060660171779821 5.060660171779821, 5.247204418453817 4.833355349529404, 5.38581929876693 4.574025148547635, 5.471177920604846 4.292635483024193, 5.5 4, 5.5 2, 5 2, 5 4, 4.98078528040323 4.195090322016129, 4.923879532511287 4.38268343236509, 4.831469612302545 4.555570233019602, 4.707106781186548 4.707106781186548, 4.555570233019602 4.831469612302545, 4.38268343236509 4.923879532511287, 4.195090322016128 4.98078528040323, 4 5, 3.804909677983872 4.98078528040323, 3.6173165676349104 4.923879532511287, 3.444429766980398 4.831469612302545, 3.2928932188134525 4.707106781186548, 0.2928932188134525 1.7071067811865475))) 

SELECT ST_RINGSIDEBUFFER('LINESTRING (1 1, 4 4, 4 2)', 0.5, 3, 
                         'join=mitre') as THE_GEOM;
-- Answer: MULTIPOLYGON (((4 2, 4 4, 1 1, 0.6464466094067263 1.3535533905932737, 4.5 5.207106781186547, 4.5 2, 4 2)), ((1 1, 0.2928932188134524 1.7071067811865475, 5 6.414213562373096, 5 2, 4.5 2, 4.5 5.207106781186547, 0.6464466094067263 1.3535533905932737, 1 1)), ((0.2928932188134525 1.7071067811865475, -0.0606601717798214 2.0606601717798214, 5.5 7.621320343559642, 5.5 2, 5 2, 5 6.414213562373096, 0.2928932188134525 1.7071067811865475))) 

SELECT ST_RINGSIDEBUFFER('LINESTRING (1 1, 4 4, 4 2)', 0.5, 3, 
                         'join=mitre',0) as THE_GEOM;
-- Answer: MULTIPOLYGON (((4 2, 4 4, 1 1, 0.6464466094067263 1.3535533905932737, 4.5 5.207106781186547, 4.5 2, 4 2)), ((4 2, 4 4, 1 1, 0.2928932188134524 1.7071067811865475, 5 6.414213562373096, 5 2, 4 2)), ((4 2, 4 4, 1 1, -0.0606601717798214 2.0606601717798214, 5.5 7.621320343559642, 5.5 2, 4 2)))

SELECT ST_RINGSIDEBUFFER('LINESTRING (1 1, 4 4, 4 2)', 0.5, 3, 
                         'join=mitre',1) as THE_GEOM;
-- Answer: MULTIPOLYGON (((4 2, 4 4, 1 1, 0.6464466094067263 1.3535533905932737, 4.5 5.207106781186547, 4.5 2, 4 2)), ((1 1, 0.2928932188134524 1.7071067811865475, 5 6.414213562373096, 5 2, 4.5 2, 4.5 5.207106781186547, 0.6464466094067263 1.3535533905932737, 1 1)), ((0.2928932188134525 1.7071067811865475, -0.0606601717798214 2.0606601717798214, 5.5 7.621320343559642, 5.5 2, 5 2, 5 6.414213562373096, 0.2928932188134525 1.7071067811865475)))

See also