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PostGIS 1.5.8 Manual209 / 3107.9 Geometry Processing Functions7.9.1 ST_BufferST_Buffer — (T) For geometry: Returns a geometry that represents all points whose distance from this Geometry is lessthan or equal to distance. Calculations are in the Spatial Reference System of this Geometry. For geography: Uses a planartransform wrapper. Introduced in 1.5 support for different end cap and mitre settings to control shape. buffer_style options:quad_segs=#,endcap=round|flat|square,join=round|mitre|bevel,mitre_limit=#.#Synopsisgeometry ST_Buffer(geometry g1, float radius_of_buffer);geometry ST_Buffer(geometry g1, float radius_of_buffer, integer num_seg_quarter_circle);geometry ST_Buffer(geometry g1, float radius_of_buffer, text buffer_style_parameters);geography ST_Buffer(geography g1, float radius_of_buffer_in_meters);DescriptionReturns a geometry/geography that represents all points whose distance from this Geometry/geography is less than or equal todistance.Geometry: Calculations are in the Spatial Reference System of the geometry. Introduced in 1.5 support for different end cap andmitre settings to control shape.NoteNegative radii: For polygons, a negative radius can be used, which will shrink the polygon rather than expanding it.NoteGeography: For geography this is really a thin wrapper around the geometry implementation. It first determines thebest SRID that fits the bounding box of the geography object (favoring UTM, Lambert Azimuthal Equal Area (LAEA)north/south pole, and falling back on mercator in worst case scenario) and then buffers in that planar spatial ref andretransforms back to WGS84 geography.For geography this may not behave as expected if object is sufficiently large that it falls between two UTM zones or crossesthe datelineAvailability: 1.5 - ST_Buffer was enhanced to support different endcaps and join types. These are useful for example to convertroad linestrings into polygon roads with flat or square edges instead of rounded edges. Thin wrapper for geography was added. -requires GEOS >= 3.2 to take advantage of advanced geometry functionality.The optional third parameter (currently only applies to geometry) can either specify number of segments used to approximate aquarter circle (integer case, defaults to 8) or a list of blank-separated key=value pairs (string case) to tweak operations as follows:• ’quad_segs=#’ : number of segments used to approximate a quarter circle (defaults to 8).• ’endcap=round|flat|square’ : endcap style (defaults to "round", needs GEOS-3.2 or higher for a different value). ’butt’ is alsoaccepted as a synonym for ’flat’.• ’join=round|mitre|bevel’ : join style (defaults to "round", needs GEOS-3.2 or higher for a different value). ’miter’ is alsoaccepted as a synonym for ’mitre’.• ’mitre_limit=#.#’ : mitre ratio limit (only affects mitred join style). ’miter_limit’ is also accepted as a synonym for ’mitre_limit’.