## Name

ST_OffsetCurve — Returns an offset line at a given distance and side from an input line.

## Synopsis

`geometry ST_OffsetCurve(`geometry line, float signed_distance, text style_parameters=''`)`;

## Descripción

Return an offset line at a given distance and side from an input line. All points of the returned geometries are not further than the given distance from the input geometry. Useful for computing parallel lines about a center line.

For positive distance the offset is on the left side of the input line and retains the same direction. For a negative distance it is on the right side and in the opposite direction.

Units of distance are measured in units of the spatial reference system.

Note that output may be a MULTILINESTRING or EMPTY for some jigsaw-shaped input geometries.

The optional third parameter allows specifying a list of blank-separated key=value pairs to tweak operations as follows:

• 'quad_segs=#' : number of segments used to approximate a quarter circle (defaults to 8).

• 'join=round|mitre|bevel' : join style (defaults to "round"). 'miter' is also accepted 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'.

Enhanced: 2.5 - added support for GEOMETRYCOLLECTION and MULTILINESTRING

 This function ignores the Z dimension. It always gives a 2D result even when used on a 3D geometry.

## Ejemplos

Compute an open buffer around roads

```SELECT ST_Union(
 15, 'quad_segs=4 join=round' original line and its offset 15 units. ```SELECT ST_AsText(ST_OffsetCurve(ST_GeomFromText( 'LINESTRING(164 16,144 16,124 16,104 16,84 16,64 16, 44 16,24 16,20 16,18 16,17 17, 16 18,16 20,16 40,16 60,16 80,16 100, 16 120,16 140,16 160,16 180,16 195)'), 15, 'quad_segs=4 join=round')); output LINESTRING(164 1,18 1,12.2597485145237 2.1418070123307, 7.39339828220179 5.39339828220179, 5.39339828220179 7.39339828220179, 2.14180701233067 12.2597485145237,1 18,1 195) ``` -15, 'quad_segs=4 join=round' original line and its offset -15 units ```SELECT ST_AsText(ST_OffsetCurve(geom, -15, 'quad_segs=4 join=round')) As notsocurvy FROM ST_GeomFromText( 'LINESTRING(164 16,144 16,124 16,104 16,84 16,64 16, 44 16,24 16,20 16,18 16,17 17, 16 18,16 20,16 40,16 60,16 80,16 100, 16 120,16 140,16 160,16 180,16 195)') As geom; notsocurvy LINESTRING(31 195,31 31,164 31) ``` double-offset to get more curvy, note the first reverses direction, so -30 + 15 = -15 ```SELECT ST_AsText(ST_OffsetCurve(ST_OffsetCurve(geom, -30, 'quad_segs=4 join=round'), -15, 'quad_segs=4 join=round')) As morecurvy FROM ST_GeomFromText( 'LINESTRING(164 16,144 16,124 16,104 16,84 16,64 16, 44 16,24 16,20 16,18 16,17 17, 16 18,16 20,16 40,16 60,16 80,16 100, 16 120,16 140,16 160,16 180,16 195)') As geom; morecurvy LINESTRING(164 31,46 31,40.2597485145236 32.1418070123307, 35.3933982822018 35.3933982822018, 32.1418070123307 40.2597485145237,31 46,31 195) ``` double-offset to get more curvy,combined with regular offset 15 to get parallel lines. Overlaid with original. ```SELECT ST_AsText(ST_Collect( ST_OffsetCurve(geom, 15, 'quad_segs=4 join=round'), ST_OffsetCurve(ST_OffsetCurve(geom, -30, 'quad_segs=4 join=round'), -15, 'quad_segs=4 join=round') ) ) As parallel_curves FROM ST_GeomFromText( 'LINESTRING(164 16,144 16,124 16,104 16,84 16,64 16, 44 16,24 16,20 16,18 16,17 17, 16 18,16 20,16 40,16 60,16 80,16 100, 16 120,16 140,16 160,16 180,16 195)') As geom; parallel curves MULTILINESTRING((164 1,18 1,12.2597485145237 2.1418070123307, 7.39339828220179 5.39339828220179,5.39339828220179 7.39339828220179, 2.14180701233067 12.2597485145237,1 18,1 195), (164 31,46 31,40.2597485145236 32.1418070123307,35.3933982822018 35.3933982822018, 32.1418070123307 40.2597485145237,31 46,31 195)) ``` 15, 'quad_segs=4 join=bevel' shown with original line ```SELECT ST_AsText(ST_OffsetCurve(ST_GeomFromText( 'LINESTRING(164 16,144 16,124 16,104 16,84 16,64 16, 44 16,24 16,20 16,18 16,17 17, 16 18,16 20,16 40,16 60,16 80,16 100, 16 120,16 140,16 160,16 180,16 195)'), 15, 'quad_segs=4 join=bevel')); output LINESTRING(164 1,18 1,7.39339828220179 5.39339828220179, 5.39339828220179 7.39339828220179,1 18,1 195) ``` 15,-15 collected, join=mitre mitre_limit=2.1 ```SELECT ST_AsText(ST_Collect( ST_OffsetCurve(geom, 15, 'quad_segs=4 join=mitre mitre_limit=2.2'), ST_OffsetCurve(geom, -15, 'quad_segs=4 join=mitre mitre_limit=2.2') ) ) FROM ST_GeomFromText( 'LINESTRING(164 16,144 16,124 16,104 16,84 16,64 16, 44 16,24 16,20 16,18 16,17 17, 16 18,16 20,16 40,16 60,16 80,16 100, 16 120,16 140,16 160,16 180,16 195)') As geom; output MULTILINESTRING((164 1,11.7867965644036 1,1 11.7867965644036,1 195), (31 195,31 31,164 31)) ```