ST_OffsetCurve
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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='');

Description

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'.

Performed by the GEOS module.

Behavior changed in GEOS 3.11 so offset curves now have the same direction as the input line, for both positive and negative offsets.

Availability: 2.0

Enhanced: 2.5 - added support for GEOMETRYCOLLECTION and MULTILINESTRING

[Note]

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

Examples

Compute an open buffer around roads.

Code
SELECT ST_Union(
 ST_OffsetCurve(f.geom, f.width/2, 'quad_segs=4 join=round'),
 ST_OffsetCurve(f.geom, -f.width/2, 'quad_segs=4 join=round')
) as track
FROM someroadstable;

Offset 15 units with quad_segs=4 join=round.

Code
SELECT 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 1,15.073645169758077 1.288220793951544,
    12.259748514523654 2.141807012330698,9.66644650470597 3.527955815461818,
    7.393398282201788 5.393398282201788,5.393398282201788 7.393398282201788,
    3.527955815461818 9.66644650470597,2.141807012330696 12.259748514523654,
    1.288220793951544 15.073645169758075,1 18,1 195)
Figure
Geometry figure for visual-st-offsetcurve-01

Offset -15 units with quad_segs=4 join=round.

Code
SELECT 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;
Output
LINESTRING(164 31,31 31,31 195)
Figure
Geometry figure for visual-st-offsetcurve-02

Apply two negative offsets to obtain a smoother curve; the distances combine to -45 units.

Code
SELECT 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;
Output
LINESTRING(164 61,61 61,61 195)
Figure
Geometry figure for visual-st-offsetcurve-03

Collect the positive offset and the double-offset to produce parallel curves.

Code
SELECT 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;
Output
MULTILINESTRING((164 1,18 1,15.073645169758077 1.288220793951544,
12.259748514523654 2.141807012330698,9.66644650470597 3.527955815461818,
7.393398282201788 5.393398282201788,5.393398282201788 7.393398282201788,
3.527955815461818 9.66644650470597,2.141807012330696 12.259748514523654,
1.288220793951544 15.073645169758075,1 18,1 195),(164 61,61 61,61 195))
Figure
Geometry figure for visual-st-offsetcurve-04

Offset 15 units with a bevel join.

Code
SELECT 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 1,7.393398282201788 5.393398282201788,
    5.393398282201788 7.393398282201788,1 18,1 195)
Figure
Geometry figure for visual-st-offsetcurve-05

Collect offsets on both sides using a mitre join and a mitre limit of 2.2.

Code
SELECT 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 1,11.786796564403577 1,1 11.786796564403577,1 195),
    (164 31,31 31,31 195))
Figure
Geometry figure for visual-st-offsetcurve-06

See Also

ST_Buffer