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ST_LocateAlong

Signature

MULTIPOINT ST_LocateAlong(GEOMETRY geom,
                          DOUBLE segmentLengthFraction,
                          DOUBLE offsetDistance);

Description

Places points along the line segments composing geom at a distance of segmentLengthFraction along the segment and at an offset distance of offsetDistance. Returns them as a MULTIPOINT.

What about orientation?

Line segment orientation is determined by the order of the coordinates. A positive offset places the point to the left of the segment; a negative offset to the right.

Only exterior rings are supported for POLYGONs.

Examples

SELECT ST_LocateAlong('LINESTRING(1 1, 5 4)', 0.5, 2);
-- Answer: MULTIPOINT((1.8 4.1))

SELECT ST_LocateAlong('LINESTRING(1 1, 5 1, 5 3)', 0.5, 1);
-- Answer: MULTIPOINT((3 2), (4 2))

SELECT ST_LocateAlong('POLYGON((1 1, 4 1, 4 3, 1 3, 1 1))', 0.5, -1);
-- Answer: MULTIPOINT((2.5 0), (5 2), (2.5 4), (0 2))

SELECT ST_LocateAlong('GEOMETRYCOLLECTION(
                           LINESTRING(1 4, 5 4, 5 2),
                           POLYGON((1 1, 4 1, 4 3, 1 3, 1 1)))',
                      2, 1);
-- Answer: MULTIPOINT((2 -1), (-2 2), (6 0), (9 5), (7 2), (3 5))

See also