ST_LineInterpolatePoint
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Name

ST_LineInterpolatePoint — Returns a point interpolated along a line at a fractional location.

Synopsis

geometry ST_LineInterpolatePoint(geometry a_linestring, float8 a_fraction);

geography ST_LineInterpolatePoint(geography a_linestring, float8 a_fraction, boolean use_spheroid = true);

Description

Returns a point interpolated along a line at a fractional location. First argument must be a LINESTRING. Second argument is a float between 0 and 1 representing the fraction of line length where the point is to be located. The Z and M values are interpolated if present.

See ST_LineLocatePoint for computing the line location nearest to a Point.

[Note]

This function computes points in 2D and then interpolates values for Z and M, while ST_3DLineInterpolatePoint computes points in 3D and only interpolates the M value.
[Note]

Since release 1.1.1 this function also interpolates M and Z values (when present), while prior releases set them to 0.0.

Availability: 0.8.2, Z and M supported added in 1.1.1

Changed: 2.1.0. Up to 2.0.x this was called ST_Line_Interpolate_Point.

This function supports 3d and will not drop the z-index.

Examples

A LineString with the interpolated point at 20% position (0.20)

This example returns the point 20 percent along a line.

SELECT ST_AsEWKT(ST_LineInterpolatePoint(
    'LINESTRING(25 50, 100 125, 150 190)',
    0.2));
POINT(51.5974135047432 76.5974135047432)

The mid-point of a 3D line:

SELECT ST_AsEWKT(ST_LineInterpolatePoint(
    'LINESTRING(1 2 3, 4 5 6, 6 7 8)',
    0.5));
POINT(3.5 4.5 5.5)

The closest point on a line to a point:

SELECT ST_AsText(ST_LineInterpolatePoint(
    line.geom,
    ST_LineLocatePoint(line.geom, 'POINT(4 3)')))
FROM (SELECT ST_GeomFromText('LINESTRING(1 2, 4 5, 6 7)') As geom) AS line;
POINT(3 4)

An interpolated point can be offset to the left or right of a line by using ST_OffsetCurve before interpolation. This is useful for locating an address point beside a street centerline.

WITH street AS (
    SELECT 'LINESTRING(0 0, 10 0)'::geometry AS geom,
           100 AS from_num,
           200 AS to_num
)
SELECT ST_AsText(
    ST_LineInterpolatePoint(
        ST_OffsetCurve(geom, -2),
        (160 - from_num)::float8 / (to_num - from_num)
    )
) AS interpolated_offset_point
FROM street;
	
 interpolated_offset_point
---------------------------
 POINT(6 -2)