ST_LineInterpolatePoint

ST_LineInterpolatePoint returns a point along a line at a fractional distance from the start of the line.

To determine point equality, ST_LineInterpolatePoint operates on the 2D projection of the input geometry. If the input geometry is empty, a copy of it is returned in the same dimension as the input. For 3DZ, 3DM, and 4D geometries, the z or m coordinate is the average of the z or m coordinates of the segment where the point lies.

Syntax

ST_LineInterpolatePoint(geom, fraction)

Arguments

geom

A value of data type GEOMETRY or an expression that evaluates to a GEOMETRY type. The subtype is LINESTRING.

fraction

A value of data type DOUBLE PRECISION that represents the position of a point along the linestring for the line. The value is a fraction in the range 0–1, inclusive.

Return type

GEOMETRY of subtype POINT.

If geom or fraction is null, then null is returned.

If geom is empty, then the empty point is returned.

The spatial reference system identifier (SRID) value of the returned geometry is the SRID value of the input geometry.

If fraction is out of range, then an error is returned.

If geom is not a linestring, then an error is returned.

Examples

The following SQL returns a point halfway along a linestring.

SELECT ST_AsEWKT(ST_LineInterpolatePoint(ST_GeomFromText('LINESTRING(0 0, 5 5, 7 7, 10 10)'), 0.50));

st_asewkt
-----------
 POINT(5 5)      

The following SQL returns a point 90 percent of the way along a linestring.

SELECT ST_AsEWKT(ST_LineInterpolatePoint(ST_GeomFromText('LINESTRING(0 0, 5 5, 7 7, 10 10)'), 0.90));

st_asewkt
-----------
 POINT(9 9)