ST_MakeLine

Description

ST_MakeLine comes in 3 forms: a spatial aggregate that takes rows of point, multipoint, or line geometries and returns a line string, a function that takes an array of point, multipoint, or line, and a regular function that takes two point, multipoint, or line geometries. You might want to use a subselect to order points before feeding them to the aggregate version of this function.

Inputs other than point, multipoint, or lines are ignored.

When adding line components common nodes at the beginning of lines are removed from the output. Common nodes in point and multipoint inputs are not removed.

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

Availability: 2.3.0 - Support for multipoint input elements was introduced

Availability: 2.0.0 - Support for linestring input elements was introduced

Availability: 1.4.0 - ST_MakeLine(geomarray) was introduced. ST_MakeLine aggregate functions was enhanced to handle more points faster.

Examples: Spatial Aggregate version

This example takes a sequence of GPS points and creates one record for each gps travel where the geometry field is a line string composed of the gps points in the order of the travel.

-- For pre-PostgreSQL 9.0 - this usually works,
-- but the planner may on occasion choose not to respect the order of the subquery
SELECT gps.gps_track, ST_MakeLine(gps.the_geom) As newgeom
	FROM (SELECT gps_track, gps_time, the_geom
			FROM gps_points ORDER BY gps_track, gps_time) As gps
	GROUP BY gps.gps_track;

-- If you are using PostgreSQL 9.0+
-- (you can use the new ORDER BY support for aggregates)
-- this is a guaranteed way to get a correctly ordered linestring
-- Your order by part can order by more than one column if needed
SELECT gps.gps_track, ST_MakeLine(gps.the_geom ORDER BY gps_time) As newgeom
	FROM gps_points As gps
	GROUP BY gps.gps_track;

Examples: Non-Spatial Aggregate version

First example is a simple one off line string composed of 2 points. The second formulates line strings from 2 points a user draws. The third is a one-off that joins 2 3d points to create a line in 3d space.

SELECT ST_AsText(ST_MakeLine(ST_MakePoint(1,2), ST_MakePoint(3,4)));
	  st_astext
---------------------
 LINESTRING(1 2,3 4)

SELECT userpoints.id, ST_MakeLine(startpoint, endpoint) As drawn_line
	FROM userpoints ;

SELECT ST_AsEWKT(ST_MakeLine(ST_MakePoint(1,2,3), ST_MakePoint(3,4,5)));
		st_asewkt
-------------------------
 LINESTRING(1 2 3,3 4 5)
			

Examples: Using Array version

SELECT ST_MakeLine(ARRAY(SELECT ST_Centroid(the_geom) FROM visit_locations ORDER BY visit_time));

--Making a 3d line with 3 3-d points
SELECT ST_AsEWKT(ST_MakeLine(ARRAY[ST_MakePoint(1,2,3),
				ST_MakePoint(3,4,5), ST_MakePoint(6,6,6)]));
		st_asewkt
-------------------------
LINESTRING(1 2 3,3 4 5,6 6 6)
			

See Also

ST_AsEWKT , ST_AsText , ST_GeomFromText , ST_MakePoint