ST_MakeLine — Creates a Linestring from point geometries.
geometry ST_MakeLine(geometry set pointfield
geometry ST_MakeLine(geometry point1, geometry point2
geometry ST_MakeLine(geometry point_array
ST_MakeLine comes in 3 forms: a spatial aggregate that takes rows of point geometries and returns a line string, a function that takes an array of points, and a regular function that takes two point geometries. You might want to use a subselect to order points before feeding them to the aggregate version of this function.
This function supports 3d and will not drop the z-index.
Availability: 1.4.0 - ST_MakeLine(geomarray) was introduced. ST_MakeLine aggregate functions was enhanced to handle more points faster.
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;
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)
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)