PostGIS
Name
ST_Split — Returns a collection of geometries created by splitting a geometry by another geometry.
Description
The function supports splitting a LineString by a (Multi)Point, (Multi)LineString or (Multi)Polygon boundary, or a (Multi)Polygon by a LineString. When a (Multi)Polygon is used as as the blade, its linear components (the boundary) are used for splitting the input. The result geometry is always a collection.
This function is in a sense the opposite of ST_Union. Applying ST_Union to the returned collection should theoretically yield the original geometry (although due to numerical rounding this may not be exactly the case).
|
Availability: 2.0.0 requires GEOS
Enhanced: 2.2.0 support for splitting a line by a multiline, a multipoint or (multi)polygon boundary was introduced.
Enhanced: 2.5.0 support for splitting a polygon by a multiline was introduced.
Examples
Split a Polygon by a Line.
Before Split |
After split |
SELECT ST_AsText( ST_Split(
ST_Buffer(ST_GeomFromText('POINT(100 90)'), 50), -- circle
ST_MakeLine(ST_Point(10, 10),ST_Point(190, 190)) -- line
));
-- result --
GEOMETRYCOLLECTION(
POLYGON((150 90,149.039264020162 80.2454838991936,146.193976625564 70.8658283817455,..),
POLYGON(..))
)Split a MultiLineString by a Point, where the point lies exactly on both LineStrings elements.
Before Split |
After split |
SELECT ST_AsText(ST_Split(
'MULTILINESTRING((10 10, 190 190), (15 15, 30 30, 100 90))',
ST_Point(30,30))) As split;
split
------
GEOMETRYCOLLECTION(
LINESTRING(10 10,30 30),
LINESTRING(30 30,190 190),
LINESTRING(15 15,30 30),
LINESTRING(30 30,100 90)
)Split a LineString by a Point, where the point does not lie exactly on the line. Shows using ST_Snap to snap the line to the point to allow it to be split.
WITH data AS (SELECT
'LINESTRING(0 0, 100 100)'::geometry AS line,
'POINT(51 50)':: geometry AS point
)
SELECT ST_AsText( ST_Split( ST_Snap(line, point, 1), point)) AS snapped_split,
ST_AsText( ST_Split(line, point)) AS not_snapped_not_split
FROM data;
snapped_split | not_snapped_not_split
---------------------------------------------------------------------+---------------------------------------------
GEOMETRYCOLLECTION(LINESTRING(0 0,51 50),LINESTRING(51 50,100 100)) | GEOMETRYCOLLECTION(LINESTRING(0 0,100 100))