ST_Difference

Definition

ST_Difference takes two geometry objects and returns a geometry object that is the difference of the source objects.

Syntax

Oracle and PostgreSQL

sde.st_difference (geometry1 sde.st_geometry, geometry2 sde.st_geometry)

SQLite

st_difference (geometry1 geometryblob, geometry2 geometryblob)

Return type

Oracle and PostgreSQL

ST_Geometry

SQLite

Geometryblob

Example

In the following examples, the city engineer needs to know the total area of the city's lot area not covered by buildings; therefore, she wants the sum of the lot area after the building area has been removed.

The city engineer equally joins the footprints and lots table on the lot_id and takes the sum of the area of the difference of the lots minus the footprints.

Oracle

--Create tables and insert values
CREATE TABLE footprints (
 building_id integer,
 footprint sde.st_geometry
);

CREATE TABLE lots (
 lot_id integer,
 lot sde.st_geometry
);

INSERT INTO footprints (building_id, footprint) VALUES (
 1, 
 sde.st_polygon ('polygon ((0 0, 0 10, 10 10, 10 0, 0 0))', 4326)
);

INSERT INTO footprints (building_id, footprint) VALUES (
 2,
 sde.st_polygon ('polygon ((20 0, 20 10, 30 10, 30 0, 20 0))', 4326)
);

INSERT INTO footprints (building_id, footprint) VALUES (
 3,
 sde.st_polygon ('polygon ((40 0, 40 10, 50 10, 50 0, 40 0))', 4326)
);

INSERT INTO lots (lot_id, lot) VALUES (
 1,
 sde.st_polygon ('polygon ((-1 -1, -1 11, 11 11, 11 -1, -1 -1))', 4326)
);

INSERT INTO lots (lot_id, lot) VALUES (
 2,
 sde.st_polygon ('polygon ((19 -1, 19 11, 29 9, 31 -1, 19 -1))', 4326)
);

INSERT INTO lots (lot_id, lot) VALUES (
 3,
 sde.st_polygon ('polygon ((39 -1, 39 11, 51 11, 51 -1, 39 -1))', 4326)
);

SELECT SUM (sde.st_area (sde.st_difference (lot, footprint)))
  FROM FOOTPRINTS bf, LOTS
  WHERE bf.building_id = lots.lot_id;

SUM(ST_AREA(ST_DIFFERENCE(LOT,FOOTPRINT)))

114

PostgreSQL

--Create tables and insert values
CREATE TABLE footprints (
 building_id integer,
 footprint sde.st_geometry
);

CREATE TABLE lots (
 lot_id integer,
 lot sde.st_geometry
);

INSERT INTO footprints (building_id, footprint) VALUES (
 1, 
 sde.st_polygon ('polygon ((0 0, 0 10, 10 10, 10 0, 0 0))', 4326)
);

INSERT INTO footprints (building_id, footprint) VALUES (
 2,
 sde.st_polygon ('polygon ((20 0, 20 10, 30 10, 30 0, 20 0))', 4326)
);

INSERT INTO footprints (building_id, footprint) VALUES (
 3,
 sde.st_polygon ('polygon ((40 0, 40 10, 50 10, 50 0, 40 0))', 4326)
);

INSERT INTO lots (lot_id, lot) VALUES (
 1,
 sde.st_polygon ('polygon ((-1 -1, -1 11, 11 11, 11 -1, -1 -1))', 4326)
);

INSERT INTO lots (lot_id, lot) VALUES (
 2,
 sde.st_polygon ('polygon ((19 -1, 19 11, 29 9, 31 -1, 19 -1))', 4326)
);

INSERT INTO lots (lot_id, lot) VALUES (
 3,
 sde.st_polygon ('polygon ((39 -1, 39 11, 51 11, 51 -1, 39 -1))', 4326)
);

SELECT SUM (sde.st_area (sde.st_difference (lot, footprint)))
 FROM footprints bf, lots
 WHERE bf.building_id = lots.lot_id;

sum

114

SQLite

--Create tables, add geometry columns, and insert values
CREATE TABLE footprints (
 building_id integer primary key autoincrement not null
);

SELECT AddGeometryColumn (
 NULL,
 'footprints',
 'footprint',
 4326,
 'polygon',
 'xy',
 'null'
);

CREATE TABLE lots (
 lot_id integer primary key autoincrement not null
);

SELECT AddGeometryColumn (
 NULL,
 'lots',
 'lot',
 4326,
 'polygon',
 'xy',
 'null'
);

INSERT INTO footprints (footprint) VALUES (
 st_polygon ('polygon ((0 0, 0 10, 10 10, 10 0, 0 0))', 4326)
);

INSERT INTO footprints (footprint) VALUES (
 st_polygon ('polygon ((20 0, 20 10, 30 10, 30 0, 20 0))', 4326)
);

INSERT INTO footprints (footprint) VALUES (
 st_polygon ('polygon ((40 0, 40 10, 50 10, 50 0, 40 0))', 4326)
);

INSERT INTO lots (lot) VALUES (
 st_polygon ('polygon ((-1 -1, -1 11, 11 11, 11 -1, -1 -1))', 4326)
);

INSERT INTO lots (lot) VALUES (
 st_polygon ('polygon ((19 -1, 19 11, 29 9, 31 -1, 19 -1))', 4326)
);

INSERT INTO lots (lot) VALUES (
 st_polygon ('polygon ((39 -1, 39 11, 51 11, 51 -1, 39 -1))', 4326)
);

SELECT SUM (st_area (st_difference (lot, footprint)))
 FROM footprints bf, lots
 WHERE bf.building_id = lots.lot_id;

sum

114.0