Description

Returns TRUE if the only points in common between g1 and g2 lie in the union of the boundaries of g1 and g2. The ST_Touches relation applies to all Area/Area, Line/Line, Line/Area, Point/Area and Point/Line pairs of relationships, but not to the Point/Point pair.

In mathematical terms, this predicate is expressed as:

TODO: Insert appropriate MathML markup here or use a gif. Simple HTML markup does not work well in both IE and Firefox.

The allowable DE-9IM Intersection Matrices for the two geometries are:

	Do not call with a GEOMETRYCOLLECTION as an argument

	This function call will automatically include a bounding box comparison that will make use of any indexes that are available on the geometries. To avoid using an index, use _ST_Touches instead.

This method implements the OpenGIS Simple Features Implementation Specification for SQL: 2.1.1.2, 2.1.13.3

This method implements the SQL/MM specification: SQL-MM 3: 5.1.28

Examples

The ST_Touches predicate returns TRUE in all the following illustrations.

POLYGON / POLYGON	POLYGON / POLYGON	POLYGON / LINESTRING
LINESTRING / LINESTRING	LINESTRING / LINESTRING	POLYGON / POINT

SELECT ST_Touches('LINESTRING(0 0, 1 1, 0 2)'::geometry, 'POINT(1 1)'::geometry);
 st_touches
------------
 f
(1 row)

SELECT ST_Touches('LINESTRING(0 0, 1 1, 0 2)'::geometry, 'POINT(0 2)'::geometry);
 st_touches
------------
 t
(1 row)