The ST_Intersects() function returns t (TRUE)
if the intersection of two geometries does not result in an empty
set; otherwise, returns f (FALSE).
Syntax
ST_Intersects (g1 ST_Geometry, g2 ST_Geometry)
Usage
The
following figure shows various geometric objects that intersect.Figure 1: A selection of geometries
that intersect
The
results of the spatial relationship of the ST_Intersects() function
can be understood or verified by comparing the results with a pattern
matrix that represents the acceptable values for the DE-9IM. The ST_Intersects() function
returns TRUE if the conditions of any of the following pattern matrices
returns TRUE.
The ST_Intersects() function
returns TRUE if the interiors of both geometries intersect.
Table 1. Pattern matrix for the
ST_Intersects() function
The
table is a matrix. The top row and first column identify the geometry.
Interior (b)
Boundary (b)
Exterior (b)
Interior (a)
T
*
*
Boundary (a)
*
*
*
Exterior (a)
*
*
*
The ST_Intersects() function returns
TRUE if the boundary of the first geometry intersects the boundary
of the second geometry.
Interior (b)
Boundary (b)
Exterior (b)
Interior (a)
*
T
*
Boundary (a)
*
*
*
Exterior (a)
*
*
*
The ST_Intersects() function returns
TRUE if the boundary of the first geometry intersects the interior
of the second.
Interior (b)
Boundary (b)
Exterior (b)
Interior (a)
*
*
*
Boundary (a)
T
*
*
Exterior (a)
*
*
*
The ST_Intersects() function returns
TRUE if the boundaries of either geometry intersect.
Interior (b)
Boundary (b)
Exterior (b)
Interior (a)
*
*
*
Boundary (a)
*
T
*
Exterior (a)
*
*
*
Return type
BOOLEAN
Example
The fire marshal wants a list
of sensitive areas within a 5-mile radius of a hazardous waste site.
The
sensitive areas are stored in the following sensitive_areas table.
The zone column is defined as an ST_Polygon type and stores
the outline of the sensitive areas:
CREATE TABLE sensitive_areas (id integer,
name varchar(128),
size float,
type varchar(10),
zone ST_Polygon);
The
hazardous sites are stored in the hazardous_sites table that
is created with the CREATE TABLE statement that follows. The location column,
which is defined as an ST_Point type, stores the geographic center
of each hazardous site:
CREATE TABLE hazardous_sites (site_id integer,
name varchar(40),
location ST_Point);
The
query returns a list of sensitive-area and hazardous-site names for
sensitive areas that intersect the 5-mile buffer radius of the hazardous
sites:
SELECT sa.name, hs.name
FROM sensitive_areas sa, hazardous_sites hs
WHERE ST_Intersects(ST_Buffer(hs.location,(5 * 5280)),sa.zone);
name Johnson County Hospital
name W. H. Kleenare Chemical Repository
name Johnson County Hospital
name Landmark Industrial
name Summerhill Elementary School
name Landmark Industrial
