# Spatial Relationships and Measurements

ST_Area Returns the area of the surface if it is a polygon or multi-polygon. For "geometry" type area is in SRID units. For "geography" area is in square meters.
float `ST_Area` geometry g1 float `ST_Area` geography g1 float `ST_Area` geography g1 boolean use_spheroid

### Description

Returns the area of the geometry if it is a polygon or multi-polygon. Return the area measurement of an ST_Surface or ST_MultiSurface value. For geometry Area is in the units of the srid. For geography area is in square meters and defaults to measuring about the spheroid of the geography (currently only WGS84). To measure around the faster but less accurate sphere -- ST_Area(geog,false).

&sfs_compliant;

&sqlmm_compliant; SQL-MM 3: 8.1.2, 9.5.3

### Examples

Return area in square feet for a plot of Massachusetts land and multiply by conversion to get square meters. Note this is in square feet because 2249 is Mass State Plane Feet

    SELECT ST_Area(the_geom) As sqft, ST_Area(the_geom)*POWER(0.3048,2) As sqm
    		FROM (SELECT
    		ST_GeomFromText('POLYGON((743238 2967416,743238 2967450,
    			743265 2967450,743265.625 2967416,743238 2967416))',2249) ) As foo(the_geom);
      sqft   |     sqm
    ---------+-------------
     928.625 | 86.27208552

Return area square feet and transform to Massachusetts state plane meters (26986) to get square meters. Note this is in square feet because 2249 is Mass State Plane Feet and transformed area is in square meters since 26986 is state plane mass meters

    SELECT ST_Area(the_geom) As sqft, ST_Area(ST_Transform(the_geom,26986)) As sqm
    		FROM (SELECT
    		ST_GeomFromText('POLYGON((743238 2967416,743238 2967450,
    			743265 2967450,743265.625 2967416,743238 2967416))',2249) ) As foo(the_geom);
      sqft   |       sqm
    ---------+------------------
     928.625 | 86.2724304199219

Return area square feet and square meters using Geography data type. Note that we transform to our geometry to geography (before you can do that make sure your geometry is in WGS 84 long lat 4326). Geography always measures in meters. This is just for demonstration to compare. Normally your table will be stored in geography data type already.

    SELECT ST_Area(the_geog)/POWER(0.3048,2) As sqft_spheroid,  ST_Area(the_geog,false)/POWER(0.3048,2) As sqft_sphere, ST_Area(the_geog) As sqm_spheroid
    		FROM (SELECT
    		geography(
    		ST_Transform(
    			ST_GeomFromText('POLYGON((743238 2967416,743238 2967450,743265 2967450,743265.625 2967416,743238 2967416))',
    				2249
    				) ,4326
    			)
    		)
    	) As foo(the_geog);
     sqft_spheroid   |   sqft_sphere    |   sqm_spheroid
    -----------------+------------------+------------------
    928.684405217197 | 927.186481558724 | 86.2776044452694

     --if your data is in geography already
     SELECT ST_Area(the_geog)/POWER(0.3048,2) As  sqft, ST_Area(the_geog) As sqm
    	FROM somegeogtable;

### See Also

, , ,

ST_Azimuth Returns the angle in radians from the horizontal of the vector defined by pointA and pointB
float `ST_Azimuth` geometry pointA geometry pointB

### Description

Returns the azimuth of the segment defined by the given Point geometries, or NULL if the two points are coincident. Return value is in radians.

The Azimuth is mathematical concept defined as the angle, in this case measured in radian, between a reference plane and a point

Availability: 1.1.0

Azimuth is especially useful in conjunction with ST_Translate for shifting an object along its perpendicular axis. See upgis_lineshift Plpgsqlfunctions PostGIS wiki section for example of this.

### Examples

--Azimuth in degrees

    SELECT ST_Azimuth(ST_MakePoint(1,2), ST_MakePoint(3,4))/(2*pi())*360 as degAz,
    	ST_Azimuth(ST_MakePoint(3,4), ST_MakePoint(1,2))/(2*pi())*360 As degAzrev

    degaz	degazrev
    ------	---------
    45		225

### See Also

,

ST_Centroid Returns the geometric center of a geometry.
geometry `ST_Centroid` geometry g1

### Description

Computes the geometric center of a geometry, or equivalently, the center of mass of the geometry as a `POINT`. For [`MULTI`]`POINT`s, this is computed as the arithmetric mean of the input coordinates. For [`MULTI`]`LINESTRING`s, this is computed as the weighted length of each line segment. For [`MULTI`]`POLYGON`s, "weight" is thought in terms of area. If an empty geometry is supplied, an empty `GEOMETRYCOLLECTION` is returned. If `NULL` is supplied, `NULL` is returned.

The centroid is equal to the centroid of the set of component Geometries of highest dimension (since the lower-dimension geometries contribute zero "weight" to the centroid).

Computation will be more accurate if performed by the GEOS module (enabled at compile time).

&sfs_compliant;

&sqlmm_compliant; SQL-MM 3: 8.1.4, 9.5.5

### Examples

In each of the following illustrations, the blue dot represents the centroid of the source geometry.

Centroid of a `MULTIPOINT` | Centroid of a `LINESTRING`
Centroid of a `POLYGON` | Centroid of a `GEOMETRYCOLLECTION`

    SELECT ST_AsText(ST_Centroid('MULTIPOINT ( -1 0, -1 2, -1 3, -1 4, -1 7, 0 1, 0 3, 1 1, 2 0, 6 0, 7 8, 9 8, 10 6 )'));
    				st_astext
    ------------------------------------------
     POINT(2.30769230769231 3.30769230769231)
    (1 row)

### See Also

ST_ClosestPoint Returns the 2-dimensional point on g1 that is closest to g2. This is the first point of the shortest line.
geometry `ST_ClosestPoint` geometry g1 geometry g2

### Description

Returns the 2-dimensional point on g1 that is closest to g2. This is the first point of the shortest line.

Availability: 1.5.0

### Examples

Closest between point and linestring is the point itself, but closest point between a linestring and point is the point on line string that is closest.
    SELECT ST_AsText(ST_ClosestPoint(pt,line)) AS cp_pt_line,
    	ST_AsText(ST_ClosestPoint(line,pt)) As cp_line_pt
    FROM (SELECT 'POINT(100 100)'::geometry As pt,
    		'LINESTRING (20 80, 98 190, 110 180, 50 75 )'::geometry As line
    	) As foo;

       cp_pt_line   |                cp_line_pt
    ----------------+------------------------------------------
     POINT(100 100) | POINT(73.0769230769231 115.384615384615)
| closest point on polygon A to polygon B
    SELECT ST_AsText(
    		ST_ClosestPoint(
    			ST_GeomFromText('POLYGON((175 150, 20 40, 50 60, 125 100, 175 150))'),
    			ST_Buffer(ST_GeomFromText('POINT(110 170)'), 20)
    			)
    		) As ptwkt;

                      ptwkt
    ------------------------------------------
     POINT(140.752120669087 125.695053378061)

### See Also

, , ,

ST_Contains Returns true if and only if no points of B lie in the exterior of A, and at least one point of the interior of B lies in the interior of A.
boolean `ST_Contains` geometry geomA geometry geomB

### Description

Geometry A contains Geometry B if and only if no points of B lie in the exterior of A, and at least one point of the interior of B lies in the interior of A. An important subtlety of this definition is that A does not contain its boundary, but A does contain itself. Contrast that to where geometry A does not Contain Properly itself.

Returns TRUE if geometry B is completely inside geometry A. For this function to make sense, the source geometries must both be of the same coordinate projection, having the same SRID. ST_Contains is the inverse of ST_Within. So ST_Contains(A,B) implies ST_Within(B,A) except in the case of invalid geometries where the result is always false regardless or not defined.

Performed by the GEOS module

Do not call with a `GEOMETRYCOLLECTION` as an argument

Do not use this function with invalid geometries. You will get unexpected results.

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 index use, use the function _ST_Contains.

NOTE: this is the "allowable" version that returns a boolean, not an integer.

&sfs_compliant; s2.1.1.2 // s2.1.13.3 - same as within(geometry B, geometry A)

&sqlmm_compliant; SQL-MM 3: 5.1.31

There are certain subtleties to ST_Contains and ST_Within that are not intuitively obvious. For details check out Subtleties of OGC Covers, Contains, Within

### Examples

The `ST_Contains` predicate returns `TRUE` in all the following illustrations.

`LINESTRING` / `MULTIPOINT` | `POLYGON` / `POINT`
`POLYGON` / `LINESTRING` | `POLYGON` / `POLYGON`

The `ST_Contains` predicate returns `FALSE` in all the following illustrations.

`POLYGON` / `MULTIPOINT` | `POLYGON` / `LINESTRING`

    -- A circle within a circle
    SELECT ST_Contains(smallc, bigc) As smallcontainsbig,
    	   ST_Contains(bigc,smallc) As bigcontainssmall,
    	   ST_Contains(bigc, ST_Union(smallc, bigc)) as bigcontainsunion,
    	   ST_Equals(bigc, ST_Union(smallc, bigc)) as bigisunion,
    	   ST_Covers(bigc, ST_ExteriorRing(bigc)) As bigcoversexterior,
    	   ST_Contains(bigc, ST_ExteriorRing(bigc)) As bigcontainsexterior
    FROM (SELECT ST_Buffer(ST_GeomFromText('POINT(1 2)'), 10) As smallc,
    			 ST_Buffer(ST_GeomFromText('POINT(1 2)'), 20) As bigc) As foo;

    -- Result
      smallcontainsbig | bigcontainssmall | bigcontainsunion | bigisunion | bigcoversexterior | bigcontainsexterior
    ------------------+------------------+------------------+------------+-------------------+---------------------
     f                | t                | t                | t          | t        | f

    -- Example demonstrating difference between contains and contains properly
    SELECT ST_GeometryType(geomA) As geomtype, ST_Contains(geomA,geomA) AS acontainsa, ST_ContainsProperly(geomA, geomA) AS acontainspropa,
       ST_Contains(geomA, ST_Boundary(geomA)) As acontainsba, ST_ContainsProperly(geomA, ST_Boundary(geomA)) As acontainspropba
    FROM (VALUES ( ST_Buffer(ST_Point(1,1), 5,1) ),
    			 ( ST_MakeLine(ST_Point(1,1), ST_Point(-1,-1) ) ),
    			 ( ST_Point(1,1) )
    	  ) As foo(geomA);

      geomtype    | acontainsa | acontainspropa | acontainsba | acontainspropba
    --------------+------------+----------------+-------------+-----------------
    ST_Polygon    | t          | f              | f           | f
    ST_LineString | t          | f              | f           | f
    ST_Point      | t          | t              | f           | f

### See Also

, , ,, ,

ST_ContainsProperly Returns true if B intersects the interior of A but not the boundary (or exterior). A does not contain properly itself, but does contain itself.
boolean `ST_ContainsProperly` geometry geomA geometry geomB

### Description

Returns true if B intersects the interior of A but not the boundary (or exterior).

A does not contain properly itself, but does contain itself.

Every point of the other geometry is a point of this geometry's interior. The DE-9IM Intersection Matrix for the two geometries matches [T**FF*FF*] used in

From JTS docs slightly reworded: The advantage to using this predicate over and is that it can be computed efficiently, with no need to compute topology at individual points.

An example use case for this predicate is computing the intersections of a set of geometries with a large polygonal geometry. Since intersection is a fairly slow operation, it can be more efficient to use containsProperly to filter out test geometries which lie wholly inside the area. In these cases the intersection is known a priori to be exactly the original test geometry.

Availability: 1.4.0 - requires GEOS >= 3.1.0.

Do not call with a `GEOMETRYCOLLECTION` as an argument

Do not use this function with invalid geometries. You will get unexpected results.

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 index use, use the function _ST_ContainsProperly.

### Examples

    	--a circle within a circle
    	SELECT ST_ContainsProperly(smallc, bigc) As smallcontainspropbig,
    	ST_ContainsProperly(bigc,smallc) As bigcontainspropsmall,
    	ST_ContainsProperly(bigc, ST_Union(smallc, bigc)) as bigcontainspropunion,
    	ST_Equals(bigc, ST_Union(smallc, bigc)) as bigisunion,
    	ST_Covers(bigc, ST_ExteriorRing(bigc)) As bigcoversexterior,
    	ST_ContainsProperly(bigc, ST_ExteriorRing(bigc)) As bigcontainsexterior
    	FROM (SELECT ST_Buffer(ST_GeomFromText('POINT(1 2)'), 10) As smallc,
    	ST_Buffer(ST_GeomFromText('POINT(1 2)'), 20) As bigc) As foo;
    	--Result
      smallcontainspropbig | bigcontainspropsmall | bigcontainspropunion | bigisunion | bigcoversexterior | bigcontainsexterior
    ------------------+------------------+------------------+------------+-------------------+---------------------
     f                     | t                    | f                    | t          | t                 | f

     --example demonstrating difference between contains and contains properly
     SELECT ST_GeometryType(geomA) As geomtype, ST_Contains(geomA,geomA) AS acontainsa, ST_ContainsProperly(geomA, geomA) AS acontainspropa,
     ST_Contains(geomA, ST_Boundary(geomA)) As acontainsba, ST_ContainsProperly(geomA, ST_Boundary(geomA)) As acontainspropba
     FROM (VALUES ( ST_Buffer(ST_Point(1,1), 5,1) ),
    		  ( ST_MakeLine(ST_Point(1,1), ST_Point(-1,-1) ) ),
    		  ( ST_Point(1,1) )
    	) As foo(geomA);

      geomtype    | acontainsa | acontainspropa | acontainsba | acontainspropba
    --------------+------------+----------------+-------------+-----------------
    ST_Polygon    | t          | f              | f           | f
    ST_LineString | t          | f              | f           | f
    ST_Point      | t          | t              | f           | f

### See Also

, , , ,, ,,

ST_Covers Returns 1 (TRUE) if no point in Geometry B is outside Geometry A. For geography: if geography point B is not outside Polygon Geography A
boolean `ST_Covers` geometry geomA geometry geomB boolean `ST_Covers` geography geogpolyA geography geogpointB

### Description

Returns 1 (TRUE) if no point in Geometry/Geography B is outside Geometry/Geography A

Performed by the GEOS module

Do not call with a `GEOMETRYCOLLECTION` as an argument

For geography only Polygon covers point is supported.

Do not use this function with invalid geometries. You will get unexpected results.

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 index use, use the function _ST_Covers.

Availability: 1.2.2 - requires GEOS >= 3.0

Availability: 1.5 - support for geography was introduced.

NOTE: this is the "allowable" version that returns a boolean, not an integer.

Not an OGC standard, but Oracle has it too.

There are certain subtleties to ST_Contains and ST_Within that are not intuitively obvious. For details check out Subtleties of OGC Covers, Contains, Within

### Examples

Geometry example

    	--a circle covering a circle
    SELECT ST_Covers(smallc,smallc) As smallinsmall,
    	ST_Covers(smallc, bigc) As smallcoversbig,
    	ST_Covers(bigc, ST_ExteriorRing(bigc)) As bigcoversexterior,
    	ST_Contains(bigc, ST_ExteriorRing(bigc)) As bigcontainsexterior
    FROM (SELECT ST_Buffer(ST_GeomFromText('POINT(1 2)'), 10) As smallc,
    	ST_Buffer(ST_GeomFromText('POINT(1 2)'), 20) As bigc) As foo;
    	--Result
     smallinsmall | smallcoversbig | bigcoversexterior | bigcontainsexterior
    --------------+----------------+-------------------+---------------------
     t            | f              | t                 | f
    (1 row)

Geeography Example

    -- a point with a 300 meter buffer compared to a point, a point and its 10 meter buffer
    SELECT ST_Covers(geog_poly, geog_pt) As poly_covers_pt,
    	ST_Covers(ST_Buffer(geog_pt,10), geog_pt) As buff_10m_covers_cent
    	FROM (SELECT ST_Buffer(ST_GeogFromText('SRID=4326;POINT(-99.327 31.4821)'), 300) As geog_poly,
    				ST_GeogFromText('SRID=4326;POINT(-99.33 31.483)') As geog_pt ) As foo;

     poly_covers_pt | buff_10m_covers_cent
    ----------------+------------------
     f              | t

### See Also

, ,

ST_CoveredBy Returns 1 (TRUE) if no point in Geometry/Geography A is outside Geometry/Geography B
boolean `ST_CoveredBy` geometry geomA geometry geomB boolean `ST_CoveredBy` geography geogA geography geogB

### Description

Returns 1 (TRUE) if no point in Geometry/Geography A is outside Geometry/Geography B

Performed by the GEOS module

Do not call with a `GEOMETRYCOLLECTION` as an argument

Do not use this function with invalid geometries. You will get unexpected results.

Availability: 1.2.2 - requires GEOS >= 3.0

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 index use, use the function _ST_CoveredBy.

NOTE: this is the "allowable" version that returns a boolean, not an integer.

Not an OGC standard, but Oracle has it too.

There are certain subtleties to ST_Contains and ST_Within that are not intuitively obvious. For details check out Subtleties of OGC Covers, Contains, Within

### Examples

    	--a circle coveredby a circle
    SELECT ST_CoveredBy(smallc,smallc) As smallinsmall,
    	ST_CoveredBy(smallc, bigc) As smallcoveredbybig,
    	ST_CoveredBy(ST_ExteriorRing(bigc), bigc) As exteriorcoveredbybig,
    	ST_Within(ST_ExteriorRing(bigc),bigc) As exeriorwithinbig
    FROM (SELECT ST_Buffer(ST_GeomFromText('POINT(1 2)'), 10) As smallc,
    	ST_Buffer(ST_GeomFromText('POINT(1 2)'), 20) As bigc) As foo;
    	--Result
     smallinsmall | smallcoveredbybig | exteriorcoveredbybig | exeriorwithinbig
    --------------+-------------------+----------------------+------------------
     t            | t                 | t                    | f
    (1 row)

### See Also

, , ,

ST_Crosses Returns `TRUE` if the supplied geometries have some, but not all, interior points in common.
boolean `ST_Crosses` geometry g1 geometry g2

### Description

`ST_Crosses` takes two geometry objects and returns `TRUE` if their intersection "spatially cross", that is, the geometries have some, but not all interior points in common. The intersection of the interiors of the geometries must not be the empty set and must have a dimensionality less than the the maximum dimension of the two input geometries. Additionally, the intersection of the two geometries must not equal either of the source geometries. Otherwise, it returns `FALSE`.

In mathematical terms, this 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 DE-9IM Intersection Matrix for the two geometries is:

- T*T****** (for Point/Line, Point/Area, and Line/Area situations)

- T*****T** (for Line/Point, Area/Point, and Area/Line situations)

- 0******** (for Line/Line situations)

For any other combination of dimensions this predicate returns false.

The OpenGIS Simple Features Specification defines this predicate only for Point/Line, Point/Area, Line/Line, and Line/Area situations. JTS / GEOS extends the definition to apply to Line/Point, Area/Point and Area/Line situations as well. This makes the relation symmetric.

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.

&sfs_compliant; s2.1.13.3

&sqlmm_compliant; SQL-MM 3: 5.1.29

### Examples

The following illustrations all return `TRUE`.

`MULTIPOINT` / `LINESTRING` | `MULTIPOINT` / `POLYGON`
`LINESTRING` / `POLYGON` | `LINESTRING` / `LINESTRING`

Consider a situation where a user has two tables: a table of roads and a table of highways.

    CREATE TABLE roads (
      id serial NOT NULL,
      the_geom geometry,
      CONSTRAINT roads_pkey PRIMARY KEY (road_id)
    );
    CREATE TABLE highways (
      id serial NOT NULL,
      the_gem geometry,
      CONSTRAINT roads_pkey PRIMARY KEY (road_id)
    );

To determine a list of roads that cross a highway, use a query similiar to:

    SELECT roads.id
    FROM roads, highways
    WHERE ST_Crosses(roads.the_geom, highways.the_geom);

ST_LineCrossingDirection Given 2 linestrings, returns a number between -3 and 3 denoting what kind of crossing behavior. 0 is no crossing.
integer `ST_LineCrossingDirection` geometry linestringA geometry linestringB

### Description

Given 2 linestrings, returns a number between -3 and 3 denoting what kind of crossing behavior. 0 is no crossing. This is only supported for `LINESTRING`

Definition of integer constants is as follows:

- 0: LINE NO CROSS

- -1: LINE CROSS LEFT

- 1: LINE CROSS RIGHT

- -2: LINE MULTICROSS END LEFT

- 2: LINE MULTICROSS END RIGHT

- -3: LINE MULTICROSS END SAME FIRST LEFT

- 3: LINE MULTICROSS END SAME FIRST RIGHT

Availability: 1.4

### Examples

Line 1 (green), Line 2 ball is start point, triangle are end points. Query below.
    SELECT ST_LineCrossingDirection(foo.line1, foo.line2) As l1_cross_l2 ,
    	  ST_LineCrossingDirection(foo.line2, foo.line1) As l2_cross_l1
    FROM (
    SELECT
     ST_GeomFromText('LINESTRING(25 169,89 114,40 70,86 43)') As line1,
     ST_GeomFromText('LINESTRING(171 154,20 140,71 74,161 53)') As line2
    	) As foo;

     l1_cross_l2 | l2_cross_l1
    -------------+-------------
               3 |          -3
| Line 1 (green), Line 2 (blue) ball is start point, triangle are end points. Query below.
    SELECT ST_LineCrossingDirection(foo.line1, foo.line2) As l1_cross_l2 ,
    	  ST_LineCrossingDirection(foo.line2, foo.line1) As l2_cross_l1
    FROM (
     SELECT
      ST_GeomFromText('LINESTRING(25 169,89 114,40 70,86 43)') As line1,
      ST_GeomFromText('LINESTRING (171 154, 20 140, 71 74, 2.99 90.16)') As line2
    ) As foo;

     l1_cross_l2 | l2_cross_l1
    -------------+-------------
               2 |          -2
Line 1 (green), Line 2 (blue) ball is start point, triangle are end points. Query below.
    SELECT
    	ST_LineCrossingDirection(foo.line1, foo.line2) As l1_cross_l2 ,
    	ST_LineCrossingDirection(foo.line2, foo.line1) As l2_cross_l1
    FROM (
     SELECT
      ST_GeomFromText('LINESTRING(25 169,89 114,40 70,86 43)') As line1,
      ST_GeomFromText('LINESTRING (20 140, 71 74, 161 53)') As line2
      ) As foo;

     l1_cross_l2 | l2_cross_l1
    -------------+-------------
              -1 |          1
| Line 1 (green), Line 2 (blue) ball is start point, triangle are end points. Query below.
    SELECT ST_LineCrossingDirection(foo.line1, foo.line2) As l1_cross_l2 ,
    	  ST_LineCrossingDirection(foo.line2, foo.line1) As l2_cross_l1
    FROM (SELECT
    	ST_GeomFromText('LINESTRING(25 169,89 114,40 70,86 43)') As line1,
    	ST_GeomFromText('LINESTRING(2.99 90.16,71 74,20 140,171 154)') As line2
    	) As foo;

     l1_cross_l2 | l2_cross_l1
    -------------+-------------
              -2 |          2

    SELECT s1.gid, s2.gid, ST_LineCrossingDirection(s1.the_geom, s2.the_geom)
    	FROM streets s1 CROSS JOIN streets s2 ON (s1.gid != s2.gid AND s1.the_geom && s2.the_geom )
    WHERE ST_CrossingDirection(s1.the_geom, s2.the_geom) > 0;

### See Also

ST_Disjoint Returns TRUE if the Geometries do not "spatially intersect" - if they do not share any space together.
boolean `ST_Disjoint` geometry A geometry B

### Description

Overlaps, Touches, Within all imply geometries are not spatially disjoint. If any of the aforementioned returns true, then the geometries are not spatially disjoint. Disjoint implies false for spatial intersection.

Do not call with a `GEOMETRYCOLLECTION` as an argument

Performed by the GEOS module

This function call does not use indexes

NOTE: this is the "allowable" version that returns a boolean, not an integer.

&sfs_compliant; s2.1.1.2 //s2.1.13.3 - a.Relate(b, 'FF*FF****')

&sqlmm_compliant; SQL-MM 3: 5.1.26

### Examples

    SELECT ST_Disjoint('POINT(0 0)'::geometry, 'LINESTRING ( 2 0, 0 2 )'::geometry);
     st_disjoint
    ---------------
     t
    (1 row)
    SELECT ST_Disjoint('POINT(0 0)'::geometry, 'LINESTRING ( 0 0, 0 2 )'::geometry);
     st_disjoint
    ---------------
     f
    (1 row)

### See Also

ST_Intersects

ST_Distance For geometry type Returns the 2-dimensional cartesian minimum distance (based on spatial ref) between two geometries in projected units. For geography type defaults to return spheroidal minimum distance between two geographies in meters.
float `ST_Distance` geometry g1 geometry g2 float `ST_Distance` geography gg1 geography gg2 float `ST_Distance` geography gg1 geography gg2 boolean use_spheroid

### Description

For geometry type returns the 2-dimensional minimum cartesian distance between two geometries in projected units (spatial ref units). For geography type defaults to return the minimum distance around WGS 84 spheroid between two geographies in meters. Pass in false to return answer in sphere instead of spheroid.

&sfs_compliant;

&sqlmm_compliant; SQL-MM 3: 5.1.23

Availability: 1.5.0 geography support was introduced in 1.5. Speed improvements for planar to better handle large or many vertex geometries

### Examples

    --Geometry example - units in planar degrees 4326 is WGS 84 long lat unit=degrees
    SELECT ST_Distance(
    		ST_GeomFromText('POINT(-72.1235 42.3521)',4326),
    		ST_GeomFromText('LINESTRING(-72.1260 42.45, -72.123 42.1546)', 4326)
    	);
    st_distance
    -----------------
    0.00150567726382282

    -- Geometry example - units in meters (SRID: 26986 Massachusetts state plane meters) (most accurate for Massachusetts)
    SELECT ST_Distance(
    			ST_Transform(ST_GeomFromText('POINT(-72.1235 42.3521)',4326),26986),
    			ST_Transform(ST_GeomFromText('LINESTRING(-72.1260 42.45, -72.123 42.1546)', 4326),26986)
    		);
    st_distance
    -----------------
    123.797937878454

    -- Geometry example - units in meters (SRID: 2163 US National Atlas Equal area) (least accurate)
    SELECT ST_Distance(
    			ST_Transform(ST_GeomFromText('POINT(-72.1235 42.3521)',4326),2163),
    			ST_Transform(ST_GeomFromText('LINESTRING(-72.1260 42.45, -72.123 42.1546)', 4326),2163)
    		);

    st_distance
    ------------------
    126.664256056812

    -- Geography example -- same but note units in meters - use sphere for slightly faster less accurate
    SELECT ST_Distance(gg1, gg2) As spheroid_dist, ST_Distance(gg1, gg2, false) As sphere_dist
    FROM (SELECT
    	ST_GeographyFromText('SRID=4326;POINT(-72.1235 42.3521)') As gg1,
    	ST_GeographyFromText('SRID=4326;LINESTRING(-72.1260 42.45, -72.123 42.1546)') As gg2
    	) As foo  ;

      spheroid_dist   |   sphere_dist
    ------------------+------------------
     123.802076746848 | 123.475736916397

### See Also

, , , ,

ST_HausdorffDistance Returns the Hausdorff distance between two geometries. Basically a measure of how similar or dissimilar 2 geometries are. Units are in the units of the spatial reference system of the geometries.
float `ST_HausdorffDistance` geometry g1 geometry g2 float `ST_HausdorffDistance` geometry g1 geometry g2 float densifyFrac

### Description

Implements algorithm for computing a distance metric which can be thought of as the "Discrete Hausdorff Distance". This is the Hausdorff distance restricted to discrete points for one of the geometries. Wikipedia article on Hausdorff distance Martin Davis note on how Hausdorff Distance calculation was used to prove correctness of the CascadePolygonUnion approach.

When densifyFrac is specified, this function performs a segment densification before computing the discrete hausdorff distance. The densifyFrac parameter sets the fraction by which to densify each segment. Each segment will be split into a number of equal-length subsegments, whose fraction of the total length is closest to the given fraction.

The current implementation supports only vertices as the discrete locations. This could be extended to allow an arbitrary density of points to be used.

This algorithm is NOT equivalent to the standard Hausdorff distance. However, it computes an approximation that is correct for a large subset of useful cases. One important part of this subset is Linestrings that are roughly parallel to each other, and roughly equal in length. This is a useful metric for line matching.

Availability: 1.5.0 - requires GEOS >= 3.2.0

### Examples

    postgis=# SELECT st_HausdorffDistance(
    				'LINESTRING (0 0, 2 0)'::geometry,
    				'MULTIPOINT (0 1, 1 0, 2 1)'::geometry);
     st_hausdorffdistance
     ----------------------
    					 1
    (1 row)

    postgis=# SELECT st_hausdorffdistance('LINESTRING (130 0, 0 0, 0 150)'::geometry, 'LINESTRING (10 10, 10 150, 130 10)'::geometry, 0.5);
     st_hausdorffdistance
     ----------------------
    					70
    (1 row)

ST_MaxDistance Returns the 2-dimensional largest distance between two geometries in projected units.
float `ST_MaxDistance` geometry g1 geometry g2

### Description

Some useful description here.

Returns the 2-dimensional maximum distance between two linestrings in projected units. If g1 and g2 is the same geometry the function will return the distance between the two vertices most far from each other in that geometry.

Availability: 1.5.0

### Examples

    postgis=# SELECT ST_MaxDistance('POINT(0 0)'::geometry, 'LINESTRING ( 2 0, 0 2 )'::geometry);
       st_maxdistance
    -----------------
     2
    (1 row)

    postgis=# SELECT ST_MaxDistance('POINT(0 0)'::geometry, 'LINESTRING ( 2 2, 2 2 )'::geometry);
      st_maxdistance
    ------------------
     2.82842712474619
    (1 row)

### See Also

,

ST_Distance_Sphere Returns minimum distance in meters between two lon/lat geometries. Uses a spherical earth and radius of 6370986 meters. Faster than ST_Distance_Spheroid, but less accurate. PostGIS versions prior to 1.5 only implemented for points.
float `ST_Distance_Sphere` geometry geomlonlatA geometry geomlonlatB

### Description

Returns minimum distance in meters between two lon/lat points. Uses a spherical earth and radius of 6370986 meters. Faster than , but less accurate. PostGIS Versions prior to 1.5 only implemented for points.

This function currently does not look at the SRID of a geometry and will always assume its in WGS 84 long lat. Prior versions of this function only support points.

Availability: 1.5 - support for other geometry types besides points was introduced. Prior versions only work with points.

### Examples

    SELECT round(CAST(ST_Distance_Sphere(ST_Centroid(the_geom), ST_GeomFromText('POINT(-118 38)',4326)) As numeric),2) As dist_meters,
    round(CAST(ST_Distance(ST_Transform(ST_Centroid(the_geom),32611),
    		ST_Transform(ST_GeomFromText('POINT(-118 38)', 4326),32611)) As numeric),2) As dist_utm11_meters,
    round(CAST(ST_Distance(ST_Centroid(the_geom), ST_GeomFromText('POINT(-118 38)', 4326)) As numeric),5) As dist_degrees,
    round(CAST(ST_Distance(ST_Transform(the_geom,32611),
    		ST_Transform(ST_GeomFromText('POINT(-118 38)', 4326),32611)) As numeric),2) As min_dist_line_point_meters
    FROM
    	(SELECT ST_GeomFromText('LINESTRING(-118.584 38.374,-118.583 38.5)', 4326) As the_geom) as foo;
    	 dist_meters | dist_utm11_meters | dist_degrees | min_dist_line_point_meters
    	-------------+-------------------+--------------+----------------------------
    		70424.47 |          70438.00 |      0.72900 |                   65871.18

### See Also

,

ST_Distance_Spheroid Returns the minimum distance between two lon/lat geometries given a particular spheroid. PostGIS versions prior to 1.5 only support points.
float `ST_Distance_Spheroid` geometry geomlonlatA geometry geomlonlatB spheroid measurement_spheroid

### Description

Returns minimum distance in meters between two lon/lat geometries given a particular spheroid. See the explanation of spheroids given for . PostGIS version prior to 1.5 only support points.

This function currently does not look at the SRID of a geometry and will always assume its represented in the coordinates of the passed in spheroid. Prior versions of this function only support points.

Availability: 1.5 - support for other geometry types besides points was introduced. Prior versions only work with points.

### Examples

    SELECT round(CAST(
    		ST_Distance_Spheroid(ST_Centroid(the_geom), ST_GeomFromText('POINT(-118 38)',4326), 'SPHEROID["WGS 84",6378137,298.257223563]')
    			As numeric),2) As dist_meters_spheroid,
    		round(CAST(ST_Distance_Sphere(ST_Centroid(the_geom), ST_GeomFromText('POINT(-118 38)',4326)) As numeric),2) As dist_meters_sphere,
    round(CAST(ST_Distance(ST_Transform(ST_Centroid(the_geom),32611),
    		ST_Transform(ST_GeomFromText('POINT(-118 38)', 4326),32611)) As numeric),2) As dist_utm11_meters
    FROM
    	(SELECT ST_GeomFromText('LINESTRING(-118.584 38.374,-118.583 38.5)', 4326) As the_geom) as foo;
     dist_meters_spheroid | dist_meters_sphere | dist_utm11_meters
    ----------------------+--------------------+-------------------
    			 70454.92 |           70424.47 |          70438.00

### See Also

,

ST_DFullyWithin Returns true if all of the geometries are within the specified distance of one another
boolean `ST_DFullyWithin` geometry g1 geometry g2 double precision distance

### Description

Returns true if the geometries is fully within the specified distance of one another. The distance is specified in units defined by the spatial reference system of the geometries. For this function to make sense, the source geometries must both be of the same coordinate projection, having the same SRID.

This function call will automatically include a bounding box comparison that will make use of any indexes that are available on the geometries.

Availability: 1.5.0

### Examples

    postgis=# SELECT ST_DFullyWithin(geom_a, geom_b, 10) as DFullyWithin10, ST_DWithin(geom_a, geom_b, 10) as DWithin10, ST_DFullyWithin(geom_a, geom_b, 20) as DFullyWithin20 from
    		(select ST_GeomFromText('POINT(1 1)') as geom_a,ST_GeomFromText('LINESTRING(1 5, 2 7, 1 9, 14 12)') as geom_b) t1;

    -----------------
     DFullyWithin10 | DWithin10 | DFullyWithin20 |
    ---------------+----------+---------------+
     f             | t        | t             |

### See Also

,

ST_DWithin Returns true if the geometries are within the specified distance of one another. For geometry units are in those of spatial reference and For geography units are in meters and measurement is defaulted to use_spheroid=true (measure around spheroid), for faster check, use_spheroid=false to measure along sphere.
boolean `ST_DWithin` geometry g1 geometry g2 double precision distance_of_srid boolean `ST_DWithin` geography gg1 geography gg2 double precision distance_meters boolean `ST_DWithin` geography gg1 geography gg2 double precision distance_meters boolean use_spheroid

### Description

Returns true if the geometries are within the specified distance of one another.

For Geometries: The distance is specified in units defined by the spatial reference system of the geometries. For this function to make sense, the source geometries must both be of the same coorindate projection, having the same SRID.

For geography units are in meters and measurement is defaulted to use_spheroid=true (measure around WGS 84 spheroid), for faster check, use_spheroid=false to measure along sphere.

This function call will automatically include a bounding box comparison that will make use of any indexes that are available on the geometries.

Prior to 1.3, ST_Expand was commonly used in conjunction with && and ST_Distance to achieve the same effect and in pre-1.3.4 this function was basically short-hand for that construct. From 1.3.4, ST_DWithin uses a more short-circuit distance function which should make it more efficient than prior versions for larger buffer regions.

&sfs_compliant;

Availability: 1.5.0 support for geography was introduced

### Examples

    --Find the nearest hospital to each school
    --that is within 3000 units of the school.
    -- We do an ST_DWithin search to utilize indexes to limit our search list
    -- that the non-indexable ST_Distance needs to process
    --If the units of the spatial reference is meters then units would be meters
    SELECT DISTINCT ON (s.gid) s.gid, s.school_name, s.the_geom, h.hospital_name
    	FROM schools s
    		LEFT JOIN hospitals h ON ST_DWithin(s.the_geom, h.the_geom, 3000)
    	ORDER BY s.gid, ST_Distance(s.the_geom, h.the_geom);

    --The schools with no close hospitals
    --Find all schools with no hospital within 3000 units
    --away from the school.  Units is in units of spatial ref (e.g. meters, feet, degrees)
    SELECT s.gid, s.school_name
    	FROM schools s
    		LEFT JOIN hospitals h ON ST_DWithin(s.the_geom, h.the_geom, 3000)
    	WHERE h.gid IS NULL;

### See Also

,

ST_Equals Returns true if the given geometries represent the same geometry. Directionality is ignored.
boolean `ST_Equals` geometry A geometry B

### Description

Returns TRUE if the given Geometries are "spatially equal". Use this for a 'better' answer than '='. Note by spatially equal we mean ST_Within(A,B) = true and ST_Within(B,A) = true and also mean ordering of points can be different but represent the same geometry structure. To verify the order of points is consistent, use ST_OrderingEquals (it must be noted ST_OrderingEquals is a little more stringent than simply verifying order of points are the same).

This function will return false if either geometry is invalid even if they are binary equal.

&sfs_compliant; s2.1.1.2

&sqlmm_compliant; SQL-MM 3: 5.1.24

### Examples

    SELECT ST_Equals(ST_GeomFromText('LINESTRING(0 0, 10 10)'),
    		ST_GeomFromText('LINESTRING(0 0, 5 5, 10 10)'));
     st_equals
    -----------
     t
    (1 row)

    SELECT ST_Equals(ST_Reverse(ST_GeomFromText('LINESTRING(0 0, 10 10)')),
    		ST_GeomFromText('LINESTRING(0 0, 5 5, 10 10)'));
     st_equals
    -----------
     t
    (1 row)

### See Also

, , ,

ST_HasArc Returns true if a geometry or geometry collection contains a circular string
boolean `ST_HasArc` geometry geomA

### Description

Returns true if a geometry or geometry collection contains a circular string

Availability: 1.2.3?

&Z_support;

&curve_support;

### Examples

    SELECT ST_HasArc(ST_Collect('LINESTRING(1 2, 3 4, 5 6)', 'CIRCULARSTRING(1 1, 2 3, 4 5, 6 7, 5 6)'));
    		st_hasarc
    		--------
    		t

### See Also

,

ST_Intersects Returns TRUE if the Geometries/Geography "spatially intersect" - (share any portion of space) and FALSE if they don't (they are Disjoint). For geography -- tolerance is 0.00001 meters (so any points that close are considered to intersect)
boolean `ST_Intersects` geometry geomA geometry geomB boolean `ST_Intersects` geography geogA geography geogB

### Description

Overlaps, Touches, Within all imply spatial intersection. If any of the aforementioned returns true, then the geometries also spatially intersect. Disjoint implies false for spatial intersection.

Do not call with a `GEOMETRYCOLLECTION` as an argument for geometry version. The geography version supports GEOMETRYCOLLECTION since its a thin wrapper around distance implementation.

Performed by the GEOS module (for geometry), geography is native

Availability: 1.5 support for geography was introduced.

This function call will automatically include a bounding box comparison that will make use of any indexes that are available on the geometries.

For geography, this function has a distance tolerance of about 0.00001 meters and uses the sphere rather than spheroid calculation.

NOTE: this is the "allowable" version that returns a boolean, not an integer.

&sfs_compliant; s2.1.1.2 //s2.1.13.3 - ST_Intersects(g1, g2 ) --> Not (ST_Disjoint(g1, g2 ))

&sqlmm_compliant; SQL-MM 3: 5.1.27

### Geometry Examples

    SELECT ST_Intersects('POINT(0 0)'::geometry, 'LINESTRING ( 2 0, 0 2 )'::geometry);
     st_intersects
    ---------------
     f
    (1 row)
    SELECT ST_Intersects('POINT(0 0)'::geometry, 'LINESTRING ( 0 0, 0 2 )'::geometry);
     st_intersects
    ---------------
     t
    (1 row)

### Geography Examples

    SELECT ST_Intersects(
    		ST_GeographyFromText('SRID=4326;LINESTRING(-43.23456 72.4567,-43.23456 72.4568)'),
    		ST_GeographyFromText('SRID=4326;POINT(-43.23456 72.4567772)')
    		);

     st_intersects
    ---------------
    t

### See Also

ST_Length Returns the 2d length of the geometry if it is a linestring or multilinestring. geometry are in units of spatial reference and geography are in meters (default spheroid)
float `ST_Length` geometry a_2dlinestring float `ST_Length` geography gg float `ST_Length` geography gg boolean use_spheroid

### Description

For geometry: Returns the cartesian 2D length of the geometry if it is a linestring, multilinestring, ST_Curve, ST_MultiCurve. 0 is returned for areal geometries. For areal geometries use ST_Perimeter. Geometry: Measurements are in the units of the spatial reference system of the geometry. Geography: Units are in meters and also acts as a Perimeter function for areal geogs.

Currently for geometry this is an alias for ST_Length2D, but this may change to support higher dimensions.

Currently applying this to a MULTI/POLYGON of type geography will give you the perimeter of the POLYGON/MULTIPOLYGON. This is not the case with the geometry implementation.

For geography measurement defaults spheroid measurement. To use the faster less accurate sphere use ST_Length(gg,false);

&sfs_compliant; s2.1.5.1

&sqlmm_compliant; SQL-MM 3: 7.1.2, 9.3.4

Availability: 1.5.0 geography support was introduced in 1.5.

### Geometry Examples

Return length in feet for line string. Note this is in feet because 2249 is Mass State Plane Feet

    SELECT ST_Length(ST_GeomFromText('LINESTRING(743238 2967416,743238 2967450,743265 2967450,
    743265.625 2967416,743238 2967416)',2249));
    st_length
    ---------
     122.630744000095

    --Transforming WGS 84 linestring to Massachusetts state plane meters
    SELECT ST_Length(
    	ST_Transform(
    		ST_GeomFromEWKT('SRID=4326;LINESTRING(-72.1260 42.45, -72.1240 42.45666, -72.123 42.1546)'),
    		26986
    	)
    );
    st_length
    ---------
    34309.4563576191

### Geography Examples

Return length of WGS 84 geography line

    			-- default calculation is using a sphere rather than spheroid
    SELECT ST_Length(the_geog) As length_spheroid,  ST_Length(the_geog,false) As length_sphere
    FROM (SELECT ST_GeographyFromText(
    'SRID=4326;LINESTRING(-72.1260 42.45, -72.1240 42.45666, -72.123 42.1546)') As the_geog)
     As foo;
     length_spheroid  |  length_sphere
    ------------------+------------------
     34310.5703627305 | 34346.2060960742
    (1 row)

### See Also

, , , ,

ST_Length2D Returns the 2-dimensional length of the geometry if it is a linestring or multi-linestring. This is an alias for `ST_Length`
float `ST_Length2D` geometry a_2dlinestring

### Description

Returns the 2-dimensional length of the geometry if it is a linestring or multi-linestring. This is an alias for `ST_Length`

### See Also

,

ST_Length3D Returns the 3-dimensional or 2-dimensional length of the geometry if it is a linestring or multi-linestring.
float `ST_Length3D` geometry a_3dlinestring

### Description

Returns the 3-dimensional or 2-dimensional length of the geometry if it is a linestring or multi-linestring. For 2-d lines it will just return the 2-d length (same as ST_Length and ST_Length2D)

&Z_support;

### Examples

Return length in feet for a 3D cable. Note this is in feet because 2249 is Mass State Plane Feet

    SELECT ST_Length3D(ST_GeomFromText('LINESTRING(743238 2967416 1,743238 2967450 1,743265 2967450 3,
    743265.625 2967416 3,743238 2967416 3)',2249));
    st_length3d
    -----------
    122.704716741457

### See Also

,

ST_Length_Spheroid Calculates the 2D or 3D length of a linestring/multilinestring on an ellipsoid. This is useful if the coordinates of the geometry are in longitude/latitude and a length is desired without reprojection.
float `ST_Length_Spheroid` geometry a_linestring spheroid a_spheroid

### Description

Calculates the length of a geometry on an ellipsoid. This is useful if the coordinates of the geometry are in longitude/latitude and a length is desired without reprojection. The ellipsoid is a separate database type and can be constructed as follows:

    SPHEROID[<NAME>,<SEMI-MAJOR
    		  AXIS>,<INVERSE FLATTENING>]

    SPHEROID["GRS_1980",6378137,298.257222101]

Will return 0 for anything that is not a MULTILINESTRING or LINESTRING

&Z_support;

### Examples

    SELECT ST_Length_Spheroid( geometry_column,
    			  'SPHEROID["GRS_1980",6378137,298.257222101]' )
    			  FROM geometry_table;

    SELECT ST_Length_Spheroid( the_geom, sph_m ) As tot_len,
    ST_Length_Spheroid(ST_GeometryN(the_geom,1), sph_m) As len_line1,
    ST_Length_Spheroid(ST_GeometryN(the_geom,2), sph_m) As len_line2
    			  FROM (SELECT ST_GeomFromText('MULTILINESTRING((-118.584 38.374,-118.583 38.5),
    	(-71.05957 42.3589 , -71.061 43))') As the_geom,
    CAST('SPHEROID["GRS_1980",6378137,298.257222101]' As spheroid) As sph_m)  as foo;
    	tot_len      |    len_line1     |    len_line2
    ------------------+------------------+------------------
     85204.5207562955 | 13986.8725229309 | 71217.6482333646

     --3D
    SELECT ST_Length_Spheroid( the_geom, sph_m ) As tot_len,
    ST_Length_Spheroid(ST_GeometryN(the_geom,1), sph_m) As len_line1,
    ST_Length_Spheroid(ST_GeometryN(the_geom,2), sph_m) As len_line2
    			  FROM (SELECT ST_GeomFromEWKT('MULTILINESTRING((-118.584 38.374 20,-118.583 38.5 30),
    	(-71.05957 42.3589 75, -71.061 43 90))') As the_geom,
    CAST('SPHEROID["GRS_1980",6378137,298.257222101]' As spheroid) As sph_m)  as foo;

    	 tot_len      |    len_line1    |    len_line2
    ------------------+-----------------+------------------
     85204.5259107402 | 13986.876097711 | 71217.6498130292

### See Also

, ,

ST_Length2D_Spheroid Calculates the 2D length of a linestring/multilinestring on an ellipsoid. This is useful if the coordinates of the geometry are in longitude/latitude and a length is desired without reprojection.
float `ST_Length2D_Spheroid` geometry a_linestring spheroid a_spheroid

### Description

Calculates the 2D length of a geometry on an ellipsoid. This is useful if the coordinates of the geometry are in longitude/latitude and a length is desired without reprojection. The ellipsoid is a separate database type and can be constructed as follows:

    SPHEROID[<NAME>,<SEMI-MAJOR
    		  AXIS>,<INVERSE FLATTENING>]

    SPHEROID["GRS_1980",6378137,298.257222101]

Will return 0 for anything that is not a MULTILINESTRING or LINESTRING

This is much like and except it will throw away the Z coordinate in calculations.

### Examples

    SELECT ST_Length2D_Spheroid( geometry_column,
    			  'SPHEROID["GRS_1980",6378137,298.257222101]' )
    			  FROM geometry_table;

    SELECT ST_Length2D_Spheroid( the_geom, sph_m ) As tot_len,
    ST_Length2D_Spheroid(ST_GeometryN(the_geom,1), sph_m) As len_line1,
    ST_Length2D_Spheroid(ST_GeometryN(the_geom,2), sph_m) As len_line2
    			  FROM (SELECT ST_GeomFromText('MULTILINESTRING((-118.584 38.374,-118.583 38.5),
    	(-71.05957 42.3589 , -71.061 43))') As the_geom,
    CAST('SPHEROID["GRS_1980",6378137,298.257222101]' As spheroid) As sph_m)  as foo;
    	tot_len      |    len_line1     |    len_line2
    ------------------+------------------+------------------
     85204.5207562955 | 13986.8725229309 | 71217.6482333646

     --3D Observe same answer
    SELECT ST_Length2D_Spheroid( the_geom, sph_m ) As tot_len,
    ST_Length2D_Spheroid(ST_GeometryN(the_geom,1), sph_m) As len_line1,
    ST_Length2D_Spheroid(ST_GeometryN(the_geom,2), sph_m) As len_line2
    			  FROM (SELECT ST_GeomFromEWKT('MULTILINESTRING((-118.584 38.374 20,-118.583 38.5 30),
    	(-71.05957 42.3589 75, -71.061 43 90))') As the_geom,
    CAST('SPHEROID["GRS_1980",6378137,298.257222101]' As spheroid) As sph_m)  as foo;

    	tot_len      |    len_line1     |    len_line2
    ------------------+------------------+------------------
     85204.5207562955 | 13986.8725229309 | 71217.6482333646

### See Also

, ,

ST_Length3D_Spheroid Calculates the length of a geometry on an ellipsoid, taking the elevation into account. This is just an alias for ST_Length_Spheroid.
float `ST_Length3D_Spheroid` geometry a_linestring spheroid a_spheroid

### Description

Calculates the length of a geometry on an ellipsoid, taking the elevation into account. This is just an alias for ST_Length_Spheroid.

Will return 0 for anything that is not a MULTILINESTRING or LINESTRING

This functionis just an alias for ST_Length_Spheroid.

&Z_support;

### Examples

    See ST_Length_Spheroid

### See Also

, ,

ST_LongestLine Returns the 2-dimensional longest line points of two geometries. The function will only return the first longest line if more than one, that the function finds. The line returned will always start in g1 and end in g2. The length of the line this function returns will always be the same as st_maxdistance returns for g1 and g2.
geometry `ST_LongestLine` geometry g1 geometry g2

### Description

Returns the 2-dimensional longest line between the points of two geometries.

Availability: 1.5.0

### Examples

Longest line between point and line
    SELECT ST_AsText(
    	ST_LongestLine('POINT(100 100)'::geometry,
    		'LINESTRING (20 80, 98 190, 110 180, 50 75 )'::geometry)
    	) As lline;

       lline
    -----------------
    LINESTRING(100 100,98 190)
| longest line between polygon and polygon
    SELECT ST_AsText(
    	ST_LongestLine(
    		ST_GeomFromText('POLYGON((175 150, 20 40,
    			50 60, 125 100, 175 150))'),
    		ST_Buffer(ST_GeomFromText('POINT(110 170)'), 20)
    		)
    	) As llinewkt;

       lline
    -----------------
    LINESTRING(20 40,121.111404660392 186.629392246051)

longest straight distance to travel from one part of an elegant city to the other Note the max distance = to the length of the line.
    SELECT ST_AsText(ST_LongestLine(c.the_geom, c.the_geom)) As llinewkt,
    	ST_MaxDistance(c.the_geom,c.the_geom) As max_dist,
    	ST_Length(ST_LongestLine(c.the_geom, c.the_geom)) As lenll
    FROM (SELECT ST_BuildArea(ST_Collect(the_geom)) As the_geom
    	FROM (SELECT ST_Translate(ST_SnapToGrid(ST_Buffer(ST_Point(50 ,generate_series(50,190, 50)
    			),40, 'quad_segs=2'),1), x, 0)  As the_geom
    			FROM generate_series(1,100,50) As x)  AS foo
    ) As c;

              llinewkt          |     max_dist     |      lenll
    ---------------------------+------------------+------------------
     LINESTRING(23 22,129 178) | 188.605408193933 | 188.605408193933

### See Also

, ,

ST_OrderingEquals Returns true if the given geometries represent the same geometry and points are in the same directional order.
boolean `ST_OrderingEquals` geometry A geometry B

### Description

ST_OrderingEquals compares two geometries and t (TRUE) if the geometries are equal and the coordinates are in the same order; otherwise it returns f (FALSE).

This function is implemented as per the ArcSDE SQL specification rather than SQL-MM. http://edndoc.esri.com/arcsde/9.1/sql_api/sqlapi3.htm#ST_OrderingEquals

&sqlmm_compliant; SQL-MM 3: 5.1.43

### Examples

    SELECT ST_OrderingEquals(ST_GeomFromText('LINESTRING(0 0, 10 10)'),
    		ST_GeomFromText('LINESTRING(0 0, 5 5, 10 10)'));
     st_orderingequals
    -----------
     f
    (1 row)

    SELECT ST_OrderingEquals(ST_GeomFromText('LINESTRING(0 0, 10 10)'),
    		ST_GeomFromText('LINESTRING(0 0, 0 0, 10 10)'));
     st_orderingequals
    -----------
     t
    (1 row)

    SELECT ST_OrderingEquals(ST_Reverse(ST_GeomFromText('LINESTRING(0 0, 10 10)')),
    		ST_GeomFromText('LINESTRING(0 0, 0 0, 10 10)'));
     st_orderingequals
    -----------
     f
    (1 row)

### See Also

,

ST_Overlaps Returns TRUE if the Geometries share space, are of the same dimension, but are not completely contained by each other.
boolean `ST_Overlaps` geometry A geometry B

### Description

Returns TRUE if the Geometries "spatially overlap". By that we mean they intersect, but one does not completely contain another.

Performed by the GEOS module

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 index use, use the function _ST_Overlaps.

NOTE: this is the "allowable" version that returns a boolean, not an integer.

&sfs_compliant; s2.1.1.2 // s2.1.13.3

&sqlmm_compliant; SQL-MM 3: 5.1.32

### Examples

    --a point on a line is contained by the line and is of a lower dimension, and therefore does not overlap the line
    			nor crosses

    SELECT ST_Overlaps(a,b) As a_overlap_b,
    	ST_Crosses(a,b) As a_crosses_b,
    		ST_Intersects(a, b) As a_intersects_b, ST_Contains(b,a) As b_contains_a
    FROM (SELECT ST_GeomFromText('POINT(1 0.5)') As a, ST_GeomFromText('LINESTRING(1 0, 1 1, 3 5)')  As b)
    	As foo

    a_overlap_b | a_crosses_b | a_intersects_b | b_contains_a
    ------------+-------------+----------------+--------------
    f           | f           | t              | t

    --a line that is partly contained by circle, but not fully is defined as intersecting and crossing,
    -- but since of different dimension it does not overlap
    SELECT ST_Overlaps(a,b) As a_overlap_b, ST_Crosses(a,b) As a_crosses_b,
    	ST_Intersects(a, b) As a_intersects_b,
    	ST_Contains(a,b) As a_contains_b
    FROM (SELECT ST_Buffer(ST_GeomFromText('POINT(1 0.5)'), 3)  As a, ST_GeomFromText('LINESTRING(1 0, 1 1, 3 5)')  As b)
    	As foo;

     a_overlap_b | a_crosses_b | a_intersects_b | a_contains_b
    -------------+-------------+----------------+--------------
     f           | t           | t              | f

     -- a 2-dimensional bent hot dog (aka puffered line string) that intersects a circle,
     --	but is not fully contained by the circle is defined as overlapping since they are of the same dimension,
    --	but it does not cross, because the intersection of the 2 is of the same dimension
    --	as the maximum dimension of the 2

    SELECT ST_Overlaps(a,b) As a_overlap_b, ST_Crosses(a,b) As a_crosses_b, ST_Intersects(a, b) As a_intersects_b,
    ST_Contains(b,a) As b_contains_a,
    ST_Dimension(a) As dim_a, ST_Dimension(b) as dim_b, ST_Dimension(ST_Intersection(a,b)) As dima_intersection_b
    FROM (SELECT ST_Buffer(ST_GeomFromText('POINT(1 0.5)'), 3)  As a,
    	ST_Buffer(ST_GeomFromText('LINESTRING(1 0, 1 1, 3 5)'),0.5)  As b)
    	As foo;

     a_overlap_b | a_crosses_b | a_intersects_b | b_contains_a | dim_a | dim_b | dima_intersection_b
    -------------+-------------+----------------+--------------+-------+-------+---------------------
     t           | f           | t              | f            |     2 |     2 |              2

### See Also

, , ,

ST_Perimeter Return the length measurement of the boundary of an ST_Surface or ST_MultiSurface value. (Polygon, Multipolygon)
float `ST_Perimeter` geometry g1

### Description

Returns the 2D perimeter of the geometry if it is a ST_Surface, ST_MultiSurface (Polygon, Multipolygon). 0 is returned for non-areal geometries. For linestrings use ST_Length. Measurements are in the units of the spatial reference system of the geometry.

Currently this is an alias for ST_Perimeter2D, but this may change to support higher dimensions.

&sfs_compliant; s2.1.5.1

&sqlmm_compliant; SQL-MM 3: 8.1.3, 9.5.4

### Examples

Return perimeter in feet for polygon and multipolygon. Note this is in feet because 2249 is Mass State Plane Feet

    SELECT ST_Perimeter(ST_GeomFromText('POLYGON((743238 2967416,743238 2967450,743265 2967450,
    743265.625 2967416,743238 2967416))', 2249));
    st_perimeter
    ---------
     122.630744000095
    (1 row)

    SELECT ST_Perimeter(ST_GeomFromText('MULTIPOLYGON(((763104.471273676 2949418.44119003,
    763104.477769673 2949418.42538203,
    763104.189609677 2949418.22343004,763104.471273676 2949418.44119003)),
    ((763104.471273676 2949418.44119003,763095.804579742 2949436.33850239,
    763086.132105649 2949451.46730207,763078.452329651 2949462.11549407,
    763075.354136904 2949466.17407812,763064.362142565 2949477.64291974,
    763059.953961626 2949481.28983009,762994.637609571 2949532.04103014,
    762990.568508415 2949535.06640477,762986.710889563 2949539.61421415,
    763117.237897679 2949709.50493431,763235.236617789 2949617.95619822,
    763287.718121842 2949562.20592617,763111.553321674 2949423.91664605,
    763104.471273676 2949418.44119003)))', 2249));
    st_perimeter
    ---------
     845.227713366825
    (1 row)

### See Also

ST_Perimeter2D Returns the 2-dimensional perimeter of the geometry, if it is a polygon or multi-polygon. This is currently an alias for ST_Perimeter.
float `ST_Perimeter2D` geometry geomA

### Description

Returns the 2-dimensional perimeter of the geometry, if it is a polygon or multi-polygon.

This is currently an alias for ST_Perimeter. In future versions ST_Perimeter may return the highest dimension perimeter for a geometry. This is still under consideration

### See Also

ST_Perimeter3D Returns the 3-dimensional perimeter of the geometry, if it is a polygon or multi-polygon.
float `ST_Perimeter3D` geometry geomA

### Description

Returns the 3-dimensional perimeter of the geometry, if it is a polygon or multi-polygon. If the geometry is 2-dimensional, then the 2-dimensional perimeter is returned.

&Z_support;

### Examples

Perimeter of a slightly elevated polygon in the air in Massachusetts state plane feet

    SELECT ST_Perimeter3D(the_geom), ST_Perimeter2d(the_geom), ST_Perimeter(the_geom) FROM
    			(SELECT ST_GeomFromEWKT('SRID=2249;POLYGON((743238 2967416 2,743238 2967450 1,
    743265.625 2967416 1,743238 2967416 2))') As the_geom) As foo;

      st_perimeter3d  |  st_perimeter2d  |   st_perimeter
    ------------------+------------------+------------------
     105.465793597674 | 105.432997272188 | 105.432997272188

### See Also

, ,

ST_PointOnSurface Returns a `POINT` guaranteed to lie on the surface.
geometry `ST_PointOnSurface` geometry g1

### Description

Returns a `POINT` guaranteed to intersect a surface.

&sfs_compliant; s3.2.14.2 // s3.2.18.2

&sqlmm_compliant; SQL-MM 3: 8.1.5, 9.5.6. According to the specs, ST_PointOnSurface works for surface geometries (POLYGONs, MULTIPOLYGONS, CURVED POLYGONS). So PostGIS seems to be extending what the spec allows here. Most databases Oracle,DB II, ESRI SDE seem to only support this function for surfaces. SQL Server 2008 like PostGIS supports for all common geometries.

&Z_support;

### Examples

    SELECT ST_AsText(ST_PointOnSurface('POINT(0 5)'::geometry));
     st_astext
    ------------
     POINT(0 5)
    (1 row)

    SELECT ST_AsText(ST_PointOnSurface('LINESTRING(0 5, 0 10)'::geometry));
     st_astext
    ------------
     POINT(0 5)
    (1 row)

    SELECT ST_AsText(ST_PointOnSurface('POLYGON((0 0, 0 5, 5 5, 5 0, 0 0))'::geometry));
       st_astext
    ----------------
     POINT(2.5 2.5)
    (1 row)

    SELECT ST_AsEWKT(ST_PointOnSurface(ST_GeomFromEWKT('LINESTRING(0 5 1, 0 0 1, 0 10 2)')));
       st_asewkt
    ----------------
     POINT(0 0 1)
    (1 row)

### See Also

,

ST_Relate Returns true if this Geometry is spatially related to anotherGeometry, by testing for intersections between the Interior, Boundary and Exterior of the two geometries as specified by the values in the intersectionMatrixPattern. If no intersectionMatrixPattern is passed in, then returns the maximum intersectionMatrixPattern that relates the 2 geometries.
boolean `ST_Relate` geometry geomA geometry geomB text intersectionMatrixPattern text `ST_Relate` geometry geomA geometry geomB

### Description

Version 1: Takes geomA, geomB, intersectionMatrix and Returns 1 (TRUE) if this Geometry is spatially related to anotherGeometry, by testing for intersections between the Interior, Boundary and Exterior of the two geometries as specified by the values in the intersectionMatrixPattern.

This is especially useful for testing compound checks of intersection, crosses, etc in one step.

Do not call with a GeometryCollection as an argument

This is the "allowable" version that returns a boolean, not an integer. This is defined in OGC spec

This DOES NOT automagically include an index call. The reason for that is some relationships are anti e.g. Disjoint. If you are using a relationship pattern that requires intersection, then include the && index call.

Version 2: Takes geomA and geomB and returns the

Do not call with a GeometryCollection as an argument

not in OGC spec, but implied. see s2.1.13.2

Both Performed by the GEOS module

&sfs_compliant; s2.1.1.2 // s2.1.13.3

&sqlmm_compliant; SQL-MM 3: 5.1.25

### Examples

    --Find all compounds that intersect and not touch a poly (interior intersects)
    SELECT l.* , b.name As poly_name
    FROM polys As b
    	INNER JOIN compounds As l
    	ON (p.the_geom && b.the_geom
    	AND ST_Relate(l.the_geom, b.the_geom,'T********'));

    SELECT ST_Relate(ST_GeometryFromText('POINT(1 2)'), ST_Buffer(ST_GeometryFromText('POINT(1 2)'),2));
     st_relate
    -----------
     0FFFFF212

    SELECT ST_Relate(ST_GeometryFromText('LINESTRING(1 2, 3 4)'), ST_GeometryFromText('LINESTRING(5 6, 7 8)'));
     st_relate
    -----------
     FF1FF0102

    SELECT ST_Relate(ST_GeometryFromText('POINT(1 2)'), ST_Buffer(ST_GeometryFromText('POINT(1 2)'),2), '0FFFFF212');
     st_relate
    -----------
     t

    SELECT ST_Relate(ST_GeometryFromText('POINT(1 2)'), ST_Buffer(ST_GeometryFromText('POINT(1 2)'),2), '*FF*FF212');
     st_relate
    -----------
     t

### See Also

, , , ,

ST_ShortestLine Returns the 2-dimensional shortest line between two geometries
geometry `ST_ShortestLine` geometry g1 geometry g2

### Description

Returns the 2-dimensional shortest line between two geometries. The function will only return the first shortest line if more than one, that the function finds. If g1 and g2 intersects in just one point the function will return a line with both start and end in that intersection-point. If g1 and g2 are intersecting with more than one point the function will return a line with start and end in the same point but it can be any of the intersecting points. The line returned will always start in g1 and end in g2. The length of the line this function returns will always be the same as st_distance returns for g1 and g2.

Availability: 1.5.0

### Examples

Shortest line between point and linestring
    SELECT ST_AsText(
    	ST_ShortestLine('POINT(100 100)'::geometry,
    		'LINESTRING (20 80, 98 190, 110 180, 50 75 )'::geometry)
    	) As sline;

       sline
    -----------------
    LINESTRING(100 100,73.0769230769231 115.384615384615)
| shortest line between polygon and polygon
    SELECT ST_AsText(
    		ST_ShortestLine(
    			ST_GeomFromText('POLYGON((175 150, 20 40, 50 60, 125 100, 175 150))'),
    			ST_Buffer(ST_GeomFromText('POINT(110 170)'), 20)
    			)
    		) As slinewkt;

     LINESTRING(140.752120669087 125.695053378061,121.111404660392 153.370607753949)

### See Also

, , , ,

ST_Touches Returns `TRUE` if the geometries have at least one point in common, but their interiors do not intersect.
boolean `ST_Touches` geometry g1 geometry g2

### 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:

- FT*******

- F**T*****

- F***T****

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.

&sfs_compliant; s2.1.1.2 // s2.1.13.3

&sqlmm_compliant; 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)

ST_Within Returns true if the geometry A is completely inside geometry B
boolean `ST_Within` geometry A geometry B

### Description

Returns TRUE if geometry A is completely inside geometry B. For this function to make sense, the source geometries must both be of the same coordinate projection, having the same SRID. It is a given that if ST_Within(A,B) is true and ST_Within(B,A) is true, then the two geometries are considered spatially equal.

Performed by the GEOS module

Do not call with a `GEOMETRYCOLLECTION` as an argument

Do not use this function with invalid geometries. You will get unexpected results.

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 index use, use the function _ST_Within.

NOTE: this is the "allowable" version that returns a boolean, not an integer.

&sfs_compliant; s2.1.1.2 // s2.1.13.3 - a.Relate(b, 'T*F**F***')

&sqlmm_compliant; SQL-MM 3: 5.1.30

### Examples

    --a circle within a circle
    SELECT ST_Within(smallc,smallc) As smallinsmall,
    	ST_Within(smallc, bigc) As smallinbig,
    	ST_Within(bigc,smallc) As biginsmall,
    	ST_Within(ST_Union(smallc, bigc), bigc) as unioninbig,
    	ST_Within(bigc, ST_Union(smallc, bigc)) as biginunion,
    	ST_Equals(bigc, ST_Union(smallc, bigc)) as bigisunion
    FROM
    (
    SELECT ST_Buffer(ST_GeomFromText('POINT(50 50)'), 20) As smallc,
    	ST_Buffer(ST_GeomFromText('POINT(50 50)'), 40) As bigc) As foo;
    --Result
     smallinsmall | smallinbig | biginsmall | unioninbig | biginunion | bigisunion
    --------------+------------+------------+------------+------------+------------
     t            | t          | f          | t          | t          | t
    (1 row)

### See Also

, ,