These functions compute measurements of distance, area and angles. There are also functions to compute geometry values determined by measurements.

# Measurement Functions

ST_Area

Returns the area of a polygonal geometry.

    			  float ST_Area
    				geometry g1

    			  float ST_Area
    				geography geog
    				boolean use_spheroid=true

### Description

Returns the area of a polygonal geometry. For geometry types a 2D Cartesian (planar) area is computed, with units specified by the SRID. For geography types by default area is determined on a spheroid with units in square meters. To compute the area using the faster but less accurate spherical model use `ST_Area(geog,false)`.

Enhanced: 2.0.0 - support for 2D polyhedral surfaces was introduced.

Enhanced: 2.2.0 - measurement on spheroid performed with GeographicLib for improved accuracy and robustness. Requires PROJ >= 4.9.0 to take advantage of the new feature.

Changed: 3.0.0 - does not depend on SFCGAL anymore.

&sfs_compliant;

&sqlmm_compliant; SQL-MM 3: 8.1.2, 9.5.3

&P_support;

For polyhedral surfaces, only supports 2D polyhedral surfaces (not 2.5D). For 2.5D, may give a non-zero answer, but only for the faces that sit completely in XY plane.

### 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 EPSG:2249 is Massachusetts State Plane Feet

    select ST_Area(geom) sqft,
        ST_Area(geom) * 0.3048 ^ 2 sqm
    from (
             select 'SRID=2249;POLYGON((743238 2967416,743238 2967450,
    				 743265 2967450,743265.625 2967416,743238 2967416))' :: geometry geom
         ) subquery;
    ┌─────────┬─────────────┐
    │  sqft   │     sqm     │
    ├─────────┼─────────────┤
    │ 928.625 │ 86.27208552 │
    └─────────┴─────────────┘

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

    select ST_Area(geom) sqft,
        ST_Area(ST_Transform(geom, 26986)) As sqm
    from (
             select
                 'SRID=2249;POLYGON((743238 2967416,743238 2967450,
                 743265 2967450,743265.625 2967416,743238 2967416))' :: geometry geom
         ) subquery;
    ┌─────────┬─────────────────┐
    │  sqft   │       sqm       │
    ├─────────┼─────────────────┤
    │ 928.625 │ 86.272430607008 │
    └─────────┴─────────────────┘

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(geog) / 0.3048 ^ 2 sqft_spheroid,
        ST_Area(geog, false) / 0.3048 ^ 2 sqft_sphere,
        ST_Area(geog) sqm_spheroid
    from (
             select ST_Transform(
                        'SRID=2249;POLYGON((743238 2967416,743238 2967450,743265 2967450,743265.625 2967416,743238 2967416))'::geometry,
                        4326
                 ) :: geography geog
         ) as subquery;
    ┌──────────────────┬──────────────────┬──────────────────┐
    │  sqft_spheroid   │   sqft_sphere    │   sqm_spheroid   │
    ├──────────────────┼──────────────────┼──────────────────┤
    │ 928.684405784452 │ 927.049336105925 │ 86.2776044979692 │
    └──────────────────┴──────────────────┴──────────────────┘

If your data is in geography already:

    select ST_Area(geog) / 0.3048 ^ 2 sqft,
        ST_Area(the_geog) sqm
    from somegeogtable;

### See Also

ST_3DArea, ST_GeomFromText, ST_GeographyFromText, ST_SetSRID, ST_Transform

ST_Azimuth

Returns the north-based azimuth of a line between two points.

    			  float ST_Azimuth
    			  geometry pointA
    			  geometry pointB

    			  float ST_Azimuth
    			  geography pointA
    			  geography pointB

### Description

Returns the azimuth in radians of the line segment defined by the given point geometries, or NULL if the two points are coincident. The azimuth angle is referenced from north (the positive Y axis), and is positive clockwise: North = 0; Northeast = π/4; East = π/2; Southeast = 3π/4; South = π; Southwest 5π/4; West = 3π/2; Northwest = 7π/4.

For the geography type, the azimuth solution is known as the inverse geodesic problem.

The azimuth is a mathematical concept defined as the angle between a reference plane and a point, with angular units in radians. The result value in radians can be converted to degrees using the PostgreSQL function `degrees()`.

Azimuth can be used in conjunction with ST_Translate to shift an object along its perpendicular axis. See the `upgis_lineshift()` function in the PostGIS wiki for an implementation of this.

Availability: 1.1.0

Enhanced: 2.0.0 support for geography was introduced.

Enhanced: 2.2.0 measurement on spheroid performed with GeographicLib for improved accuracy and robustness. Requires PROJ >= 4.9.0 to take advantage of the new feature.

### Examples

Geometry Azimuth in degrees

    SELECT degrees(ST_Azimuth( ST_Point(25, 45),  ST_Point(75, 100))) AS degA_B,
    	   degrees(ST_Azimuth( ST_Point(75, 100), ST_Point(25, 45) )) AS degB_A;

          dega_b       |     degb_a
    ------------------+------------------
     42.2736890060937 | 222.273689006094

Green: the start Point(25,45) with its vertical. Yellow: degA_B as the path to travel (azimuth). | Green: the start Point(75,100) with its vertical. Yellow: degB_A as the path to travel (azimuth).

### See Also

ST_Angle, ST_Point, ST_Translate, ST_Project, PostgreSQL Math Functions

ST_Angle

Returns the angle between two vectors defined by 3 or 4 points, or 2 lines.

    			  float ST_Angle
    			  geometry point1
    			  geometry point2
    			  geometry point3
    			  geometry point4

    			  float ST_Angle
    			  geometry line1
    			  geometry line2

### Description

Computes the clockwise angle between two vectors.

Variant 1: computes the angle enclosed by the points P1-P2-P3. If a 4th point provided computes the angle points P1-P2 and P3-P4

Variant 2: computes the angle between two vectors S1-E1 and S2-E2, defined by the start and end points of the input lines

The result is a positive angle between 0 and 2π radians. The radian result can be converted to degrees using the PostgreSQL function `degrees()`.

Note that `ST_Angle(P1,P2,P3) = ST_Angle(P2,P1,P2,P3)`.

Availability: 2.5.0

### Examples

Angle between three points

    SELECT degrees( ST_Angle('POINT(0 0)', 'POINT(10 10)', 'POINT(20 0)') );

     degrees
    ---------
         270

Angle between vectors defined by four points

    SELECT degrees( ST_Angle('POINT (10 10)', 'POINT (0 0)', 'POINT(90 90)', 'POINT (100 80)') );

          degrees
    -------------------
     269.9999999999999

Angle between vectors defined by the start and end points of lines

    SELECT degrees( ST_Angle('LINESTRING(0 0, 0.3 0.7, 1 1)', 'LINESTRING(0 0, 0.2 0.5, 1 0)') );

          degrees
    --------------
               45

### See Also

ST_Azimuth

ST_ClosestPoint

Returns the 2D 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.

If you have a 3D Geometry, you may prefer to use ST_3DClosestPoint.

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_3DClosestPoint,ST_Distance, ST_LongestLine, ST_ShortestLine, ST_MaxDistance

ST_3DClosestPoint

Returns the 3D point on g1 that is closest to g2. This is the first point of the 3D shortest line.

    				geometry ST_3DClosestPoint

    				geometry
    				g1

    				geometry
    				g2

### Description

Returns the 3-dimensional point on g1 that is closest to g2. This is the first point of the 3D shortest line. The 3D length of the 3D shortest line is the 3D distance.

&Z_support;

&P_support;

Availability: 2.0.0

Changed: 2.2.0 - if 2 2D geometries are input, a 2D point is returned (instead of old behavior assuming 0 for missing Z). In case of 2D and 3D, Z is no longer assumed to be 0 for missing Z.

### Examples

linestring and point -- both 3d and 2d closest point
    SELECT ST_AsEWKT(ST_3DClosestPoint(line,pt)) AS cp3d_line_pt,
    		ST_AsEWKT(ST_ClosestPoint(line,pt)) As cp2d_line_pt
    	FROM (SELECT 'POINT(100 100 30)'::geometry As pt,
    			'LINESTRING (20 80 20, 98 190 1, 110 180 3, 50 75 1000)'::geometry As line
    		) As foo;

     cp3d_line_pt						|               cp2d_line_pt
    -----------------------------------------------------------+------------------------------------------
     POINT(54.6993798867619 128.935022917228 11.5475869506606) | POINT(73.0769230769231 115.384615384615)
linestring and multipoint -- both 3d and 2d closest point
    SELECT ST_AsEWKT(ST_3DClosestPoint(line,pt)) AS cp3d_line_pt,
    		ST_AsEWKT(ST_ClosestPoint(line,pt)) As cp2d_line_pt
    	FROM (SELECT 'MULTIPOINT(100 100 30, 50 74 1000)'::geometry As pt,
    			'LINESTRING (20 80 20, 98 190 1, 110 180 3, 50 75 900)'::geometry As line
    		) As foo;

                           cp3d_line_pt                        | cp2d_line_pt
    -----------------------------------------------------------+--------------
     POINT(54.6993798867619 128.935022917228 11.5475869506606) | POINT(50 75)
Multilinestring and polygon both 3d and 2d closest point
    SELECT ST_AsEWKT(ST_3DClosestPoint(poly, mline)) As cp3d,
        ST_AsEWKT(ST_ClosestPoint(poly, mline)) As cp2d
            FROM (SELECT  ST_GeomFromEWKT('POLYGON((175 150 5, 20 40 5, 35 45 5, 50 60 5, 100 100 5, 175 150 5))') As poly,
                    ST_GeomFromEWKT('MULTILINESTRING((175 155 2, 20 40 20, 50 60 -2, 125 100 1, 175 155 1),
                    (1 10 2, 5 20 1))') As mline ) As foo;
                       cp3d                    |     cp2d
    -------------------------------------------+--------------
     POINT(39.993580415989 54.1889925532825 5) | POINT(20 40)

### See Also

ST_AsEWKT, ST_ClosestPoint, ST_3DDistance, ST_3DShortestLine

ST_Distance

Returns the distance between two geometry or geography values.

    			float ST_Distance

    			geometry
    			g1

    			geometry
    			g2

    			float ST_Distance

    			geography
    			geog1

    			geography
    			geog2

    			boolean
    			use_spheroid=true

### Description

For geometry types returns the minimum 2D Cartesian (planar) distance between two geometries, in projected units (spatial ref units).

For geography types defaults to return the minimum geodesic distance between two geographies in meters, compute on the spheroid determined by the SRID. If `use_spheroid` is false, a faster spherical calculation is used.

&sfs_compliant;

&sqlmm_compliant; SQL-MM 3: 5.1.23

&curve_support;

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

Enhanced: 2.1.0 improved speed for geography. See Making Geography faster for details.

Enhanced: 2.1.0 - support for curved geometries was introduced.

Enhanced: 2.2.0 - measurement on spheroid performed with GeographicLib for improved accuracy and robustness. Requires PROJ >= 4.9.0 to take advantage of the new feature.

Changed: 3.0.0 - does not depend on SFCGAL anymore.

### Basic Geometry Examples

Geometry example - units in planar degrees 4326 is WGS 84 long lat, units are degrees.

    SELECT ST_Distance(
    		'SRID=4326;POINT(-72.1235 42.3521)'::geometry,
    		'SRID=4326;LINESTRING(-72.1260 42.45, -72.123 42.1546)'::geometry
    	);
    st_distance
    -----------------
    0.00150567726382282

Geometry example - units in meters (SRID: 3857, proportional to pixels on popular web maps). Although the value is off, nearby ones can be compared correctly, which makes it a good choice for algorithms like KNN or KMeans.

    SELECT ST_Distance(
    			ST_Transform('SRID=4326;POINT(-72.1235 42.3521)'::geometry, 3857),
    			ST_Transform('SRID=4326;LINESTRING(-72.1260 42.45, -72.123 42.1546)'::geometry, 3857)
    		);
    st_distance
    -----------------
    167.441410065196

Geometry example - units in meters (SRID: 3857 as above, but corrected by cos(lat) to account for distortion)

    SELECT ST_Distance(
    			ST_Transform('SRID=4326;POINT(-72.1235 42.3521)'::geometry, 3857),
    			ST_Transform('SRID=4326;LINESTRING(-72.1260 42.45, -72.123 42.1546)'::geometry, 3857)
    		) * cosd(42.3521);
    st_distance
    -----------------
    123.742351254151

Geometry example - units in meters (SRID: 26986 Massachusetts state plane meters) (most accurate for Massachusetts)

    SELECT ST_Distance(
    			ST_Transform('SRID=4326;POINT(-72.1235 42.3521)'::geometry, 26986),
    			ST_Transform('SRID=4326;LINESTRING(-72.1260 42.45, -72.123 42.1546)'::geometry, 26986)
    		);
    st_distance
    -----------------
    123.797937878454

Geometry example - units in meters (SRID: 2163 US National Atlas Equal area) (least accurate)

    SELECT ST_Distance(
    			ST_Transform('SRID=4326;POINT(-72.1235 42.3521)'::geometry, 2163),
    			ST_Transform('SRID=4326;LINESTRING(-72.1260 42.45, -72.123 42.1546)'::geometry, 2163)
    		);

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

### Geography Examples

Same as geometry example but note units in meters - use sphere for slightly faster and less accurate computation.

    SELECT ST_Distance(gg1, gg2) As spheroid_dist, ST_Distance(gg1, gg2, false) As sphere_dist
    FROM (SELECT
    	'SRID=4326;POINT(-72.1235 42.3521)'::geography as gg1,
    	'SRID=4326;LINESTRING(-72.1260 42.45, -72.123 42.1546)'::geography as gg2
    	) As foo  ;

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

### See Also

ST_3DDistance, ST_DWithin, ST_DistanceSphere, ST_Distance_Spheroid, ST_MaxDistance, ST_HausdorffDistance, ST_FrechetDistance, ST_Transform

ST_3DDistance

Returns the 3D cartesian minimum distance (based on spatial ref) between two geometries in projected units.

    			float ST_3DDistance

    			geometry
    			g1

    			geometry
    			g2

### Description

Returns the 3-dimensional minimum cartesian distance between two geometries in projected units (spatial ref units).

&Z_support;

&P_support;

&sqlmm_compliant; SQL-MM ?

Availability: 2.0.0

Changed: 2.2.0 - In case of 2D and 3D, Z is no longer assumed to be 0 for missing Z.

Changed: 3.0.0 - SFCGAL version removed

### Examples

    -- Geometry example - units in meters (SRID: 2163 US National Atlas Equal area) (3D point and line compared 2D point and line)
    -- Note: currently no vertical datum support so Z is not transformed and assumed to be same units as final.
    SELECT ST_3DDistance(
    			ST_Transform('SRID=4326;POINT(-72.1235 42.3521 4)'::geometry,2163),
    			ST_Transform('SRID=4326;LINESTRING(-72.1260 42.45 15, -72.123 42.1546 20)'::geometry,2163)
    		) As dist_3d,
    		ST_Distance(
    			ST_Transform('SRID=4326;POINT(-72.1235 42.3521)'::geometry,2163),
    			ST_Transform('SRID=4326;LINESTRING(-72.1260 42.45, -72.123 42.1546)'::geometry,2163)
    		) As dist_2d;

         dist_3d      |     dist_2d
    ------------------+-----------------
     127.295059324629 | 126.66425605671

    -- Multilinestring and polygon both 3d and 2d distance
    -- Same example as 3D closest point example
    SELECT ST_3DDistance(poly, mline) As dist3d,
        ST_Distance(poly, mline) As dist2d
            FROM (SELECT  'POLYGON((175 150 5, 20 40 5, 35 45 5, 50 60 5, 100 100 5, 175 150 5))'::geometry as poly,
                   'MULTILINESTRING((175 155 2, 20 40 20, 50 60 -2, 125 100 1, 175 155 1), (1 10 2, 5 20 1))'::geometry as mline) as foo;
          dist3d       | dist2d
    -------------------+--------
     0.716635696066337 |      0

### See Also

ST_Distance, ST_3DClosestPoint, ST_3DDWithin, ST_3DMaxDistance, ST_3DShortestLine, ST_Transform

ST_DistanceSphere

Returns minimum distance in meters between two lon/lat geometries using a spherical earth model.

    			float ST_DistanceSphere
    			geometry  geomlonlatA
    			geometry  geomlonlatB

### Description

Returns minimum distance in meters between two lon/lat points. Uses a spherical earth and radius derived from the spheroid defined by the SRID. Faster than ST_Distance_Spheroid, but less accurate. PostGIS Versions prior to 1.5 only implemented for points.

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

Changed: 2.2.0 In prior versions this used to be called ST_Distance_Sphere

### Examples

    SELECT round(CAST(ST_DistanceSphere(ST_Centroid(geom), ST_GeomFromText('POINT(-118 38)',4326)) As numeric),2) As dist_meters,
    round(CAST(ST_Distance(ST_Transform(ST_Centroid(geom),32611),
    		ST_Transform(ST_GeomFromText('POINT(-118 38)', 4326),32611)) As numeric),2) As dist_utm11_meters,
    round(CAST(ST_Distance(ST_Centroid(geom), ST_GeomFromText('POINT(-118 38)', 4326)) As numeric),5) As dist_degrees,
    round(CAST(ST_Distance(ST_Transform(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 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, ST_Distance_Spheroid

ST_DistanceSpheroid

Returns the minimum distance between two lon/lat geometries using a spheroidal earth model.

    			float ST_DistanceSpheroid
    			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 ST_Length_Spheroid.

This function does not look at the SRID of the geometry. It assumes the geometry coordinates are based on the provided spheroid.

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

Changed: 2.2.0 In prior versions this was called ST_Distance_Spheroid

### Examples

    SELECT round(CAST(
    		ST_DistanceSpheroid(ST_Centroid(geom), ST_GeomFromText('POINT(-118 38)',4326), 'SPHEROID["WGS 84",6378137,298.257223563]')
    			As numeric),2) As dist_meters_spheroid,
    		round(CAST(ST_DistanceSphere(ST_Centroid(geom), ST_GeomFromText('POINT(-118 38)',4326)) As numeric),2) As dist_meters_sphere,
    round(CAST(ST_Distance(ST_Transform(ST_Centroid(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 geom) as foo;
     dist_meters_spheroid | dist_meters_sphere | dist_utm11_meters
    ----------------------+--------------------+-------------------
    			 70454.92 |           70424.47 |          70438.00

### See Also

ST_Distance, ST_DistanceSphere

ST_FrechetDistance

Returns the Fréchet distance between two geometries.

    			float ST_FrechetDistance

    			geometry
    			g1

    			geometry
    			g2

    			float
    			densifyFrac = -1

### Description

Implements algorithm for computing the Fréchet distance restricted to discrete points for both geometries, based on Computing Discrete Fréchet Distance. The Fréchet distance is a measure of similarity between curves that takes into account the location and ordering of the points along the curves. Therefore it is often better than the Hausdorff distance.

When the optional densifyFrac is specified, this function performs a segment densification before computing the discrete Fréchet 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.

Units are in the units of the spatial reference system of the geometries.

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

The smaller densifyFrac we specify, the more acurate Fréchet distance we get. But, the computation time and the memory usage increase with the square of the number of subsegments.

Performed by the GEOS module.

Availability: 2.4.0 - requires GEOS >= 3.7.0

### Examples

    postgres=# SELECT st_frechetdistance('LINESTRING (0 0, 100 0)'::geometry, 'LINESTRING (0 0, 50 50, 100 0)'::geometry);
     st_frechetdistance
    --------------------
       70.7106781186548
    (1 row)

    SELECT st_frechetdistance('LINESTRING (0 0, 100 0)'::geometry, 'LINESTRING (0 0, 50 50, 100 0)'::geometry, 0.5);
     st_frechetdistance
    --------------------
                     50
    (1 row)

### See Also

ST_HausdorffDistance

ST_HausdorffDistance

Returns the Hausdorff distance between two geometries.

    			float ST_HausdorffDistance

    			geometry
    			g1

    			geometry
    			g2

    			float ST_HausdorffDistance

    			geometry
    			g1

    			geometry
    			g2

    			float
    			densifyFrac

### Description

Returns the Hausdorff distance between two geometries, a measure of how similar or dissimilar 2 geometries are.

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.

Units are in the units of the spatial reference system of the geometries.

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

### Examples

For each building, find the parcel that best represents it. First we require the parcel intersect with the geometry. DISTINCT ON guarantees we get each building listed only once, the ORDER BY .. ST_HausdorffDistance gives us a preference of parcel that is most similar to the building.

    SELECT DISTINCT ON(buildings.gid) buildings.gid, parcels.parcel_id
       FROM buildings INNER JOIN parcels ON ST_Intersects(buildings.geom,parcels.geom)
         ORDER BY buildings.gid, ST_HausdorffDistance(buildings.geom, parcels.geom);

    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)

### See Also

ST_FrechetDistance

ST_Length

Returns the 2D length of a linear geometry.

    			  float ST_Length
    				geometry a_2dlinestring

    			  float ST_Length
    				geography geog
    				boolean use_spheroid=true

### Description

For geometry types: returns the 2D Cartesian length of the geometry if it is a LineString, MultiLineString, ST_Curve, ST_MultiCurve. For areal geometries 0 is returned; use ST_Perimeter instead. The units of length is determined by the spatial reference system of the geometry.

For geography types: computation is performed using the inverse geodesic calculation. Units of length are in meters. If PostGIS is compiled with PROJ version 4.8.0 or later, the spheroid is specified by the SRID, otherwise it is exclusive to WGS84. If `use_spheroid=false`, then the calculation is based on a sphere instead of a spheroid.

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

Changed: 2.0.0 Breaking change -- in prior versions applying this to a MULTI/POLYGON of type geography would give you the perimeter of the POLYGON/MULTIPOLYGON. In 2.0.0 this was changed to return 0 to be in line with geometry behavior. Please use ST_Perimeter if you want the perimeter of a polygon

For geography the calculation defaults to using a spheroidal model. To use the faster but less accurate spherical calculation 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.

&sfcgal_enhanced;

### Geometry Examples

Return length in feet for line string. Note this is in feet because EPSG:2249 is Massachusetts 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

    -- the default calculation uses a 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
    ------------------+------------------
     34310.5703627288 | 34346.2060960742

### See Also

ST_GeographyFromText, ST_GeomFromEWKT, ST_Length_Spheroid, ST_Perimeter, ST_Transform

ST_Length2D

Returns the 2D length of a linear geometry. Alias for `ST_Length`

    			float ST_Length2D
    			geometry  a_2dlinestring

### Description

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

### See Also

ST_Length, ST_3DLength

ST_3DLength

Returns the 3D length of a linear geometry.

    			float ST_3DLength
    			geometry  a_3dlinestring

### Description

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

&Z_support;

Changed: 2.0.0 In prior versions this used to be called ST_Length3D

### Examples

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

    SELECT ST_3DLength(ST_GeomFromText('LINESTRING(743238 2967416 1,743238 2967450 1,743265 2967450 3,
    743265.625 2967416 3,743238 2967416 3)',2249));
    ST_3DLength
    -----------
    122.704716741457

### See Also

ST_Length, ST_Length2D

ST_LengthSpheroid

Returns the 2D or 3D length/perimeter of a lon/lat geometry on a spheroid.

    			float ST_LengthSpheroid
    			geometry  a_geometry
    			spheroid  a_spheroid

### Description

Calculates the length or perimeter 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 spheroid is specified by a text value as follows:

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

For example:

    SPHEROID["GRS_1980",6378137,298.257222101]

Availability: 1.2.2

Changed: 2.2.0 In prior versions this was called ST_Length_Spheroid and had the alias ST_3DLength_Spheroid

&Z_support;

### Examples

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

    SELECT ST_LengthSpheroid( geom, sph_m ) As tot_len,
    ST_LengthSpheroid(ST_GeometryN(geom,1), sph_m) As len_line1,
    ST_LengthSpheroid(ST_GeometryN(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 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_LengthSpheroid( geom, sph_m ) As tot_len,
    ST_LengthSpheroid(ST_GeometryN(geom,1), sph_m) As len_line1,
    ST_LengthSpheroid(ST_GeometryN(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 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_GeometryN, ST_Length

ST_LongestLine

Returns the 2D longest line between two geometries.

    			geometry ST_LongestLine

    			geometry
    			g1

    			geometry
    			g2

### Description

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

The function returns the first longest line if more than one is found. The line returned starts on g1 and ends on g2. The length of the line is equal to the distance returned by ST_MaxDistance.

Availability: 1.5.0

### Examples

Longest line between a point and a 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 two polygons
    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 a city to another. Note that the maximum distance is equal to the length of the line.
    SELECT ST_AsText( ST_LongestLine(c.geom, c.geom)) AS llinewkt,
           ST_MaxDistance( c.geom,c.geom) AS max_dist,
           ST_Length( ST_LongestLine(c.geom, c.geom)) AS lenll
    FROM (SELECT ST_MakeValid( ST_Collect(geom)) AS 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 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_MaxDistance, ST_MakeValid, ST_ShortestLine, ST_3DLongestLine

ST_3DLongestLine

Returns the 3D longest line between two geometries

    			geometry ST_3DLongestLine

    			geometry
    			g1

    			geometry
    			g2

### Description

Returns the 3-dimensional longest line between two geometries. The function returns the first longest line if more than one. The line returned starts in g1 and ends in g2. The 3D length of the line is equal to the distance returned by ST_3DMaxDistance.

Availability: 2.0.0

Changed: 2.2.0 - if 2 2D geometries are input, a 2D point is returned (instead of old behavior assuming 0 for missing Z). In case of 2D and 3D, Z is no longer assumed to be 0 for missing Z.

&Z_support;

&P_support;

### Examples

linestring and point -- both 3d and 2d longest line
    SELECT ST_AsEWKT(ST_3DLongestLine(line,pt)) AS lol3d_line_pt,
    		ST_AsEWKT(ST_LongestLine(line,pt)) As lol2d_line_pt
    	FROM (SELECT 'POINT(100 100 30)'::geometry As pt,
    			'LINESTRING (20 80 20, 98 190 1, 110 180 3, 50 75 1000)'::geometry As line
    		) As foo;

               lol3d_line_pt           |       lol2d_line_pt
    -----------------------------------+----------------------------
     LINESTRING(50 75 1000,100 100 30) | LINESTRING(98 190,100 100)
linestring and multipoint -- both 3d and 2d longest line
    SELECT ST_AsEWKT(ST_3DLongestLine(line,pt)) AS lol3d_line_pt,
    		ST_AsEWKT(ST_LongestLine(line,pt)) As lol2d_line_pt
    	FROM (SELECT 'MULTIPOINT(100 100 30, 50 74 1000)'::geometry As pt,
    			'LINESTRING (20 80 20, 98 190 1, 110 180 3, 50 75 900)'::geometry As line
    		) As foo;

              lol3d_line_pt          |      lol2d_line_pt
    ---------------------------------+--------------------------
     LINESTRING(98 190 1,50 74 1000) | LINESTRING(98 190,50 74)
MultiLineString and Polygon both 3d and 2d longest line
    SELECT ST_AsEWKT(ST_3DLongestLine(poly, mline)) As lol3d,
        ST_AsEWKT(ST_LongestLine(poly, mline)) As lol2d
            FROM (SELECT  ST_GeomFromEWKT('POLYGON((175 150 5, 20 40 5, 35 45 5, 50 60 5, 100 100 5, 175 150 5))') As poly,
                    ST_GeomFromEWKT('MULTILINESTRING((175 155 2, 20 40 20, 50 60 -2, 125 100 1, 175 155 1),
                    (1 10 2, 5 20 1))') As mline ) As foo;
                lol3d             |          lol2d
    ------------------------------+--------------------------
     LINESTRING(175 150 5,1 10 2) | LINESTRING(175 150,1 10)

### See Also

ST_3DClosestPoint, ST_3DDistance, ST_LongestLine, ST_3DShortestLine, ST_3DMaxDistance

ST_MaxDistance

Returns the 2D largest distance between two geometries in projected units.

            float ST_MaxDistance
            geometry  g1
            geometry  g2

### Description

Returns the 2-dimensional maximum distance between two geometries, in projected units. The maximum distance always occurs between two vertices. This is the length of the line returned by ST_LongestLine.

If g1 and g2 are the same geometry, returns the distance between the two vertices farthest apart in that geometry.

Availability: 1.5.0

### Examples

Maximum distance between a point and lines.

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

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

Maximum distance between vertices of a geometry.

    SELECT ST_MaxDistance('POLYGON ((10 10, 10 0, 0 0, 10 10))'::geometry,
                          'POLYGON ((10 10, 10 0, 0 0, 10 10))'::geometry);
      st_maxdistance
    ------------------
     14.142135623730951

### See Also

ST_Distance, ST_LongestLine, ST_DFullyWithin

ST_3DMaxDistance

Returns the 3D cartesian maximum distance (based on spatial ref) between two geometries in projected units.

    			float ST_3DMaxDistance

    			geometry
    			g1

    			geometry
    			g2

### Description

Returns the 3-dimensional maximum cartesian distance between two geometries in projected units (spatial ref units).

&Z_support;

&P_support;

Availability: 2.0.0

Changed: 2.2.0 - In case of 2D and 3D, Z is no longer assumed to be 0 for missing Z.

### Examples

    -- Geometry example - units in meters (SRID: 2163 US National Atlas Equal area) (3D point and line compared 2D point and line)
    -- Note: currently no vertical datum support so Z is not transformed and assumed to be same units as final.
    SELECT ST_3DMaxDistance(
    			ST_Transform(ST_GeomFromEWKT('SRID=4326;POINT(-72.1235 42.3521 10000)'),2163),
    			ST_Transform(ST_GeomFromEWKT('SRID=4326;LINESTRING(-72.1260 42.45 15, -72.123 42.1546 20)'),2163)
    		) As dist_3d,
    		ST_MaxDistance(
    			ST_Transform(ST_GeomFromEWKT('SRID=4326;POINT(-72.1235 42.3521 10000)'),2163),
    			ST_Transform(ST_GeomFromEWKT('SRID=4326;LINESTRING(-72.1260 42.45 15, -72.123 42.1546 20)'),2163)
    		) As dist_2d;

         dist_3d      |     dist_2d
    ------------------+------------------
     24383.7467488441 | 22247.8472107251

### See Also

ST_Distance, ST_3DDWithin, ST_3DMaxDistance, ST_Transform

ST_MinimumClearance

Returns the minimum clearance of a geometry, a measure of a geometry's robustness.

    					float ST_MinimumClearance
    					geometry g

### Description

It is possible for a geometry to meet the criteria for validity according to ST_IsValid (polygons) or ST_IsSimple (lines), but to become invalid if one of its vertices is moved by a small distance. This can happen due to loss of precision during conversion to text formats (such as WKT, KML, GML, GeoJSON), or binary formats that do not use double-precision floating point coordinates (e.g. MapInfo TAB).

The minimum clearance is a quantitative measure of a geometry's robustness to change in coordinate precision. It is the largest distance by which vertices of the geometry can be moved without creating an invalid geometry. Larger values of minimum clearance indicate greater robustness.

If a geometry has a minimum clearance of `e`, then:

- No two distinct vertices in the geometry are closer than the distance `e`.

- No vertex is closer than `e` to a line segement of which it is not an endpoint.

If no minimum clearance exists for a geometry (e.g. a single point, or a MultiPoint whose points are identical), the return value is `Infinity`.

To avoid validity issues caused by precision loss, ST_ReducePrecision can reduce coordinate precision while ensuring that polygonal geometry remains valid.

Availability: 2.3.0

### Examples

    SELECT ST_MinimumClearance('POLYGON ((0 0, 1 0, 1 1, 0.5 3.2e-4, 0 0))');
     st_minimumclearance
    ---------------------
                 0.00032

### See Also

ST_MinimumClearanceLine, ST_IsSimple, ST_IsValid, ST_ReducePrecision

ST_MinimumClearanceLine

Returns the two-point LineString spanning a geometry's minimum clearance.

    			Geometry ST_MinimumClearanceLine

    			geometry
    			g

### Description

Returns the two-point LineString spanning a geometry's minimum clearance. If the geometry does not have a minimum clearance, `LINESTRING EMPTY` will be returned.

Performed by the GEOS module.

Availability: 2.3.0 - requires GEOS >= 3.6.0

### Examples

    SELECT ST_AsText(ST_MinimumClearanceLine('POLYGON ((0 0, 1 0, 1 1, 0.5 3.2e-4, 0 0))'));
    st_astext
    -------------------------------
    LINESTRING(0.5 0.00032,0.5 0)

### See Also

ST_MinimumClearance

ST_Perimeter

Returns the length of the boundary of a polygonal geometry or geography.

    			  float ST_Perimeter
    				geometry g1

    			  float ST_Perimeter
    				geography geog
    				boolean use_spheroid=true

### Description

Returns the 2D perimeter of the geometry/geography if it is a ST_Surface, ST_MultiSurface (Polygon, MultiPolygon). 0 is returned for non-areal geometries. For linear geometries use ST_Length. For geometry types, units for perimeter measures are specified by the spatial reference system of the geometry.

For geography types, the calculations are performed using the inverse geodesic problem, where perimeter units are in meters. If PostGIS is compiled with PROJ version 4.8.0 or later, the spheroid is specified by the SRID, otherwise it is exclusive to WGS84. If `use_spheroid=false`, then calculations will approximate a sphere instead of a spheroid.

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

Availability 2.0.0: Support for geography was introduced

### Examples: Geometry

Return perimeter in feet for Polygon and MultiPolygon. Note this is in feet because EPSG:2249 is Massachusetts 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)

### Examples: Geography

Return perimeter in meters and feet for Polygon and MultiPolygon. Note this is geography (WGS 84 long lat)

    SELECT  ST_Perimeter(geog) As per_meters, ST_Perimeter(geog)/0.3048 As per_ft
    FROM ST_GeogFromText('POLYGON((-71.1776848522251 42.3902896512902,-71.1776843766326 42.3903829478009,
    -71.1775844305465 42.3903826677917,-71.1775825927231 42.3902893647987,-71.1776848522251 42.3902896512902))') As geog;

       per_meters    |      per_ft
    -----------------+------------------
    37.3790462565251 | 122.634666195949

    -- MultiPolygon example --
    SELECT  ST_Perimeter(geog) As per_meters, ST_Perimeter(geog,false) As per_sphere_meters,  ST_Perimeter(geog)/0.3048 As per_ft
    FROM ST_GeogFromText('MULTIPOLYGON(((-71.1044543107478 42.340674480411,-71.1044542869917 42.3406744369506,
    -71.1044553562977 42.340673886454,-71.1044543107478 42.340674480411)),
    ((-71.1044543107478 42.340674480411,-71.1044860600303 42.3407237015564,-71.1045215770124 42.3407653385914,
    -71.1045498002983 42.3407946553165,-71.1045611902745 42.3408058316308,-71.1046016507427 42.340837442371,
    -71.104617893173 42.3408475056957,-71.1048586153981 42.3409875993595,-71.1048736143677 42.3409959528211,
    -71.1048878050242 42.3410084812078,-71.1044020965803 42.3414730072048,
    -71.1039672113619 42.3412202916693,-71.1037740497748 42.3410666421308,
    -71.1044280218456 42.3406894151355,-71.1044543107478 42.340674480411)))') As geog;

        per_meters    | per_sphere_meters |      per_ft
    ------------------+-------------------+------------------
     257.634283683311 |  257.412311446337 | 845.256836231335

### See Also

ST_GeogFromText, ST_GeomFromText, ST_Length

ST_Perimeter2D

Returns the 2D perimeter of a polygonal geometry. Alias for `ST_Perimeter`.

    			float ST_Perimeter2D
    			geometry  geomA

### Description

Returns the 2-dimensional perimeter of a polygonal geometry.

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_Perimeter

ST_3DPerimeter

Returns the 3D perimeter of a polygonal geometry.

    			float ST_3DPerimeter
    			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;

Changed: 2.0.0 In prior versions this used to be called ST_Perimeter3D

### Examples

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

    SELECT ST_3DPerimeter(geom), ST_Perimeter2d(geom), ST_Perimeter(geom) FROM
    			(SELECT ST_GeomFromEWKT('SRID=2249;POLYGON((743238 2967416 2,743238 2967450 1,
    743265.625 2967416 1,743238 2967416 2))') As geom) As foo;

      ST_3DPerimeter  |  st_perimeter2d  |   st_perimeter
    ------------------+------------------+------------------
     105.465793597674 | 105.432997272188 | 105.432997272188

### See Also

ST_GeomFromEWKT, ST_Perimeter, ST_Perimeter2D

ST_Project

Returns a point projected from a start point by a distance and bearing (azimuth).

    				geography ST_Project

    				geography
    				g1
    				float
    				distance
    				float
    				azimuth

### Description

Returns a point projected from a start point along a geodesic using a given distance and azimuth (bearing). This is known as the direct geodesic problem.

The distance is given in meters. Negative values are supported.

The azimuth (also known as heading or bearing) is given in radians. It is measured clockwise from true north (azimuth zero). East is azimuth π/2 (90 degrees); south is azimuth π (180 degrees); west is azimuth 3π/2 (270 degrees). Negative azimuth values and values greater than 2π (360 degrees) are supported.

Availability: 2.0.0

Enhanced: 2.4.0 Allow negative distance and non-normalized azimuth.

### Example: Projected point at 100,000 meters and bearing 45 degrees

    SELECT ST_AsText(ST_Project('POINT(0 0)'::geography, 100000, radians(45.0)));

                     st_astext
    --------------------------------------------
     POINT(0.635231029125537 0.639472334729198)
    (1 row)

### See Also

ST_Azimuth, ST_Distance, PostgreSQL function radians()

ST_ShortestLine

Returns the 2D 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_ClosestPoint, ST_Distance, ST_LongestLine, ST_MaxDistance

ST_3DShortestLine

Returns the 3D shortest line between two geometries

    			geometry ST_3DShortestLine

    			geometry
    			g1

    			geometry
    			g2

### Description

Returns the 3-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 3D length of the line this function returns will always be the same as ST_3DDistance returns for g1 and g2.

Availability: 2.0.0

Changed: 2.2.0 - if 2 2D geometries are input, a 2D point is returned (instead of old behavior assuming 0 for missing Z). In case of 2D and 3D, Z is no longer assumed to be 0 for missing Z.

&Z_support;

&P_support;

### Examples

linestring and point -- both 3d and 2d shortest line
    SELECT ST_AsEWKT(ST_3DShortestLine(line,pt)) AS shl3d_line_pt,
    		ST_AsEWKT(ST_ShortestLine(line,pt)) As shl2d_line_pt
    	FROM (SELECT 'POINT(100 100 30)'::geometry As pt,
    			'LINESTRING (20 80 20, 98 190 1, 110 180 3, 50 75 1000)'::geometry As line
    		) As foo;

     shl3d_line_pt						                 |               shl2d_line_pt
    ----------------------------------------------------------------------------+------------------------------------------------------
     LINESTRING(54.6993798867619 128.935022917228 11.5475869506606,100 100 30)  | LINESTRING(73.0769230769231 115.384615384615,100 100)
linestring and multipoint -- both 3d and 2d shortest line
    SELECT ST_AsEWKT(ST_3DShortestLine(line,pt)) AS shl3d_line_pt,
    		ST_AsEWKT(ST_ShortestLine(line,pt)) As shl2d_line_pt
    	FROM (SELECT 'MULTIPOINT(100 100 30, 50 74 1000)'::geometry As pt,
    			'LINESTRING (20 80 20, 98 190 1, 110 180 3, 50 75 900)'::geometry As line
    		) As foo;

                           shl3d_line_pt                                       | shl2d_line_pt
    ---------------------------------------------------------------------------+------------------------
     LINESTRING(54.6993798867619 128.935022917228 11.5475869506606,100 100 30) | LINESTRING(50 75,50 74)
MultiLineString and polygon both 3d and 2d shortest line
    SELECT ST_AsEWKT(ST_3DShortestLine(poly, mline)) As shl3d,
        ST_AsEWKT(ST_ShortestLine(poly, mline)) As shl2d
            FROM (SELECT  ST_GeomFromEWKT('POLYGON((175 150 5, 20 40 5, 35 45 5, 50 60 5, 100 100 5, 175 150 5))') As poly,
                    ST_GeomFromEWKT('MULTILINESTRING((175 155 2, 20 40 20, 50 60 -2, 125 100 1, 175 155 1),
                    (1 10 2, 5 20 1))') As mline ) As foo;
                       shl3d                                                                           |     shl2d
    ---------------------------------------------------------------------------------------------------+------------------------
     LINESTRING(39.993580415989 54.1889925532825 5,40.4078575708294 53.6052383805529 5.03423778139177) | LINESTRING(20 40,20 40)

### See Also

ST_3DClosestPoint, ST_3DDistance, ST_LongestLine, ST_ShortestLine, ST_3DMaxDistance