Description

Computes a point which is the geometric center of mass of a geometry. For [MULTI]POINTs, the centroid is the arithmetic mean of the input coordinates. For [MULTI]LINESTRINGs, the centroid is computed using the weighted length of each line segment. For [MULTI]POLYGONs, the centroid is computed in terms of area. If an empty geometry is supplied, an empty GEOMETRYCOLLECTION is returned. If NULL is supplied, NULL is returned. If CIRCULARSTRING or COMPOUNDCURVE are supplied, they are converted to linestring with CurveToLine first, then same than for LINESTRING

For mixed-dimension input, the result is equal to the centroid of the component Geometries of highest dimension (since the lower-dimension geometries contribute zero "weight" to the centroid).

Note that for polygonal geometries the centroid does not necessarily lie in the interior of the polygon. For example, see the diagram below of the centroid of a C-shaped polygon. To construct a point guaranteed to lie in the interior of a polygon use ST_PointOnSurface.

New in 2.3.0 : supports CIRCULARSTRING and COMPOUNDCURVE (using CurveToLine)

Availability: 2.4.0 support for geography was introduced.

This method implements the OGC Simple Features Implementation Specification for SQL 1.1.

This method implements the SQL/MM specification. SQL-MM 3: 8.1.4, 9.5.5

Examples

Centroid of a MultiPoint.

SELECT ST_Centroid(
  'MULTIPOINT (8 24,10 92,12 154,17 68,28 10,29 52,29 84,55 50,56 24,131 14,160 180,189 180)');

POINT(60.333 77.667)

0101000000ABAAAAAAAA2A4E40ABAAAAAAAA6A5340

Figure

Centroid of a LineString.

SELECT ST_Centroid(
  'LINESTRING (190 160,10 190,40 90,20 70,10 10,30 40,30 10,110 40,70 10,110 10,140 40,140 10,160 30,180 10)');

POINT(76.191 79.876)

0101000000DF2DB9D4340C5340FD2ADAB809F85340

Figure

Centroid of a Polygon.

SELECT ST_Centroid(
  'POLYGON ((190 190,10 190,10 10,190 10,190 20,160 30,60 30,60 130,190 140,190 190))');

POINT(80.251 113.405)

01010000003B4056AE0E105440B06749D0EB595C40

Figure

Centroid of the highest-dimension components of a GeometryCollection.

SELECT ST_Centroid(
  'GEOMETRYCOLLECTION (POLYGON ((190 170,180 100,80 140,80 160,130 160,110 180,110 190,180 180,190 170)),
    LINESTRING (80 120,120 20,140 70,150 30,180 50,190 10),
    MULTIPOINT (19 150,22 49,30 13,32 101,45 35,67 88,75 16))');

POINT(143.361 148.263)

010100000022906B2290EB6140FF6C48FF6C886240

Figure

SELECT ST_Centroid(g)
FROM  ST_GeomFromText('CIRCULARSTRING(0 2,-1 1,0 0,0.5 0,1 0,2 1,1 2,0.5 2,0 2)')  AS g ;

  st_astext
-------------
 POINT(0.5 1)
(1 row)

0101000000FCFFFFFFFFFFDF3F000000000000F03F

Figure

SELECT ST_Centroid(g)
FROM  ST_GeomFromText('COMPOUNDCURVE(CIRCULARSTRING(0 2,-1 1,0 0),(0 0,0.5 0,1 0), CIRCULARSTRING( 1 0,2 1,1 2),(1 2,0.5 2,0 2))' ) AS g;

  st_astext
-------------
 POINT(0.5 1)
(1 row)

0101000000FCFFFFFFFFFFDF3F000000000000F03F

Figure

Centroids of the parts of a MultiPolygon.

SELECT ST_Collect(ST_Centroid(geom) ORDER BY path)
FROM ST_Dump('MULTIPOLYGON (
    ((0 0,0 1,1 1,1 0,0 0)),
    ((2 2,2 3,3 3,3 2,2 2))
  )'::geometry);

MULTIPOINT((0.5 0.5),(2.5 2.5))

0104000000020000000101000000000000000000E03F000000000000E03F010100000000000000000004400000000000000440

Figure

See Also

ST_Collect, ST_Dump, ST_PointOnSurface, ST_GeometricMedian