This topic describes the ST_GeometricMedian function. This function returns the geometric median of a geometry object.

Syntax

geometry  ST_GeometricMedian (geometry  g , float8  tolerance , int  maxIter , boolean  failIfNotConverged);

Parameters

Parameter Description
g The geometry object that you want to specify.
tolerance The tolerance that you want to specify.
maxIter The maximum number of iterations.
failIfNotConverged Specifies whether to report an error if this function cannot find the geometric median of the geometry object after the maximum number of iterations is reached.

Description

  • This function performs iterations until the distance change between successive iterations is less than the value of the tolerance parameter. If the distance change between successive iterations remains greater than or equal to the value of the tolerance parameter after the maximum number of iterations is reached, this function returns an error and exits unless you set the failIfNotConverged parameter to False.
  • If you do not specify the tolerance parameter, this function calculates the default tolerance based on the extent of the geometry object that you specify.
  • If the m coordinates of the points of the geometry object that you specify are available, the m coordinates are interpreted as the relative weights of the points.

Examples

The following example shows the difference between the ST_GeometricMedian function and the ST_Centroid function:
SELECT ST_AsText(ST_GeometricMedian(geom)) as GeometricMedian, ST_AsText(ST_Centroid(geom)) as Centroid
    from (SELECT 'MULTIPOINT((0 0), (0 1), (1 1), (2 0))'::geometry as geom) as test;
              geometricmedian               |    centroid
--------------------------------------------+-----------------
 POINT(0.665913838138866 0.666097415551148) | POINT(0.75 0.5)
(1 row)
12