ST_PointOnSurface

Introduction: Returns a POINT guaranteed to lie on the surface.

Format: ST_PointOnSurface(A:geometry)

Examples:

SELECT ST_AsText(ST_PointOnSurface(ST_GeomFromText('POINT(0 5)')));
 st_astext
------------
 POINT(0 5)

SELECT ST_AsText(ST_PointOnSurface(ST_GeomFromText('LINESTRING(0 5, 0 10)')));
 st_astext
------------
 POINT(0 5)

SELECT ST_AsText(ST_PointOnSurface(ST_GeomFromText('POLYGON((0 0, 0 5, 5 5, 5 0, 0 0))')));
   st_astext
----------------
 POINT(2.5 2.5)

SELECT ST_AsText(ST_PointOnSurface(ST_GeomFromText('LINESTRING(0 5 1, 0 0 1, 0 10 2)')));
   st_astext
----------------
 POINT Z(0 0 1)