ST_Force3D — Force the geometries into XYZ mode. This is an alias for ST_Force3DZ.
geometry ST_Force3D(geometry  geomA, float  Zvalue = 0.0);
Forces the geometries into XYZ mode. This is an alias for ST_Force3DZ. If a geometry has no Z component, then a Zvalue Z coordinate is tacked on.
Miglioramento: nella versione 2.0.0 è stato introdotto il supporto per le superfici poliedriche.
Changed: 2.1.0. Up to 2.0.x this was called ST_Force_3D.
Changed: 3.1.0. Added support for supplying a non-zero Z value.
            
 Questa funzione supporta le Polyhedral Surface. 
            
 Questo metodo supporta le Curve e le Circular String. 
            
 Questa funzione supporta il 3d e non distrugge gli z-index. 
--Nothing happens to an already 3D geometry
                SELECT ST_AsEWKT(ST_Force3D(ST_GeomFromEWKT('CIRCULARSTRING(1 1 2, 2 3 2, 4 5 2, 6 7 2, 5 6 2)')));
                                   st_asewkt
-----------------------------------------------
 CIRCULARSTRING(1 1 2,2 3 2,4 5 2,6 7 2,5 6 2)
SELECT  ST_AsEWKT(ST_Force3D('POLYGON((0 0,0 5,5 0,0 0),(1 1,3 1,1 3,1 1))'));
                                                 st_asewkt
--------------------------------------------------------------
 POLYGON((0 0 0,0 5 0,5 0 0,0 0 0),(1 1 0,3 1 0,1 3 0,1 1 0))