ST_3DPerimeter — Returns the 3D perimeter of a polygonal geometry.
float ST_3DPerimeter(geometry  geomA);
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.
            
 Questa funzione supporta il 3d e non distrugge gli z-index. 
            
 Questo metodo implementa la specifica SQL/MM.  SQL-MM ISO/IEC 13249-3: 8.1, 10.5
Changed: 2.0.0 In prior versions this used to be called ST_Perimeter3D
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