PostGIS  2.1.10dev-r@@SVN_REVISION@@
PG_FUNCTION_INFO_V1 ( LWGEOM_perimeter_poly  )

find the "perimeter of a geometry" perimeter(point) = 0 perimeter(line) = 0 perimeter(polygon) = sum of ring perimeters uses euclidian 3d/2d computation depending on input dimension.