PostGIS  2.5.0dev-r@@SVN_REVISION@@
PG_FUNCTION_INFO_V1 ( LWGEOM_length2d_linestring  )

find the "length of a geometry" length2d(point) = 0 length2d(line) = length of line length2d(polygon) = 0 – could make sense to return sum(ring perimeter) uses euclidian 2d length (even if input is 3d)