ST_Length — Returns the 2d length of the geometry if it is a linestring or multilinestring. geometry are in units of spatial reference and geography are in meters (default spheroid)
float ST_Length(geometry a_2dlinestring
float ST_Length(geography gg
float ST_Length(geography gg, boolean use_spheroid
For geometry: Returns the cartesian 2D length of the geometry if it is a linestring, multilinestring, ST_Curve, ST_MultiCurve. 0 is returned for areal geometries. For areal geometries use ST_Perimeter. Geometry: Measurements are in the units of the spatial reference system of the geometry. Geography: Units are in meters and also acts as a Perimeter function for areal geogs.
Currently for geometry this is an alias for ST_Length2D, but this may change to support higher dimensions.
Currently applying this to a MULTI/POLYGON of type geography will give you the perimeter of the POLYGON/MULTIPOLYGON. This is not the case with the geometry implementation.
For geography measurement defaults spheroid measurement. To use the faster less accurate sphere use ST_Length(gg,false);
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. s22.214.171.124
This method implements the SQL/MM specification. SQL-MM 3: 7.1.2, 9.3.4
Availability: 1.5.0 geography support was introduced in 1.5.
Return length in feet for line string. Note this is in feet because 2249 is Mass State Plane Feet
SELECT ST_Length(ST_GeomFromText('LINESTRING(743238 2967416,743238 2967450,743265 2967450, 743265.625 2967416,743238 2967416)',2249)); st_length --------- 122.630744000095 --Transforming WGS 84 linestring to Massachusetts state plane meters SELECT ST_Length( ST_Transform( ST_GeomFromEWKT('SRID=4326;LINESTRING(-72.1260 42.45, -72.1240 42.45666, -72.123 42.1546)'), 26986 ) ); st_length --------- 34309.4563576191
Return length of WGS 84 geography line
-- default calculation is using a sphere rather than spheroid SELECT ST_Length(the_geog) As length_spheroid, ST_Length(the_geog,false) As length_sphere FROM (SELECT ST_GeographyFromText( 'SRID=4326;LINESTRING(-72.1260 42.45, -72.1240 42.45666, -72.123 42.1546)') As the_geog) As foo; length_spheroid | length_sphere ------------------+------------------ 34310.5703627305 | 34346.2060960742 (1 row)