ST_StartPoint

Description

Returns the first point of a LINESTRING or CIRCULARLINESTRING geometry as a POINT . Returns NULL if the input is not a LINESTRING or CIRCULARLINESTRING .

This method implements the SQL/MM specification.

SQL-MM 3: 7.1.3

This function supports 3d and will not drop the z-index.

This method supports Circular Strings and Curves.

Enhanced: 3.2.0 returns a point for all geometries. Prior behavior returns NULLs if input was not a LineString. Changed: 2.0.0 no longer works with single geometry MultiLineStrings. In older versions of PostGIS a single-line MultiLineString would work happily with this function and return the start point. In 2.0.0 it just returns NULL like any other MultiLineString. The old behavior was an undocumented feature, but people who assumed they had their data stored as LINESTRING may experience these returning NULL in 2.0.0.

Examples

Start point of a LineString

SELECT ST_AsText(ST_StartPoint('LINESTRING(0 1, 0 2)'::geometry));
 st_astext
------------
 POINT(0 1)

Start point of a non-LineString is NULL

SELECT ST_StartPoint('POINT(0 1)'::geometry) IS NULL AS is_null;
  is_null
----------
 t

Start point of a 3D LineString

SELECT ST_AsEWKT(ST_StartPoint('LINESTRING(0 1 1, 0 2 2)'::geometry));
 st_asewkt
------------
 POINT(0 1 1)

Start point of a CircularString

SELECT ST_AsText(ST_StartPoint('CIRCULARSTRING(5 2,-3 1.999999, -2 1, -4 2, 6 3)'::geometry));
 st_astext
------------
 POINT(5 2)

See Also

ST_EndPoint , ST_PointN