PostGIS
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.
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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
----------
tStart 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)