ST_PointN — Return the Nth point in the first linestring or circular linestring in the geometry. Return NULL if there is no linestring in the geometry.
geometry ST_PointN(geometry a_linestring, integer n
Return the Nth point in a single linestring or circular linestring in the geometry. Return NULL if there is no linestring in the geometry.
Index is 1-based as for OGC specs since version 0.8.0. Previous versions implemented this as 0-based instead.
If you want to get the nth point of each line string in a multilinestring, use in conjunction with ST_Dump
This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1.
This method implements the SQL/MM specification. SQL-MM 3: 7.2.5, 7.3.5
This function supports 3d and will not drop the z-index.
This method supports Circular Strings and Curves
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.
-- Extract all POINTs from a LINESTRING SELECT ST_AsText( ST_PointN( column1, generate_series(1, ST_NPoints(column1)) )) FROM ( VALUES ('LINESTRING(0 0, 1 1, 2 2)'::geometry) ) AS foo; st_astext ------------ POINT(0 0) POINT(1 1) POINT(2 2) (3 rows) --Example circular string SELECT ST_AsText(ST_PointN(ST_GeomFromText('CIRCULARSTRING(1 2, 3 2, 1 2)'),2)); st_astext ---------- POINT(3 2)