ST_PointN
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## Name

ST_PointN — Returns the Nth point in the first LineString or circular LineString in a geometry.

## Synopsis

`geometry ST_PointN(`geometry a_linestring, integer n`)`;

## Description

Return the Nth point in a single linestring or circular linestring in the geometry. Negative values are counted backwards from the end of the LineString, so that -1 is the last point. Returns NULL if there is no linestring in the geometry.

Index is 1-based as for OGC specs since version 0.8.0. Backward indexing (negative index) is not in OGC Previous versions implemented this as 0-based instead.

If you want to get the Nth point of each LineString in a MultiLineString, use in conjunction with ST_Dump

This method implements the OGC 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. Changed: 2.3.0 : negative indexing available (-1 is last point)

## Examples

    -- 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)
    (1 row)

    SELECT ST_AsText(f)
    FROM ST_GeomFromText('LINESTRING(0 0 0, 1 1 1, 2 2 2)') AS g
      ,ST_PointN(g, -2) AS f; -- 1 based index

        st_astext
    -----------------
     POINT Z (1 1 1)
    (1 row)

## See Also

ST_NPoints

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