ST_PointN

Definition

ST_PointN takes an ST_LineString and an integer index and returns a point that is the nth vertex in the ST_LineString's path.

Syntax

Oracle and PostgreSQL

sde.st_pointn (line1 sde.st_linestring, index integer)

SQLite

st_pointn (line1 st_linestring, index int32)

Return type

ST_Point

Example

The pointn_test table is created with the gid column, which uniquely identifies each row, and the ln1 ST_LineString column. The INSERT statements insert two linestring values. The first linestring doesn't have z-coordinates or measures, while the second linestring has both.

The SELECT query uses the ST_PointN and ST_AsText functions to return the well-known text for the second vertex of each linestring.

Oracle

CREATE TABLE pointn_test (
 gid integer,
 ln1 sde.st_geometry
);


INSERT INTO POINTN_TEST VALUES (
 1,
 sde.st_linefromtext ('linestring (10.02 20.01, 23.73 21.92, 30.10 40.23)', 4326)
);

INSERT INTO POINTN_TEST VALUES (
 2,
 sde.st_linefromtext ('linestring zm(10.02 20.01 5.0 7.0, 23.73 21.92 6.5 7.1, 30.10 40.23 6.9 7.2)', 4326)
);

SELECT gid, sde.st_astext (sde.st_pointn (ln1, 2)) The_2ndvertex
 FROM POINTN_TEST;

GID The_2ndvertex

1   POINT (23.73 21.92)
2   POINT ZM (23.73 21.92 6.5 7.1)

PostgreSQL

CREATE TABLE pointn_test (
 gid serial,
 ln1 sde.st_geometry
);


INSERT INTO pointn_test (ln1) VALUES (
 sde.st_linestring ('linestring (10.02 20.01, 23.73 21.92, 30.10 40.23)', 4326)
);

INSERT INTO pointn_test (ln1) VALUES (
 sde.st_linestring ('linestring zm(10.02 20.01 5.0 7.0, 23.73 21.92 6.5 7.1, 30.10 40.23 6.9 7.2)', 4326)
);

SELECT gid, sde.st_astext (sde.st_pointn (ln1, 2)) 
 AS The_2ndvertex
 FROM pointn_test;

gid the_2ndvertex

1   POINT (23.73 21.92)
2   POINT ZM (23.73 21.92 6.5 7.1)

SQLite

CREATE TABLE pointn_test (
 gid integer primary key autoincrement not null
);

SELECT AddGeometryColumn(
 NULL,
 'pointn_test',
 'ln1',
 4326,
 'linestringzm',
 'xyzm',
 'null'
);

INSERT INTO pointn_test (ln1) VALUES (
 st_linestring ('linestring (10.02 20.01, 23.73 21.92, 30.10 40.23)', 4326)
);

INSERT INTO pointn_test (ln1) VALUES (
 st_linestring ('linestring zm(10.02 20.01 5.0 7.0, 23.73 21.92 6.5 7.1, 30.10 40.23 6.9 7.2)', 4326)
);

SELECT gid, st_astext (st_pointn (ln1, 2)) 
 AS "Second Vertex"
 FROM pointn_test;

gid  Second Vertex

1   POINT ( 23.73000000 21.92000000)
2   POINT ZM ( 23.73000000 21.92000000 6.50000000 7.10000000)