ST_PointN
Finds the nth point of a spatial object. If you pass a negative number, zero, or a number larger than the total number of points on the linestring, ST_PointN returns NULL.
The vertex order is based on the Well-Known Text (WKT) representation of the spatial object.
Behavior Type
Syntax
ST_PointN( g, n )
Arguments
g |
Spatial object to search, type GEOMETRY or GEOGRAPHY |
n |
Point in the spatial object to be returned. The index is one-based, type INTEGER |
Returns
GEOMETRY or GEOGRAPHY
Supported Data Types
Data Type | GEOMETRY | GEOGRAPHY (Perfect Sphere) | GEOGRAPHY (WGS84) |
Point | Yes | Yes | Yes |
Multipoint | Yes | Yes | Yes |
Linestring | Yes | Yes | Yes |
Multilinestring | Yes | Yes | Yes |
Polygon | Yes | Yes | Yes |
Multipolygon | Yes | Yes | Yes |
GeometryCollection |
No |
No | No |
Examples
The following examples show how to use ST_PointN.
Returns the fifth point:
=> SELECT ST_AsText(ST_PointN(ST_GeomFromText(' POLYGON(( 2 6, 2 9, 6 9, 7 7, 4 6, 2 6))'), 5)); ST_AsText ------------- POINT (4 6) (1 row)
Returns the second point:
=> SELECT ST_AsText(ST_PointN(ST_GeographyFromText(' LINESTRING(23.41 24.93,34.2 32.98,40.7 41.19)'), 2)); ST_AsText -------------------- POINT (34.2 32.98) (1 row)