ST_Simplify

ST_Simplify returns a simplified copy of the input geometry using the Ramer-Douglas-Peucker algorithm with the given tolerance. The topology of the input geometry might not be preserved. For more information about the algorithm, see Ramer–Douglas–Peucker algorithm in Wikipedia.

When ST_Simplify calculates distances to simplify a geometry, ST_Simplify operates on the 2D projection of the input geometry.

Syntax

ST_Simplify(geom, tolerance)

Arguments

geom

A value of data type GEOMETRY or an expression that evaluates to a GEOMETRY type.

tolerance

A value of data type DOUBLE PRECISION that represents the tolerance level of the Ramer-Douglas-Peucker algorithm. If tolerance is a negative number, then zero is used.

Return type

GEOMETRY.

The spatial reference system identifier (SRID) value of the returned geometry is the SRID value of the input geometry.

The dimension of the returned geometry is the same as that of the input geometry.

If geom is null, then null is returned.

Examples

The following SQL simplifies the input linestring using a Euclidean distance tolerance of 1 with the Ramer-Douglas-Peucker algorithm. The units of the distance are the same as those of the coordinates of the geometry.

SELECT ST_AsEWKT(ST_Simplify(ST_GeomFromText('LINESTRING(0 0,1 2,1 1,2 2,2 1)'), 1));

 st_asewkt
-----------
LINESTRING(0 0,1 2,2 1)