ST_Simplify — Returns a "simplified" geometry version of the given TopoGeometry using the Douglas-Peucker algorithm.
geometry ST_Simplify(TopoGeometry tg, float8 tolerance);
Returns a "simplified" geometry version of the given TopoGeometry using the Douglas-Peucker algorithm on each component edge.
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The returned geometry may be non-simple or non-valid. Splitting component edges may help retaining simplicity/validity.  | 
Performed by the GEOS module.
Availability: 2.1.0