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ST_Simplify

Simplifies a geometry using the Douglas-Peucker algorithm.

Syntax​

ST_Simplify(geometry, tolerance)

Parameters​

ParameterTypeDescription
geometryGeometryInput geometry
toleranceFloat64Distance tolerance for simplification

Returns​

TypeDescription
Binary (WKB)Simplified geometry as WKB with geoarrow.wkb metadata

Examples​

Simplify LineString​

SELECT ST_Simplify(
    ST_GeomFromText('LINESTRING(0 0, 1 0.1, 2 0, 3 0.1, 4 0)'),
    0.2
);
-- Returns: LINESTRING(0 0, 4 0) - removes small variations

Simplify Polygon​

SELECT ST_Simplify(geom, 0.001) as simplified
FROM coastlines;

Compare Original and Simplified​

SELECT
    ST_NumPoints(geom) as original_points,
    ST_NumPoints(ST_Simplify(geom, 0.01)) as simplified_points
FROM roads;

Varying Tolerance​

SELECT id,
       ST_Simplify(geom, small_tolerance) as detail,
       ST_Simplify(geom, large_tolerance) as overview
FROM boundaries;

Notes​

  • Larger tolerance = more simplification
  • May produce invalid geometries (self-intersections)
  • Use ST_SimplifyPreserveTopology if validity is required
  • Points remain unchanged
  • Tolerance is in geometry coordinate units

See Also​