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This function computes a topology-preserving simplified hull, either outer or inner, for a polygonal geometry input. An outer hull fully encloses the original geometry, while an inner hull lies entirely within. The result maintains the same structure as the input, including handling of MultiPolygons and holes, represented as a polygonal geometry formed from a subset of vertices. ST_SimplifyPolygonHull Vertex reduction is governed by the vertexFactor parameter ranging from 0 to 1, with lower values yielding simpler outputs with fewer vertices and reduced concavity. For both hull types, a vertexFactor of 1.0 returns the original geometry. Specifically, for outer hulls, 0.0 computes the convex hull; for inner hulls, 0.0 produces a triangular geometry. The simplification algorithm iteratively removes concave corners containing the least area until reaching the target vertex count. It preserves topology by preventing edge crossings, ensuring the output is a valid polygonal geometry in all cases.

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Signatures

ST_SimplifyPolygonHull(geom: Geometry, vertexFactor: Double, isOuter: Boolean = true)

ST_SimplifyPolygonHull(geom: Geometry, vertexFactor: Double)

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Parameters

​
geom
Geometry
required
The input geometry.
​
vertexFactor
Double
required
The vertex factor value.
​
isOuter
Boolean
default:"true"
The is outer value.

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Return type

The resulting geometry.

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Examples

SELECT ST_SimplifyPolygonHull(
        ST_GeomFromText('POLYGON ((30 10, 40 40, 45 45, 50 30, 55 25, 60 50, 65 45, 70 30, 75 20, 80 25, 70 10, 30 10))'),
       0.4
)

POLYGON ((30 10, 40 40, 45 45, 60 50, 65 45, 80 25, 70 10, 30 10))

SELECT ST_SimplifyPolygonHull(
        ST_GeomFromText('POLYGON ((30 10, 40 40, 45 45, 50 30, 55 25, 60 50, 65 45, 70 30, 75 20, 80 25, 70 10, 30 10))'),
       0.4, false
)

POLYGON ((30 10, 70 10, 60 50, 55 25, 30 10))