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Computes an approximate medial axis of a polygonal geometry. The medial axis is a representation of the “centerline” or “skeleton” of the polygon. This function first computes the straight skeleton and then prunes insignificant branches to produce a cleaner result. The pruning removes small branches that represent minor penetrations into corners. A branch is pruned if its penetration depth is less than 20% of the width of the corner it bisects. This function may have significant performance limitations when processing polygons with a very large number of vertices. For very large polygons (e.g., 10,000+ vertices), applying vertex reduction or simplification is essential to achieve practical computation times.

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Signatures

ST_ApproximateMedialAxis(geom: Geometry)

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Parameters

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geom
Geometry
required
The input geometry.

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Return type

The resulting geometry.

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Examples

SELECT ST_ApproximateMedialAxis(
  ST_GeomFromWKT('POLYGON ((45 0, 55 0, 55 40, 70 40, 70 50, 30 50, 30 40, 45 40, 45 0))')
)

MULTILINESTRING ((50 45, 50 5), (50 45, 35 45), (65 45, 50 45), (35 45, 65 45))
ST_ApproximateMedialAxis

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L-shape

SELECT ST_ApproximateMedialAxis(
  ST_GeomFromWKT('POLYGON ((0 0, 10 0, 10 5, 5 5, 5 10, 0 10, 0 0))')
)

MULTILINESTRING ((2.5 2.5, 2.5 7.5), (7.5 2.5, 2.5 2.5), (2.5 7.5, 2.5 7.5))