docs/api/sql/Geometry-Processing/ST_ConcaveHull.md

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# ST_ConcaveHull

Introduction: Return the Concave Hull of polygon A, with alpha set to pctConvex[0, 1] in the Delaunay Triangulation method, the concave hull will not contain a hole unless allowHoles is set to true

![ST_ConcaveHull](../../../image/ST_ConcaveHull/ST_ConcaveHull.svg "ST_ConcaveHull")

Format:

`ST_ConcaveHull (A: Geometry, pctConvex: Double)`

`ST_ConcaveHull (A: Geometry, pctConvex: Double, allowHoles: Boolean)`

Return type: `Geometry`

Since: `v1.4.0`

SQL Example

```sql
SELECT ST_ConcaveHull(ST_GeomFromWKT('POLYGON((175 150, 20 40, 50 60, 125 100, 175 150))'), 1)
```

Output:

```
POLYGON ((125 100, 20 40, 50 60, 175 150, 125 100))
```