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# GeoDataFrame.concave_hull

> Return a GeoSeries of geometries representing the concave hull of vertices of each geometry.

Return a `GeoSeries` of geometries representing the concave hull
of vertices of each geometry.

A concave hull is a concave or convex `Polygon` containing all the
vertices in each geometry. For two vertices, the hull collapses to a
`LineString`; for one vertex, it collapses to a `Point`.

The hull is constructed by removing border triangles of the Delaunay
triangulation. The ratio determines the maximum edge-length threshold
by interpolating between the shortest and longest edges in the
triangulation.

## Signature

```python theme={"system"}
concave_hull(ratio=0.0, allow_holes=False)
```

## Parameters

<ParamField path="ratio" type="float" default="0.0">
  Number in the range \[0, 1]. Higher numbers will include fewer vertices
  in the hull.
</ParamField>

<ParamField path="allow_holes" type="bool" default="False">
  If set to True, the concave hull may have holes.
</ParamField>

## Returns

<ResponseField name="return" type="GeoSeries" />

**See also**

* `GeoSeries.convex_hull`: convex hull geometry

<Note>
  The algorithm considers only the vertices of each geometry. As a result,
  the hull may not fully enclose the edges of the input geometry. Increasing
  `ratio` should resolve that case.

  Sedona and GeoPandas use the JTS and GEOS implementations, respectively.
  When candidate border triangles have the same edge length and area, the
  implementations may choose different, equally valid concave hulls.
</Note>

## Examples

```python theme={"system"}
>>> from sedona.spark.geopandas import GeoSeries
>>> from shapely.geometry import MultiPoint
>>> s = GeoSeries(
...     [MultiPoint([(0, 0), (1, 0), (0.5, 0.5), (1, 1), (0, 1)])]
... )
>>> s.concave_hull(ratio=0.3)
0    POLYGON ((0 0, 0 1, 0.5 0.5, 1 1, 1 0, 0 0))
dtype: geometry
```


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