geopandas.GeoSeries.concave_hull

GeoSeries.concave_hull(ratio=0.0, allow_holes=False)

Returns a GeoSeries of geometries representing the concave hull of each geometry.

The concave hull of a geometry is the smallest concave Polygon containing all the points in each geometry, unless the number of points in the geometric object is less than three. For two points, the concave hull collapses to a LineString; for 1, a Point.

The hull is constructed by removing border triangles of the Delaunay Triangulation of the points as long as their “size” is larger than the maximum edge length ratio and optionally allowing holes. The edge length factor is a fraction of the length difference between the longest and shortest edges in the Delaunay Triangulation of the input points. For further information on the algorithm used, see https://libgeos.org/doxygen/classgeos_1_1algorithm_1_1hull_1_1ConcaveHull.html

Parameters:

ratiofloat, (optional, default 0.0)

Number in the range [0, 1]. Higher numbers will include fewer vertices in the hull.

allow_holesbool, (optional, default False)

If set to True, the concave hull may have holes.

See also

GeoSeries.convex_hull

convex hull geometry

Examples

>>> from shapely.geometry import Polygon, LineString, Point, MultiPoint
>>> s = geopandas.GeoSeries(
...     [
...         Polygon([(0, 0), (1, 1), (0, 1)]),
...         LineString([(0, 0), (1, 1), (1, 0)]),
...         MultiPoint([(0, 0), (1, 1), (0, 1), (1, 0), (0.5, 0.5)]),
...         MultiPoint([(0, 0), (1, 1)]),
...         Point(0, 0),
...     ],
...     crs=3857
... )
>>> s
0                       POLYGON ((0 0, 1 1, 0 1, 0 0))
1                           LINESTRING (0 0, 1 1, 1 0)
2    MULTIPOINT ((0 0), (1 1), (0 1), (1 0), (0.5 0...
3                            MULTIPOINT ((0 0), (1 1))
4                                          POINT (0 0)
dtype: geometry

>>> s.concave_hull()
0                      POLYGON ((0 1, 1 1, 0 0, 0 1))
1                      POLYGON ((0 0, 1 1, 1 0, 0 0))
2    POLYGON ((0.5 0.5, 0 1, 1 1, 1 0, 0 0, 0.5 0.5))
3                               LINESTRING (0 0, 1 1)
4                                         POINT (0 0)
dtype: geometry