# libpysal.cg.alpha_shape¶

libpysal.cg.alpha_shape(xys, alpha)[source]

Alpha-shape delineation (Edelsbrunner, Kirkpatrick & Seidel, 1983) from a collection of points …

Parameters
xysndarray

(N, 2) array with one point per row and coordinates structured as X and Y

alphafloat

Alpha value to delineate the alpha-shape

Returns
shapesGeoSeries

Polygon(s) resulting from the alpha shape algorithm. The GeoSeries object remains so even if only a single polygon is returned. There is no CRS included in the object.

References

Edelsbrunner, H., Kirkpatrick, D., & Seidel, R. (1983). On the shape of

a set of points in the plane. IEEE Transactions on information theory, 29(4), 551-559.

Examples

>>> pts = np.array([[0, 1], [3, 5], [4, 1], [6, 7], [9, 3]])
>>> alpha = 0.1
>>> poly = alpha_shape(pts, alpha)
>>> poly
0    POLYGON ((0.00000 1.00000, 3.00000 5.00000, 6....
dtype: geometry
>>> poly.centroid
0    POINT (4.69048 3.45238)
dtype: geometry