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. Note that the returned shape(s) may have holes, as per the definition of the shape in Edselbrunner et al. (1983)

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