pygeos 0.3

Why ufuncs?

A universal function (or ufunc for short) is a function that operates on n-dimensional arrays in an element-by-element fashion, supporting array broadcasting. The for-loops that are involved are fully implmemented in C, diminishing the overhead of the python interpreter.

Pygeos aims to expose the geometry functions from GEOS into python to provide a fast and flexible means to work with large sets of geometries from python.

The GEOSGeometry object

GEOS geometry objects are stored in a static attribute of the Python extension type pygeos.GEOSGeometry. This keeps the python interpreter out of the ufunc inner loop. The GEOSGeometry object keeps track of the underlying geometry and allows the python garbage collector to free memory when the geometry is not used anymore.

GEOSGeometry objects are immutable. Construct them as follows:

>>> from pygeos import GEOSGeometry

>>> geometry = GEOSGeometry.from_wkt("POINT (5.2 52.1)")

Or simply:

>>> from pygeos import points

>>> point = points(5.2, 52.1)

Examples

Compare an grid of points with a polygon:

>>> geoms = points(*np.indices((4, 4)))
>>> polygon = box(0, 0, 2, 2)

>>> contains(polygon, geoms)

  array([[False, False, False, False],
         [False,  True, False, False],
         [False, False, False, False],
         [False, False, False, False]])

Compute the area of all possible intersections of two lists of polygons:

>>> from pygeos import box, area, intersection

>>> polygons_x = box(range(5), 0, range(10, 15), 10)
>>> polygons_y = box(0, range(5), 10, range(10, 15))

>>> area(intersection(polygons_x[:, np.newaxis], polygons_y[np.newaxis, :]))

array([[100.,  90.,  80.,  70.,  60.],
     [ 90.,  81.,  72.,  63.,  54.],
     [ 80.,  72.,  64.,  56.,  48.],
     [ 70.,  63.,  56.,  49.,  42.],
     [ 60.,  54.,  48.,  42.,  36.]])

Installation

Pygeos uses shapely’s installing scripts. If you have libgeos at a standard location, the following should work:

$ pip install pygeos

Installation for developers

Clone the package:

$ git clone https://github.com/caspervdw/pygeos.git

Install it using pip:

$ pip install -e .

Run the unittests:

$ python -m pytest pygeos/test.py

References

• GEOS: http://trac.osgeo.org/geos

• Shapely: https://shapely.readthedocs.io/en/latest/

• Numpy ufuncs: https://docs.scipy.org/doc/numpy/reference/ufuncs.html

• Joris van den Bossche’s blogpost: https://jorisvandenbossche.github.io/blog/2017/09/19/geopandas-cython/

• Matthew Rocklin’s blogpost: http://matthewrocklin.com/blog/work/2017/09/21/accelerating-geopandas-1

Copyright & License

Copyright (c) 2019, Casper van der Wel. BSD 3-Clause license.