Fix invalid polygon in Shapely

Question

Shapely defines a Polygon as invalid if any of its segments intersect, including segments that are colinear. Many software packages will create a region or area with a "cutout" as shown here which has colinear segments:

>>> pp = Polygon([(0,0), (0,3), (3,3), (3,0), (2,0),                    (2,2), (1,2), (1,1), (2,1), (2,0), (0,0)]) >>> pp.is_valid WARNING:shapely.geos:Self-intersection at or near point 2 0 False 

Naturally, the cutout can be implemented natively in Shapely, or this same geometry can be implemented as two valid polygons, but if I only have the list of points shown above, is there an easy to "fix" this (create valid geometry from this list of points)?

Answer 1

I found a solution that works for the specific case given:

>>> pp2 = pp.buffer(0) >>> pp2.is_valid True >>> pp2.exterior.coords[:] [(0.0, 0.0), (0.0, 3.0), (3.0, 3.0), (3.0, 0.0), (2.0, 0.0), (0.0, 0.0)] >>> pp2.interiors[0].coords[:] [(2.0, 1.0), (2.0, 2.0), (1.0, 2.0), (1.0, 1.0), (2.0, 1.0)] 

Answer 2

Untested, but it appears that Shapely have added a function to support this now.

https://shapely.readthedocs.io/en/latest/manual.html#validation.make_valid