geopandasshapely
Given a Shapely MultiPolygon, how can I extract the biggest Polygon?
For example, given a MultiPolygon as follows:
from shapely.geometry import Polygon, MultiPolygon
multipolygon = MultiPolygon([Polygon([(0,0), (1,0), (1,0.25), (1, 0.5), (1,0.75), (1,1), (0,1)]),
Polygon([(2,0), (1.2,0.25), (1.2,0.25), (1.2,0.75), (2,0.75)])])
How can I get just the largest part?
I've no idea if this works or if it's fast enough, but I'd try this:
What makes or breaks this approach is if the buffer intersects A or not (because buffer is a circle's approximation, it might not).
If you don't get an intersection, you could increase either:
until you get an intersection.
Here's a diagram of a buffer slightly bigger then the distance to illustrate what I mean:
You need to understand the Shapely binary predicates:
1) If the two polygons intersects the result of union or unary_union (in red) is a Polygon therefore you can computes the exterior
2) If the two polygons are disconnected, the result is necessary a MultiPolygon (in red with two polygons)
And if you work with Shapefiles, without topology, this may occur
A solution is to compute the Concave Hull but it is not really an union.
Best Answer
Here's what I would do:
The built-in max function used this way will return the item from the list where
lambda a: a.areais maximized.