I have a List of Points which I transform to circles. Code from here

circles = [Point(random.random(), random.random()).buffer(random.random() * 0.1) for i in range(3)]

I want to know which circles within this List intersect each other. Is there a way to achieve that with a native shapely function, or do I have to iterate over the all possible combinations?

  • By definition a Point has zero area and zero length, therefore no intersection : Shapely: points
    – gene
    Apr 21, 2016 at 15:12
  • @gene as you can see, there is a buffer around the points - so an intersection should be possible! I have written a function which does what I want, but i wonder if there is a native way in shapely to do that.
    – four-eyes
    Apr 21, 2016 at 15:25
  • You can intersect the buffers, but not the Points
    – gene
    Apr 21, 2016 at 15:34
  • @gene but when I create points like this, the buffers are stored within circles?! I edit the question.
    – four-eyes
    Apr 21, 2016 at 15:35

1 Answer 1


The native shapely function is unary_union (Planar graph)

The circles

enter image description here

1) Using the script of How to find the intersection areas of overlapping buffer zones in single shapefile?

rings = [LineString(pol.exterior.coords) for pol in circles]
union = unary_union(rings)
result = [geom for geom in polygonize(union)]

Result: you have all the intersections

enter image description here

2) You can also use other solutions according to the position of an element in a list (look at Shapely/ Python looping through a number of polygons with itertools)

import itertools
for  i,j in itertools.combinations(enumerate(circles), 2):
    if i[1].intersects(j[1]):
        print "polygons", i[0],j[0] 
polygons 0 1
polygons 1 2

for  i,j in itertools.permutations(enumerate(circles), 2):
    if i[1].intersects(j[1]):
        print "polygons", i[0],j[0]

polygons 0 1
polygons 1 0
polygons 1 2
polygons 2 1

3) you can use a spatial index as rtree (look at Faster way of polygon intersection with shapely)

 from rtree import index
 idx = index.Index()
 # create the spatial index
 for pos, cell in enumerate(circles):
    idx.insert(pos, cell.bounds)
 # loop through each polygon
 for poly in circles:
    # Merge cells that have overlapping bounding boxes
    merged_cells = unary_union([circles[pos] for pos in idx.intersection(poly.bounds)])
    # Do actual intersection

enter image description here

(the two intersections here)


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.