How to access members of GeometryCollection - Python

Question

I am using 'intersection' function from Shapely to find junctions of a road network. As i found, intersection returns GeometryCollection. In my case it could be Point, LineString or perhaps MultiLineString. I want to segregate these objects based on their geometry. I only want Point objects for further use. I found similar post here

It suggests to use as.GeometryCollection however, in my case it gives:
p = l1.intersection(l2).asGeometryCollection()
AttributeError: 'GeometryCollection' object has no attribute 'asGeometryCollection'

here is the sample code: (I expect to get points in junctions[])

with open('./lines.geojson') as f:
routes = json.load(f)
junctions =[]
for i in range(len(routes['features'])-1): 
 j =i+1 
 while (j < len(routes['features'])):
 l1 = LineString(routes['features'][i]['geometry']['coordinates'])
 l2 = LineString(routes['features'][j]['geometry']['coordinates'])
 p = l1.intersection(l2).asGeometryCollection()
 junctions.append(p[0]) 
 j = j+1 

Answer 1

If an object A is a GeometryCollection, its content can be accessed using :

for geom in A.geoms:
 ...

except if A is a GEOMETRYCOLLECTION EMPTY.

• swiss_knight: In shapely 2.0.0: TypeError: 'GeometryCollection' object is not iterable
• Damien: In Shapely 2+ you must access A.geoms
• Eric H.: Damien, you are right, A.geoms is the answer. I edit my answer.

Answer 2

You've confused the QGIS and Shapely libraries. The code in the similar post doesn't apply to Shapely.

In your case, p = l1.intersection(l2) returns an instance of Shapely's GeometryCollection. p[0] is the first part of that collection. All you need is:

p = l1.intersection(l2)
junctions.append(p[0])