How to include car ferries in OSMnx graphs

Question

Is it possible to have OSMnx (great tool BTW) include car ferries when building a graph? Failing that, what would be the most direct way to build such a graph? The problem isn't just that the ferry routes themselves aren't present but, without the ferries, islands that are in reality reachable by car aren't included in the road network.

I have tried using osmnx.settings.useful_tags_way to no avail. Using 'route'='ferry' in overpass-api returns what I would like to include in the graph so I have been editing the OSMnx downloads.py file trying to alter the overpass-api call directly.

Thanks!

Answer 1

First pass (hacky)

I've came up with fairly hacky partial solution by editing osmnx's downloads.py file and replacing the line (originally around line 350):

query_str = f"{overpass_settings};(way{osm_filter}(poly:'{polygon_coord_str}');>;);out;"

with:

osm_filter2 = f'["route"="ferry"]'
query_str = f"{overpass_settings};(way{osm_filter}(poly:'{polygon_coord_str}');>;way{osm_filter2}(poly:'{polygon_coord_str}');>;);out;"

The query string format took some trial and error. If this, or something like it, turns out to be the best approach, I'll try to make it more broadly applicable (add "ferry" to the predefined filter list rather than hardcoded, pass a list of filters, etc).

Much Better

I found that building separate graphs and unioning them using networkx.union or networkx.disjoint_union did not give usable results. So I have added a multiple filter capability to my version of the osmnx downloads.py file. I also added some additional network type options. So it's now possible to pass, for instance, "ferry" as a network_type for the osmnx.graph_from_* functions:

network_type = "ferry"

I can also now pass multiple network types using a pipe delimiter:

network_type = "drive|ferry"

to get a graph that is the union of the two. When doing this, I found that it's useful to create a second ferry-only graph and use that as a reference to update the tags in the combined network graph. It is also better to load non-simplified graphs at first and and simplify it/them yourself after this step.

Still experimenting

Still having some issues with non-connectedness - now in the ferry-only network. Car ferries at isolated crossings than don't share a harbor with a through-ferry are not included in the ferries-only graphs and therefore the tags of their counterparts in the combined network aren't getting updated as needed. The ferries in the combined network (network_type = "drive|ferry") are all present and connected correctly and therefore their respective islands are now on the road network - which is great. But, because their tags aren't being updated, these isolated ferries are getting default highway speeds (and I'm doing travel time analysis). I can use work around this using:

if not 'highway' in edge[3]:

but, for a robust solution, I think we want to be able to tag them explicitly.

I'd still love to hear what other think.