ENH: support bi-directional roads in gdf_to_nx

[kopytjuk]

Some road sections can be passed in a bidirectional manner. Either the user has to preprocess his GeoDataFrame (to add an additional LineString in a opposite direction) or we can introduce a function where based on a boolean column, a user can specify which linestrings (roads) are oneway or not:

This functionality is helpful for path finding applications in directed graphs, where the same road can be traversed in the opposite direction.

[codecov]

Codecov Report

Merging #357 (0ae017c) into main (c6b9b2d) will decrease coverage by 0.0%.
The diff coverage is 88.9%.

❗ Current head 0ae017c differs from pull request most recent head 6f376a5. Consider uploading reports for the commit 6f376a5 to get more accurate results

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- Coverage   95.9%   95.8%   -0.0%     
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  Files         13      13             
  Lines       2811    2818      +7     
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+ Hits        2695    2701      +6     
- Misses       116     117      +1     

Impacted Files	Coverage Δ
momepy/utils.py	98.8% <88.9%> (-0.6%)	⬇️

[martinfleis]

Thanks a lot! This is surely useful. I've left two notes in the code.

If you want, you can also add this to the user guide page http://docs.momepy.org/en/stable/user_guide/graph/convert.html. (not strictly needed though).

One more thing we should certainly note - when you do this, gdf_to_nx -> nx_to_gdf will not roundtrip as the gdf coming from the bidirectional graph will contain duplicated geometries. That needs to be documented and we may even think about a way of dealing with this when needed.

[martinfleis]

This could in theory work also for networkx.DiGraph, not only MultiDiGraph, right? Can we allow it?

[kopytjuk]

You are right, removed the restriction.

[kopytjuk]

Thanks a lot! This is surely useful. I've left two notes in the code.

If you want, you can also add this to the user guide page http://docs.momepy.org/en/stable/user_guide/graph/convert.html. (not strictly needed though).

One more thing we should certainly note - when you do this, gdf_to_nx -> nx_to_gdf will not roundtrip as the gdf coming from the bidirectional graph will contain duplicated geometries. That needs to be documented and we may even think about a way of dealing with this when needed.

Agreed, I added a note in the docstring of the function that with oneway-option nx_to_gdf(gdf_to_nx(gdf, directed=True, oneway_column="oneway")) an extended geodataframe is returned.

Regarding the user guide, I would prefer a separate PR for that, I guess writing it and generating images will be more work than this PR - if it is OK for you, I would leave this PR as it is.

[kopytjuk]

Hello again @martinfleis, am I missing something?

[martinfleis]

Sorry, long backlog of open source tasks :D. I think it is ready to go. I'll give it another look later today and merge unless I find some issue.

[martinfleis]

Thanks a lot @kopytjuk!