[Talk-us] Underground railways, indoor mapping, and overlapping features

[Minh Nguyen]

Vào lúc 10:28 2020-05-05, Michael Reichert đã viết:
> Using the same nodes (like mapping to adjacent landuse polygons) breaks
> routing because routing engines would allow trains to switch between the
> levels. Using duplicated nodes at the same location is likely to trigger
> quality assurance services and therefore mappers trying to "repair" it
> by merging them. Using two identical geometries in straight sections
> with nodes at different locations, will likely provoke the same as
> duplicated nodes.

Just as a double-decker bridge requires layer tags on each deck, so 
would a double-decker subway tunnel, whether the ways are coincident or 
offset by some arbitrarily small amount. Adding layer tags, as suggested 
in [1], would likely suppress any validator warnings about coincident 
ways. But it's true that mappers could still be confused by coincident 
ways if editors don’t provide intuitive ways to navigate among them.

> Regarding option 2: GraphHopper assembles its routing graph by relying
> on the node IDs in OSM. It would not suffer from using this option but I
> doubt that it is safe for the future. If OSM adopts to drop its 64 bit
> node IDs in favour of the location (32 bit latitude + 32 bit longitude),
> such cases will cause difficulties.

This is an intriguing notion I had not come across before. Has it ever 
been seriously considered? It seems to me that distinguishing nodes only 
by their coordinates would be tantamount to merging all coincident nodes 
everywhere, which we probably would never allow as part of a mechanical 
edit, much less a history-less database schema update. (For one thing, 
everyone who dislikes joining borders to roadways would be appalled to 
see just about every CDP boundary consistently joined that way.)

[1] https://lists.openstreetmap.org/pipermail/talk-us/2020-May/020015.html

-- 
minh at nguyen.cincinnati.oh.us