Hi Minh - Thanks for clarifying the more specific cases. I realize that my example would not cover all the possible permutations. Thank you for bringing more specific cases to the table. My colleague Kristen also has some more specific examples I know she intends to share here. Your specific cases actually make a lot of sense to me. I want to discuss this with my colleagues and get their opinions as well.
I apologize for the confusion around the term 'braiding' - we used this term internally for a while (and it ended up in some changeset comments) not realizing that this had a different meaning that traces back to the TIGER source data. Thank you for your feedback! On Tue, Oct 15, 2013 at 3:51 AM, Minh Nguyen <m...@nguyen.cincinnati.oh.us> wrote: > On 2013-10-14 10:42 AM, Martijn van Exel wrote: >> >> So what are we talking about? Intersections like this one, where one >> or more dual carriageways come together at an at-grade intersection: >> >> >> https://www.evernote.com/shard/s9/sh/6438c196-bb92-4f66-81dc-9b75186286ba/0e8f07ff527c6a85c0dec426b9b79f1e >> >> One of my colleagues at Telenav has remapped this intersection as follows: >> >> >> https://www.evernote.com/shard/s9/sh/3491f1fe-6afa-4571-bc43-7cb31c9c2625/9dd47d1445fdcf03d3f0bbd93b8e0f92 >> >> The main difference, and the source of some feedback we have received >> over the past few days, is that the dual carriageway roads are >> straightened out, creating multiple intersection nodes (4 in this >> case) instead of the original single intersection node that connects >> all the incoming and outgoing ways. That technique turns out to yield >> more reliable and correct routing and guidance ('keep left, turn >> right') through these intersections in our testing. But of course, >> that cannot dictate how we map as a community, so let's discuss. > > > I'm one of the troublemakers who complained about your colleague's edits. > However, the example you give bears little resemblance to the intersections > I disagree on. Your "before" screenshot depicts individual lanes (ew) that > converge into a single-point intersection, even when the main road is > divided on both sides of the intersection (ew). My quibble relates to > divided roads that become undivided at an intersection. > > Screenshots tell it best, but unfortunately we don't seem to have a tool to > visualize historical revisions of ways. So I recreated their changes from > memory in iD (because that's how I roll). > > > > ** Example A ** > > Ryans Way and Sycamore Grove Ln. meet Fields Ertel Rd. at the same > intersection. Fields Ertel is undivided. Ryans Way is briefly divided at the > subdivision entrance, a very common configuration in newer subdivisions, but > Sycamore Grove is not. > > I mapped the intersection as a single point: > > <http://nguyen.cincinnati.oh.us/minh/osm/talk-us/braided_intersections/ryans_before.png> > > Your colleague redrew it as a two-point intersection, dividing the very tip > of Sycamore Grove (to the south): > > <http://nguyen.cincinnati.oh.us/minh/osm/talk-us/braided_intersections/ryans_after.png> > > I prefer the former approach, because the latter shows a false traffic > island on the south side of the intersection. Imagine a pedantic navigation > tool that tells a driver coming from Sycamore Grove to "keep/bear right and > immediately turn left". > > ** Example B ** > > A divided Main St. intersects a divided Remick Blvd. Like everyone else here > -- and unlike the "before" example Martijn provided -- I prefer a four-point > intersection. But just to the east, Remick and a service road both become > undivided at the same intersection. I mapped it as a single point: > > <http://nguyen.cincinnati.oh.us/minh/osm/talk-us/braided_intersections/remick_before.png> > > Your colleague redrew it as a four-point intersection, this time with two > triangles: > > <http://nguyen.cincinnati.oh.us/minh/osm/talk-us/braided_intersections/remick_after.png> > > ** Example C ** > > Originally, State Route 4 became undivided at an intersection with Walden > Ponds Cir. (divided) and Fairham Rd. (undivided). SR 4, with a speed limit > of at least 45 mph, was redrawn to shuffle about 25 feet to the left right > after the intersection. But on major roads like SR 4, the landscaped median > ends several hundred feet before the intersection to make room for a long > left-turn lane. So I prefer to join the carriageways atop the left-turn > lane, at a much gentler angle, without cutting into the median. > > Since I first mapped the area, the median on SR 4 was extended well past > this intersection, so no "braiding" was necessary: > > <http://osm.org/browse/way/240893333> > > > > In all three examples, my original rendition was called "braiding", but the > ways were never intertwined as in the much-ridiculed TIGER data. > > I don't know what specific issues you found with the way I'd been mapping. > But I think routers should handle both styles gracefully, because mappers > will intuitively gravitate towards one or the other, depending on what > factors they consider. As intersections go, these examples are rather > straightforward. On the other hand, I've mapped plenty of intersections > where the traffic engineers clearly got carried away. If someone corrects me > on one of those, I'm all ears! :-) > > <http://osm.org/browse/relation/1843583> > <http://osm.org/browse/relation/1284976> > <http://osm.org/go/ZR~9kObUM> > > -- > m...@nguyen.cincinnati.oh.us > > > _______________________________________________ > > Talk-us mailing list > Talk-us@openstreetmap.org > https://lists.openstreetmap.org/listinfo/talk-us _______________________________________________ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us