[Talk-us] Fwd: FW: Complex intersection mapping

Kristen Kam kristenk at telenav.com
Tue Oct 15 17:44:42 UTC 2013


Hello All,

**

** **

My name is Kristen and I am the colleague that Martijn mentioned in his
e-mail regarding complex intersection mapping. I am also the recipient of
the messages of disagreement from Minh.  I am chiming in because my edit is
an example cited by Martijn and that I have received feedback regarding my
edits of intersections. ****

** **

During my time editing OSM data I've encountered instances of intersections
that include, but not limited to: ****

** **

•             Dual carriageway road intersecting with a road that changes
from a dual- to single carriageway roadway at the intersection (example 1)**
**

•             Single carriageway road intersecting with a road that changes
from a dual- to single carriageway roadway at the intersection (example 2)**
**

•             Dual carriageway road changing to a single carriageway road
intersecting with another dual carriageway road changing to a single
carriageway road (example 3)****

•             T-intersection with an island facilitating and protecting
vehicular movement  (example 4)****

** **

Images of the types of cases I’ve encountered and tackled can be found
here: ****

** **

https://www.evernote.com/shard/s366/sh/914b7699-8377-4862-b90b-e56f5d41792d/d42f6f273b15e84d1ba309d3b4be998b
****

** **

The goal of my edits was to best model the vehicular movement through an
intersection---especially those that involved changing road configuration.
I forked the single-carriageway to a dual carriageway prior to the actual
intersection so it’d be consistent with the dual carriageway road
configuration within the intersection.  I acknowledge I could have forked
the single carriageway within the intersection box, or forked together the
two directions of a dual carriageway to a single carriageway through the
intersection (Martin’s example, attached). However, neither technique
“looked right”  in terms consistency to how things looked on the ground
(aerial).  This obviously is debatable. Feedback on my examples *with*
illustrations—like Minh’s response-- would be super helpful in facilitating
this discussion and work toward a consensus.****

** **

As I said early there are a few folks that actually contacted me about my
edits. One has joined the discussion, another is following it, the third
I’m not sure. If you’re out there, please don’t be shy, chime in!****

** **

That’s my $0.02****

** **

Best,****

** **

Kristen****

** **

---****

** **

OSM Profile → http://www.openstreetmap.org/user/KristenK****

** **

** **

-----Original Message-----
From: Minh Nguyen
[mailto:minh at nguyen.cincinnati.oh.us<minh at nguyen.cincinnati.oh.us>]

Sent: Tuesday, October 15, 2013 2:52 AM
To: talk-us at openstreetmap.org
Subject: Re: [Talk-us] Complex intersection mapping****

** **

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-9b7518628****

> 6ba/0e8f07ff527c6a85c0dec426b9b79f1e****

>** **

> One of my colleagues at Telenav has remapped this intersection as follows:
****

>** **

> https://www.evernote.com/shard/s9/sh/3491f1fe-6afa-4571-bc43-7cb31c9c2****

> 625/9dd47d1445fdcf03d3f0bbd93b8e0f92****

>** **

> 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>****

** **

--****

minh at nguyen.cincinnati.oh.us****

** **

** **

_______________________________________________****

Talk-us mailing list****

Talk-us at openstreetmap.org****

https://lists.openstreetmap.org/listinfo/talk-us****
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