[OSM-talk-be] Complex kruispunt / Complex crossing

Tue May 13 20:33:14 UTC 2014

Marc,

The difference between following N47 with separate cycleways and
without separate cycleways is that in the first case the router will
tell you that you are cycling over a road without cycleways, while in
the second case the router will tell you that you are following a road
with lanes. For a cyclist, this is exactly what matters.
Or otherwise said, if for all practical purposes you ignore the
parallel cycleways, why would you map them in the first place? Because
they show on the standard map (aka mapping for the renderer)?

The badly connected cycleways have nothing to do with device
precision, but everything with network topology. It is the same reason
why a junction between two roads should happen in one node and why two
nodes very very very close to each other is not good enough.

wouter

On Tue, May 13, 2014 at 5:58 PM, Marc Gemis <marc.gemis at gmail.com> wrote:
> Jo,
>
> a can of worms ? I hope it , this mailing list is too quiet :-)
>
> Wouter,
>
> While I understand that for routing one does not need the separate
> cycleways, I don't see much difference in a router that sends me over the
> N47 with separate cycleways (illegal in your eyes) or without separate
> cycleways (ok for you).
>
> The possible problem with a badly connected separate cycleway, is that a GPS
> with very high precision, won't let me make the second left turn into Baan
> nr. 90
>
> So as long as the N47 is not tagged with bicycle = no, there won't be any
> problem IMHO
> But as you wrote, you get the same result with less work by putting tags on
> the main road.
>
> regards
>
> m
>
>
>
> On Tue, May 13, 2014 at 10:34 AM, Wouter Hamelinck
> <wouter.hamelinck at gmail.com> wrote:
>>
>> OK, I'll bite about the cycleway.
>>
>> Go a bit south and you will see something called Macharisdreef and
>> something called Baan nr. 90. Imagine you want to cycle from
>> Macharisdreef to Baan nr. 90 along that N47 and use only the map data
>> as a routing algorithm would do.
>> * First attempt: well it is obvious, you just take the cycleway at the
>> east of the N47 to cycle from the one to the other. Shortest, lots of
>> cycleway, it looks perfect. Reality: this is illegal, you only can
>> follow that cycleway north, otherwise you cycle on the wrong side of
>> the road. So we have to correct the data. Let's say we put a
>> oneway=yes on the eastern cycleway.
>> * Second attempt: well obvious again, you simply take the N47 instead
>> of that cycleway. Only slightly longer, a bit less attractive, but not
>> too bad. Reality: this is illegal. There are cycleways, you have to
>> follow those. So we have to correct the data. Somehow we have to make
>> explicit that you are not supposed to cycle on the N47 but have to
>> follow the parallel cycleways. So let's put some tag explaining that
>> on the N47. I don't really care which one. It could be boldly
>> bicycle=no or the proposed bicycle=use_sidepath or whatever. I'm just
>> not supposed to cycle over the highway=primary.
>> * Third attempt: let's see. When leaving Macharisdreef, I have only
>> two options. Either I take the N47, but that is illegal, or I take the
>> cycleway east of N47. Nothing else connects to Marcharisdreef. So my
>> only option is to follow the eastern cycleway to the north. Hmm, I
>> then can cross the N47 right before that terribly complicated junction
>> and start following the western cycleway. Until I find a place to
>> cross the N47 again. The first one that I find is right at the
>> roundabout about 500m to the south. There, I can traverse to the
>> eastern cycleway and follow that north to Baan nr. 90. OK, I have a
>> solution. Not exactly short (about 1km instead of the 50m in my
>> previous attempts), but at least it is legal. Reality: not entirely
>> legal (at least at the roundabout you should go around it instead of
>> traversing before the roundabout), but close enough for me. With the
>> slightest bit of common sense I wouldn't follow that anyhow. What I
>> would do is traverse N47, follow the western cycleway and traverse
>> again when I am at Baan nr. 90. Why didn't the algorithm propose that?
>> Simple: the road to the east of N47 are not connected to the western
>> cycleway and vice verse. So we have to modify the data again. At every
>> point where there is a sideroad from only one side we need to add a
>> short cycleway to connect the cycleway on the other side with the
>> junction.
>>
>> Once those junctions are made, I will get the obvious, correct route.
>>
>> Conclusion: lots of work and near impossible to maintain.
>>
>> Now, let's see what happens if I tag the cycle paths on the
>> highway=primary in stead of drawing them separately. It is in any case
>> a lot less work. No need to draw the separate cycleways and no need to
>> add all the technical tags on both highway=primary and
>> highway=cycleway that I described previously to get correct results. I
>> just add cycleway=lane or something similar to the highway=primary.
>> What does the algorithm say? I will just say: "At the end of
>> Macharisdreef turn left on N47. I know there are are cycle lanes so
>> you should follow those instead of cycling in the middle of the road.
>> And after 50m you turn left in Baan nr. 90.".
>> Simple, clear, robust.
>>
>> That is why I only will draw separate cycleways if there really is no
>> other option. Even if it is not wrong to draw to the cycleway
>> separately, it is just a lot of work, impossible to maintain and a
>> huge source of errors waiting to happen.
>>
>> Bonus question 1: what happens with routing for pedestrians in both
>> situations?
>> Bonus question 2: in how many ways is it possible to make mistakes
>> when mapping cycling routes? Especially the case of a route that can
>> be followed in both directions is enlightening.
>> Bonus question 3: which situation has the least tags (=lowest database
>> size) and the least junctions and ways (=greater efficiency for
>> routing algorithms like Dijkstra)?
>>
>> wouter
>>
>> On Tue, May 13, 2014 at 9:16 AM, Jo <winfixit at gmail.com> wrote:
>> > We have more recent AGIV imagery now. All I see wrong is that the
>> > cycleway
>> > is connected to the underground waterway. But the main road is too.
>> > Probably
>> > to silence validator warnings in a totally inappropriate way...
>> >
>> > I still think it's correct to draw the cycleways separate cases like
>> > this.
>> >
>> > Marc, you opened a can of worms there :-) But it's good that the subject
>> > of
>> > using separate ways to represent lanes is brought up on the list.
>> >
>> > Jo
>> >
>> >
>> > 2014-05-13 8:15 GMT+02:00 Wouter Hamelinck <wouter.hamelinck at gmail.com>:
>> >
>> >> Wow, based on the Bing images a simple T-crossing and a bypass is all
>> >> there is in reality.
>> >> Also, note the nice examples of about everything that can go wrong
>> >> when drawing parallel cycleways along the N47.
>> >>
>> >> wouter
>> >>
>> >> 2014-05-13 6:35 GMT+02:00 Jo <winfixit at gmail.com>:
>> >> > Zeker wel, het klopt niet om een aparte weg te tekenen voor elk
>> >> > rijvak.
>> >> >
>> >> > Absolutely, using a separate way to represent traffic lanes is not
>> >> > how
>> >> > it's
>> >> > supposed to be done.
>> >> >
>> >> > Jo
>> >> >
>> >> >
>> >> > 2014-05-13 5:48 GMT+02:00 Marc Gemis <marc.gemis at gmail.com>:
>> >> >>
>> >> >> Hallo,
>> >> >>
>> >> >> Ik vraag me af of het OK is het volgende kruispunt te vereenvoudigen
>> >> >> via
>> >> >> turn:lanes : http://osm.org/go/0Ejo5_fqb--?way=51738440
>> >> >>
>> >> >> I wonder whether it's ok to simplify the following crossing with
>> >> >> turn:lanes tagging: http://osm.org/go/0Ejo5_fqb--?way=51738440
>> >> >>
>> >> >> met vriendelijke groeten
>> >> >> regards
>> >> >>
>> >> >> m
>> >> >>
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>> >> >
>> >> >
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>> >>
>> >>
>> >>
>> >> --
>> >> "Den som ikke tror på seg selv kommer ingen vei."
>> >>                                        - Thor Heyerdahl
>> >
>> >
>>
>>
>>
>> --
>> "Den som ikke tror på seg selv kommer ingen vei."
>>                                        - Thor Heyerdahl
>>
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