[Tagging] Route members: ordered or not

Volker Schmidt voschix at gmail.com
Thu May 3 17:34:24 UTC 2018


My fault.
Loops (in the sense of self-intersections)  are not a problem. Drop rule
B(2)!
What I had in mind was roundabouts. They are not loops. Thy are special
cases of the rule B(3)

On 3 May 2018 at 19:10, marc marc <marc_marc_irc at hotmail.com> wrote:

> "impossible" only due to missing tools to be able to do the job
> and the time it take do it "by hand"
> try to order this one http://www.openstreetmap.org/relation/1744381
> I spent a little time sorting these members, but it's a waste,
> it's deteriorating faster than it's getting better.
>
> Le 03. 05. 18 à 18:49, Colin Smale a écrit :
> > Why does a loop make it impossible to sort the ways? It implies that a
> > section of the route is present twice in the relation, but there is
> > surely no distinction between the first traversal of a way and the
> > second traversal?
> >
> >
> > On 2018-05-03 18:42, Volker Schmidt wrote:
> >
> >> I will try to explain this in a more systematic way:
> >>
> >> Routes belong to either of two categories:
> >> (A) Those whose members can be sorted into a single ordered sequence
> >> (B) Those that cannot be sorted into a single ordered sequence of
> members
> >> Sorting makes only sense for category (A)
> >> Routes of type (B) can be subdivided into routes of type (A), each of
> >> which can be sorted, but the overall route can not be sorted.
> >>
> >> Routes are of type (A) if
> >> (1) the path from begin to end is identical to the reverse path with
> >> all members traversed in the reverse order and in the opposite direction
> >> or
> >> (2) all members have the role forward
> >> or
> >> (3) all members have the role backward
> >>
> >> Any route
> >> (1) that has more than two ends
> >> or
> >> (2) that contains any loop (except the case that the entire route is a
> >> single loop)
> >> or
> >> (3) that contains any element with role forword or role backward
> >> (except the cases of all-forward or all-backward)
> >> or
> >> (4) that contains node or area elements
> >> is of type B
> >>
> >> I am not sure if I have taken care of all cases - please complete as
> >> necessary
> >>
> >>
> >>
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> >
> >
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