@Colin: You got me there: I implicitly excluded the possibility that a way may be part of the route more than once. I assumed this to be a general rule. If you do not exclude it also the more than-than-two-ends exclusion rule falls apart. @Adrian: What does RA do with routes where the same member appears several times?
On 3 May 2018 at 18:49, Colin Smale <[email protected]> wrote: > 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 > > > > > _______________________________________________ > Tagging mailing list > [email protected] > https://lists.openstreetmap.org/listinfo/tagging > > > _______________________________________________ > Tagging mailing list > [email protected] > https://lists.openstreetmap.org/listinfo/tagging > >
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