I can see *a lot* of shared routes in my area because most of the buses
heavily use a star topography (everything must take you to a central
station) as opposed to a hybrid mesh/star topography (everywhere has
access to a service to a central station, but there are circular routes
to allow quicker travel in some circumstances). for example my local
service has one incredibly early train station detour (presumably for
long distance commuters), the two main routes (incoming/outgoing) and a
route that stops at the bus depot. all 4 of these routes share a large
part of it and that's just one route number! such route segments could
help shrink and simplify maintaining the relations a lot. for example if
there's a detour due to roadworks, you don't have to edit the very large
number of relations individually, (our bus station has around 20 bays,
each taking multiple services...) just the shared child relations. I
don't think we need a specially labelled super route relation, but
perhaps we do need a way to tell the data user that a segment is shared.
these are the problems I see:
1. where do the tags go?
2. do you need a separate one for each direction?
3. is type=super_route or similar the best idea?
4. how far can they nest?
5. a shared route is being used for public transport, should the stop
positions and bus stops be included with all the ways?
so... what do we do? this is what I see as a solution:
1. if a route is shared, tags should be minimal and only related to the
physical route itself perhaps not even including the usual route tag
(AFAIK wouldn't just about any route relation in existence define
the route tag? so this would just be another pointer to the software
that this isn't your regular route. but maybe it still is best to
tag it, in which case.... maybe route=shared?), rather than things
such as what bus routes it is part or anything, this can easily be
seen simply by looking at parent relations
2. maybe use the roles forward/backward? I don't think these are used
for much any more
3. what do we gain? I think this can more easily be solved by simply
adding another tag such as shared=yes which can tell the software
that there are route relations that are intended to be treated as
just one big way. see below for a more detailed explanation.
4. I don't see a reason to limit the nesting, I imagine in most use
cases, the benefit of sharing duplicate relation data probably
outweighs any impact from processing nesting
5. if a shared route is used for both a numbered road route and public
transport it's probably unfair on the road user that doesn't need
them if they are included. also this would make it difficult to work
out where to place it in a public transport V2 relation.. as they
have stops at the top, ways at the bottom but this has both!
so here's an indented, somewhat simplified example of how it roughly
would nest based on the idea of a public transport route, a cycle route
and a road relation that share the same set of ways (_underlined_=can be
shared in parent nesting level, *bold*=can be shared in nesting levels
outside of the parent one, italic=the level at which main tagging should
occur. for easier referencing each equivalent level of nesting has been
assigned a letter):
_______________________________________________________________________________
/bus network///[A]/
/
/route_master=bus /[B]
//
/route variant/ [C]
_*route segments*_ [D]
__
_combined bus stop/way relation suitable for public
transport v2_ [E]
__
_shared bus stop relation_ [F]_
_
_*shared way relation*_ [G]
/road network///[A]/
/
/road /[C]
_*shared way relation*_ [G]*
*
/cycle network//**/[A]/*
*/
/cycle route /[C]
__
__
*_shared way relation_* [G]
_____________________________________________________________________________
potential new tags that may be required:
[C]: shared=yes (defaults to no)
[E/F/G]: route=shared (this is questionable in terms of benefits though)
_____________________________________________________________________________
notes:
[G] may be infinitely nested as required to prevent duplicate sets of
ways (although this should rarely be required)
as you can see, this allows a lot of the data to be shared between the
various types of relations, whilst also allowing current relation
structure to remain the same, this is just an extra higher level of
detail, where required. due to the way public transport relations are
handled it may be required to even have every segment in [D] contained
in a relation, however as cycle and road relations are purely made up of
ways they may not need the same kind of treatment and be able to mix
items from [G] with directly referenced ways. the separation of bus stop
and way data allows public transport relations to still correctly
identify the different bus stops in each direction but not have to
duplicate the way data. the naming of parts is solved, as this can be
applied to [G] level relations. the use of [G] and [C] would help solve
where routes need to be split up to keep maintenance possible. [E], [F]
and [G] theoretically shouldn't need to be tagged as the fact they
include any child relations at all should be enough to indicate what
they are, however if not route=shared would certainly make it obvious. I
hope this theory on how we could solve it was helpful, if any further
clarification is required or there's a notable mistake/error please let
me know and I'll try to respond as best as I can to that. I have thought
about perhaps making an example of this, if it would help please let me
know.
**
On 3/15/19 12:07 PM, marc marc wrote:
Le 15.03.19 à 12:27, Hufkratzer a écrit :
is that a good/sufficient reason to define a new relation type?
imho nearly no routing tools (nor foot nor bus) is currently able
to use a relation type=route with relations as child.
so that's a good reason to create/improve a doc if superrelation is
needed for ex for routing (of course maybe some mapper need superroute
only for the fun of having a relation that collect all other).
for ex how a "data user" can detect "it 's a superroute" <> "it's 2
route with a shared segment" ?
for the moment, the trick is to notice that the name of the main
relationship is close to the name of the children's relationships
and to know that the names of all these children's relationships
are fake names (which should therefore be removed/corrected).
there is for ex nothing called "European long distance path E4 - part
France". it's an artificial name to descript how the relation is splited
maybe the tag network should be the same and/or the name (the country
XYZ may move the a scope tag)
the main relation must/should/mustn't/shouldn't have all/some same tag
as the child ?
all/a lot of child tag must move to the main relation only ? (that's
what we do with MP : we don't duplicate alls tags to way + relation)
etc...
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