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<p>I can see <b>a lot</b> 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:</p>
<ol>
<li>where do the tags go?</li>
<li>do you need a separate one for each direction?</li>
<li>is type=super_route or similar the best idea?</li>
<li>how far can they nest?</li>
<li>a shared route is being used for public transport, should the
stop positions and bus stops be included with all the ways?<br>
</li>
</ol>
<p>so... what do we do? this is what I see as a solution:</p>
<ol>
<li>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</li>
<li>maybe use the roles forward/backward? I don't think these are
used for much any more<br>
</li>
<li>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.<br>
</li>
<li>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</li>
<li>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!</li>
</ol>
<p>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
(<u>underlined</u>=can be shared in parent nesting level, <b>bold</b>=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):</p>
<p>_______________________________________________________________________________<br>
</p>
<p><i>bus network</i><i> </i>[A]<i><br>
</i></p>
<blockquote>
<p><i>route_master=bus </i>[B]<br>
<i></i></p>
</blockquote>
<blockquote>
<blockquote>
<p><i>route variant</i> [C]<br>
</p>
</blockquote>
<blockquote>
<blockquote><u><b>route segments</b></u> [D]<br>
<u></u>
<blockquote><u>combined bus stop/way relation suitable for
public transport v2</u> [E]<br>
<u></u></blockquote>
</blockquote>
<blockquote>
<blockquote>
<blockquote><u>shared bus stop relation</u> [F]<u><br>
</u></blockquote>
</blockquote>
<blockquote>
<blockquote><u><b>shared way relation</b></u> [G]<br>
</blockquote>
</blockquote>
</blockquote>
</blockquote>
</blockquote>
<i>road network</i><i> </i>[A]<i><br>
</i>
<blockquote><i>road </i>[C]<br>
</blockquote>
<blockquote>
<blockquote>
<blockquote>
<p><u><b>shared way relation</b></u> [G]<b><br>
</b></p>
</blockquote>
</blockquote>
</blockquote>
<p><br>
<i>cycle network</i><i><b> </b></i>[A]<i><b><br>
</b></i></p>
<blockquote><i>cycle route </i>[C]<br>
</blockquote>
<blockquote>
<blockquote> <u> </u>
<blockquote><u> </u>
<p><b><u>shared way relation</u></b> [G]</p>
</blockquote>
</blockquote>
</blockquote>
<p>_____________________________________________________________________________</p>
<p>potential new tags that may be required:</p>
<p>[C]: shared=yes (defaults to no)</p>
<p>[E/F/G]: route=shared (this is questionable in terms of benefits
though)</p>
<p>_____________________________________________________________________________</p>
<p>notes:</p>
<p>[G] may be infinitely nested as required to prevent duplicate
sets of ways (although this should rarely be required)<br>
</p>
<p>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.<br>
<b> </b></p>
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<blockquote> </blockquote>
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<div class="moz-cite-prefix">On 3/15/19 12:07 PM, marc marc wrote:<br>
</div>
<blockquote type="cite"
cite="mid:DB6P190MB0279E7C4A8E651B6048541B1B7440@DB6P190MB0279.EURP190.PROD.OUTLOOK.COM">
<pre class="moz-quote-pre" wrap="">Le 15.03.19 à 12:27, Hufkratzer a écrit :
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">is that a good/sufficient reason to define a new relation type?
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">
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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</pre>
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