The wanted effect is to fix incorrect route hints when the road layout
in OSM is correct but ambiguous. Personally I see a through_route as
being no different to no_left_turn or no_right_turn or similar
restrictions in that it gives a routing engine the full information it
needs to be able to make correct decisions and issue correct
instructions. If we didn't add a no_left_turn at a junction where you
can't turn left how is a routing engine to know that? It's purpose
therefore is to issue a turn warning when you need to turn off a highway
or to not give a turn warning when one isn't needed. The proposal can
still be found at
http://wiki.openstreetmap.org/wiki/Proposed_features/through_route but
I'll try to explain it here
Consider this
A B
\ |
\ | A682
A56\ |
\ |
\|C
|
|
A56 |
|
D
This is a real world example and is the one I used in the proposal
(http://www.openstreetmap.org/#map=18/53.68901/-2.30585). The lanes here
are marked as the (hopefully) attached jpg. Therefore if you're heading
north on the A56 and want to stay on the A56 you have to make a left
turn. Without the through_route relation a routing engine probably can't
determine that you need to make a left turn at this point as presumably
the angle between this and the A682 is too small. Before I added a
through_route at this point then if I was driving north on the A56 and
wanted to head towards Accrington (staying on the A56 but needing to
make a left turn) then I received no indication that I needed to turn
left at this junction and therefore would end up in Rawtenstall.
Conversely if you're heading north on the A56 and want to head towards
Rawtenstall then without the through_route you are told to stay right to
join the A682. This is incorrect as you do not need to keep right you
just need to continue in the lane you are in but not as bad as missing a
turn.
In short....
If you're travelling D->C->A then without a through_route you are NOT
told to turn left when you should be even though that's the way the
route is taking
If you're travelling D->C->B then without a through_route you are told
to stay right (or turn right, I can't remember which) when you need to
just keep going along the carriageway you're on
There is another example here
(http://www.openstreetmap.org/#map=17/53.67505/-2.30756). If you're
travelling north on the B6527 (Market Street) and want to stay on the
B6257 (Blackburn Road) then you have to turn left otherwise you will end
up on Burnley Road. The road markings here indicate that Market Street
onto Burnley Road is the through_route and therefore if your route keeps
you on the B6527 you need to turn left at this junction
All the above are corrected with a through_route
The second use for this is below but to me this is of lesser importance
A
|
|
|
|
B------------D
|
|
|
|
C
C->B->D is Smith Road for example. B->A is Jones Road.
The road markings indicate that at point B Smith Lane makes a 90 degree
turn so anyone driving along here (C->B->D) would automatically follow
the road. However in this case you may be told to turn right onto Smith
Road. Adding a through_route for C->B->D tells a routing engine that it
only needs to issue a turn warning if you are turning onto Jones Road
I hope that helps but if not then please ask
Thanks
Paul
On 01/10/2017 11:22 AM, Gerd Petermann wrote:
Hi Paul,
sorry , I still have no idea what the wanted effect is. If you think that my
example is tagged correctly,
in what case should it change the routing hints and to what?
Or maybe point me to another example.
thanks,
Gerd
________________________________________
Von: mkgmap-dev <[email protected]> im Auftrag von News
<[email protected]>
Gesendet: Dienstag, 10. Januar 2017 11:55:06
An: [email protected]
Betreff: Re: [mkgmap-dev] type=through_route relations and mkgmap r3743
If I remember correctly the idea of a through_route was first raised by
Mark Burton a few years ago. It was intended to solve the problem of
TOTSO's
(https://en.wikipedia.org/wiki/Glossary_of_road_transport_terms#TOTSO)
which is a situation where you have to turn off the carriageway you are
currently travelling on in order to stay on the same named road. In
these circumstances it is (almost) impossible for any routing engine to
deduce that it needs to give you a routing hint in order for you to stay
on the road that you are currently on. At the time I had a couple of
these near me where I knew that my Garmin was effectively missing a turn
and hence you would end up travelling in the wrong direction. Adding a
through_route at these places fixes this problem.
There is also a secondary use where a road e.g. Smith Road, bends 90
degrees and you are sometimes told to turn left/right to stay on Smith
Road even though there is no turning
A few years ago I tried to get this accepted into the list of official
tags however the vote resulted in a draw and I didn't have chance to
pursue it further.
I have now moved and there are none currently near me that I could use
to check if this is still working
See also......
http://www.mkgmap.org.uk/pipermail/mkgmap-dev/2013q2/017429.html
http://www.mkgmap.org.uk/pipermail/mkgmap-dev/2010q1/007028.html
Thanks
Paul
On 01/10/2017 08:31 AM, Gerd Petermann wrote:
I found one that might be interesting:
https://www.openstreetmap.org/relation/406379
If I got that right the intention was to tell mkgmap that
it should change the bearing (heading) values in the map so that the Garmin
algo doesn't produce a
hint like "Turn left onto Calle Botánico Rivas Mateos" when travelling from
way 24647941 (Calle José Luis Cotallo) to way 24311294 (Calle Botánico Rivas
Mateos).
(this is what happens now)
What would you want instead?
@Carlos: You have created that relation in 2010, maybe you remember?
Gerd
Gerd Petermann wrote
Hi all,
I've noticed that mkgmap still checks these relations for correctness but
they have no influence on the created map.
Part of the code that handled them was removed with r3649:
http://www.mkgmap.org.uk/websvn/revision.php?repname=mkgmap&rev=3649
If your map was created with r3743 or later, please check if you find a
crossing with such a relation which where routing
hints are wrong. In that case I would try to add code for the support,
else some unused code can be removed.
Gerd
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