[mkgmap-dev] type=through_route relations and mkgmap r3743

Tue Jan 10 14:19:16 GMT 2017

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 <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von News <news at pointdee.co.uk>
> Gesendet: Dienstag, 10. Januar 2017 11:55:06
> An: mkgmap-dev at lists.mkgmap.org.uk
> 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
>>> _______________________________________________
>>> mkgmap-dev mailing list
>>
>>> mkgmap-dev at .org
>>
>>> http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
>>
>>
>>
>>
>>
>> --
>> View this message in context: http://gis.19327.n8.nabble.com/type-through-route-relations-and-mkgmap-r3743-tp5888958p5889077.html
>> Sent from the Mkgmap Development mailing list archive at Nabble.com.
>> _______________________________________________
>> mkgmap-dev mailing list
>> mkgmap-dev at lists.mkgmap.org.uk
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>>
>
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