[mkgmap-dev] Support for "through_route" relations?

Thu Apr 11 23:02:09 BST 2013

Steve

Like you I think this is a useful option which should stay so I guess 
it's down to us to drum up some action on the wiki although I'll confess 
that I don't know where the best place to start is as I haven't spent 
much time on any wiki let alone one as large and well established as 
OSM. However if you feel you have the knowledge to make a start point me 
at the relevant page and I'll gladly pitch in

Thanks

Paul

On 10/04/13 12:14, Steve Hosgood wrote:
> On 2013-04-03 21:43, WanMil wrote:
>>> 0>  In article<515C8E7F.4000004 at web.de>,
>>> 0>  WanMil<URL:mailto:wmgcnfg at web.de>  ("Wanmil") wrote:
>>>
>>> Wanmil>  mkgmap contains some code to support "through_route" relations.
>>> [...]
>>> Wanmil>  Shall we still support this type of relation?
>>> Wanmil>  Can anybody explain what this relation does?
> Sorry - I've not kept my attention on this mailing list much recently,
> and I missed this one. I believe I may have been the user who asked
> Steve Ratcliffe for such a feature a few years back, and he agreed, and
> patched it in over a weekend or so.
>
> Sorry it didn't get documented. I think it was initially nothing more
> than an experiment, but it works brilliantly for me (since I know what
> it does!) and evidently a few others must have picked up on it too.
>
> Basically, it's markup that exists to convince the Garmin units to issue
> better verbal instructions when a road hits a junction but that the
> logical "main" route through that junction takes you to a different road.
>
> I.e. the road-number (even the road class) changes magically in the
> junction, but on the ground you think you're still "on the main road" so
> to speak.
>
> Look at
> http://www.openstreetmap.org/?lat=51.44852&lon=-3.49448&zoom=16&layers=M
>
> (I'm going to have to fix this example: someone's broken it! The road
> heading NE towards Cowbridge is the B4270, not the B4268). But anyway -
> if you approach that junction from the south (on the B4270) intending to
> drive through Llysworney (further to the north) but without "through
> route" being enabled, your Garmin will tell you to "turn left" at that
> junction. However, if you look at it on the road, you actually want to
> "go straight on". There *is* a turn left, but that's down a small
> uncategorised road which you certainly don't want to be on!
>
> Conversely, on the same junction, had you approached from the south (on
> the B4270) intending to drive to Cowbridge then it would say nothing as
> you hit the junction because after all you want to leave the junction on
> the B4270 - the same road that you approached on. But when you get
> there, to stay on the B4270 to Cowbridge is clearly a "turn right", and
> should be announced as such.
>
> With the "through route" system it all works fine. Without it: confusing
> directions for the motorist. I request that the feature be kept -
> possibly enhanced. I have noticed that the existing system can be
> accidentally broken when others alter the roads around a junction and
> leave "through route" set on too many ways in the vicinity. I think
> Steve R's implementation only works if there are exactly 3 nodes in the
> relation: two roads and the junction node itself.
>
> I did catch a few cases around my home town where some bus routes had
> been edited in, and when approach-roads to junctions marked with
> "through route" got split to allow for these bus routes doing funny
> things, then the two split fragments all ended up in the "through route"
> relation (taking the basic item-count above 3) and it failed. The system
> needs to count only the junction node and the two ways that must be
> *directly* connected to it.
>>>
>>> I think the best explanation is in the patch announcement email[1] -
>>> perhaps that could be adapted for the OSM Wiki?
>>>
>>> [1]<URL: http://www.mail-archive.com/mkgmap-dev@lists.mkgmap.org.uk/msg04975.html>
>> Thanks for the link!
>>
>> Now there have been 3 years after Mark proposed to document it in the
>> Wiki... I will wait for another two months. If the relation is not
>> documented after that time I think we can remove the code because the
>> usage is very rare. I guess only a very few people know how to use this
>> relation type correctly.
>>    From my point of view we shouldn't support inofficial undocumented
>> stuff (although it sounds useful...)
>>
>> Please don't feel offended. Just add the required documentation ;-)
>>
>> WanMil
>>
>> _______________________________________________
>
> I could do the documentation (based on the text I just wrote above). But
> it would be nice to get that "split approach road" bug out of the system
> as currently implemented (sorry, Steve - more work for you I guess).
>
> "Through route" should be used by more mappers! Definitely very useful
> on British roads - and I'd have thought useful on everyone else's too.
>
>
> Steve Hosgood
>
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