[mkgmap-dev] [PATCH v3] heed the through_route relation when adjusting turn headings

Tue Feb 16 18:33:35 GMT 2010

Hi Steve,

Thanks for the feedback.

> Mark - I've been giving the 'through_route' patch a bit of use, and I 
> must say it does a great job of allowing the mapper to 'fix' those 
> annoying junctions where there was no way for mkgmap to decide the road 
> priority.

Good.

> I have a couple of issues still, and a few suggestions:
> 
> 1) Could you arrange for mkgmap to honour the "continuity" of a drawn 
> way? In other words, if a way with a given name has a bend in it, and a 
> stub of the same road class and same road name makes a "T" junction with 
> it, then assume that the continuously-drawn way is the through-route? 
> Here's an example:
> 
> http://www.openstreetmap.org/?mlat=51.577273&mlon=-4.041473&zoom=17&layers=B000FTF
> 
> ..if you drive south-east on Kilfield Road, then as you approach the 
> marker you'll be told to "turn right" where really the entire length of 
> Kilfield Road is drawn as a single way, with the smaller stub being 
> another way in its own right. I don't know about other mappers, but I 
> know a *lot* of cases (mostly in residential areas) where a long curve 
> of road had small stubs sticking off it, and they'll all generate bogus 
> instructions if this isn't dealt with.

I have just tried routing on that road and mapsource did not give me a
"turn right" at that junction. However, I have tweaked the code as it
could get confused as to which is the through route as all the roads
at that junction have the same name. So now the one-piece road will take
precedence over the stub even though they have the same name. I will
post a new patch shortly, please see if it does the right thing there.

> 2) Can we invent some way to mark up traffic lanes? Here's a case in point:
> 
> http://www.openstreetmap.org/?mlat=51.61219&mlon=-3.961323&zoom=18&layers=B000FTF
> 
> You probably want to look at the area in Potlatch to see what's 
> happening. Yes - I know I'm probably rather stretching the rules here, 
> but the idea was that if a driver approaches on the A4067 from the east, 
> wanting to take the right turn onto the stub of B4290 and thence to 
> follow the B4290 towards the northeast, then he'd get a "keep right" 
> instruction about 150m before the junction itself (that's where a 
> dedicated traffic lane starts) and then get a "turn right" at the 
> junction itself, followed by another "turn right" 30m later to the north 
> as he joins the northeast-bound B4290.
> 
> It used to work like that, but now I get a "turn right" (not "keep 
> right") at 150m short of the junction because the heading of the 
> junction has been tweaked. If we could mark up traffic lanes it might 
> allow you to maintain that useful "keep right" where the lane branches 
> off. Additionally, one day we might find how "lane assist" works in 
> Garmin maps and be able to code for it properly.
> 
> I wonder if marking a lane like this one as "highway=primary" 
> "primary=traffic_lane" "ref=A4076" (etc) would be useful and desirable 
> and would you be able to handle it anyway?

This is a difficult situation to handle. A problem is that if you
don't tweak the heading for the link road you will then get "keep left"
instructions for each exit you approach. It currently does a good job
of not telling you to "keep left" on motorways and trunk roads and I
would prefer that it stays that way. More thought required...

Cheers,

Mark