[mkgmap-dev] Turn Restrictions using three ways - design guide for OSM mappers?

Sat Oct 5 07:53:21 BST 2019

Gerd,

Thanks for the reply.

So it looks like it's still being handled, but would you say that these 
should be changed in OSM?

It seems a bit strange that if you're on way A, you must travel through 
way B and get to way C, but indeed it is true that if you weren't allowed 
to make any turn at the point between A and B (and B and C), you'd get the 
same result -- is this the prefered way of denoting such?

For this particular example in OSM I suspect the mapper did not 
want to allow right turns at the intersection (even if it's not 
illegal) and hence wrote the restriction as an only left way-way-way 
instead of a way-point-way no right turn, perhaps because of either a sign 
or the paintings on the road and you can't make an "only left turn" on the 
first intersection of the dual carriageway because that's the wrong 
direction.

How should this particular intersection be restricted from travel to not 
emit warnings?  Adding that no right turn at the first intersection 
would probably have the effect, but I've seen a lot of these way-way-ways 
around (mostly dealing with complex dual carriageway intersections between 
multiple roads) and wonder if it's worth "fixing" them, or should these 
warnings be simply ignored for the most part?

Thanks!

On Sat, 5 Oct 2019, Gerd Petermann wrote:

> Date: Sat, 5 Oct 2019 05:43:56 +0000
> From: Gerd Petermann <gpetermann_muenchen at hotmail.com>
> Reply-To: Development list for mkgmap <mkgmap-dev at lists.mkgmap.org.uk>
> To: "mkgmap-dev at lists.mkgmap.org.uk" <mkgmap-dev at lists.mkgmap.org.uk>
> Subject: Re: [mkgmap-dev] Turn Restrictions using three ways - design guide
>     for OSM mappers?
> 
> Hi blc,
>
> the code that produces these warnings is this:
>                if (valid && !viaWays.isEmpty() && restriction.startsWith("only")){
>                        log.warn(messagePrefix, "check: 'via' way(s) are used in",restriction,"restriction");
>                }
>
> So, mkgmap considers them valid, but dubious. I think that's what they are. The restriction says something like
> "when you want to travel from way A via way B to way C you MUST travel from A via B to C"
> What kind of restriction is that? In my eyes, the given example is completely obsolete.
> On the other hand, a "no-" restriction with via way(s) means
> It is not allowed to go from A to C via B. This cannot be expressed with a single via node.
>
> Hope that helps?
>
> Gerd
>
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von blc <blc+mkgmap at mail.vanade.com>
> Gesendet: Samstag, 5. Oktober 2019 06:31
> An: mkgmap-dev at lists.mkgmap.org.uk
> Betreff: [mkgmap-dev] Turn Restrictions using three ways - design guide for     OSM mappers?
>
> Hello, I thank all who have been working on this neat program to allow our
> otherwise old Garmins sit in the dust heap when we can't afford to
> subscribe to new maps.
>
> I've been trying to improve the quality of OSM by fixing the errors
> that mkgmap emits, which a lot of times mirrors what's seen in
> KeepRight.  However there's one variant of turn restriction I've noticed
> that warns in mkgmap but do not show up in KeepRight (and iD seems to
> understand this type of turn restriction) - the way-way-way type
> restriction where three connected ways are in series for non no-u-turn
> restrictions.
>
>
> example:
>
> Turn restriction (only_left_turn) 2256354 (at
> https://www.openstreetmap.org/?mlat=47.777585&mlon=-122.319488&zoom=17)
> check: 'via' way(s) are used in only_left_turn restriction
>
> The way-way-way type is the proper method for restricting u-turns
> on dual carriageway roads which is understood by mkgmap.  On the
> other hand, iD and KeepRight it seems to be valid to do way-way-way
> instead of way-POINT-way for no/only left/right turn restrictions, no/only
> straight on restrictions, etc.  I've seen a lot of the non no-u-turn
> way-way-way restrictions in the USA.
>
> These type of non no-u-turn restrictions seems to cause a warning in
> mkgmap and probably not translating them.  My question is that should
> these be supported in mkgmap, or should these be fixed in OSM so that they
> are simple way-via-way despite iD and KeepRight seem to claim them
> valid?  Or perhaps way-way-way is deprecated but still supported by OSM
> but should be changed to way-point-way?
>
> way-point-way = relation
> from: some-street-way
> via: some-intersection-point
> to: some-street-way
> (this is the most common type of turn restriction)
>
> way-way-way = relation
> from: some-street-way
> via: some-street-way
> to: some-street-way
> (this is necessary specifically for dual carriageway u-turn restriction,
> but it's used for other types as well which mkgmap complains about.)
>
> Thanks for shedding some light on the discrepancy here!  Note: I'm
> currently depending on OpenMapChest data for mkgmap runs as my computer
> and internet connection are not large or fast enough for the quantity of
> data I'd like to work with.
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