[mkgmap-dev] question about ignored no_u_turn restriction

Tue Jul 28 15:50:30 BST 2015

Hi Gerd,

In this example, if you're travelling southbound on North Harlem Avenue and
you miss your right turn onto Quick Avenue, the GPS might suggest that you
make a u-turn at the North Harlem Avenue / Ontario Street intersection so
that you can double back get back to your original route. The traffic rule
is saying that you're not allowed to make a u-turn at this intersection and
the OSM data is capturing the traffic rule correctly.

I've never been to this area so I can't actually test to see if the Garmin
routing algorithm would try to do this u-turn. This is just an example that
I'm using to try to figure if why the restriction is being ignored. I don't
actually know the details Garmin routing algorithm but I have been routed
on such u-turns in the past when I've missed a turn.

Given that this is a legitimate type of 'no u-turn' restriction, if the
Garmin map format or routing algorithm can't deal with it, there should be
a message that says so in the warning. In this case, maybe an info message
makes more sense - but you should probably decide how you want to present
it since you wrote it. :-) The other side of this is that the Garmin map
format or routing algorithm can actually handle this specific type of 'no
u-turn' restriction, in which case it would be nice to have the restriction
included in the maps.

Thanks for your help and all your hard work on mkgmap!

Ben

On Tue, Jul 21, 2015 at 10:44 AM, Gerd Petermann <
gpetermann_muenchen at hotmail.com> wrote:

> Hi Ben,
>
> unfortunately I did not add a comment to that part of the source which
> would explain
> why I coded it, but I think the reason is that the restriction has no
> effect on route calculation.
> I can't think of any case where the Garmin algo would route you along that
> u-turn.
> Do you have an example that proves this assumption to be wrong?
>
> If not, I can change the msg to say something like "has no effect", or
> please suggest a better text.
>
> Gerd
>
> ------------------------------
> Date: Mon, 6 Jul 2015 13:34:12 +0200
>
> From: ben at bagu.org
> To: mkgmap-dev at lists.mkgmap.org.uk
> Subject: Re: [mkgmap-dev] question about ignored no_u_turn restriction
>
> Just to follow up ... Does anybody know concretely that the Garmin format
> cannot handle and u-turn restriction with the same from and two way?
>
> Thanks, Ben
>
> On Sun, Jul 5, 2015 at 9:20 PM, Ben Konrath <ben at bagu.org> wrote:
>
> Hi Anor,
>
> Thanks for the tip but it seems that your suggestion breaks the OSM rule
> of manipulating the map for specific renderers (the renderer here being
> mkgmap). If the Garmin format truly doesn't support the u-turn restriction
> with the same to and from way at an intersection, we should come up with
> another solution.
>
> Ben
>
> On Sun, Jul 5, 2015 at 4:01 PM, A. Carlos <anorcarlos at hotmail.com> wrote:
>
>
>  Ben
>
> There I draw two routes, one in each direction, since there is a false
> median, then with 2-way, it's easy for a restriction
>
>
>
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> *_______________________________________________________________________________________________________*
>
>  *Anor                                                              Co*
> *ncórdia SC *
>
>
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>
> ------------------------------
> Date: Sun, 5 Jul 2015 15:53:50 +0200
> From: ben at bagu.org
> To: mkgmap-dev at lists.mkgmap.org.uk
> Subject: Re: [mkgmap-dev] question about ignored no_u_turn restriction
>
>
> Hi Thorsten,
>
> Thanks for your reply. This type of restriction is probably a country
> specific thing. In Ontario Canada, you can make u-turns at intersections
> (regardless of the road is separation) if there is no sign indicating that
> you can't make the u-turn. Here's the information directly from the Ontario
> Ministry of Transportation:
>
> http://www.mto.gov.on.ca/english/dandv/driver/handbook/section2.6.11.shtml
>
> I realize that the link I sent previously is in the US but I suspect that
> it's the same policy there which is why the restriction is tagged like it
> is.
>
> Since the tagging seems to be valid, does the Garmin format support this
> type of restriction? If not then it's probably a good idea to indicate this
> in the warning message. Maybe the message should also be changed to an info
> message if there's no problem with the data. Does anybody have other
> insights?
>
> Thanks, Ben
>
> On Sun, Jul 5, 2015 at 2:47 PM, Thorsten Kukuk <kukuk at suse.de> wrote:
>
> On Sun, Jul 05, Ben Konrath wrote:
>
> > Does anybody know why this particular restriction is being ignored?
>
> Beside that this particular type of restrictions doesn't make
> any sense to me, I would guess the GARMIN format does not support it.
>
> If the to and from ways are the same, I have never seen a sign forbidding
> u-turns. Only, if you have two ways, structural seperated. But then I
> should tag the street that way and the restriction will not be ignored.
>
>   Thorsten
>
> --
> Thorsten Kukuk, Senior Architect SLES & Common Code Base
> SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nuernberg, Germany
> GF: Felix Imendörffer, Jane Smithard, Dilip Upmanyu, Graham Norton, HRB
> 21284 (AG Nürnberg)
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