[mkgmap-dev] question about ignored no_u_turn restriction

Tue Jul 28 16:22:52 BST 2015

Hi Ben,

okay, I did not yet think about the case that the device knows in which direction you are currently driving
when it re-calculates a route. I did only consider the case that you are planning while standing still.
If I remember correctly, this case will produce a message like "please make a u-turn", 
I never saw that it tells me to make a u-turn at a specific place.

It's not easy to test if Garmin uses this restriction (when written by mkgmap), I have to think 
about it.
@Steve: Do you see these restrictions in Garmin maps?

Gerd
PS: Your example is not good, as Quick Avenue is a (wrong) oneway, but that shouldn't matter here ;-)

Date: Tue, 28 Jul 2015 16:50:30 +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 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

_______________________________________________________________________________________________________

Anor                                                              Concórdia SC   

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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