[Routing] Restrictions demo and proposal

[Nic Roets]

First an online demo of turn restrictions :
Heading East in the secondary road, you are allowed to turn left into the
service road :

http://tile.openstreetmap.nl/%7Elambertus/routing-world/?flat=-25.783255&flon=28.300531&tlat=-25.784299&tlon=28.303921&v=motorcar&fast=1

But heading West, you're not allowed a right turn over on coming traffic :
http://tile.openstreetmap.nl/%7Elambertus/routing-world/?flat=-25.787855&flon=28.30736&tlat=-25.784338&tlon=28.304055&v=motorcar&fast=1

>From the service road you can turn left
http://tile.openstreetmap.nl/%7Elambertus/routing-world/?tlat=-25.787855&tlon=28.30736&flat=-25.784338&flon=28.304055&v=motorcar&fast=1
or right
http://tile.openstreetmap.nl/%7Elambertus/routing-world/?flat=-25.784345&flon=28.303986&tlat=-25.783418&tlon=28.300531&v=motorcar&fast=1

--
Next I'd like to propose a small modification to the turn_restriction
proposal, that will get rid of the need to split ways (
http://lists.openstreetmap.org/pipermail/talk/2008-June/027664.html ) :

We add two tags to the existing proposal called 'from_heading' and
'to_heading'. The values can be any integer from 0 to 360. These headings
are only approximations. When routing software generates the 'to'
possibilities that match the way in the 'to' member, it must only apply the
restriction to the segment that most closely match the 'to_heading'. The
same calculations must be made for 'from_heading'

There are therefore in each case a range of 180 degrees that will produce
the desired result. If a user is only accurate to 45 degrees when he creates
the restriction and someone else subsequently moves a node slightly, it will
not result in a misinterpreted restriction.

Regards,
Nic
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