[OSM-talk] routing across open spaces

Dave F. davefox at madasafish.com
Sun Dec 5 16:03:41 GMT 2010


On 01/12/2010 00:48, David Murn wrote:
> On Tue, 2010-11-30 at 19:14 -0500, Anthony wrote:
>
>>>>> That's nonsense.  A way does not show a right of passage.  A
>>>>> particularly tagged way shows a right of passage.  And a park is a
>>>>> particularly tagged way.
>>> No, a park *CAN BE* a particularly tagged way.
>> Can be?  How can you represent a park in OSM without using a way which
>> is tagged with leisure=park?
> Okay, a park that you can route through, is a particularly tagged park.
> The point still remains that with incomplete tagging, you have to make
> assumptions about whether the park is traversable.
>
>>> Just like a road, if it
>>> isnt tagged properly with oneway/access/barrier/etc, the routing will be
>>> inaccurate.
>> Correct.  What are you getting at?
> See above
>
>>> Actually, the fact that its not tagged correctly is a big part of the
>>> issue.  The renderer has to make assumptions if its not tagged.  If
>>> there was a tagging scheme to indicate that an area was traversable,
>>> then routing engines could start to use it,
>> There is such a tagging scheme.  It is described at
>> http://wiki.openstreetmap.org/wiki/Access
> There is also a tagging scheme footway=yes or highway=path.  Simply
> putting an access=yes tag onto an area doesnt give you any more
> information about it.  It doesnt tell you if theres a barrier or gate,
> it doesnt tell you if theres a big pond or lake smack-bang in the middle
> of the park which you have to walk around.
>
>>> but Id hate for a routing
>>> engine to try and take a short cut 'as the crow flies' through an area
>>> which hasnt got ways marked to follow.
>> I'd love it.  It's a feature I'm quite looking forward to.
> If you want routers to route through unmapped areas, then you can simply
> ignore the directions given and keep following the map, once you emerge
> out the other side of the park, the routing can carry-on from wherever
> you happen to come out.
>
>> One day OSM will be able to route me from Linkwood Avenue to Pine Bay Drive
>> through the park
>> (http://www.openstreetmap.org/?lat=28.07187&lon=-82.550402&zoom=18&layers=M),
>> saving me 50 minutes of walking.
> Imagine if you tried to save 50min by getting routed across Albert
> Park[1].  That big thing in the middle of the screen is a lake that
> extends almost the entire length of the park, hence you'll notice all
> the walking paths have been mapped in, to allow you to be routed through
> the park appropriately.

The way to avoid getting a soaking is to use multipolygon relations (as 
has already been done for the lakes island). It creates a rough doughnut 
shape.

An area way such as this park doesn't *need* linear ways to cross it. An 
area has an infinite number of ways criss-crossing it. If there are 
obstructions, then they should be mapped to make OSM more accurate..

As long as there are external ways connecting  to the area, a router 
should be able to find the appropriate entrances & exits by tracking the 
perimeter. I thought they were already able to do that, but maybe not.


Cheers
Dave F.



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