[OSM-talk] routing across open spaces

Anthony osm at inbox.org
Wed Dec 1 01:24:46 GMT 2010


On Tue, Nov 30, 2010 at 7:48 PM, David Murn <davey at incanberra.com.au> 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.

A way which is tagged with leisure=park is a particularly tagged way.

> The point still remains that with incomplete tagging, you have to make
> assumptions about whether the park is traversable.

Correct.  The same is true of a way tagged with highway=footway or
highway=steps or highway=proposed or highway=motorway, if it doesn't
have any access tags, of course.

> See above

Indeed.

>> > 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.

Sure it does, it tells you the area is a right of way.

> 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.

Well, no, of course not.  Neither does footway=yes, or highway=path,
access=yes, tell you if there's a barrier or gate or a big pond or
lake in the middle of the footway/path.  If someone maps an area,
sticks access=yes on it, and doesn't map the gates, the routers can't
be expected to work correctly.

Whether or not access=permissive (not access=yes) should be the
default is something I can't really say, because I haven't taken a
sample to see how common it is for parks with fences to mapped as
leisure=park and with no mention of the fence.

>> > 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.

I don't want them to route through unmapped areas.  I want them to
route (via foot) through mapped areas tagged with leisure=park.

>> 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.

You forgot the link, so I'm going to imagine that the lake was mapped.
 Obviously a lake is by default foot=no.

>> what if someone marked a national park as an area, should routers simply
>> show a route ATCF or should it only route through a national park area
>> if there is a way to follow?
>>
>> Routers shouldn't route through all areas the same, any more than they
>> should route along all non-areas the same.  An area tagged with
>> leisure=park wouldn't have the same access defaults as an area tagged
>> with building=yes.
>
> Okay, so what areas are routable then?  Is leisure=playground passable?

Not sure what the default for that should be.  Probably foot=permissive.

> What about parking areas,

Default is probably foot=permissive, vehicle=destination.

> golf courses, schools, graveyards, farms?

I'd say the default there is access=private.

> All
> of these places can sometimes be travelled across, but not all.  These
> places often also have paths to follow, as do most parks, especially
> between entrances.

You don't seem to be using the term "park" the same way as is intended
by leisure=park.  leisure=park is meant for open areas.  Just because
something is called a park doesn't mean it should be tagged with
leisure=park.

In any case, as you allude to, routing of vehicles through a parking
lot generally shouldn't use shortest path.  For foot traffic, shortest
path is probably a good approximation.

Thanks for the discussion.  You raise a lot of good points about how
much detail will have to go into the routers in order to properly
handle this.  I have no doubt one day that detail will be added,
though.  It's just too huge of a potential time saver for it not to be
incorporated, and is a place where OSM and its high level of detail
might just be able to get a leg up on the competition.



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