[OSM-talk] routing across open spaces

[David Murn]

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.

> 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?
What about parking areas, golf courses, schools, graveyards, farms?  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.

David