[OSM-talk] routing across open spaces

David Murn davey at incanberra.com.au
Sun Dec 5 01:36:24 GMT 2010


On Wed, 2010-12-01 at 00:00 -0500, Anthony wrote:

> Anyway, I looked around at a few places labelled leisure=park, and the
> usage is all over the place.  I'd say based on that very unscientific
> sample that it's probably best for routers to use a default of
> access=unknown for leisure=park areas, and only use parks for short
> cuts if they're explicitly tagged with something like foot=permissive.
> 
> Alternatively, I guess it wouldn't be horrible to add something like a
> highway=shortcut tag, so mappers could be explicit about it.  If we've
> gotta add foot=permissive by hand anyway, it's not that much more work
> to add a few extra ways.

I was thinking of this issue last night while playing with my routing
software.  One issue I thought about which makes this difficult, is
different shapes.  If youre trying to route across a square area or any
area which has a direct path from start to finish, routing in your
method is easy.  But I was thinking, what happens if youve got an
L-shaped park or even a U-shaped park.

  +-----+        +-------+
  |     |        |       |
  |     |        | +-C-+ |
A |     | B    A | |   | | B
  +-----+        +-+   +-+

Do you cross the open part of the area in the second example, in a
straight line from A to B?  Do you form an arc?  Do you simply go from A
to B, but go around the edge near C?  As an area is unlikely to be a
perfect oblong, this situation may arise more often than one would
think.

David




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