[talk-au] Junctions (to name or not to name)

[Jack Burton]

On Sun, 2009-06-28 at 10:03 +1000, Sam Couter wrote:
> Only to say that the same questions are raised by motorway_link and
> primary_link, except they're even more important when listening to
> routing directions. And those questions aren't answered in the Wiki
> either, as far as I can tell.

Any decent routing algorithm should look ahead to the turn after the
next one (or even the one after that, etc. etc., if need be) if the
current turn is to an un-named way.

e.g. if the route goes from a motorway to an unnamed link road to a
named way called "foo", the router should announce "exit left to foo",
not "exit left on unnamed ramp".

This works well in practise, since the physical signage leading up to
most motorway links (and other un-named link roads) usually indicates
the name of the road that the link leads to, so the router announcement
corresponds with what the driver actually sees.

Having said that, though, if the signage leading up to to a
motorway_link does _not_ contain the name of the road it leads to, then
we should probably be naming that link in accordance with the signage
(e.g. "Footown exit").

With roundabouts, the need to name un-named segments is even less, since
even if the above method fails (e.g. if all ways on the route from the
roundabout to the final destination are un-named), the router can at
least announce "enter roundabout, then take the nth exit".

As others have said, the issue seems to be a bug in the validator and/or
in gosmore, rather than any deficiency in the method most mappers are
using to map un-named ways (although of course, as Darrin pointed out,
those roundabouts [or link roads] that _do_ have names in the real world
should of course be named in OSM too).

Just my 2c worth...

Regards,


Jack Burton
<jack at saosce.com.au>