Anthony wrote:
On Sat, Jul 17, 2010 at 10:52 PM, Alan Millar <[email protected]
<mailto:[email protected]>> wrote:
Am I really asking something unreasonable of a router that when an
xxxx_link way meets an xxxx way at a very low angle, the router should
know to go forward and not almost reverse?
To some extent yes, this is unreasonable to ask of the router. While it
is not totally impossible to build a router to do this, routing
algorithms do not deal with geometry they only deal with connectivity.
You have to have geometry to deal with angles. While this could be added
to the preprocessing of the data into the graph file you would have to
represent it as another cost constraint or as a turn restriction and the
router would need to be "aware" of how to handle these.
It is better to fix the data, period!
You can not expect all routers to implement every weird hack to work
around all the weird data problems that various data sources have and
might want the router to handle. This is just not reasonable.
-Steve W
I don't know. It sounds like a reasonable rule, but 1) is it
necessarily *illegal* to make these turns, or is it just generally
discouraged? and 2) Is it always the case? Marcus says that "such
intersections with very sharp angles exist in many cities and are
valid". He didn't make it clear whether these are instances of
xxxx_link meeting xxxx (as opposed to xxxx meeting xxxx or yyyy), but if
so, I'd like to see examples, and I suppose that kills this solution.
I think if you want this enacted the first step would be to go through
the database and provide a list of all the situations where it happens.
Then we can go through, take a random sample, and get an idea of how
often this type of turn is legal or illegal. We also can get an answer
as to how widespread it is. If the numbers are low, we should just fix
them by hand. If it's high, then maybe a different solution is going to
have to be made.
I just found one near where I live
(http://www.openstreetmap.org/?lat=28.077361&lon=-82.570335&zoom=18&layers=B000FTF
<http://www.openstreetmap.org/?lat=28.077361&lon=-82.570335&zoom=18&layers=B000FTF>
any route from Alloway Street to/via Ehrlich Road). And if you look at
the aerial, it's definitely not a dual carriageway. I'm not 100% sure
whether or not it's a legal turn, though. I suspect it might be legal,
*if* it can be done safely and without blocking traffic (i.e. when
traffic is low). In which case, what is a router even supposed to do?
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