marc.gemis at gmail.com
Wed Jul 29 11:23:10 UTC 2015
What I try to say is that you should not map a important road for large
distances as "secondary + works_as_primary" just because it is a smaller,
has a different surface, a different ref or whatever.
Then (large distance, important road) it is a primary road IMHO, regardless
of any other tags.
If one downgrades such a road to secondary, the router can no longer prefer
it over other (real secondary) roads. (as you wrote)
Perhaps Ralph Aytoun expressed it better. But I tried to say the same as he.
Of course we shouldn't tag secondary or primary roads as trunk road or
motorways, but secondary & primary roads should only be tagged based on
their function, not on their appearance.
On Wed, Jul 29, 2015 at 1:11 PM, moltonel 3x Combo <moltonel at gmail.com>
> On 29/07/2015, Marc Gemis <marc.gemis at gmail.com> wrote:
> > On Tue, Jul 28, 2015 at 5:29 PM, moltonel 3x Combo <moltonel at gmail.com>
> > wrote:
> >> A router won't care about classification differences between far away
> >> places like Germany to Ethiopia. They just care about taking the best
> >> road in the area, and as long as OSM is locally consistent, this
> >> works. Even if a trunk turns into a primary for no physical reason and
> > Seems like I didn't make my point correctly.
> > I was trying to ask for global consistency so the router can use the same
> > default weights for street types, everywhere in the world. Something
> > 'prefer primary roads over secondary' roads to travel large distances.
> Routers can already use 'prefer primary to secondary' worldwide.
> Nowhere in the OSM world is secondary defined as better than primary.
> In any given area. a car router can confidently prefer 'primary'.
> What's true is that 'primary is X times better than secondary' will
> have different X values from one place to the next. But the
> differences between section of a given road can already be more
> important than the average difference between primary and secondary
> (for example an Irish secondary´s maxspeed can go from 60 to 100, but
> a primary isn´t generally 1.6x better than a secondary).
> Consider also the case of motorways : in all countries I've driven in
> they are very clearly defined and have legal specificities. OSM
> couldn't afford to mistake a motoway with something else. Yet the
> difference between a motorway and the next best thing is bigger in
> Germany than in Ireland.
> TD;DR: It's naive to think that routers can make a good decision using
> the highway tag alone. Harmonising highway tag worldwide would be of
> little use, and it would break local expectations. A locally coherent
> highway tag is preferable, and if you want more precise routing add
> the other tags.
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