On Fri, Jan 11, 2013 at 8:52 AM, Michael Patrick <geodes...@gmail.com> wrote:
> Just my clarification ... we are blessed just about all those bridge types
> except the gondola. First,on first glance 'movable' subsumes all the other
> movable types. if it is exclusive of those, I might suggest 'movable_other',
> or something similar (our former I-520 Evergreen Point bridge had a bulge,
> which had a 'retractable' span (see
> http://ww1.hdnux.com/photos/03/01/47/793032/3/628x471.jpg ). Also, when the
> bridge has multiple types of structures and spans, how is that addressed -
> i.e. beam, floating, truss, and viaduct probably simultaneously exist on the
> same named 'bridge, is each way segment named the same but separately? Or
> just the primary distinctive feature? Could you tag the I-90 Bridge from
> Seattle to Bellevue as an example (Tunnel - beam - viaduct - float - beam -
> etc.)?
Michael,
Comments at the bottom of the proposal have also suggested creating a
separate tag for the types of movable bridge. I think I like the
"bridge:movable" suggestion made there. (So movable bridges would be
tagged, e.g., "bridge=movable; bridge:movable= bascule" and so forth.)
That also makes it a little easier to parse for a (hypothetical)
downstream piece of routing software; it doesn't care to learn about
all the different varieties of movable bridge, it just needs to be
able to spot bridges that could open and leave you stuck in a traffic
jam.
In the case of complex bridges, there would be a different way segment
for each type of span the way passed over. (If you have, say, several
consecutive truss spans, I don't see a need to break that into
multiple segments.) This is my approximation for the eastbound lanes
of I-90, moving from west to east. Segment 1 (over roads):
"bridge=yes; bridge_type=beam". Segment 2: "bridge=yes;
bridge_type=truss". ("bridge=viaduct" might be OK for this, too;
that's sort of a matter of taste.) Segment 3: "bridge=yes;
bridge_type=arch". Segment 4: "bridge=yes; bridge_type=floating".
Segment 5: "bridge=yes; bridge_type=arch". Segment 6: "bridge=yes;
bridge_type=beam".
That seems rather extreme, but in practice, I think people will
largely continue using "bridge=yes" for most road and highway bridges
and largely concentrate on marking "charismatic" things like covered
bridges, (stone) arches, and so on; detailed tagging like this example
will probably be the province of bridge aficionados. And this kind of
"span-by-span" breakdown does have some potential when it comes to
navigation. In bridges crossing navigable estuaries, it's not uncommon
to have a long series of fixed spans with a movable span somewhere in
the middle over the navigation channel. In that case, it's certainly
useful to distinguish between the movable and the fixed spans, as it
defines the location of the channel.
Yours,
--
Chris Hoess
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