On 27/07/2010 10:21, John Smith wrote:
Why do taggers have to compensate for poorly written programs making
use of the data?
Why does the data model have to make it so difficult for data consumers
in the first place?
You cannot tell from our data model whether a bridge supports two ways
or whether there are two parallel bridges, unless you, the tagger, says
so (in a relation, on which there is no common agreement). e.g.:
http://osm.org/go/0EQSjpjFr-- where the two roads are actually on
*separate* bridges,. but the cycleway to the north shares the northern
bridge with the road. Even if you did this as a separate polygon (which
there is no support for in any of our software and would be a big burden
on data producers, and doesn't take account of the hundreds of thousands
of bridges already out there), you'd still need the relation for
applications other than just rendering.
You *can* tell which ways go underneath a bridge without tagging help.
But you *can't* do it fast as it requires a search and some moderately
complicated geometry. No doubt you want fast rendering as well as
efficient tagging.
You cannot tell from our model, without additional information such as a
relation, whether two parallel ways are part of a dual carriageway or
just parallel roads.
You cannot reliably tell which street a property fronts onto.
You can't even easily tell what a street is. Yes you can deduce it, but
I now regret the loss of segments that cause streets to be broken up
into dozens of ways. It's not the renderer that's poorly written here,
nor the tagger, it's the data model that forces vast amounts of
heuristic code onto the consumer just to tell what a street is.
David
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