[Tagging] Tunnels and bridges

Peter Wendorff wendorff at uni-paderborn.de
Fri Feb 1 14:33:31 GMT 2013

Am 01.02.2013 15:01, schrieb Janko Mihelic':
> 2013/2/1 Peter Wendorff <wendorff at uni-paderborn.de 
> <mailto:wendorff at uni-paderborn.de>>
>     but on the other hand it's a reasonable preprocessing step to
>     calculate these conflicts (sharing nodes between ways having
>     bridge=* and ways having the bridge-area-tag => remove the
>     bridge=yes tag for rendering).
> I think that's harder than you think. What if you have the next example:
> http://i.imgur.com/ETBsfSQ.png
> How does the renderer preprocesor know if the middle line is inside 
> the bridge area? It has to make some difficult calculations for that. 
> And the blue line is outside, although it shares two nodes with the 
> bridge. (I know it would rarely happen, but it will happen.)
Sure it will happen.
And yes, that's more complicated to achieve, but look at the renderings 
in many ordinary streets on all common osm renderings: As soon as was 
are divided into pieces, you likely get very dense lables as mapnik 
renders labels on every part of the street individually. Examples:
http://osm.org/go/0GPCAb0oG-- (Ostenallee near the intersection)
http://osm.org/go/0GlK2S06_-- (Liboriberg: two parts bridge (as the bus 
routes use the bridge Kasseler-Tor-Brücke), two labels left and right 
for the non-bridge-part of the street.

So that's a general problem of renderers, yet - but it should be solved 
imho, and this might be done independent of concrete tags or features, 
to combine features sharing the matching properties for a particular 
style. Other use cases for something like that:
- dashed line patterns now interfere when coming together on different 
ways as there occur shorter or longer dashes or spaces at the connection 
- labels (see above) could be rendered after combining more parts of the 
street, if they are skipped due to their size on the short single way parts
- the bridge example of course
> And I don't know why you guys think black borders on the street over a 
> bridge look ugly. We have examples:
> http://osm.org/go/0BOd2GJhP--
I personally never said this looks ugly. I didn't even look into what 
would happen in the current style with these casings,
but for any style using mapnik the way I described should work to not 
interfere with a possibly more verbose bridge casing than in the mapnik 
style in more or less any case.
> Which look good to me, and if you zoom out, those black borders are 
> needed again:
> http://osm.org/go/0BOd2B4U--
> because the street outgrows the bridge area.
That's why I promoted to keep bridge=yes nevertheless (see previous posts)

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