[OSM-dev] Mapnik rendering

Andy Allan gravitystorm at gmail.com
Mon Dec 1 19:48:46 GMT 2008

On Mon, Dec 1, 2008 at 3:38 PM, Ed Loach <ed at loach.me.uk> wrote:
> I've just noticed if you have a bridge going over a trunk dual carriageway the oneway arrows render above the bridge,
> e.g.
> http://www.openstreetmap.org/?lat=51.872301&lon=0.316664&zoom=18
> And if you zoom out a bit the arrow on the opposite carriageway overlays the bridge rather than the one shown here.
> I've checked the tagging and the bridge over is at layer 1 and the trunk road has no layer tag.
> I guess this isn't an easy thing to resolve. Go to decimal layers and have the arrows at +0.5 layer or whatever?
> Just thought I'd mention it in case it isn't known about.

Yep, it's a known issue. Fixing it 'a bit' would involve having a
one-way icons definition for each road type in each road layer (so
every bridge layer etc) which would then overdraw the icon if another
feature goes over the road. Fixing it 'properly' (i.e. draw all the
roads, figure out which bits are obscured and therefore not drawing
icons half-under bridges) would then need a fairly big rethink on both
the osm.xml and mapnik's rendering engine.

There's almost certainly a more sensible way to generate the rules
files than specifying each rule by hand, but it gets discussed and
then not implemented.


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