[OSM-dev] Mapnik style broken?

Jon Burgess jburgess777 at googlemail.com
Tue May 15 12:21:10 BST 2007

On 15/05/07, Martijn van Oosterhout <kleptog at gmail.com> wrote:
> On 5/14/07, Artem Pavlenko <artem at mapnik.org> wrote:
> > As I mentioed in another email, I think the layering model of mapnik is
> > currently slightly different to other renderers. I think Mapnik always
> > draw lines over the top of areas even if the area has a higher layer set
> > than the line. This is because it renders all polygons, then lines, then
> > points, then text / symbols (at least this is what I understand, perhaps
> > Artem can confirm or correct me).
> >
> > At the moment, yes polys->lines->points. But we can change this by storing
> > mixed geometries (as used to be:)
> > in one big table and using global z_ordering. It will work but we need well
> > defined rules for how to order features.
> It seems to me you don't ever want areas to be drawn over roads. Even
> in the case of a tunnel, you draw the area first and then the road as
> a dotted outline. It's still drawn after. Drawing areas later just
> obliterates anything underneath (unless you have alpha blending, but I
> didn't think so).
> Have a nice day,
> --
> Martijn van Oosterhout <kleptog at gmail.com> http://svana.org/kleptog/

In the example I saw, someone had used an area over the top of a
motorway to fabricate a bridge-like structure and then placed several
other roads over the top of the area. I think this was done as a
workaround for osmarender not being able to adequately draw a bridge
with multiple ways going across it.

This probably isn't a good example of how areas should be used.

If we all agree that polygons should always be rendered first then
mapnik is correct and we may need to fix other renderers to match :-)


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