[OSM-dev] (Multi)Polygon handling

nimix melchiormoos at gmail.com
Fri Jul 13 15:59:13 BST 2012


Even Rouault wrote
> 
>> 2) valid
> 
> Why do you need to reverse the winding order ? I thought that the WKT
> convention
> did not say anything about that, or did I miss something ? (Winding order
> is
> indeed significant in shapefiles, but that's another story). So I'd say it
> is up
> to the rendering engine to do any transformation that is needed for
> correct
> rendering according to the filling algorithm it uses.
> 
> 

If I remember it right mapnik requires normalized geometries, so outer in
clockwise and inners in counterclockwise order. I'm not sure if that is
still the case, but osm2pgsql still does the normalization. That's why I
defined the result in clockwise orientation...

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