Ben, It would be helpful if you could paste your whole XML or python script. That way I could see issues more clearly like: are you remembering to set the layer 'srs' value? When loaded via XML a layer without an 'srs' value set will default to the map 'srs'. But in python a layer created from scratch (since it is not part of any map yet) will default to EPSG:4326 (+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs).
Also, spherical mercator, or the google projection you want is likely: +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over The +nadgrids=@null is the key part you are missing. Dane On Jun 27, 2011, at 3:49 AM, Ben Crane wrote: > Hi all, > > I've installed and got mapnik working for shape, tab and postgis and am > making good progress...but I have a question regarding projections : > > My shape file is in WGS84. I reference a particulare area of the world file > in standard lat/long notation in the python script eg: > > bbox = mapnik.Envelope(mapnik.Coord(-180.0, -75.0), mapnik.Coord(180.0, 90.0)) > > What I was wondering is that if I change the projection of the python > script/XML styles to EPSG: 3857 (Popular Visualizations) and the shape file > remains in WGS84 is that going to cause a conflict in terms of which > projection is used? The reason I ask is that I altered the projection to: > srs="+proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +a=6378137 +b=6378137 > +towgs84=0,0,0,0,0,0,0 +units=m +no_defs" > > and then altered the Envelope clause to bbox = > mapnik.Envelope(mapnik.Coord(-2022737, 476045), mapnik.Coord(3223267, > 5458042)) (focussing on Spain) but no joy - I get a white png image and no > errors which makes be think it's just taken a snapshot of nothing since > lat/long isn't in this range. > > So either I cannot override the shape file projection, or I am doing it > incorrectly...is this possible > > Many thanx, > > BC > _______________________________________________ > Mapnik-users mailing list > [email protected] > https://lists.berlios.de/mailman/listinfo/mapnik-users
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