Hi there, I'm working from http://trac.mapnik.org/wiki/XMLGettingStarted - so far so good but I'd like to change the projection, with the ultimate aim of rendering tiles that match up with Google Maps etc. I've taken the first example on that page, using the Mapping Hacks borders file, and changed it slightly to work with the Thematic Mapping update, as follows.
In the python code I've changed the envelope to what I believe are Mercator coordinates that define a square Google-like map, and changed the dimensions to be 600px square: #!/usr/bin/env python from mapnik import * mapfile = 'world_styles.xml' map_output = 'hello_world_using_xml_config.png' m = Map(600, 600) load_map(m, mapfile) bbox = Envelope(Coord(-20037508.34, -20037508.34), Coord(20037508.34, 20037508.34)) m.zoom_to_box(bbox) render_to_file(m, map_output) And in the xml file, I've changed the Map's srs to match the one that OpenStreetMap specifies in http://svn.openstreetmap.org/applications/rendering/mapnik/osm.xml and added a latlong srs to the world layer: <?xml version="1.0" encoding="utf-8"?> <!DOCTYPE Map> <Map bgcolor="white" srs="+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 [EMAIL PROTECTED] +no_defs +over"> <Style name="My Style"> <Rule> <PolygonSymbolizer> <CssParameter name="fill">black</CssParameter> </PolygonSymbolizer> <LineSymbolizer> <CssParameter name="stroke">white</CssParameter> <CssParameter name="stroke-width">0.1</CssParameter> </LineSymbolizer> </Rule> </Style> <Layer name="world" srs="+proj=latlong +datum=WGS84 +over"> <StyleName>My Style</StyleName> <Datasource> <Parameter name="type">shape</Parameter> <Parameter name="file">/home/tom/mapnik/TM_WORLD_BORDERS-0.2</Parameter> </Datasource> </Layer> </Map> The output of the code above seems to only show countries reliably in the northeast, except for one or two others: http://www.tom-carden.co.uk/hello_world_using_xml_config_merc.png And I get almost the same issues with the original mapping hacks "world_borders.shp" file instead: http://www.tom-carden.co.uk/hello_world_using_xml_config_mh.png However the output using the original projection settings on the wiki (with modified colours) works just fine: http://www.tom-carden.co.uk/hello_world_using_xml_config_merc.png The comments on Thematic Mapping's blog suggest that I'll have an issue reprojecting this data because of multi-polygons that cross the date line: http://blog.thematicmapping.org/2008/03/world-borders-for-thematic-web-mapping.html Can anyone suggest a way around this? Many thanks, Tom. _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
