[OSM-dev] Projection Issues

[Nick Whitelegg]

Without an in-depth knowledge of projections, I know that tile.js takes in
a "real" longitude and latitude and converts the latitude to a Mercator
latitude (see e.g. http://nick.dev.openstreetmap.org/javascript/tile.js)
The OSM tile renderer then accepts a bounding box of regular longitudes
and Mercator latitudes.

Actually I don't think that's quite right... it converts the regular 
latitudes into Mercator latitudes (e.g. 51N becomes 59N) in order to 
divide up the tiles evenly. However the tile server itself accepts regular 
latitudes, i.e. if you ask it for 51N, 1W it will give you data actually 
at 51N, 1W. This is evidenced by accessing the OSM tile server directly:


http://tile.openstreetmap.org/cgi-bin/steve/mapserv?map=/usr/lib/cgi-bin/steve/wms.map&service=WMS&WMTVER=1.0.0&REQUEST=map&BBOX=-1.5,50.8,-1.3,51.0&WIDTH=400&HEIGHT=320&LAYERS=landsat,streets

The Landsat you get is recognisable as the Southampton area which is at 
that latitude and longitude.

Nick