[OSM-dev] openlayers, projections and WMS

[Nick Whitelegg]

There are one or two things that I think I may have missed in my understanding 
of projections and WMS which mean that (for the moment) I'm migrating back 
from OpenLayers to the OSM-patched tile.js slippy map for Freemap, as I want 
something approximating to a Mercator projection. 

tile.js does this by grabbing tiles with differing latitude width so that they 
are effectively Mercator-projected. However  OpenLayers does not - the idea 
is that the WMS server should do the projection itself. Fair enough in terms 
of the curvature aspect - but given that OpenLayers appears to send the WMS 
server evenly-spaced latitudes for each tile, I don't really see how a 
Mercator projection returned from the WMS server can ever be displayed 
properly. Indeed if you try renderer.rb (which does an internal Mercator 
projection) on OpenLayers, gaps appear for this reason. Freemap works with 
OpenLayers (but non-Mercator projected) because it doesn't do any internal 
Mercator projection - the only Mercator projection involved in any version of 
Freemap is that in tile.js.

Can anyone give me any guidelines as to how I can make the Freemap renderer 
compatible with OL? Or is it just not possible without modifying the 
OpenLayers JavaScript tile engine, something which there are no plans to do. 

Thanks,
Nick