[OSM-dev] Code to convert lat/lon to metres in Mercator projection?

[Nick Whitelegg]

Hello everyone,

Has anyone written any code to convert lat/lon to Mercator projection in metre 
units (metres east and north of the intersection of the Greenwich meridian 
and equator)? There's plenty of lat/lon to Mercator converters around (e.g. 
that in JOSM) but they give the answer in obscure units, e.g:

51.05 -0.72

becomes

-0.0125664 1.03951

I need this to generate Freemap tiles using Mapnik in mercator projection, but 
I want to be able to specify the scale in something like pixels/km.

Thanks,
Nick