[OSM-dev] Mapnik rendering: Zoom-Level to Width/Height

[Peter Körner]

Hello

I'm writing on a simple Frontend for the mapnik-toolchain. Currently you 
can call it like this:

osm-render --bbox 8.2011,49.9649,8.3278,50.0327 --size 8192x4096

I'd like to add another option like this:

osm-render --bbox 8.2011,49.9649,8.3278,50.0327 --zoom 14

The combination of bbox-size (in lat/lon or maybe kilometers?) and 
output-size (in pixels) somehow leads to the ScaleDenominator used in 
the mapnik style, so i think it could be calculated to a zoomlevel and 
vice versa.

Does anyone has a formular for that (especially bbox & zoom --> width & 
height) or is this just not possible?

Thank you,
Peter