Re-Proejections and Calculation of Zooms

[Stefan Schwarzer]

Hi,

I don't understand how I can calculate the extent of the zoom for a  
reprojected map,i.e.
- my original layers are in Latlong
- they are being (upon user request) reprojected (into for example  
Mollweide)
- upon display of the global map, the user draws a rectangle to zoom in

How do I have to deal now with the Latlong/DD and Mollweide/Meters  
parameters to get the proper extension of the chosen rectangle and  
zoom into that? I don't have clue...

Thanks for any help,

Stefan