MASK and r.cost?

[Lars Schylberg]

I have a student here that have been doing his Msc thesis project about
finding optimal gravel pits for different building sites.  He has been
using r.cost to compute cost for different locations.  

If he only wants to travel along roads it would be nice if we could
use the MASK to filter out surrounding fields and forest.  But it seems
like r.cost is ignoring the MASK.   We had to solve it by setting very 
high cost values for the areas beside the roads.

Is there some reason why the MASK is not considered in r.cost ?
Couldn't the calculation be speeded up if you could mask pixels ?
Is there something that I have overseen here ?  I haven't used
r.cost so much myself.

Lars

Lars Schylberg                          Email: larss at fmi.kth.se  
Dept. of Geodesy and Photogrammetry 
Royal Institute of Technology (KTH)     Tel.   +46 8 790 86 33   
S-100 44  STOCKHOLM, SWEDEN             Fax.   +46 8 790 66 10