

r.cost - 

r.cost determines the cumulative cost of moving to each \cell\ on a
cost surface (the input raster map layer) from other user-specified
cells whose locations are specified by their geographic coordinate(s).
Each cell in the original cost surface map will contain a \category\
value which represents the cost of traversing that cell.  r.cost will
produce an output raster map layer in which each cell contains the
lowest total cost of traversing the spce between each cell and the
user-specified points.

Manual entry for \r.cost\
