The function spCovDel allows to build optimization scenarios based on spatial coverage method.
spCovDel(observations, candidates, nDiff, plotOptim = TRUE, ...)data.frame of optimized locations
object of class data.frame with x,y coordinates
not compulsory used only for plotting purpose -- a 
         SpatialPolygonsDataFrame describing the study area
number of stations to add or delete
logical; to plot the result or not
other arguments to be passed on at lower level functions such as 
              nndist
Olivier Baume
This function allows to build optimization scenarios based on spatial coverage method. 
When action is "del", the function maximizes the mean distance of measurements with direct neighbours using function 
nndist. The heuristic search uses a 
swapping algorithm to converge more rapidly to the best solution.