as.SpatialGrid,prevR-method: Create a spatial grid from an object of class prevR.
Description
This function generates a spatial rectangular grid from the slot boundary of an object of class prevR; function used in particular by the methods kde, krige and idw.
This function generates a spatial rectangular grid, each cell being a square of side cell.size. If cell.size is not defined, side of cells will be calculated as the longuest side of the slot boundary of object divided by nb.cells.