Raster* object (or a SpatialPixels* or SpatialGrid* object)
cell
cell number(s)
Details
The colFromCell and similar functions accept a single value, or a vector or list of these values,
Cell numbers start at 1 in the upper left corner, and increase from left to right, and then from top to bottom.
The last cell number equals the number of cells of the Raster* object.