SpatialPixelsDataFrame returns an object of class
SpatialPixelsDataFrame-class; SpatialGridDataFrame returns an object
of class SpatialGridDataFrame-class.
Arguments
points
coordinates, either as numeric matrix or as object of class
SpatialPoints-class
grid
grid topology; object of class GridTopology-class; for
calls to SpatialPixelsDataFrame a value of NULL implies that this will
be derived from the point coordinates
data
data.frame; contains the attribute (actual grid) data
tolerance
precision up to which extent points should be
exactly on a grid
round
default NULL, otherwise a value passed to as the digits argument to round for setting cell size
proj4string
object of class CRS-class in the first
form only used when points does not inherit from Spatial-class