Returns an object of class list with the following components:
optan integer indicating the option that will be used to define the interpolation grid. Where
    opt = 1 indicates grid boundaries based on the extent of point data
      and a resolution of 100 rows and 100 columns;
    opt = 2 indicates grid boundaries based on the extent of point data
      and a cell resolution defined by the res component;
    opt = 3 indicates that the grid geometry is explicitly defined by the geo component.
  resnumeric vector of length 2 with components x and y giving the grid spacing
    along the x- and y-axis, respectively.
  geonumeric vector of length 6 with components
    nrows and ncols giving the number of rows and columns, and
    xmn, xmx, ymn, and ymx giving the limits of the grid boundary
    along the x- and y-axis.