Object of class ursaGrid
is a list with items:
columnsNumber of columns (samples)
rowsNumber of rows (lines)
resxGrid cell size by horizontal axis
resyGrid cell size by vertical axis
minxLeft margin of boundary box
maxxRight margin of boundary box
minyBottom margin of boundary box
maxyTop margin of boundary box
proj4PROJ.4 string
%%~ \code{is.grig} returns \code{TRUE}, if class of \code{x} is \code{ursaGrid}
Function dim for object of class ursaGrid returns named vector of length 2: number of rows ("lines") and number of elements in a row ("samples")