The properties of the four families of the recently introduced special functions of two real variables, denoted here by E± and cos±, are studied. The superscripts + and − refer to the symmetric and antisymmetric functions, respectively. The functions are considered in all details required for their exploitation in Fourier expansions of digital data, sampled on square grids of any density, and for general position of the grid in the real plane relative to the lattice defined by the underlying group theory. The quality of continuous interpolation, resulting from the discrete expansions, is studied, exemplified, and compared for some model functions.