To store 2D polynomials. This is to store a 2D Lookup Table. E.g, a low resolution raster of baselines etc. To store functions that are separable in two dimensions - f(x) .op. g(y) . This is a time-tagged list of 1D functions often used in radar processing - (t_i, f_i(x)) . This is used for storing Doppler, FMrate and slant_range_to_ground_range polynomials/ LUTs.