A least-squares procedure is described for modeling an empirical transmission surface as sampled by multiple symmetry-equivalent and/or azimuth rotation-equivalent intensity measurements. The fitting functions are sums of real spherical harmonic functions of even order, ylm(-u0) + ylm(u1), 2 < or = l = 2n < or = 8. The arguments of the functions are the components of unit direction vectors, -u0 for the reverse incident beam and u1 for the scattered beam, referred to crystal-fixed Cartesian axes. The procedure has been checked by calculations against standard absorption test data.