  To derive physical properties of the neutron star surface with observed
spectra, a realistic model spectrum of neutron star surface emission is
essential. Limited by computing resources, a full computation of the radiative
transfer equations without the diffusion approximation has been conducted up to
date only for the case of local magnetic fields being perpendicular to the
stellar surface. In this paper we report the full-computation result for an
arbitrary field direction. For comparison we also compute the radiative
transfer equation using the diffusion approximation. For a given effective
temperature, the computed spectrum with the diffusion approximation is always
softer than that of a full computation at a non-negligible level. It leads to
an over-estimate of the effective temperature if the diffusion approximation
spectrum is employed in the spectral fitting. Other characteristics for
different magnetic field orientations, such as the beaming pattern of the two
polarization modes and the structure of the atmosphere, are also discussed.
