  We introduce a new model for the spectral energy distribution of galaxies,
GRASIL-3D, which includes a careful modelling of the dust component of the
interstellar medium. GRASIL-3D is an entirely new model based on the formalism
of an existing and widely applied spectrophotometric model, GRASIL, but
specifically designed to be interfaced with galaxies with any arbitrarily given
geometry, such as galaxies calculated by theoretical hydrodynamical galaxy
formation codes. GRASIL-3D is designed to separately treat radiative transfer
in molecular clouds and in the diffuse cirrus component. The code has a general
applicability to the outputs of simulated galaxies, either from Lagrangian or
Eulerian hydrodynamic codes. As an application, the new model has been
interfaced to the P-DEVA and GASOLINE smoothed-particle hydrodynamic codes, and
has been used to calculate the spectral energy distribution for a variety of
simulated galaxies from UV to sub-millimeter wavelengths, whose comparison with
observational data gives encouraging results. In addition, GRASIL-3D allows 2D
images of such galaxies to be obtained, at several angles and in different
bands.
