  [Abridged] AGB stars are significant contributors to the metal enrichment of
the interstellar medium. In this paper, we adapted models from advanced RHD
simulations as input for radiative transfer software to create synthetic
observables. A major goal is to describe an AGB star's non-sphericity and to
simulate its effects on the surrounding dusty envelope. We developed tools to
translate models of an AGB star and its dust-driven wind from simulations with
CO5BOLD into the format used by RADMC-3D. We preserved the asymmetric shape of
the star by including it as a `dust species' and by using temperature data
computed in CO5BOLD. Circumstellar dust is included using Mg2SiO4 opacity data
with spatially dependent grain sizes. We compared images and SEDs created with
RADMC-3D of a model with similar output made with a spherically symmetric star.
Our CO5BOLD model features substantial and clumpy dust formation just above 3.4
au from the grid centre, and large-scale structures due to giant convection
cells are visible on the stellar surface. With the properties of VLTI as a
basis, we have created simple synthetic observables. Such optical
interferometers should be able to detect these dust clouds. We find that it is
important to include asymmetric stellar models since they even affect the SEDs.
Effects on flux levels can be linked to the clumpiness of the circumstellar
dust and the angle-dependent illumination resulting from temperature variations
on the stellar surface causes shifts in the wavelengths of the flux maximum.
The methods presented here are an important step towards producing realistic
synthetic observables and testing predictions of advanced 3D RHD models. Taking
the angle-dependence of SEDs as a proxy for temporal variations in unresolved
data, we conclude that not all variability observed in AGB stars should be
interpreted as global changes in the sense of spherical models.
