  The era of interferometric observations leads to the need of a more and more
precise description of physical structures and dynamics of star-forming
regions, from pre-stellar cores to protoplanetary discs. The molecular emission
can be traced in multiple physical components such as infalling envelopes,
outflows and protoplanetary discs. To compare with the observations, a precise
and complex radiative transfer modelling of these regions is needed. We present
GASS (Generator of Astrophysical Sources Structure), a code that allows us to
generate the three-dimensional (3D) physical structure model of astrophysical
sources. From the GASS graphical interface, the user easily creates different
components such as spherical envelopes, outflows and discs. The physical
properties of these components are modelled thanks to dedicated graphical
interfaces that display various figures in order to help the user and
facilitate the modelling task. For each component, the code randomly generates
points in a 3D grid with a sample probability weighted by the molecular
density. The created models can be used as the physical structure input for 3D
radiative transfer codes to predict the molecular line or continuum emission.
An analysis of the output hyper-spectral cube given by such radiative transfer
code can be made directly in GASS using the various post-treatment options
implemented, such as calculation of moments or convolution with a beam. This
makes GASS well suited to model and analyse both interferometric and
single-dish data. This paper is focused on the results given by the association
of GASS and LIME, a 3D radiative transfer code, and we show that the complex
geometry observed in star-forming regions can be adequately handled by
GASS+LIME.
