  B[e] supergiants are luminous, massive post-main sequence stars exhibiting
non-spherical winds, forbidden lines, and hot dust in a disc-like structure.
The physical properties of their rich and complex circumstellar environment
(CSE) are not well understood, partly because these CSE cannot be easily
resolved at the large distances found for B[e] supergiants (typically $\ga
1$~kpc). From mid-IR spectro-interferometric observations obtained with
VLTI/MIDI we seek to resolve and study the CSE of the Galactic B[e] supergiant
CPD-57\degr\,2874. For a physical interpretation of the observables
(visibilities and spectrum) we use our ray-tracing radiative transfer code
(FRACS), which is optimised for thermal spectro-interferometric observations.
Thanks to the short computing time required by FRACS ($<10$~s per monochromatic
model), best-fit parameters and uncertainties for several physical quantities
of CPD-57\degr\,2874 were obtained, such as inner dust radius, relative flux
contribution of the central source and of the dusty CSE, dust temperature
profile, and disc inclination. The analysis of VLTI/MIDI data with FRACS
allowed one of the first direct determinations of physical parameters of the
dusty CSE of a B[e] supergiant based on interferometric data and using a full
model-fitting approach. In a larger context, the study of B[e] supergiants is
important for a deeper understanding of the complex structure and evolution of
hot, massive stars.
