RADMC-3D is a code package for diagnostic radiative transfer calculations in astronomy and astrophysics. It calculates, for a given geometrical distribution of gas and/or dust, what its images and/or spectra look like when viewed from a certain angle, allowing modelers to compare their models with observed data.
Typical applications are dusty molecular clouds, protoplanetary disks, circumstellar envelopes, dusty tori around AGN and models of galaxies. But the code is also regularly applied to other kinds of objects.
The code package is well documented and has numerous simple examples that can be used as templates for one's own models.
The RADMC-3D code is freely available and open source. It runs on linux and OS X. The main code is written in Fortran 90, but all interaction with the code is done through Python interfaces.