This option can be used to carry out a 3D calculation with a 1D-solver, where a 3D-cloud file as used for MYSTIC (flag 3) serves as an input file. Further, a sample grid needs to be specified via mc_sample_grid, where the grid and the resolution has to be the same as in the 3D-cloud file (Nx, Ny, dx, dy). To calculate heating rates, mc_backward_output heat K_per_day must stand in the input file.