The Photon Simulator (PhoSim) is a set of fast photon Monte Carlo codes used to calculate the physics of the atmosphere, telescope, and detector. It does this using modern numerical techniques applied to comprehensive physical models. PhoSim generates images by collecting photons into pixels.  This movie shows the photon raytracing method used in the simulation. The links below describe more detailed technical information about using it and its current fidelity. Comprehensive information can also be found in the PhoSim Reference Document.