PhoSim Tutorial 8: How to turn on and off Physics Modules
PhoSim has many options to modify or override the default settings. The nominal settings are based on the most realistic physics. There are many cases where it is useful to study parts of the simulation to determine what aspect of the simulation may affect a particular measurement or property of the images. A series of commands can be placed in an physics override file for many different kinds of simulations. One example of this would be to place these commands in a file (called commandfile):
opticsonlymode 0
backgroundmode 0
pixelsize 0.1
This would then ignore aspects of the sensor and atmosphere simulation and simulate objects with very small pixel sizes (0.1 microns). Then a simulation with the following command
phosim examples/brightstar -i lsst -c commandfile
would produce an image like this: