With modern computers, Monte-carlo ray tracing methods are widely used for [[View Factor]] and [[Grey Body Factor]] calculation ## 1. View Factor Calculation Rays are shot at random directions for surface $i$. View factor is calculated based on number of rays that hit a surface $j$ divided by the number of rays shot from a surface $j$ ## 2. Grey body factor calculation For calculating grey body factors, the rays emitted from a source surface at an energy equal to the emissivity of the source surface. They are not terminated once they hit a target surface (as in the case while calculating view factors) but are reflected carrying a fraction of the original energy (based on the emissivity of the target surface). When the ray loses energy below a tolerance value, it is eventually absorbed. Or if it goes to space, it is terminated **Energy Cutoff Factor** is what is used to cut off the ray. Dont set it to zero or it might reflect for ever ## 3. Intersection Test Intersection test determines which surface is get hit by the ray. If you had a second surface overlapping, software picks a surface in random. Especially a problem when you start a ray from a overlapping surface then the ray might get terminated where it started. $B_{ij}$ can be greater than 1 when you have overlapping surfaces.. i.e you are creating energy. So be wary of them