The source radius, Rmil, is typically taken to be similar to the filtering radius. The automatic default option uses the filter radius, Rmil = Rmin. Once all the milling fields, , have been computed, they are combined using an approximate maximum operator:

A large aggregation exponent, pmil, gives a good approximation of a maximum operator. However, this can also cause numerical problems so the default automatic option uses pmil = 10. The final milling material volume factor, θm, is often significantly larger than 1 so it is important to use projection with milling constraints.