How are the early-dates and late-dates curves calculated?

The baseline curve can be calculated as Rn = Rn-1 + i = 1j Rni where Rn is cummulative resource usage till nth period and j denotes total number of activities consuming resources on the nth period. The early-dates is equal to the baseline curve where the drift has been removed from all activities. The late-dates is equal to the baseline curve where the float has been removed from all activities.