There's no reason to calculate touchdown point for normal landings at all. We screen all landings by the "G" on touchdown and flag those above the type limit, look for side drift above limits on vulnerable fleets (e.g. Airbus A300-600, look for long touchdowns by a specified time after 50 ft Radio Ht and will soon start looking at short touchdowns again by less than say 5 secs from 50 RA.
The only time we do an accurate calculation is where ther's been a hard landing because they are almost always short and its worth being accurate about where it happened.