All this stuff may work out on paper. It's fun to do the math. The problem is.. Non-Military GPS is not as accurate as you would like to think. To prove this...Go to the waypoint of your choice and "MARK" the position on your GPS.
Now: Go back tomorrow to the same waypoint you "marked" yesterday and see if the multiple digits match up. Civilian GPS
Repeatability is maybe good for +/- 100 feet. ..Maybe.
GPS is a GIFT from the military. They still regulate the results on your civilain GPS unit. Just Sayin...
NB