JD-EE / Deltas
You are right, delta's are used succesfully in many other applications. I would just like to point out that the delta of two positions paired with time stamps is nothing else than ......
..... a groudspeed vector! Any GPS chip talking NMEA protocol provides this information free of charge, and one byte for course and one for speed every minute would be perfectly good enough for locating purposes. One additional byte for ROD or ROC would be luxury.