@arjanvanb .. storing gps data in a 24 bit integer has nothing to do with any number of decimals, it is not 4 and also not 5 decimals, it lies somewhere in between:
the calculation for storing in integers is MUCH simpler: a int24 has 2ˆ24 (= 16777216) possibilities and in the int you just store the full range of -180 to +180 degrees. The equatorial radius of the earth is about 40075000 meters so the accuracy of a gps longitude in a 24 bit integer is 40075000/(2ˆ24) = +/- 2.39 meters.