I skimmed that paper... math is hard.<p>I kinda wonder if the path created by the inertial system is being used to correct the sequence of GPS derived points. Reason being the inertial systems error is tiny, but cumulative over time. Where the GPS error is large per measurement but tiny when averaged over a set of geographically spaced points.<p>You have two errors, plain noise that causes the position at a particular location to vary. And a location&#x2F;time[1] specific error that is an offset. If you know the shape of your path precisely then you can rectify both.<p>[1] Location due to interference of things like trees, buildings, etc. Time because the positions of the satellites changes over time.