I looked at Kalman filtering and realised that to do it properly I would be inverting 11x11 matrixes, which is
unrealistic on the arduino. So I did it another way.
But there is a long thread on the forum here about kalman filtering, so I guess you should do it their way.
The problem with "dead reckoning" is that trying to measure your motion with accelerometers and gyros
accumulates a large noise error very quickly, which almost makes it useless. Measuring position with
reliable wheel encoders is an improvement.
The thing is, with outdoors, you might expect lapses in GPS to be transient as you go past a building
or under a freeway overpass, and after you have done that the GPS will work again.
But indoors, you might never get a GPS reading.
I suspect the long term solution to this, is some kind of indoor re-broadcasting of the GPS signal.