On Friday, October 23, 2015 at 12:57:08 AM UTC-7, krasw wrote:
Kalman (and EKF) is a process that you run into pretty much everywhere. It's quite elementary way of correct predicted state of something on basis of comparing previous predicted state to current observations. It doesn't do theh inertial navigation itself, it's just way of polishing things numerically. For example, if airspeed measurement is systematically too small, Kalman filter corrects that error (this is maybe too elementary example, reality is more complex for sure). I think important part of achieving this state of inertial navigation (without GPS) is by using measured TAS.

TAS (calculated, not measured) is probably the most important input to the algorithm, but navigation without GPS cannot be done without heading information as well. interestingly, accurate heading cannot be computed without at least a rough idea of where you are on the planet due to magnetic declination. so this system would not work as well (in most places) without an initial GPS fix. this purely academic though because any navigation system would be useless without at least knowing the starting point.

also interesting is that having a rough idea of where you are also improves the accuracy of the accelerometer because the force of gravity differs depending on where you are on the planet. remember that at rest, an accelerometer will always show roughly 9.8m/s^2 in the downward direction.