Most problems will require 6 degrees of Freedom

3 Axes of lateral acceleration

3 Axes of rotation

Attempt to constrain the degrees of freedom

Constrain acceleration or rotation axes

Allows fewer sensors to be used

Simplifies mathematics

Try to take advantage of the constraints of the mechanical system

I.e. cars can only pitch or roll a few degrees

Attempt to limit time between absolute updates

Attempt to have periodic absolute position updates

Reduce dead reckoning time to a minimum

Combine absolute and relative position sensors

Example: Magnetics, encoders, LED's etc.

Use signature analysis

Look at the spectral response of one or more axis to make a very educated guess as to what the mechanical system is doing