Determining the position of a mobile device in a geographical area

A method of optimising an orientation error for a device carried by a user, the orientation error being the difference between an estimated orientation calculated from signals from one or more sensors of the device and the real orientation, the method comprising:

• receiving acceleration and orientation signals from the one or more sensors responsive to the acceleration and orientation of the device,
• classifying motion of the device as a symmetric motion mode or an asymmetrical motion mode, the symmetric motion mode having similar periodic acceleration signals with a period corresponding to a single step of the user, and the asymmetrical motion mode having similar periodic orientation patterns with a period corresponding to two steps of the user,
• obtaining a set of vector values of the acceleration of the device from the acceleration signals for an interval of one or more whole periods of a single step, or a two steps, of the user, according to the classification of the motion of the device as the symmetrical motion mode or the asymmetrical motion mode, and
• optimising the orientation error using the set of acceleration values subject to physical constraints on the motion that apply during the interval.