Method for determining the orientation of a sensor frame of reference tied to a mobile terminal carried or worn by a user

A method for determining an orientation of a trajectory being traversed by a pedestrian with respect to a reference frame, said pedestrian being furnished with a sensor housing comprising a sensor assembly comprising at least one motion sensor including at least one accelerometer, comprising the steps of:

• generating data representative of motion of the sensor housing using said sensor assembly in the reference frame, said motion of the sensor housing caused by the pedestrian traversing the trajectory, wherein the sensor housing is not permanently fixed to said pedestrian, thereby having an orientation with respect to said pedestrian that is initially unknown and can change during use,
• determining at least one of a footstep frequency and a stride frequency using an acceleration signal from the at least one accelerometer in relation to a vertical axis in a pedestrian frame defined by the pedestrian's antero-posterior, medio-lateral, and vertical axes, said pedestrian frame being tied to a trajectory frame of said trajectory,
• computing a first rotation transformation operator representative of the orientation of the reference frame with respect to the trajectory frame, compensating for the initially unknown orientation of the sensor housing with respect to said pedestrian, that transforms the generated data representative of the motion to cause exhibition of a medio-lateral motion characteristic, wherein the medio-lateral motion characteristic is one characteristic of a set of characteristics which are representative of signals of walking or running motion of a pedestrian and are expressed in the trajectory frame and exhibition of an antero-posterior motion characteristic, wherein the antero-posterior motion characteristic is another characteristic of a set of characteristics which are representative of signals of walking or running motion of a pedestrian and are expressed in the trajectory frame, wherein the first rotation transformation operator is computed by at least one of:
• i) maximizing the antereo-posterior motion characteristic and minimizing the medio-lateral characteristic at the footstep frequency;
• and ii) minimizing the antereo-posterior motion characteristic and maximizing the medio-lateral motion characteristic at the stride frequency, and
• determining the orientation of the trajectory traversed by the pedestrian using the computed first rotation transformation operator.