Method and apparatus for determination of misalignment between device and pedestrian

A device portable by a pedestrian for enhancing a navigation solution of a device and a pedestrian by determining misalignment between the device and the pedestrian, wherein the misalignment is a heading misalignment angle between a heading of the device and a heading of the pedestrian and wherein the heading of the pedestrian is a pedestrian direction of motion, the device comprising:

• a) a tri-axial accelerometer;
• and
• b) a processor, coupled to receive readings from the tri-axial accelerometer, and operative to determine the misalignment between the device and the pedestrian and wherein the processor is operable when the device is associated with the pedestrian in a constrained manner and when the device is associated with the pedestrian in an unconstrained manner, such that the device is tiltable to any orientation, wherein the processor is operative to:
• i) calculate a plurality of levelled accelerometer readings from readings of the tri-axial accelerometer by transforming the tri-axial accelerometer readings into a levelled vertical accelerometer reading component and first and second horizontal acceleration components;
• ii) generate a vertical acceleration component from the levelled vertical accelerometer reading component;
• iii) calculate an along-track angle based at least in part on the first and second horizontal acceleration components, wherein the along-track angle is one of a forward or a backward direction of the heading misalignment angle;
• iv) determine a use case of the device based at least in part on the levelled acceleration components, wherein the use case of the device represents how the device is associated with the pedestrian;
• v) determine if a 180 degrees error in the calculated along-track angle is present based on the determined use case, wherein one or more techniques for determining if the 180 degrees error is present are selected from multiple techniques based on the use case;
• and
• vi) calculate a misalignment angle from the along-track angle and, if present, the 180 degrees error.