Abstract: A technique for automatically determining direction of motion of a pedestrian is described. In embodiments, accelerometer measurements obtained from an accelerometer of a mobile device are converted from a mobile device reference frame to a local level reference frame. The local level accelerometer measurements are filtered to obtain a first series of frequency components representing acceleration at an estimated stride frequency of the pedestrian in a first direction and a second series of frequency components representing acceleration at the estimated stride frequency of the pedestrian in a second direction that is orthogonal to the first direction. A heading angle of a major axis or semi-major axis of an ellipse defined at least by one or more frequency components in the first series and one or more frequency components in the second series is then determined The direction of motion of the pedestrian is determined based on the heading angle.