Camera Based Object Position Estimation for Mobile Devices

This paper describes a method for calculating a smartphones distance to a known object on the ground plane and the height of the camera above this plane. For that matter a camera with known intrinsics and given angle of view is used. The pitch angle of the smartphone is measured by an implemented inertial system, which is based on magnetic field sensors and accelerometers inside the smartphone. The distance to the object and the height above the ground plane are calculated basically using trigonometry. Besides trigonometry a perspective transformation is used to enable in-image distance measurements and therefore for determining the length of the field of view in pixels and as well as in millimeters. The developed method may be improved by more precise feature determination. It has an average deviation of 4.6 and 10.1 %, mainly depending on the accuracy of the calculated field of view length.