Initial test on the use of GPS and sensor data of modern smartphones for vehicle tracking in dense high rise environments

Modern smartphones normally incoporate a high sensitivity GPS receiver, Wi-Fi card, and sensors such as accelerometer, digital compass and digital barometer. These components are low-cost, and are designed mainly for leisure and gaming applications. This study aims to investigate the combination of the built-in GPS and sensor data of smartphones for localization in dense urban environments, where very often satellite signals are obstructed by tall buildings or large structures, causing insufficient number of GNSS measurement data for successful position determination. This paper is the continuation of our investigations on the characteristics of data outputs from a digital compass and accelerometer in relation to the orientation and phone movements presented in Mok et al. (2011) [7]. In the following, we will focus our discussions on the integration of GPS, digital compass, and accelerometer for vehicle tracking applications. Our investigation results show that the distance and orientation data derived from the outputs of the accelerometer and digital compass is generally sufficient to provide the shape of the path that the vehicle has travelled, with a varying scalar error. Magnetic to grid north correction, however, is necessary to improve the heading. By reducing the data sampling period from 30 seconds to 1 second, the scalar error can be significantly reduced. Moreover, correction for the gravity effect on the x-, y-and z-axes of the smartphone's local coordinate system is the key to correct the determination of accelerometer-derived distance travelled.