Precise Indoor and Outdoor Altitude Estimation Based on Smartphone

The altitude information of smartphones is playing a more and more important role in some location-based service applications. The global navigation satellite system is the most convenient method for altitude information collection, but it is low accuracy and unavailable for indoor environments. The relative altitude change of smartphones can be estimated with the help of built-in barometers. Considering challenges in systematic biases calibration and the acquisition of pressure at the mean sea level (MSL) of the user location, the absolute height determination is still an unsolved problem. In this article, we propose a precise and effective altitude estimation framework based on the smartphone platform. First, the systematic biases are estimated by using a precise local digital terrain model. Then, an adaptive interpolation method is proposed to obtain the MSL pressure at the user location based on the measurements from surrounding meteorological stations. The proposed method works for both indoor and outdoor environments, with the average root-mean-square error of 0.65 and 1.39 m, the average standard deviation of 0.58 and 1.34 m, and the average mean absolute error of 0.54 and 1.13 m, respectively.