Use of smartphones for determining orientation angles in the field

The purpose of the study is to investigate the feasibility of using smartphones to determine orientation angles in the field, in particular, magnetic azimuths and horizontal angles.  The paper also aims to assess the accuracy of measurements performed using built-in magnetometers and to determine the suitability of such devices for orientation tasks when the use of traditional geodetic instruments is impossible or impractical. Methodology. To achieve this goal, an experiment was conducted involving 12 observers using 11 smartphone models from different manufacturers. Measurements were performed by sighting the smartphone’s digital compass in three consecutive directions, followed by determining horizontal angles as the differences between magnetic azimuths. Reference values of azimuths and angles were obtained using technical theodolites. Results. It was established that the first magnetic-azimuth measurement after compass calibration has the smallest error, typically 1–3°. In subsequent measurements without repeated calibration, the error increased on average by a factor of 2–3. The mean deviations of azimuths for consecutive directions were approximately 1.9°, 5.5°, and 6.9°, and the root-mean-square error (RMSE) of azimuth determination in most cases did not exceed 2°. When measuring horizontal angles, the majority of errors did not exceed 6°, and the RMSE for most smartphones ranged within 3–4°. At the same time, in isolated measurements, significant deviations of up to 13–25° were recorded, caused by  accumulated errors, magnetic interference, and human factors. A significant dependence of measurement accuracy on the smartphone model, sensor quality, data-processing algorithms, and adherence to the calibration procedure was revealed. Scientific novelty lies in a comprehensive analysis of the accuracy of measuring magnetic azimuths and horizontal angles using smartphones under field conditions, accounting for cross-model variability and statistical properties of measurement errors. Practical significance lies in defining the limits of smartphone applicability for orientation tasks, reconnaissance, and navigation, as well as in formulating recommendations to improve measurement accuracy. The obtained results may be used in education, tourism, search-and-rescue, and military field activities, and may also serve as a basis for developing methodological guidelines and mobile applications.