Inside GNSS Media & Research

MAR-APR 2018

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54 Inside GNSS M A R C H / A P R I L 2 0 1 8 On-Phone Analysis You can also do some basic analysis directly on the phone, using the Gnss- Logger App. is app was developed to: • Exercise and validate the application- facing Android GNSS APIs • Compute real-time (least-squares) position from raw measurements • Collect data for offline analysis e Settings View also shows impor- tant device related info such as the GNSS HW Year, Android Platform Number, Android Api Level and GnssLogger ver- sion. Log View in which the switched ON GNSS outputs will be shown ( Figure 4 ). is view also adds the capability to log the GNSS data for offline processing and as well to send the logged files via email or other sharing options. The offset between the two posi- tions is also shown ( Figure 5 ). As the device location is generally filtered, off- sets of 5-10 meters may occur between device location and WLS (weighted least squares) location; even in open sky. With even higher offsets expected as the device moves to urban areas, or indoors. Map view where one would see on Google Map the position reported by the device vs the weighted least square posi- tion (Figure 5, bottom). e Signal Strength View is shown in Figure 6 . The Residual Error plot is FIGURE 3 Three satellites selected for analysis: two high in the sky, and one low. The loss of line- of-sight, and the effect of reflections are clearly visible on the signal from G22. FIGURE 4 Settings View with which one can choose which GNSS outputs to turn ON/OFF. FIGURE 5 Position Offset view where one would see the positions reported by the device vs. the positions computed using weighted least squares from the raw GNSS measurements provided via Android APIs. ANALYSIS TOOLS shown in Figure 7 , using ground truth location entered by the user. If the ground truth-location is unknown, the

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