A VIO-aided partial ambiguity resolution for RTK positioning in complex urban environments

In Real-Time Kinematic (RTK) positioning, centimeter-level accuracy can be achieved through Partial Ambiguity Resolution (PAR). However, in complex urban environments, significant errors in GNSS observations, particularly in pseudoranges, not only undermine the effectiveness of traditional metrics (e.g., signal-to-noise ratio, float ambiguity variance) in observation or ambiguity quality indicating but also expand the ambiguity search space, making the PAR challenging. To address these limitations, we proposed a Visual–Inertial Odometry (VIO)-aided PAR method. This approach introduced a novel metric based on Double-Differenced (DD) pseudorange and phase residuals computed using VIO Predicted Positions (VIOPPs) to enhance the satellite ranking. Additionally, the VIOPPs-derived DD geometric ranges and relative movements were utilized to smooth DD pseudorange and detect false fixing in the position domain, respectively. We tested the proposed method against the classic PAR and two established commercial solutions using 6-min data from a simulated urban scenario and 60-min data collected in a real urban setting, separately. The simulation tests demonstrated that the proposed method led to a substantial improvement in RTK position accuracy, fixing rate, and the VIOPPs precision compared to the classic PAR method. The real-world test showed that the fixing rate of the VIO-aided PAR-enhanced RTK (VRTK) solutions reached 92.7%, which is slightly lower than that of the FixPosition solutions (97.2%) but higher than that of the Sino solutions (88.7%). Meanwhile, the VRTK solutions also exhibited smaller maximum coordinate biases than both the FixPosition and Sino solutions. Furthermore, the RMS values of the fixed solutions obtained by VRTK in the E, N components (0.02 m and 0.03 m) were equal to those of FixPosition and about 33.3% and 50.0% better than those of Sino (0.03 m and 0.06 m). These results suggested that the proposed method achieved a high fixing rate and position accuracy in urban areas, representing a meaningful contribution to the high-precision positioning community.