Extend the RTK Survey to GNSS-Denied Areas Using a Low-Cost Inertial-Aided Positioning Pole

Changxin Lai and Ruonan Guo

Peer Reviewed

Abstract:	ION GNSS+ 2021 Student Paper Award winner. The global navigation satellite system (GNSS) real-time kinematics (RTK) is a high-precision positioning technique that has been widely used as a versatile surveying tool. However, RTK becomes invalid in GNSS-denied areas due to signal blockage. The GNSS is thus often used in combination with inertial navigation system (INS) to obtain greater utility during GNSS signal outages, while GNSS/INS integrated systems still suffer from the rapid accumulation of INS navigation errors over time, especially for low-cost systems. In this work, we aim to extend the high-precision RTK positioning capability to GNSS-denied areas by using a low-cost inertia-aided positioning pole that contains a dollar-level inertial measurement unit (IMU) chip and an RTK receiver. The key to maintaining the positioning accuracy at an acceptable level is to manipulate the pole as a walking stick, in which case, the pole tip lands on the ground periodically. The pole tip velocity is zero when it maintains contact with the solid ground, and thus, lever-arm compensated zero-velocity updates (LA-ZUPTs) can be utilized to suppress INS navigation errors effectively in GNSS-denied areas. In addition, the coordinate updates (CUPTs) of RTK positioning are used at RTK-friendly positions to provide strict geometric constraints and reduce INS errors. Furthermore, INS-based filtering, along with a smoothing algorithm, is applied in postprocessing to further reduce the INS positioning error. Regularly aided by LA-ZUPTs and enhanced by the smoothing algorithm, the INS is able to maintain centimeter-level positioning accuracy in postprocessing when the operator walks through GNSS-denied areas over short distances. The experimental results show that the positioning accuracy can be maintained at 5 cm and 8 cm in terms of root-meansquare error (RMSE) for I-shaped surveying trajectories of 20 meters and L-shaped surveying trajectories of 20 meters through GNSS-denied areas, respectively. In addition, the combination of forward and reverse measurements can further improve the positioning robustness and lead to an accuracy improvement of over 40%. Therefore, it is feasible to use a low-cost inertia-aided positioning pole to bridge the GNSS gap and extend the RTK survey ability to GNSS-denied areas within a certain distance.
Published in:	Proceedings of the 34th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2021) September 20 - 24, 2021 Union Station Hotel St. Louis, Missouri
Pages:	3212 - 3226
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
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