Rapid and accurate initial alignment of the low-cost MEMS IMU chip dedicated for tilted RTK receiver
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ORIGINAL ARTICLE
Rapid and accurate initial alignment of the low‑cost MEMS IMU chip dedicated for tilted RTK receiver Qijin Chen1 · Huan Lin1 · Ruonan Guo1 · Xiaoji Niu1,2 Received: 18 March 2020 / Accepted: 7 September 2020 / Published online: 6 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The new global navigation satellite system real-time kinematic (RTK) receivers with tilt compensation extend the applicability of high-precision RTK positioning to previously restrictive environments since the pole is no longer required to be maintained vertically. The rapid and accurate initial alignment of the built-in low-cost inertial measurement unit (IMU) is a critical technical issue and currently remains a challenge for the tilted RTK. We address this problem by proposing a method specific to the determination of the IMU initial heading for the tilted RTK. In this approach, the IMU heading is calculated from the angle between the inertial navigation system (INS)- and RTK-indicated position increment vectors in the horizontal plane based on the fact that the INS- and RTK-indicated trajectories in the short term are similar in shape. Instead of conventional INS mechanization, the INS-indicated trajectory is determined using the gyro-derived attitude and pole length by treating the pole movement as the motion of a rigid body with a fixed point to enhance the trajectory accuracy. The experiment results indicate that the initial heading is accurately determined to 1.15° at a 98.2% confidence level within only 2–3 s when using a dollar-level IMU chip without any additional sensors, e.g., a magnetometer. The proposed algorithm satisfactorily meets the requirements of the tilted RTK application, and its accuracy and convergence speed are higher than those of the current methods reported in publications and product sheets. Keywords INS initial alignment · RTK with tilt compensation · GNSS surveying · Low-cost IMU · Rigid body motion
Introduction Real-time kinematic (RTK) positioning is a global navigation satellite system (GNSS) navigation technique with a centimeter-level accuracy. In traditional RTK surveys, the pole on which the rover receiver is mounted should be vertically placed, as depicted by the dashed line in Fig. 1. Then, the antenna phase center (APC) position is reduced to the point of interest on the ground, by considering the vertical offset between the APC and pole tip. In recent years, RTK receivers with a tilt compensation function, hereafter referred to as tilted RTK receivers, have emerged, which do not require the pole to be held vertically when measuring points on the ground, as illustrated in * Xiaoji Niu [email protected] 1
GNSS Research Center, Wuhan University, Wuhan 430072, China
Collaborative Innovation Center of Geospatial Technology, Wuhan University, Wuhan 430079, China
2
Fig. 1. Leica Geosystems AG (Switzerland), Trimble Inc. (Sunnyvale, California, USA), and several Chinese RTK receiver manufacturers have developed tilted RTK receivers. The tilte
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