A Novel High-performance Attitude Determination System Based on MEMS IMU and a Single High-precision GNSS Antenna

Stefan Schaufler, Xiaoguang Luo, Matteo Carrera, Ismail Celebi, and Bernhard Richter

Abstract:	Due to the complementary nature of inertial measurement units (IMUs) and GNSS, lots of research to couple these two technologies date back to the early days of GPS, primarily aiming at bridging GPS outages during absolute positioning. A precise and robust determination of all six degrees of freedom (6DoF: x, y, z, pitch, roll, heading) is essential for numerous aerial and land-based applications, such as machine guidance, mobile mapping systems, UAVs and precision farming. Determining the 6DoF in a robust manner is not possible with a single system – GNSS or IMU – when the trajectory of the movement is unpredictable or when the system needs to work stable over a longer static period as well. In particular, navigation systems aided by cameras (visual inertial systems – VIS), LiDAR or scanning benefit from precise attitude information. Yet, systems that require high-precision attitude information in real time are based on high-grade, expensive IMUs or multiple GNSS antennas, which are typically not portable. Existing smaller, lower-cost attitude systems either require time-consuming calibration procedures or do not fulfil the requirements on robustness and reliability in high-precision, real-time applications. This paper analyses the potential and limits of a novel technology that is used in the Leica GS18 T GNSS smart antenna to automatically compensate the position errors of a tilted survey pole by continuously determining the 6DoF. The sensor fusion of a high-precision, multi-GNSS smart antenna with an industrial-grade MEMS IMU allows the determination of pitch and roll with an accuracy of better than 0.2 degrees. The sensor heading with respect to true north is achievable instantaneously through metre-level movements, where the associated accuracy reaches 1 degree. Due to an advanced production procedure, the GS18 T does not require any on-site calibrations and works out of the box. Furthermore, using an innovative way of determining the sensor’s attitude based on velocity, the system is entirely immune to magnetic disturbances during operation. Based on the 6DoF and the length of the pole, the antenna phase centre coordinates are reduced to the pole tip without noticeably increasing the position error budget. GNSS RTK can now be applied in more restrictive situations with enhanced productivity by simply forgetting the level bubble. Since knowledge of the uncertainty and reliability of position and attitude is crucial when the highest accuracy is demanded, the GS18 T provides the user with coordinate quality estimates indicating the expected position and attitude uncertainty. In this study, accurate laser tracker measurements are used as reference to assess the quality of the 6DoF delivered by the GS18 T. Representative tests were carried out in static and kinematic application scenarios to evaluate the performance of the position and attitude determination with respect to accuracy, reliability and robustness. The test results also show that the high requirements for surveying-grade applications have enormous future potential in land-based applications or other applications where positioning and attitude information can be mission critical. For example, image-based reality capturing technologies, such as point cloud creation with UAVs or terrestrial mobile mapping systems, require precise 6DoF for their cameras and sensors. These applications and industries are constantly looking to drive costs and size down. The presented technology of a robust and reliable determination of the 6DoF can be one answer to save costs, space and complexity in such systems.
Published in:	Proceedings of the 31st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2018) September 24 - 28, 2018 Hyatt Regency Miami Miami, Florida
Pages:	2034 - 2050
Cite this article:	Schaufler, Stefan, Luo, Xiaoguang, Carrera, Matteo, Celebi, Ismail, Richter, Bernhard, "A Novel High-performance Attitude Determination System Based on MEMS IMU and a Single High-precision GNSS Antenna," Proceedings of the 31st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2018), Miami, Florida, September 2018, pp. 2034-2050. https://doi.org/10.33012/2018.16019
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