The traditional pile positioning method for offshore piling uses the intersection of lines of sight with two or three theodolites. This method has certain limits, including using post-mission pile positioning, being time-consuming and lacking position accuracy. A novel pile positioning model using four kinds of sensors (GNSS—Global Navigation Satellite System receivers, tiltmeters, laser rangefinders and calibrated CCD cameras) for sea piling was developed. Firstly, with Real Time Kinematics (RTK) GNSS and tiltmeter data, the piling ship’s position and attitude was achieved in real time, and then the coordinates of the pile center in the Ship Fixed Coordinate System (SFCS) were calculated by a laser rangefinder and a CCD camera data. Finally, using the coordinate transformation, the coordinates of the pile center construction were figured out and used to guide the pile movement to the right place in real time. Because of the poor RTK GNSS vertical accuracy (normally 2–3 cm) and complex piling ship structure, it is difficult to get the accurate penetration value per hammering, which is a very important parameter for structural engineers. A Scale Invariant Feature Transform (SIFT) algorithm was created to get the pixel difference between the two pile images captured before and after one hammering, respectively, which was then used to calculate the penetration. A case study on the piling ship named “YangShanHao” with the sensors and algorithms was also described and discussed in the paper. The results showed the high accuracy of the proposed position model and the pile sinking distance of the pixel, thanks to the SIFT algorithm.
The last satellite of BeiDou Navigation Satellite System with Global Coverage (BDS-3) constellation was successfully launched on June 23rd, 2020, and the entire system began to provide Positioning, Navigation, and Timing (PNT) services worldwide. We evaluated the performance of location services using BDS with a smartphone that can track the Global Navigation Satellite System (GNSS) satellites in Nottingham, UK. The static and kinematic experiments were conducted in an open meadow and a lakeside route covered by trees, respectively. Experimental results show that BDS has good visibility, and its overall signal carrier-to-noise density ratio (C/N0) is comparable to that of Global Positioning System (GPS). The average C/N0 of BDS-3 satellites with elevation angles above 45° on B1 band is the highest among all systems, reaching 40.0 dB·Hz. The noise level of the BDS pseudorange measurements is within 0.5 m, and it has a good consistency among satellites. In the static experiment, the standard deviations of BDS positioning in the east, north and up directions are 1.09, 1.16, and 3.02 m, respectively, and the R95 value of the horizontal position is 2.88 m. In harsh environments, the number of BDS satellites tracked by the smartphone is susceptible to environmental factors. The bias Root Mean Squares (RMS) in the three directions of the whole kinematic positioning are 6.83, 6.68, 11.67 m, in which the positioning bias RMS values in a semi-open environment are only 2.81, 1.11, 3.29 m. Furthermore, the inclusion of BDS in multiple GNSS systems can significantly improve the positioning precision. This study intends to provide a reference for the further improvements of BDS global PNT services, particularly for Location-Based Services (LBS).
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