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Analysis of the performance of various GNSS positioning concepts dedicated to precision agriculture

02-04-2024

Fig. 1. Test trajectories with PDOP (left); exemplary field photo (right)

Automated guidance systems for precision agriculture rely on GNSS and correction services to achieve high accuracy and precision during field operations. The study evaluated the performance of selected GNSS positioning services for precision agriculture in a field experiment. Three correction services were used: SF1, SF3 and RTK, which apply different positioning concepts, i.e. WADGNSS, PPP, and RTK, respectively. The tractor was autonomously steered along several defined paths in open-sky areas as well as near heavy tree cover. The vehicles reference route was determined using a robotic total station.

Results
Trajectories of the tractor using SF1 and SF3 corrections are shifted from the defined straight paths, which was not the case with RTK positioning. Offsets of up to several decimeters were service- and area-specific, indicating an issue with the stability of the reference frame. The pass-to-pass analysis revealed that SF1 exceeds declared accuracy, while SF3 is less reliable in obstructed areas. RTK remains a stable source for determining position. Under favorable conditions, the pass-to-pass accuracy at 95% confidence level is better than 11.5 cm, 8.5 cm, and 4.5 cm for SF1, SF3, and RTK, respectively. In the worst-case scenario, the corresponding accuracies are 25.5 cm, 65.5 cm, and 22.5 cm.


Fig. 2. Shift of the trajectory determined by the total station with respect to the defined coordinates of the straight paths; the values in the upper right corner indicate the systematic offsets by which the presented results were corrected.

Future research should identify the source of coordinate offsets, ideally in cooperation with the service provider. Additionally, it is important to investigate the accuracy of positioning using other services dedicated to precision agriculture, define diverse trajectories, and compensate for tilt in the tractors vertical axis.

The research was conducted as part of engineering thesis of Wiktoria Kowalczyk and was published in:
Kowalczyk W.Z., Hadas T. (2024): A comparative analysis of the performance of various GNSS positioning concepts dedicated to precision agriculture. Reports on Geodesy and Geoinformatics, 117(1), 11-20, https://doi.org/10.2478/rgg-2024-0002