Performance assessment of no-fee GNSS augmentation systems for tractor guidance

• Unaugmented GNSS gives 2–3 m guidance errors, reduced below 1 m for pass-to-pass < 15 min. • EGNOS reduces guidance errors by ∼40% compared with unaugmented GNSS. • GLIDE reduces guidance errors below 20 cm for pass-to-pass intervals < 15 min. • VRS-NRTK slightly outperforms RTK with similar baseline lengths. • RTK guidance errors begin at 1 cm for on-site RTK and grow with baseline length. This study assesses the performance of no-fee GNSS augmentation systems for tractor guidance. Five no-fee augmentation systems: EGNOS, GLIDE, RTK, VRS-NRTK, and on-site RTK were evaluated in both static and guidance tests over short- and long‑term periods using three GNSS receiver types: low-cost Navilock NL8022MP, mid-range Novatel Smart2, and high-end Harxon TS108PRO. Static tests recorded 24 h of position data from 14 receiver-augmentation configurations on a fixed surface. Guidance tests recorded trajectory data from the 14 configurations during straight-line guidance using a tractor equipped with two GNSS receivers, one under test and one high-precision reference. Results found that: (i) unaugmented GNSS resulted in guidance errors of 2–3 m, reduced below 1 m in pass-to-pass intervals shorter than 15 min; (ii) EGNOS reduced these guidance errors by ∼41%; (iii) GLIDE reduced guidance errors to below 20 cm for pass-to-pass intervals shorter than 15 min, with no long-term improvement; (iv) RTK guidance error decreased as baseline length shortened: >100 km yielded > 17 cm, 20–100 km yielded 3–20 cm, and < 20 km yielded 2–3 cm; (v) VRS-NRTK slightly outperformed RTK with similar baseline lengths; and (vi) on-site RTK enabled 1 cm guidance error. In summary: low-cost receivers without augmentation or with EGNOS result in metre-level errors; mid-range receivers with GLIDE deliver decimetre-level guidance errors in the short term; and high-end receivers using on-site RTK or VRS-NRTK on baselines up to 100 km achieve centimetre-level errors, enabling farmers to replicate tractor trajectories consistently year to year.