A low-cost multi-GNSS PPP-RTK solution for precision agriculture: a preliminary test

The agriculture and food sector will increasingly play a major role in the well-being of humanity. World-scale events, such as wars, climate changes, desertification, pandemic, etc., revealed how fragile humanity is from the point of view of food supply. Therefore, precision farming can provide a remarkable positive contribution to the primary sector globally at various levels. Nowadays, the employment of platforms for product data capture related to farming production and management is extensively available in several fields through local devices. Those systems comprehend sensors, automatic guidance systems with Global Navigation Satellite Systems (GNSSs), and central processing systems. Specifically, GNSS technology plays a central role in the autonomous guidance of tractors and farming robots. Until some years ago, high accuracy was a prerogative of expensive geodetic receivers whereas today high accuracy can be achieved also with low-cost receivers thanks to several factors, among all: the increased availability of GNSS interoperable constellations as well as the accessibility to several augmentation techniques both satellite- and ground-based. These factors are triggering the diffusion of autonomous machinery for farming purposes. This research aims to investigate the performance of a commercial Precise Point Positioning-Real Time Kinematic (PPP-RTK) correction service, employing a low-cost receiver. Two tests have been carried out with two different-grade antennas (a geodetic and a low-cost one). The tests showed that the employment of cost-effective equipment along with the exploitation of correction services allows reaching subdecimetre-level precision in less than one minute when employing a geodetic antenna; accuracy slightly degrades to decimetre-level with the low-cost antenna but the integer ambiguity is resolved in less time. Mean time-to-fix attests to 57 s for test 1 (geodetic antenna) and 30 s for test 2 (low-cost antenna). The times to obtain the first float ambiguity solution are equal to about 15 s for both tests. Integer ambiguity fixed solutions reveal a DRMS of 0.09 m and 0.012 m for test 1 and test 2, respectively. Float solutions reach a DRMS of 0.45 m and 0.63 m for test 1 and test 2, respectively. Lastly, when corrections are not available at all, single point positioning solutions reveal a DRMS of 1.36 m for test 1 and 3.15 m for test 2.