Three fundamental types of precision to increase productivity in agricultural operations

Essential for providing an accurate position for agricultural equipment, GNSS (Global Navigation Satellite System) receiver technology is better when it does not work alone. When combined with a signal correction solution, it minimises positioning errors during farming processes, ensuring the accuracy and consistency of operations. In any agricultural machinery activity, there are three types of precision that are relevant: absolute, relative and static precision.

According to Alexandre Ballarotti, Agriculture Sales Manager – LATAM at Hexagon's Autonomy & Positioning division, together they allow farmers to optimise the use of resources, improve productivity and reduce environmental impacts. However, for this to be possible, signal reception needs to overcome some obstacles. “The signal's journey from the satellites to the receiver is not without its challenges. Effects along this path cause delays, distortions and inaccurate positioning, which can result in a horizontal inaccuracy of more than 7 metres,” he explains.

Therefore, to ensure that the equipment receives accurate positioning information, correction services help to resolve the sources of error in the raw GNSS data, allowing the receiver to calculate a more precise position. Services such as TerraStar-C PRO, for example, developed by Hexagon | NovAtel,  is capable of transmitting correction data in real-time to a receiver anywhere in the world. “It was developed for operations that require precision of 2.5 centimetres, like agriculture and provides a convergence time around 5 minutes,” adds Ballarotti.

Ballarotti explains in more detail the differences between the three types of accuracy in positioning:

Absolute accuracy

Absolute accuracy refers to the receiver's ability to accurately determine a specific point on Earth. “Simpler systems have a margin of error of metres or more and tend to beused in low accuracy applications, like to track deliveries, but they are not effective for use in agriculture. For agriculture, small variations in the location of machines such as tractors, harvesters and sprayers can have a significant impact on the efficient use of inputs, crop productivity and waste reduction,” Ballarotti illustrates.

A receiver with an absolute accuracy of 2.5 centimetres provides geospatial coordinates with a margin of error of just 2.5 centimetres in relation to the calculated coordinates. In practice, this means that the receiver can recognise where it has been and return to them at any time within the receiver’s level of precision. This is used in precision agriculture practices to allow machines to accurately follow pre-determined or existing guidance lines.

Relative accuracy

Relative accuracy (pass-to-pass) is the receiver’s ability to return to a previous point within 15 minutes. “This accuracy helps to minimise gaps and overlaps when applying seeds, chemicals and other agricultural inputs; reduce operator fatigue, especially in conditions of low visibility, such as adverse weather conditions or at night; and collect accurate field data for terrain, soils and yields,” Ballarotti explains. So, if the pass-to-pass accuracy is 3 centimetres, then after the machine turns around at the end of the field, it can return to within 3 centimetres of its last pass.

Static accuracy (repeatability)

Repeatability, or static accuracy, is measured by the receiver's ability to return to a previously measured point at some point in the future, be it a day, a month or a year. After returning, the guidance line may be off by a certain distance, which is called static error. According to Ballarotti, repeatability translates into the operator's ability to follow the same path with the machine through the seasons, allowing machines to follow the same path, reducing soil compaction in planting areas. It also allows for automatic steering adoption in all phases of agricultural operations.