Why the precise positioning is so important in agricultural production
Modern agricultural machines are usually already prepared for or directly equipped with electronic control systems, so called autopilots that use a GPS navigation system for automated machine guidance. In the automatic mode, the operator does not have to be occupied with driving the machine, but checks the correct operation of all systems and pays attention to potential hazards that could endanger an employee or a machine in the field. The operator operates the machine according to the instructions of the control system only at turnabouts. The autopilot function is controlled with a prepared configuration and map data that are pre-loaded into the machine, so the operation itself is not complicated.
The problem with the use of GPS navigation for the control of agricultural technology is a lack of accuracy. GPS system standardly achieves an accuracy of three meters on average, which, moreover, changes over time. If the configuration of satellites to the GPS receiver is unfavourable, the error can be even greater. This is sufficient for most applications, but for the needs of agricultural production, this is insufficient. For the improvement of accuracy, various correction methods are used. The best performance is reached with systems with a reference station. Deviation on the border area with a maximum distance from a reference station oscillates up to 3 cm using these systems. They have very good repeatability, so when the machine returns to the same place in half a year, it drives along the same line, along the same furrow and so does not destroy grown plants. Without the use of precise navigation tools, approximately 20% of the fields remain unused. A man driven machine can never be as precise as a machine controlled by robotic navigation.
Large machines also have problems in turns. Sharp turns are very complicated and slow down the cultivation of the needed area. Using precise navigation of a working machine, the option of a field cultivation with omitting a line and with wide turns can be used. Skipped rows are cultivated during the second passage.
If spraying is inaccurate, there occur areas that are unsprayed and strips where the spray was applied twice. In both cases this costs farms considerable sums of money because spraying was consumed, but a part of the surface was not treated and a part was sprayed too much.
Data from machines controlled this way can be used for reverse engineering, which can track the yield of each crop in an observed area and adapt the machines for seeding or fertilizing.
A great advantage is that when the machine is controlled by autopilot the same results can be achieved in reduced visibility or at night and the machine can be utilised for the maximum period possible.
Another reason for accurate positioning is subsidies and division of land, where the absolute position against the Czech cadastre is crucial. The problem is that the GPS system uses the WGS84 coordinate system and the Czech cadastre uses the S-JTSK coordinate system. These coordinate systems are calculated in a completely different way. Conversion of these exists but thanks to the movement of lithospheric plates, it changes over time. It should not happen that the machinery gets in someone else´s land during the cultivation. As for getting subsidies, the exact localizing of land is also important because there is a relatively small tolerance of up to 10% of the cultivated area.
System for increasing the accuracy of satellite navigation with GPS system
Correction with a ground reference station
Ground correction systems use correction against a fixed point where the location is precisely known. In such an explicitly defined point, a correction station is placed. It determines individual satellites´ errors against the actual position.
Global systems use a network of stations and interpolate correction for a given area of interest. They offer sending correction signals as a service. The price of the service consists of a fixed price for a license for each machine and an annual fee for service operation. The price of these services is relatively high for Czech farmers. Further problems with these global solutions are reliability and availability of these services in the required area. In countries with a flat terrain such as the USA or the Netherlands, these systems work well. Data from these services are transmitted via mobile networks. The availability of these networks in sparsely populated areas with a complex terrain profile is usually not good enough to enable infallible usage of this system. In case that an agricultural machine loses a correction signal, it stops within 30 seconds and must be controlled by an operator.
Agro Pilot system
Our solution uses its own reference base station with a transmitter of correction signals in the VHF or UHF bands; both bands are suitable for this purpose. Correction data are encoded into a data stream and continuously transmitted by a reference station. In individual agricultural machines, radio modems are placed, which receive the signal, decode and transmit it to the control computer. With one reference station built up in this way, an area with a radius of approximately 15 kilometres can be operated. When building up a system for the distribution of correction data, building a reference station is the most expensive. On the other hand the number of machines which can use the data from the reference station is not limited (data travel unidirectionally from the reference station to the machines). Individual farms in the region can share a reference station, use it together, and the cost of the initial investment can be divided among multiple users.
To cover the area which is not available due to the terrain profile or the distance of a machine from the reference station, repeaters that receive signals from the main reference station and transmit it to the desired area can be built. Unlike other solutions, an unlimited number of repeater stations can be theoretically realised. Data from one reference station are applicable with repetition of up to 30 km from the reference station with respect to the maximum permissible error. Agricultural machinery in operation automatically chooses the best signal and smoothly moves from the coverage area of one reference station to another.
As part of this project even a reference station located in a place without electricity was successfully implemented using solar panels.
The system offers a very quick return of investment because as for big modern machines financial losses per hour of work without an autopilot can reach several thousand Czech crowns according to the experience of users.
Our company has many years´ experience building radio and telemetry networks and we are able to provide the user with a complex service ranging from a radio project with arranging the appropriate permits, delivery and installation to the subsequent long-term maintenance of the technology.
Advantages of the solution
- Affordable price
- Coverage of a vast territory according to customer needs
- Using repeaters for enlarging the area covered
- Private radio network which is not dependent on another provider and the need to pay charges for data transfer
- Accuracy and repeatability of positioning with a tolerance of 3 cm
- Simultaneous support of two different protocols for the transmission of correction data
- Considerable saving of fertilizer, seeds, fuel, more efficient use of fields, full use of modern technology
- Possibility of sharing a reference station among multiple farms in the region
- Unlimited number of machines using a reference station
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