GPS System: ± 10 mm of accuracy
The GPS (Global Positioning System) was created in 1973 in the USA, and in 2000 it was liberalised for civil use by the US government. In order to do so, a network of 31 artificial satellites were positioned in space, that revolve around Earth at different heights and which transmit their position to all GPS receivers. The GPS receiver picks up satellite signals that give the horizontal position of the receiver on Earth (longitude and latitude).
Thanks to specific software, a high accuracy of around ± 10 mm has been obtained over the last few years even in elevation (in indicating the vertical position), thanks to the RTK (Real Time Kinematic) system, which provides real-time positioning and high frequency of the signals transmitted (about 10 Hz).
The MARA machines also work with GPS systems and are compatible with all GPS systems on the market. The operation of the MARA GPS grader is identical to that of laser systems, with the exception that the reference height is provided directly from the GPS. The GPS system can be used to create a horizontal plan, with 1 or 2 gradients, with variable gradients or ones programmed using software. The MARA graders, controlled by the GPS system, receive signals from satellites that draw up the plan and copy it on the ground. The different accuracy that is delivered with this technology compared to the laser is due to the lower intrinsic accuracy of GPS systems, which is also subject to periodical variations linked to the change of satellite constellations every 12.5 minutes. On the other hand, the GPS system provides considerable flexibility of use, especially on vast areas of land and with different gradients, and is also used for other kinds of work both in the agricultural industry and for civil construction as well as for shifting large amounts of earth.
The GPS system is equipped with a receiver (mobile base) placed on the grader that runs on the field and a fixed receiver (static base) of differential reference, namely that defines the difference in displacement between the mobile station and the fixed one. A screen is located in the cabin, next to the operator (embedded PC – industrial PC) that processes data transmitted by the mobile receiver (via cable) and the fixed receiver (via radio) and sends an electrohydraulic command that controls the height of the blade, allowing it to implement the plan on the ground. This allows for horizontal and vertical positioning accuracies of around one centimetre, with a maximum distance of 5 km between the two receivers. The more the distance between the two receivers increases, beyond 5 km, the less accuracy there is.