In the last years the use of the Global Positioning System (GPS) has acquired importance. The development of light, easy to carry and use receivers, the use of a fixed base point that allows high precision measurements, has gathered this method high acceptance and use in difficult terrain.
GPS is based on the distance measurements between several satellites and a receiver. Only one receiver allows an accuracy of few meters, depending of the quality of the satellite signal. The accuracy is strongly improved by the use of a second receiver – the reference- set up at a fixed point, that measuring his position several times and so compensating the “noise” .
During the measurement of the surface the second receiver – the rover- is moved, and comparing his relative position to the reference.