@@iagomaquinas GPS means Global Positional System and is a system which I understand is connected to a satellite and which enables the user to position a ship or in this case, an excavator , in an exact position. An excavator, I believe, would have a piece of electronic equipment attached to the boom which the operator monitors so that the depth of excavation is known as work proceeds and which can determine the gradient to enable effective drainage to be achieved. Other viewers are likely to simplify this explanation!
