A method includes: taking a topographical survey of a plurality of geographical points near a structure to be built, the position of each point being determined in an absolute frame of reference XYZ; installing a plurality of reflectors, each reflector being placed at a geographical point of the topographical survey; measuring distances between reflectors and optical devices, using at least three optical devices fixed on a moving arm of an insertion device that bears an element to be inserted; computing, by trilateration, the absolute position of the arm of the insertion device from the measured distances and from the known position of each optical reflector; and moving the arm of the insertion device based on the computed absolute position, so as to bring the element to be inserted into a predetermined implantation position.

A derail alarm system for notifying a tamping machine operator that a tamping projector buggy is in a derailed condition. A rail sensor with an ultrasonic beam attaches to a tamping projector buggy to sense alignment with a metal rail. When the ultrasonic sensor detects an out-of-tolerance condition, aural and red-LED light visual indications are electronically provided to the tamping machine operator. The tamping machine operator may disable the aural indication and change the red-LED indication to an amber-LED indication until the ultrasonic sensor detects an in-tolerance condition. A limit switch deactivates the cradle sensor when the tamping projector buggy is raised and stored in the travel position for a higher speed transport condition.