Technofile : Fast track

The machines that lay the foundations for roads and railways use mechanical
sensors that follow a guide string to keep them on track. But the machines often
rip out the string. Researchers at the Fraunhofer Institute for Automation in
Stuttgart, Germany, have developed an automatic system that is guided by a beam
of light and a surveyor’s tacheometer—a type of theodolite. The
foundations can be laid to an accuracy of 1 millimetre. The system is being
tested by engineers building a new high-speed railway near Berlin.