Could the laser tracker AT401 replace digital levelling and "ecartometry" for the smoothing and realignment of the LHC?

The laser tracker AT401 appeared on the market a couple of years ago with a very accurate distance meter, as a matter of fact the one of the Mekometer ME5000, and angular encoders almost as accurate as the ones of the best total stations. For the smoothing and realignment of the LHC components, the Survey team at CERN normally uses digital levelling measurements to determine the vertical position and offsets to a stretched wire measurements, also called “ecartometry”, for the horizontal one. During the last winter technical stop, a measurement of an LHC sector (3km) was realised using these three technologies in order to compare the AT401 capabilities with respect to the others. The paper will present the methodology applied, the data processing, the results obtained and the conclusions drawn for the future LHC realignment campaign which will take place during the long shut-down of 20 months starting at the end of 2012.