Geodetic metrology of particle accelerators and physics equipment

Since the construction of the first particle accelerator at CERN, in 1954, the Applied Geodesy Group has gained great experience in the metrology of large or very large objects. This initial machine was the largest in the world at that time, with its 200 m diameter. CERN has now built LEP (Large Electron Positron Collider), a new accelerator 27 km in circumference, for which the Geometrical tolerances have been tighter: a relative accuracy of 0.1 mm all along the machine and the best possible absolute accuracy with respect to the theoretical geometry. To achieve such requirements, many specific devices and methods have been developed at CERN. Most of them have been widely described in various articles and the purpose of this paper is mainly to give a review of the more recent developments in instrumentation, techniques and processing methods, with emphasis on some particular problems related to the exceptional size of such machines. This paper presents a review of the instrumentation, techniques and processing methods used at CERN for the metrology of large scientific equipment (from a few meters to several kilometers), the positioning of which requires high accuracy. Some specific features of tridimensional geodesy and comparative surveys of such objects are treated and illustrated