During the year 2000, an investigation into the potential use of Global Positioning System (GPS) at the ESRF was made. There are two reasons to use the GPS at the ESRF. The first is (re)-determine the positions of exterior pillars and points used in general site activities (e.g. construction of new buildings etc...) Implicit in this is the avoidance of problems with lines of site between points associated with classical measurements (theodolite angles and distances). These types of measures have already been extensively used at the ESRF. The second reason to employ the GPS at the ESRF is to attempt to ameliorate the machine survey networks. Due to the nature of these networks there is an envelope of global incertitude in the determination of their points of approximately ±0.15 mm (maximum ±0.4mm). Measurements from exterior pillars whose position has been determined by GPS could decrease the imprecision of this envelope. However, in order to do so, the GPS measures must be of the same order of precision.

Great care must be taken to have results of the highest precision. In order to evaluate the potential of the system, measurements were taken on three isolated pillars free of problems associated with masks (objects blocking the clear view of the satellites - buildings, cars etc...) and multiple trajectories (confusing signals reflected from walls, leaves, trees, cars etc...). Results of this test showed a difference between measurements made with a precise distance meter and the GPS to between 0.1 to 0.3 mm! 

The method adopted to test the validity of injecting GPS measures into the Storage Ring network was to determine the distance between two diametrically opposed exterior pillars using the GPS and an independent method (machine co-ordinates and two distances). After treatment, both the distance calculated using the GPS measurements and the independent distance were found to be equal (365.5080 m)! This remarkable performance confirms the possibility of integrating this type of measure into the Storage Ring network. Nevertheless, in order to achieve this level of sub-millimetric precision, a very rigorous procedure must be respected.