2. Reference systems and operational constraints

2.1 Older networks

For centuries, until the 1990s, national geodetic networks were obtained by triangulation, with rather difficult scaling, since distance measurements have only been easily carried out over long distances since the 1970s. The history of global network design implied highly complex error models, due to the imperfections of the processes employed. Typically, the coordinates disseminated in France for the NTF (France's new triangulation system, materialized by some 90,000 groups of landmarks throughout the country) deviated from the exact values (which would have been obtained if everything had been perfect) by magnitudes that increased with distance from Paris, reaching up to 10 m towards Nice, for example, simply through the accumulation of measurement errors. The...