4. Conclusion

The development of four different space-based positioning systems took place gradually, over four decades, in extremely varied environments. Changes over this period have been numerous and continuous, and users of these GNSS, including for high-precision measurements, may have believed that no equilibrium could be reached. However, by 2021, this seems to have been the case, as no further systems are under consideration, and the existing space packages are fully functional and satisfactory. Geodesists and surveyors now have, and will no doubt have for a long time to come, an extremely high-performance tool, which we can only expect to continue to be well maintained by the four powers that set it up. These high-precision users are well aware, however, that these extraordinary tools were not created with them in mind, and that it is the multiplicity of mainstream users that guarantees their...