  The project SYPOR wishes to use the global navigation satellite system
GALILEO as an autonomous relativistic positioning system for the Earth.
Motivations and a sketch of the basic concepts underlying the project are
presented. For non geodetic (perturbed) satellites, a two-dimensional example
describes how the dynamics of the constellation of satellites and that of the
users may be deduced from the knowledge of the dynamics of only one of the
satellites during a partial interval.
