  The motion of satellite constellations similar to GPS and Galileo is
numerically simulated and, then, the region where bifurcation (double
positioning) occurs is appropriately represented. In the cases of double
positioning, the true location may be found using additional information
(angles or times). The zone where the Jacobian, J, of the transformation from
inertial to emission coordinates vanishes is also represented and interpreted.
It is shown that the uncertainties in the satellite world lines produce
positioning errors, which depend on the value of |J|. The smaller this quantity
the greater the expected positioning errors. Among all the available 4-tuples
of satellites, the most appropriate one -for a given location- should minimize
positioning errors (large enough |J| values) avoiding bifurcation. Our study is
particularly important to locate objects which are far away from Earth, e.g.,
satellites.
