Dual frequency GPS observables only allow the elimination of the 1st–order ionospheric term. Although higher–order ionospheric terms may cause a range bias of several centimeters, accounting for such effects is not yet a common strategy for GPS data analysis. In comparison to previous investigations a rigorous application of 2nd and 3rd–order ionospheric corrections is examined for the estimation not only of receiver positions but of all included parameters. The results reveal a linear dependence of the frame's origin on the integrated electron density. Furthermore, satellite positions are affected at the centimeter level when applying the above–mentioned corrections. Since the ionospheric correction terms show a significant impact on various GPS estimates, their consideration becomes necessary for scientific applications. Hence, the modeling of 2nd and 3rd–order ionospheric correction terms is part of the optimized strategy in an ongoing reprocessing project dealing with a global GPS network and spanning the time period from 1994 up to present time.