Determination of a geocentric coordinate frame for GPS measurements

Two strategies for determining the offset from the geocenter for GPS measurements are considered. In the first strategy, VLBI-determined relative positions are used to fix the frame orientation and the absolute scaling, while the geocenter offset is determined from GPS measurements. In the second strategy, the absolute scaling is determined by the adopted gravitational constant of earth and the adjusted periods of GPS orbits, with the latitude being obtained from the time signature of earth rotation in the GPS measurements. The results indicate that geocentric positioning to an accuracy of a few centimeters can be achieved with just one day of precise GPS pseudorange and carrier phase data.