Models for fitting gravimetric geoids and GPS results

The aim of this investigation is to study how to use a gravimetric (quasi) geoid for levelling by GPS data in an optimal way. The advent of precise geodetic GPS has made the use of a technique possible, which might be called GPS-gravimetric geoid determination. In this approach, GPS heights above the reference ellipsoid are determined for points whose levelled (orthometric) heightH is above sea level people have already surveyed; for these points, we thus have the values of the geoid undulationN. These values are then used to constrain the geoid undulationsN′obtained from the gravimetric solution.