Use of GPS in unification of vertical datums and detection of levelling network errors

We discuss the interconnection of vertical networks using GPS and gravimetric geoid models, and give some examples how this can be done in practice. We also discuss several error sources of GPS-based methods which degrade the accuracy of height determination. GPS can be used for interpolation of heights, and some medium/low precision spirit levelling may be replaced by GPS. It can also be utilised in maintaining country-wide levelling networks or connecting national levellings. However, many ordinary spirit levelling errors cannot be con-trolled by GPS and it will not replace precise levelling over relatively short distances