Alternative Strategies for the Optimal Combination of GNSS and Classical Geodetic Networks: A Case-Study in Greece

The present study discusses two alternative strategies for the optimal combination of different geodetic reference frames in a rigorous way. The methodological variations stem from the (un)availability and types of the 3D network observables. The alternative strategies are tested in Drama region, Northern Greece, where two local networks were established; a 3D one expressed in ITRF2008 (a modern GNSS network established for precise surveying) and a classical one which refers to the official Greek Geodetic Reference System, the Hellenic Geodetic Reference System of 1987. The concept of the proposed strategy is based on the rigorous combination of the different networks at the Normal Equation (NEQ) level. The zenith angles play crucial role for the implementation of the alternative strategies, especially for the correct use of the vertical information. The results of the case study show that the combined solutions provide generally a good level of consistency with the individual networks (GNSS and conventional land surveying).