The correct determination of geodetic datum is an obligatory condition for the proper determination of the point displacements. There are various methods of deformation analysis focused on the right identification of stable points, which may define an appropriate coordinate basis for calculating the displacements of other points. These methods are largely based on the statistical testing and represent a comprehensive and complex analysis of change of geometry of geodetic network and allow definition of statistically significant displacements. Knowing the characteristics of the transformation between the solutions of displacements that are based on different definitions of geodetic datums, the problem of defining an appropriate geodetic datum can be solved in a slightly different way. In this article we have focused on the problem of determining the appropriate weighting matrix E in the model of S-transformation. We used the generally known methods of robust statistics. The robustness of the three selected methods were tested on two different situations of preselected displacements in the considered geodetic network and the results on selected case of geodetic network with results of conventional methods of deformation analysis were compared.

Key words: geodetic datum, S transformation, robust statistics, displacement, influence function, IWP – iterative weighted projection