Accuracy validation of official Croatian geoid solutions over the area of City of Zagreb

Height (altitude) determination in geodesy is faced with problems that are directly attributed to the method of measurements and used geoid solutions. Due to the reliability of CROPOS as well as growing progress in geoid determination (increase of their external and internal accuracy), GNSS observations using CROPOS_VRS_HTRS96 VPPS service became most commonly used method of height determination in Croatian every day geodetic practice. This paper describes establishment of 33 GNSS/levelling points using CROPOS_VRS_HTRS96 VPPS service and geometric levelling at the area of the City of Zagreb. It also gives the analysis of the quality of performed GNSS observations, analysis and comparison of the geoid undulations from official geoid solutions of the Republic of Croatia, HRG2000 and HRG2009 with undulations obtained by GNSS/levelling for established GNSS/levelling points and brief overview of current state of vertical network of the City of Zagreb.