The orientation of the WGS-84 ellipsoid was accomplished under conditions of it’s best fitting to the Hon Dau local quasi-geoid and the parallelism of its axes to the corresponding axes of the national WGS-84 reference ellipsoid allows get national quasi-geoid heights and coordinate transformation parameters that have been used for conversion of the mixed quasi-geoid heights from the VIGAC2014 quasi-geoid model to the initial national quasi-geoid model VIGAC2017. | Vietnam Journal of Earth Sciences 39(2), 155-166, DOI: Vietnam Academy of Science and Technology (VAST) Vietnam Journal of Earth Sciences Construction of initial national quasi-geoid model VIGAC2017, first step to national spatial reference system in Vietnam Ha Minh Hoa Vietnam Institute of Geodesy and Cartography Received 08 March 2017. Accepted 31 March 2017 ABSTRACT Vietnam national WGS-84 reference ellipsoid was obtained in 1999 from results of an orientation of the global WGS-84 reference ellipsoid. However, usage of the broadcast satellite messages doest not give high accuracy in determination of national quasi-geoid heights. Based on the determined geopotential of the Hon Dau local geoid and constructed initial mixed quasi-geoid model VIGAC2014, this scientific article presents results of building of initial national quasi-geoid model VIGAC2017. Used data consisting of geodetic coordinates B, L, H of 164 first and second orders benchmarks of the national leveling networks was obtained from GPS data processing in ITRF according to global WGS-84 ellipsoid with satellite ephemeris accuracy at level of ± 2,5 cm, and the initial mixed quasi-geoid model VIGAC2014 was constructed from the EGM2008 model. The orientation of the WGS-84 ellipsoid was accomplished under conditions of it’s best fitting to the Hon Dau local quasi-geoid and the parallelism of its axes to the corresponding axes of the national WGS-84 reference ellipsoid allows get national quasi-geoid heights and coordinate transformation parameters dX 0 , dY0 , dZ 0 , that have been used for conversion of the mixed quasi-geoid heights from the VIGAC2014 quasi-geoid model to the initial national quasi-geoid model VIGAC2017. * Along withquasi-geoid heights , which were obtained from the initial national quasi-geoid model * * VIGAC2017, an estimation of the accuracy of differences ( ) shows that quasi-geoid heights have the .
