@article{Hoa_2017, title={Construction of initial national quasi-geoid model VIGAC2017, first step to national spatial reference system in Vietnam}, volume={39}, url={https://vjs.ac.vn/index.php/jse/article/view/9702}, DOI={10.15625/0866-7187/39/2/9702}, abstractNote={<p>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 <em>B, L, H</em> 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 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.</p> <p>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 accuracy at the level of  ± 6,2 cm. Apart from that determination of seven coordinate transformation parameters  leads to the  building of the initial national spatial reference system in Vietnam.</p><p><strong>References</strong></p> <p>Bursa M., Kenyon S., Kouba J., Sima Z., Vatrt V., Vitek V., Vojtiskova M., 2007. 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Vietnam Journal of Earth Sciences, 38(1), 14-21.</p>}, number={2}, journal={Vietnam Journal of Earth Sciences}, author={Hoa, Ha Minh}, year={2017}, month={Apr.}, pages={155–166} }