Nationwide Level Network Adjustment of Helmert Orthometric Heights in the Republic of Korea

In 2020, the National Geographic Information Institute (NGII) of the Republic of Korea (Korea) completed gravity observations at all vertical control points, and a basis was prepared for calculating the orthometric height. In this study, nationwide level network adjustment via the least-squares method was performed in two stages using the leveling and gravity data held by NGII, and the normal orthometric and orthometric heights at 11638 vertical control points were calculated. As a result of the nationwide level network adjustment, the orthometric height of the vertical control points in Korea ranged from a minimum of 0.5898 m to a maximum of 1325.2648 m. The difference between the normal orthometric and orthometric heights ranged from a minimum of –0.0178 m to a maximum of 0.0933 m, with an average of 0.0007 m. Therefore, the orthometric height tended to be slightly more than the normal orthometric height. After level network adjustment, the post-standard deviations of the normal orthometric and orthometric heights were identical at 2.4 mm. Because Korea has completed gravity measurements and calculated the orthometric height at all vertical control points, it is now possible to transform the height reference system to an orthometric height system.