AbstractThe national/regional unified height datum is of great importance for the establishment of geospatial information infrastructure and the corresponding surveying applications. The geopotential-difference method is proposed for long-distance height-datum connection across seas based on global positioning system (GPS)/leveling, global geopotential model (GGM), and satellite altimetry data sets. For a case study, the Chinese height datum 1985 (CNHD85) in the mainland was connected to the local vertical datum (LVD) in Hainan across Qiongzhou Strait up to a distance over 30 km. The results show that this method is independent of the selection of virtual leveling lines. Furthermore, evaluation with an indirect approach shows that the choice of GGM affects the quality of the normal height connection, where the relative accuracies of the solutions based on the Earth Gravity Model 2008 (EGM2008), European Improved Gravity Model of the Earth by New Techniques 6C (EIGEN-6C), EIGEN-6C3STAT, and EIGEN-6C4 model...