Integration of UAV-derived digital elevation model and GNSS for orthometric height determination in urban mapping

Accurate orthometric height information is critical for a variety of urban geospatial applications, including cadastral mapping, infrastructure development, and flood risk assessment. Traditional techniques such as differential leveling, while precise, are labour-intensive, time-consuming, and often impractical in densely built or rapidly expanding urban environments. This study investigates the integration of Unmanned Aerial Vehicle (UAV)-derived Digital Elevation Models (DEMs) and differential Global Navigation Satellite System (GNSS) observations for orthometric height determination in an urban environment. High-resolution DEMs were generated from UAV photogrammetry, while ellipsoidal heights obtained from GNSS surveys were converted to orthometric heights using the Earth Gravitational Model 2008 (EGM08). The resulting orthometric heights from both UAV and GNSS methods were compared against leveling-based reference heights to assess their accuracy and consistency. The UAV-derived orthometric heights achieved a Root Mean Square Error (RMSE) of 0.514 m, while the GNSS-derived orthometric heights yielded a slightly lower RMSE of 0.470 m. These results demonstrate the potential of integrating UAV photogrammetry with GNSS and geoid model for generating reliable and accurate orthometric heights, offering a cost-effective and efficient alternative to conventional surveying in urban areas where access may be constrained.