High-Precision UAV Photogrammetry with RTK GNSS: Eliminating Ground Control Points

The advancements in Unmanned Aerial Vehicles (UAVs) have significantly enhanced the capability of the photogrammetric approaches, particularly with the integration of Real-Time Kinematic (RTK) sensors. That approach enables the operators to use the Global Navigation Satellite System (GNSS) more efficiently with the production of high-precision 3D Digital Terrain Models (DTMs). Traditionally, Ground Control Points (GCPs) are used to link those models to a ground coordinate system, but their establishment is time-consuming and labor-intensive, requiring static or rapid-static GNSS observations over two hours for each point. However, RTK-embedded UAVs offer a significant improvement by facilitating direct geo-referencing of DTMs, which includes the estimation of internal and external orientation parameters more efficiently and potentially eliminating the need for GCPs. In this study, UAV flights over a test area at various altitudes (30m, 45m, 60m) were conducted to evaluate the 3D positioning accuracy of photogrammetric models generated without using any GCP, and their locations were compared against the precise GNSS observations for 22 control points. Results indicated that UAVs with RTK ability could achieve centimeter-level accuracy in positioning, making this kind of evaluation a viable alternative to traditional methods. This study also discusses the implications of those results within the context of large-scale map production and their regulations in Türkiye. The elimination of GCPs should significantly reduce the time and effort associated with map production, suggesting a potential alternative in regulatory standards to incorporate these technological approaches.