Ground control points (GCPs)
Ground Control Points (GCPs) are physical markers or points on the ground with known coordinates that are used in aerial mapping projects to ensure accuracy. They are typically pinpointed using GPS or GNSS technology and are essential for accurately mapping large areas with drones.
Proper placement of GCPs involves distributing them evenly around the survey area, including at the lowest and highest elevations, and ensuring they have a clear view of the sky without any obstructions. Placing GCPs too close together in one spot or in areas with poor visibility can actually decrease accuracy. The optimal geometry of GCPs across the entire surveyed area is more important than the number of GCPs in a particular geographic location.
Liu, J., Shi, W., & Li, X. (2021). UAV-based high-density point cloud generation for 3D city modeling using GCPs with RTK-GNSS. ISPRS Journal of Photogrammetry and Remote Sensing, 172, 36-51.
Khosravipour, M., Nassiri, M., & Sarvi, M. (2019). UAS-based photogrammetry for generating high-resolution DSMs and orthophotos of urban environments: A review. International Journal of Applied Earth Observation and Geoinformation, 87, 102-114.