The effect of the distribution and numbers of ground control points on the precision of producing orthophoto maps with an unmanned aerial vehicle

Ground control points (GCPs) are used in the process of indirectly georeferencing unmanned aerial systems (UAS) images. The aim of this study was to determined how many GCPs and what kind of distribution is required in order to obtain high precision results. In the study, three scenarios were investigated. The GCPs were tested in edge distribution in the first scenario, in the middle distribution in the second scenario, and in homogeneous distribution in the third scenario. In the first scenario, the edge distribution was supported by the central GCPs, while in the second scenario, the central GCPs were supported by the edge GCPs. Each scenario was initiated with four GCPs. The number of GCPs was increased by four, resulting in the utilization of a total of 35 GCPs. In addition, 30 check points (CHP) were used. The number of orthophoto and DSM produced in the study was 33. In the study, the best planimetric accuracy was obtained with the first scenario, namely with the edge distribution (RMSE xy: 0.033 m). Altimetric accuracy was obtained with the third scenario, namely with homogeneous distribution (RMSE z: 0.048 m).