OPTIMIZATION OF GROUND CONTROL POINT (GCP) CONFIGURATION FOR UNMANNED AERIAL VEHICLE (UAV) SURVEY USING STRUCTURE FROM MOTION (SFM)
This research presents a method in assessing the impact of Ground Control Point (GCP) distribution, quantity, and inter-GCP distances on the output Digital Elevation Model (DEM) by utilizing SfM and GIS. The study was carried out in a quarry site to assess the impacts of these parameters on the accuracy of accurate volumetric measurements UAV derivatives. Based on GCP Root Mean Square Error (RMSE) and surface checkpoint error (SCE), results showed that the best configuration is the evenly distributed GCP set (1.58 m average RMSE, 1.30 m average SCE). Configurations clumped to edge and distributed to edge follow suit with respective RMSE (SCE) of 2.53 m (2.13 m) and 3.11 m (2.54 m). The clumped to center configuration yielded 6.23 m RMSE and 4.66 m SCE. As the number of GCPs used increase, the RMSE and SCE are observed to decrease consistently for all configurations. Further iteration of the best configuration showed that from RMSE of 4.11 m when 4 GCPs are used, there is a drastic decrease to 0.86 m once 10 GCPs are used. From that quantity, only centimeter differences can be observed until the full set of 24 GCPs have been used with a 0.012 m error. This is reflected in the stockpile measurement when the iteration results are compared to the reference data. The dataset processed with a minimum of 4 GCPs have a 606,991.43 m3 difference, whereas the dataset processed with 23 out of 24 has a 791.12 m3 difference from the reference data. The accuracy of the SfM-based DEM increases with the quantity of the GCPs used with an even distribution.