Investigating the Length, Area and Volume Measurement Accuracy in UAV-Based Oblique Photogrammetry Models produced with and without Ground Control Points

This study was aimed to investigate the performance and sensitivity of a 3D photogrammetric model generated without GCPs (Ground Control Points). To see if the models with no GCPs show the accuracy in every types of terrain as well as climate or metrological conditions, two separate studies are done in two areas with different characteristics such as Altitude, slope, topography, and meteorological varieties. The study areas were initially modelled with GCPs and later without GCPs. Furthermore, some of the dimensions and areas within the modelled area were measured using terrestrial techniques (with GPS/GNSS) for accuracy analysis. After modelling within the areas with and without GCPs, different territories with different slope and geometric shapes were selected. Various measurement in terms of length, area and volume carried out over the selected territories within both model (generated with and without GCPs) of each 2 studies. The datasets obtained as results of measurements were compared to each other and the measurements carried out over the models produced with GCPs were accepted as true values. Results from length measurement provided various level of success. First study area exhibited very promising results in length measurement with a relative error of less than 1% and RMSE (Root Mean Square Error) of 0.139m. In the case of area measurement, in the first study area (Sivas), a minimum relative error of 0.04% and a maximum relative error of 1.05% with a RMSE of 1.264 m² is obtained. In the second study areas (Artvin) for area measurement a minimum relative error of 0.56% and a maximum relative error of 5.27% with a RMSE of 1.76m² is achieved. And finally, in the case of volume measurement, for fist study area (Sivas) a minimum relative error of 0.8% and a maximum relative error of 6.8% as well as 2.301 m³ is calculated. For second study area (Artvin) minimum relative error for volume measurement is 0.502% as well as maximum relative error is 2.01% with a 7.061m³ RMSE.