Optimization of Ground Control Point (Gcp) Configuration for Unmanned Aerial Vehicle (Uav) Survey Using Structure From Motion (Sfm)

Abstract

<p><strong>Abstract.</strong> 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 m<sup>3</sup> difference, whereas the dataset processed with 23 out of 24 has a 791.12 m<sup>3</sup> difference from the reference data. The accuracy of the SfM-based DEM increases with the quantity of the GCPs used with an even distribution.</p>

High-Quality UAV-Based Orthophotos for Cadastral Mapping: Guidance for Optimal Flight Configurations

“…In their meta-study, [23] did not find a clear relationship between the number of GCPs and the size of the study area, but investigated a weak negative relationship between statistics of the residuals and the number of GCPs collected per hectare. Data from several sources confirm that the distribution of GCPs strongly impacts the spatial accuracy, and an equal distribution is recommended [35][36][37]. However, looking at the results of the optimal number of GCPs, different conclusions are evident.…”

Combining Interior Orientation Variables to Predict the Accuracy of Rpas–Sfm 3D Models

“…With respect to the 30 surveyed points, a cross-validation was run in a progressive mode, i.e., progressively migrating 1 point a time from the training (GCPs) to the validation (CPs) set. The choice of those points to be progressively moved from GCPs to CPs was accomplished in a balanced way; peripheral and central points were alternatively migrated taking care of maintaining a proper spatial distribution of remaining GCPs ( [22,57]). Thirty one chunks of CPs were finally obtained varying from 0 (all surveyed points were used as GCPs) to 30 points (all surveyed points were used as CPs and the image orientation completely relied on a direct georeferencing approach) [50,58].…”

Uav-Based Photogrammetry for Archaeological Heritage Site Survey and 3d Modeling of the Sardus Pater Temple (Italy)

“…The integrated use of the most conventional system of the Global Navigation Satellite System (GNSS) reinforces the data derived from images and offers validation and quality control of the work; furthermore, the integration of this system allows for a georeferenced 3D model. The setting of the survey has included a preliminary study aimed at defining the number and position of the markers: this step is particularly important in order to achieve an optimal result (Villanueva and Blanco, 2019). The GNSS survey was performed with a Magellan Promark 500 in Real-Time Kinematic mode.…”

“…A second set of 4 Quality Control points (QCPs) has been adopted for checking the quality of the model. The markers were placed over the entire area, with a uniform but not regular distribution, around the temple and keeping the QCPs placed at a certain distance from each other (Villanueva and Blanco, 2019). The drone flights were performed after recording the system of control points (Figure 3).…”