Accurate measurement of volume is essential to successful monitoring of quarries and resource management. Existence of stable ground control points (GCPs) ensures aerial surveys to remain precise. However, in quarries, such as in the clay quarry in Ataqa, Suez, Egypt, quarrying activities destroy these points, where volume estimation is challenging. This study investigates the impact of GCP destruction during quarry activities and explores the use of UAV-based photogrammetry supported by natural landmarks (NLMs) as an alternative georeferencing method in the absence of GCPs. While the photogrammetric workflow remained consistent, the key difference lay in the georeferencing stage—using GCPs in the first two steps and exclusively depending on NLMs in the final step. To carry out the study, a three-step process was followed: first, a baseline survey was done using four GCPs; second, the same survey was repeated after quarry operations, still using the four original GCPs; and third, a final survey was performed without using any GCPs—relying only on eight NLMs for positioning—to simulate a situation where the GCPs had been lost or destroyed. In addition, the current research found that volume calculated using NLMs shows approximately 2% difference from the reference volume, which validates their efficiency in ensuring measurement precision without GCPs.
Nabil A. Samir, Osama M. Moussa, A. Elsharkawy et al.· IOP Conference Series: Earth...· 0 citations
Unmanned aerial vehicles are a modern technology for collecting data for aerial surveying to produce high-resolution digital elevation models (DEMs). This accuracy is achieved using ground control points (GCPs), which are specific locations on the ground with known coordinates that help improve the precision of aerial data collection. Digital elevation models are used in many applications such as topographic mapping, land-use planning, and levelling. This study aims to identify the optimum number of GCPs to achieve high accuracy for digital elevation models and reduced fieldwork. 1 km2 was imaged with a commercial UAV named Matrice 300 at a height of 200 m above the ground, with 80% forward overlap and 70% side overlap. 25 ground control points and 5 check points were created using the GPS technique. The images were processed using Agisoft Metashape software by an adjustment process with an incremental number of GCPs starting with 4 and ending with 25. The remaining points were used as a checkpoint to determine the precision of the model at each trial. Root Mean Square Error (RMSE) was used as an accuracy measurement. The study demonstrates that horizontal accuracy (RMSE XY) stabilizes after 5 ground control points (GCPs), with a marginal enhancement from 1.2 cm to 1.1 cm after 13 GCPs. The vertical accuracy (RMSE Z) improves markedly from 3.1 cm to 2.1 cm with 18 GCPs, demonstrating that height precision is more responsive to the quantity of control points. The 3D accuracy (RMSE XYZ) enhances by 1 cm with the addition of ground control points (GCPs) up to 18 but becomes stable at 2.3 cm after that, which is consistent with the vertical accuracy measurements. A medium GCP density of 9–12 is recommended for general UAV-based digital elevation model (DEM) generation, balancing accuracy and efficiency.
Kamal M. Gamal, A. Elshrkawy, Osama M. Moussa et al.· IOP Conference Series: Earth...· 0 citations
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