1：Experimental Design and Method Selection:

The study involved photographing an area of about 1 ha with a DJI Phantom 3 Standard UAS at two different heights (28 m and 35 m above ground) and measuring 50 GCPs using a total station. The UAS images were processed using Pix4D Mapper Pro and 3DF Zephyr software with a full bundle adjustment process, gradually increasing the number of GCPs from three to 40. A third test was conducted using 3DF Zephyr Pro software with a free-network approach in the bundle adjustment. The point clouds and mesh surfaces derived from these processes were compared with a TLS point cloud for accuracy assessment.

2：A third test was conducted using 3DF Zephyr Pro software with a free-network approach in the bundle adjustment. The point clouds and mesh surfaces derived from these processes were compared with a TLS point cloud for accuracy assessment. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: The study area was located near the Faculty of Hydrotechnical Engineering, Geodesy and Environmental Engineering at the 'Gheorghe Asachi' Technical University of Iasi, Romania. The 50 GCPs were uniformly distributed over the study area.

3：List of Experimental Equipment and Materials:

DJI Phantom 3 Standard UAS, total station for measuring GCPs, Pix4D Mapper Pro software, 3DF Zephyr Pro software, Maptek I-Site 8820 terrestrial laser scanner.

4：Experimental Procedures and Operational Workflow:

The UAS images were processed with a minimum number of GCPs, gradually increasing to 40, with the remaining points serving as check points for accuracy assessment. The accuracy was evaluated by comparing the manually measured coordinates of the CPs on each oriented image with those determined by GNSS technology.

5：Data Analysis Methods:

The Euclidian distance between the two coordinate sets for a point was calculated, followed by the determination of the root mean square error (RMSE). The accuracy of the 3D point clouds and mesh surfaces was assessed by comparing them with the TLS point cloud using CloudCompare software.