3.4.1. GCPs Measurements

GCPs were placed on natural features, such as the corner of the pagoda, and several on the interior of the interested area to assess the accuracy of the UAV-SfM method. Checkpoints (CPs) were used to check the pagoda accuracy in detail, and points were placed on the nature features of the pagoda façade.

#### 3.4.2. Terrestrial Laser Scanning

The accuracy of a UAV-derived model was compared with that of the TLS data model, using a Riegl LMS-Z210 scanner recorded from multiple stations with high and medium resolution. TLS is a reference data model—its point cloud referred to known control points received from the RTK total station survey from benchmarks given by the Royal Thai Survey Department. The TLS device was set up at first at known XYZ coordinates, which were initiated from the total station. Finally, the result was applied as a reference for the UAV model. The accuracy of TLS is 3–5 mm. The 3D pagoda model was developed using the standard procedure implemented by CloudCompare software.
