Monitoring the cylindrical minarets of a holy shrines using UAV photogrammetry

Religious and historical buildings are among the most important objects of cultural heritage. They reflect the history of countries. Therefore, it is important to preserve this religious heritage from neglect and vandalism, weather conditions and natural threats. Especially the religious and historical buildings consisting of towers and circular and cylindrical minarets of high heights. Those minaret structures are impacted over the long years of construction which causes its inclination and deviation from the center of the basic base. In this research, the four minarets of the Kadhimiya Holy Shrine in Iraq were monitored using two techniques. The first technique is used for a ground survey using the Total Station device where the coordinates of the control points distributed on multi-level circles on the minaret bodies are monitored. The amount of inclination in three minarets is 0.357m, 0.377m, and 0.223 m, respectively. The second technique is applied using photogrammetry, which was represented by using an unmanned aerial vehicle (UAV) of the type (Mavic 2 Pro), and images were taken in the form of vertical strips with high overlap to cover all parts of the minaret. Then a dense point cloud was reconstructed and a three-dimensional model of the same minarets was produced using Agisoft Metashape software. The amount of inclination in the minarets is computed and found 0.361m, 0.38m, 0.225 m respectively. These results confirmed the convergence between the ground scanning technology and UAV photogrammetry in observing the vertical inclination in the minarets of the Kadhimiya shrine. The results are promising to use the UAVs for engineering projects and 3D modeling.