Using LiDAR for digital documentation of ancient city walls

Ancient city walls, a kind of important cultural heritage, have important historical, cultural, and research value. The digital documentation of ancient city walls is a key means of protecting them and facilitates the understanding of their present state, construction and rehabilitation, and exhibition and promotion. LiDAR technology enables us to obtain continuous points of the surfaces compared to a time consuming conventional measurement, and is applied to the digital documentation of ancient city walls. A “horizontal detection – vertical detection” method to obtain top and side points of city walls is proposed to achieve automatic extraction of point cloud information for digital documentation. We tested and verified the effectiveness and feasibility of this method through an experiment on the Nanjing city wall, included in China's 2012 World Cultural Heritage Tentative List together with eight city walls of Ming and Qing Dynasties in China.