A study on the detection of bulging disease in ancient city walls based on fitted initial outer planes from 3D point cloud data

Bulging is a common disease suffered by ancient city walls, especially clay brick walls. Bulging affects or even threatens the stability of outer structures of ancient city walls. Therefore, accurate identification of bulges is one of the urgent issues to be addressed in ancient city wall conservation. In this study, a novel method is proposed for detecting and identifying bulge information using point cloud data collected from the outer surface of an ancient city wall. The non-bulging points are identified in the sliced point cloud of a city wall, and then the initial plane of the city wall is fitted more accurately with the aid of spatial constraints. Finally, the bulging damage is identified and extracted by comparing the initial plane with the original point cloud. This method was applied to the project of ancient city wall conservation and was compared with other existing methods in effectiveness and accuracy. The results show that the proposed method can detect efficiently budging disease in ancient city walls for architectural heritage conservation.