Accurate Overlapping Method of Ultra-Long Interval Time-Lapse Images for World Heritage Site Investigation

In this article, a method is proposed to accurately overlap multiple high-quality images with different shooting positions and intervals by combining corresponding point information between images and 3D shape information. In the proposed method, the correct feature matching of images obtained by rendering the 3D model of the subject is used. In this research, the subjects were the pillars of the Angkor Thom Bayon Temple and the epilithic microorganisms adhering to and eroding their surfaces. Synthetic transformation of a homography utilizing the correct matches is employed to overlap the target images. When overlapping different background images using the conventional method, estimation of the homography matrix becomes difficult owing to incorrect matches; thus, high-quality overlapping images cannot be obtained. The objective of this research was to realize the overlapping image process even under conditions that cause incorrect feature matches, such as differences in background and illumination. In this study, the damaged parts of the pillar surfaces were visualized using the proposed method. Based on the results of an experiment comparing the proposed method with an existing state-of-the-art method, the effectiveness and higher accuracy of the proposed method were verified. The findings of this research contribute to Angkor Thom Bayon Temple preservation, including a preservation project that the present authors are organizing for this culturally and historically valuable United Nations Educational, Scientific and Cultural Organization World Heritage site.