Image analysis system for areal measurement to preserve historic masonry wall, Japan

摘要

This study examined historic masonry walls called “Kogoishi” constructed in the seventh century AD. The stones constituting the walls have been moving discontinuously, individually and gradually due to the looseness of the surrounding ground caused by prolonged weathering and plant root growth. For daily preservation management by non-experts, we created an image analysis system that combines precise close-range photogrammetry analysis with laser profiler measurement to overcome respective weaknesses. The system automatically extracts and vectorizes the edges of stones from photographs. And the image coordinates of the vectors are converted into model coordinates by using the results of laser profiler measurement. This system allows us to compute the movement of the stones easily from several photographs taken with time. This paper introduces the developed image analysis system and its application to the masonry walls.