Vision-based self-calibrating measurement method for structural settlement using gravity balance

Structural settlement is one of the most critical indicators in structural health monitoring. In long-term vision-based measurement, the stability of the observation platform is a major bottleneck limiting its application. Due to the optical lever effect, a slight angular change in the camera during long-distance measurements can result in significant errors, even leading to measurement failures. This paper proposes a vision-based self-calibrating measurement method using gravity balance for field applications. In this method, the main camera, sub-camera, and a plumb line are rigidly connected. The sub-camera tracks the plumb line to obtain the angular changes of the main camera. The rigid connection between the main and sub-cameras is used for angle compensation, enabling self-calibrating measurements on unstable observation platforms. Experimental results demonstrate the accuracy and effectiveness of the proposed method. This method has the potential to extend the application of visual measurement in monitoring large-scale engineering structural deformations.