The displacement measurement in structural health monitoring (SHM), though important,
was not popular due to inaccessibility of the civil infrastructures and high installation cost.
The currently popular approaches use accelerometer, strain gauge, PZT, GPS, etc., most of
which indirectly measure the displacement and require high cost to install and maintain.
Thus the development of SHM system that directly measures the displacement of the
structure using low-cost sensors is urgently needed. In this article, a multiple paired structured
light (SL) system is proposed as a displacement measurement system for a massive
structure. The proposed paired SL module which consists of cheap cameras and lasers is
inexpensive to implement and can directly measure the accurate relative displacement
between any two locations on the structure. Based on various simulations, a minimal configuration
of the paired SL module is found. And Newton–Raphson and extended Kalman
filter-based displacement estimation methods are proposed by deriving a kinematic equation
and its constraints. By building a prototype of the paired SL module, some real experiments
are performed to show the feasibility of the system for long-span structural
displacement measurement.