A novel network control method for photogrammetric bridge measurement

An alternative approach for establishing a network control called refined distance constraint (RDC) is presented to reduce field work and to focus on the photogrammetric bridge deflection measurement. In a RDC approach, three reference target points are adjusted in the same elevation with a level to define a horizontal plane and plumb vertical direction, while the scale bars are used to define the object to image scale. It takes only a fraction of the time to perform compared to the conventional control-point method. Based on the results, the RDC method provides an effective way to establish a reference system for measuring vertical geometry and deflection for many bridge engineering applications of close-range photogrammetry. It is comparable to control-point method but the former significantly reduces the field work thus, can be used effectively and efficiently for network control method.