Photogrammetric characterization of laboratory rivulets for cable-stayed bridges

Research into the exact exciting mechanism behind the 'rain-wind' oscillation phenomenon associated with cable-stayed bridges is ongoing. This paper presents photogrammetry, the three-dimensional reconstruction of an object's geometry from two or more still images, as a method to characterize the water rivulets that form on stay-cables that may be causing this unstable motion. Because of the sensitive time varying nature of running water, laboratory experiments were implemented using 'static' rivulet shaped objects to determine the feasibility of using photogrammetry to measure the geometry of rivulets. Two different approaches for three-dimensional reconstruction were implemented using the commercial software, Photomodeler. The first method used the curve and loft tools in Photomodeler to construct a three-dimensional model of the static rivulet shaped objects. The second approach used auto-detection of grid points surrounding the rivulet, including those that are hidden from view in some images to determine the location and width of the static rivulet. Both approaches were able to approximate cross-section geometry of the rivulets. Therefore, photogrammetry, and the time sequenced videogrammetry, show promise for field implementation and identification of moving water rivulets.