Abstract: In view of the advantages of the digital close shot photogrammetry and the deformation characteristics of the stay cable of the sloping stay bridge, a contactless inspection technique for the deformation of the stay cable model using a household digital camera was proposed. Based on the direct linear transformation accounting for the camera optical distortion, the 3-dimensional coordinates of the target point in the object space can be calculated from a single image if the deformation plane has been determined. The proposed technique was verified experimentally and presented, including the placement of the control points, the image acquisition, the parameters computation, the deformation plane determination, and the deformation calculation of the stay cable target point. It was showed through a comparison with the coordinates of the check points, the precision achieved by the technique is high enough for the measurement in the lab test of the stay cable.

Key words: information processing, close shot photogrammetry, stay cable, sloping stay bridge, deformation measurement, direct linear transformation (DLT), digital camera