Photogrammetry is "The science or art of deducing the physical dimensions of objects from measurements on photographs of the objects". It includes the generation of three-dimensional (3D) models from stereo pairs of imagery in order to obtain depth and height information, and is part of the larger field of 3D optics, and can be referred to as 3D photogrammetry. Stereo images have to be collected with an approximate 60% overlap in order to generate these models 2. The project team's use of 3D optics through development of an integrated system called the 3D Optical Bridge-evaluation Systems (3DOBS) was a technology demonstration to apply a potentially lowcost remote sensing method not yet typically seen in transportation applications. At the distance used in this project, the deployment can be described as an implementation of close range photogrammetry. 3 Several bridge condition indicators were evaluated to see if they could be assessed with 3D optics, with a focus on spalling and surface roughness. The 3DOBS system proved capable of accurately assessing the percent of a bridge deck area that was spalled along with related condition indicator data.
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