Photogrammetry Applications in Routine Bridge Inspection and Historic Bridge Documentation

This study explored the use of digital close-range photogrammetry for routine bridge inspection and historic bridge documentation. The major objective of the research was to evaluate the feasibility of photogrammetry for these two bridge engineering applications. Study results indicated that photogrammetry provides sufficient accuracy and is a noncontact, inexpensive, and practical measurement option. The research involved two photogrammetry projects. In the first project, photogrammetry techniques were employed in geometry measurement of a simple-span prestressed concrete bridge. The bridge was measured and evaluated according to routine bridge inspection guidelines. PhotoModeler, a consumer-grade photogrammetry software program, was used to process the images for measurements of vertical clearance, lateral clearance, deck width, and structure length. Comparison between photogrammetric and hand measurements showed minor differences, with the percentage error ranging from 0.06% to 1.43%. In the second project, a historic noncomposite, steel girder bridge was selected for documentation. Three-dimensional models of the bridge in elevation and of the pier were developed with PhotoModeler. Dimensions obtained from the models were compared with the design drawings, which showed that photogrammetry measurements differed by 0.23% to 8.00%. Two-dimensional, orthographic photographs (orthophotos) were also developed in PhotoModeler and edited with AutoCAD to provide scaled elevation drawings of the bridge.