Verification of image orthorectification techniques for low-cost geometric inspection of masonry arch bridges

A low-cost image orthorectification tool based on the utilization of compact cameras and scale bars is developed to obtain the main geometric parameters of masonry bridges for inventory and routine inspection purposes. The technique is validated in three different bridges by comparison with laser scanning data. The surveying process is very delicate and must make a balance between working distance and angle. Three different cameras are used in the study to establish the relationship between the error and the camera model. Results depict nondependence in error between the length of the bridge element, the type of bridge, and the type of element. Error values for all the cameras are below 4 percent (95 percent of the data). A compact Canon camera, the model with the best technical specifications, shows an error level ranging from 0.5 to 1.5 percent.