• Reliability of photography for traffic measurement

      O'Grady, James Bradley (The University of Arizona., 1973)
      This thesis describes a simplified method for estimating distances directly from terrestrial photographs. It was felt that any method devised must overcome present limitations and meet three basic criteria to be practical. These criteria are: 1) that the method require no subject-visible markings, 2) that it require no special equipment or training to use, and 3) that it provides sufficient accuracy to be useful. A number of possible methods were considered, and were evaluated against these criteria. the Accuacy ( reliablity) of the methods was tested using a variety of statistical tests. The recommended method consists of first selecting a reference distance whose length is known. This reference should be in a plane parallel to and approximately the same distance from the camera as the desired distance. It was found that a vehicle dimension such as the tire track gives consistently the best results. Both the reference and the desired distances are then scaled on the photograph and a ratio is applied to drectly estimate the desired distance. Greatest reliability is achieved when the subject is directly in fromt of, or behind the camera and at a distance between 50 and 250 feet. By following thers guidelines the stated objectives can be met by using this method.