Some influences of the photographic process on the accuracy of close range photogrammetry with a non-metric camera

The physical properties of photographic roll film in conjunction with the design of small format cameras are generally optimised for ease of use and reliability during pictorial photography. Such design contributes greatly to the problems associated with the accuracy of camera calibration and analytical data reduction of non and semi metric small format imagery. The results of experimentation into both in-plane and out-of-plane film deformation, using a variety of commercially available monochrome small format film stocks, are presented. Physical parameters Investigated include environmental conditions, image density, processing regime, measurement and film back variations. A standardised photographic process is arrived at, such that in-plane deformations are minimised. The procedure permits modification by variation of emulsion type and development to match the recording characteristics of the photographic material with the subject areas of interest. In the light of results obtained from the measurement of reseau images produced from an in-house modified Hasselblad SWC camera, film deformations occurring in-camera are found to be an order of magnitude larger than in-plane deformations. In-camera deformations are attributed to unflatness at exposure and tensions during film wind- on, both of which are functions of camera design. Results from the close range calibration of variety of metric, semi-metric and non-metric cameras are discussed in the light of the above experiments. The accuracies of derived coordinates are examined and show that the small format camera can be considered to be of photogrammetric importance. Transformation methods associated with the use of reseau photography to correct for image deformation are investigated and their suitability compared in terms of their ability to model the specific problems associated with semi-metric photography. Whilst network geometry is shown to provide the major factor influencing the determination of photogrammetric coordinates, it is shown that given good camera design, analytical photogrammetry using small format images can be limited by the image quality produced by the lens and film combination