The Role of Image Quality in Photogrammetric Pointing Accuracy

摘要

The acuity of the visual pointing operations - alignment of lines and pointing at circular targets - is discussed with respect to the visual stimuli involved and its limens. Computations and derivations are based on the optical convolution of the object's intensity distribution with the human eye's spread function, its 2-sigma-width being selected between 300 and 500 microrad. Relations with the visibility of points, lines, and straight and undulating edges and with simple geometrical forms are established and presented in a diagram as a function of the angular subtense in object space. Accidental and systematic errors are given as function of image quality, magnification, and target contrast. The best attainable pointing accuracy under specific conditions can now be predicted; this allows the photogrammetric systems designer to evaluate the improvement of imaging quality of the optical-photographic system in terms of accuracy. Extension of the methods for application on subjective edge-location and on stereoscopic height measurements is indicated; various definitions of the subjective width of unsharp targets and boundaries are explored and will be researched on in the follow-up study on edge location and parallax clearance. (Author)