STEREOSCOPIC VISION APPLIED TO PHOTOGRAMMETRY

In Part I the visual processes involved in depth perception are briefly described and discussed, while in Part II their application in stereo plotting and allied observations is considered. Reference is made to the visual axis, the need for and nature of eye movements, the conception of the horopter space within which fusion of the binocular images occurs and objects are seen in three‐dimensions, and the tolerances for fusion implied by the existence of Panum's areas. Monocular clues make an important contribution to the perception of depth, and the apparent location of an object in space is determined by the factors of retinal disparity, convergence, angular size, perspective, motion parallax, elevation, aerial haze, etc. The following problems are then discussed: The significance of the horopter in relation to the general contour in a stereo photograph; the fusion of the images in a stereo plotting machine; the arguments for and against some convergence of the eyepiece axes; the special problems of spectacle wearers; the functions of field stop. An analysis of the visual task in contour plotting is attempted, but a more complete analysis would be possible if records were available of the observer's eye movements while plotting. Finally, chromatic aberration in relation to the Multiplex system is considered, and also in connection with the stereoscopic effect observed with differently coloured objects lying in a plane.