Visual Factors Affecting the Precision of Coordinate Measurements in Aerotriangulation

摘要

This investigation had as its aim a study of the precision of centering black circular measuring marks in sharp circular targets simulating artificial pass-points with homogeneous backgrounds of different contrasts, imaged in the vicinity of the fovea centralis. The task was related to the general area of visual acuity, and the results confirm that the eye is remarkably sensitive to tasks of this type, threshold pointing standard deviations of the order of 0.5 seconds of arc having been obtained. The investigation went further than recent photogrammetric tests using comparators with a least count of the order of 1 micron, which subtends a visual angle of 10 seconds at magnification 12x. Special instrumentation involving 6 meter viewing was used, with a least-count of the order of 0.02 seconds of subtended angle. The results demonstrated that the precision of pointing to artificial pass-points in aerotriangulation may be significantly affected by the size relationship between the measuring mark and pass-point, the background density, and the adaptation level, provided that the instruments used are sufficiently sensitive. (Author)