An automatic orthophoto printer and display for the preparation of orthophotographs from a pair of stereo aerial photographs is described which includes circuitry for compensating for position errors of the transports holding the photographs. Position sensors provide digital position signals representing the actual position of each transport in X and Y directions to digital comparators which subtractively combine the position signals with digital stage coordinate signals representing desired position of each transport in X and Y. The resultant error signals are used to proportionately shift the rasters of video scanners scanning a portion of each photograph. A specific embodiment of a photo-positioning transport and a position sensor comprising an incremental encoder is also described.
A control system of a step motor and a method thereof are capable of evenly maintaining a traveling distance and a torque in a moving section, especially in an accelerating section, by limiting a start excitation phase or a final stop phase to a specific phase, even though an excitation and the torque are unevenly generated due to an imbalance in a step angle generated during the manufacturing and/or assembly of the step motor.
