Abstract: An automatic map complication system, for deriving information from a pair of stereoscopic photographs by scanning portions thereof which represent homologous imagery comprising:first means for scanning at least portions of a pair of stereoscopic photographs and developing video signals in accordance therewith;second means, including computing means, operable in a sequence of cycles of operation, for estimating for successive cycles of operation, on the basis of at least photogrammetric data related to said pair of photographs, the portions of said photographs which represent homologous imagery and controlling said first means to synchronously scan said portions; andthird means responsive to said video signals for comparing said video signals therein and producing error signals which represent the degree of error in said second means in estimating said portions of said photographs as representing homologous imagery, said second means including means responsive to said error signals for updating the estimate o

Abstract: A mechanical element positioning control system. Position measuring means supply actual position and a computer supplies desired position as the least significant 11 bits of an 18 bit signal to corresponding digital to analog units, each comprising an 11 bit register and an 11 bit digital to analog converter. A differential amplifier compares the outputs of the digital to analog converters and generates a position error signal. A threshold circuit operates to complement the most significant bit of the D/A registers when exceeding of a maximum allowable analog error occurs. A servo system responsive to the position error signal positions the mechanical element to eliminate difference between desired and actual position. By eliminating the seven most significant bits representing desired and actual position, the total range is divided into 2.sup.7 separate fields so that D/A units of practical accuracy may be employed to make feasible a positioning control system of required accuracy and range.