Abstract

A small fraction of the area shown in an ultraminiature color transparency of a standard navigating chart is projected onto a viewing screen, and the transparency is moved by a precision step-driven transport mechanism to hold the present position of the ship (or other craft) at crosshairs on the screen. The transport mechanism is controlled by a digital electronic computer that receives data from a human operator, from speed and direction sensors carried in the craft, and/or from radio navigational-aid (such as Loran) signals. The computer includes separate dedicated microprocessors for managing the transport mechanism and the receipt of sensor or radio signals, and a master general-purpose processor for performing calculations and coordinating the system functions with operator instructions.The computer calculates position, "course to steer," and other parameters based on dead reckoning, manually entered bearings of navigational objects, and/or the data automatically received from such radio aids; and it controls the transparency transport on the basis of calculated position. By comparing dead-reckoning results with actual position fixes the computer determines set and drift, and it reads out "course to steer" that is corrected for set and drift. The computer can also control an autopilot, automatically setting a heading that produces the desired track, practically independent of currents.