Passive optical rangefinder-sextant

Claim 1

A remotely controllable navigational instrument, comprised of: a concave spherical reflector exposable to objects lying along its principal axis, having a single focal point; a first and a second set of orthogonally arranged and remotely adjustable sextant optics, each including an index mirror disposed along a radial normal to the principal axis, and each reflecting onto the spherical reflector a primary image of one or more objects distant from the instrument; a first index mirror rotatable about a horizontal axis normal to the principal axis of the spherical reflector; the second index mirror rotatable about a third axis normal to the horizontal and the principal axes; the horizontal and third axes equidistant from the principal axis; first and second encoder means each mechanically linked to a different one of the sextant optics and each independently producing a position signal indicative of angular movement of the linked sextant optics; first and second circuit means each coupled to a different one of the encoder means and each providing an output indicative of the respective angular movement; an electronic camera located beyond the focal point for converting images upon the spherical reflector into a video signal for display; control means including means for eliminating all components of the video signal but those components representing pairs of parallel features of the primary images having a preferred orientation, means for displaying the pairs of parallel features by scanning a display surface, means for selecting from the display surface of field-of-view containing a pair of the parallel features, and means for producing a control signal varying in proportion to the spacing between the pair of parallel features; and, means controlled by the control signal for producing a signal representative of the spacing.