Detection of angular position

A device for detecting a direction, comprising a grating having parallel bars orientated in the direction to be detected, a continuously rotating disc having alternately light and dark radii, means for forming an image of the grating on the disc, thereby producing morie figures, means for sensing the average light intensity modulation on the superimposed grating image and disc, and optical means for rotating said grating image around an axis parallel to the axis of disc rotation from a first, initial angular position to a second angular position, at which a peak amplitude is sensed by said light intensity modulation sensing means, said second angular position being indicative of the direction to be detected.