In Canadian Pat. No. 762,044 to John Stewart and Helmuth R. E. von Beckmann issued June 27, 1967 there is described a railway track surveying apparatus comprising a light frequency beam transmitter mounted for movement along a track and for transmitting a light frequency beam substantially longitudinally of the track. A pair of beam receivers are provided, one for each rail of the track, mounted for movement along the track in spaced relationship to the transmitter within the transmitted beam, a shadowboard for each receiver is mounted for movement along the track and located intermediate the transmitter and receivers and substantially nearer to the receivers than to the transmitters, means is provided for adjusting the vertical height of the receivers, controlled by a gravity sensing means, so that the vertical height of a selected one of the receivers may be adjusted to maintain the receivers in cross level relative to the grade rail.
The present invention is concerned with improvements in systems of this type.