Process and apparatus for surveying a railway track for any deviation from a track survey plan

Process for surveying a railway track for any deviation from a track survey plan having values which set forth the desired position of the course of the track relative to first, second and third reference marks spaced sequentially along the track, each reference mark having light reflectors located on upstanding supports in the vicinity of the track, comprising the steps of:

• (1) providing a track measurement platform on the track for rolling movement therealong, the platform having a light receiving and laser-emitting head capable of swivelling about vertical and pitch axes;
• (2) initially determining the position of the platform on the track relative to the first reference mark by measuring the distance between the platform and the first reference mark;
• (3) aligning a laser light beam from the head with the second reference mark such that the laser light beam is reflected by the reflector thereon;
• (4) moving the platform along the track and repeatingly measuring the changes, relative to the platform, in the angle of the laser light beam, which remains aligned with the second reference mark by readjusting the head about one or both said axes;
• (5) repeatingly determining the relative change in position of the platform to a previous measured position by means of a space-stabilized gyro device mounted on the platform;
• (6) repeatingly obtaining values on the change in position of the gyro device for use as correction values for the change in the angular position of the laser light beam;
• (7) comparing the values obtained to the desired values of the survey plan to determine any deviations of the track from the desired values for correcting the track on the basis of any of such deviations, and
• (8) when the reflector on the second reference mark disappears from a defined window of a visible range of the light-receiving and laser-emitting head, realigning the laser light beam with the third reference mark.