Triangulation is a method for distance measurements, often using a laser.
It is based on the ability of a Laser beam to propagate in well collimated form (i.e., without large divergence) over large distances. Typically, the Laser Beam illuminates a point the distance of which from the laser device is going to be measured; the laser is essentially used as a pointer. Diffuse or specular reflections from that point are monitored with a Detector which is mounted in some distance from the laser beam. A Lens focuses the reflected Light onto a CCD chip, and the position of the bright spot on the chip reveals the direction of the incoming light, i.e., the angle between the laser beam and the returning light, from which the distance can be calculated.
The high detection speed makes it possible to Monitor the position of a moving or vibrating part e.g. of some machinery. The obtained accuracy may typically be 1/1000 of the measured distance. For diffuse reflections, the distance can be limited by the requirement to receive a sufficient amount of reflected optical power; with specular reflections, much larger distances can be measured, but some kind of angular alignment is required.