Machine Vision

The simplest way to extract three-dimensional information from a scene is to do it one point at a time, using a method known as point triangulation. The working principle behind this method is based on simple trigonometry. A right triangle is formed between a laser, a video camera, and the laser's spot on the object. Measurement of the camera-to-laser distance and the camera-to-laser projection angle allows for easy determination of the camera-to-object distance (for a particular object point). This range gives the third dimension, and can be determined for every object point by scanning the laser beam across the surface.

This is a very powerful technique and is used quite commonly for three-dimensional scanning because of its straightforwardness. The problem for this type of system, though, is that it has a relatively slow scan speed. A typical image may contain over a quarter of a million points. Recording only a fraction of these points, one at a time, tends to be quite time-consuming. The three-dimensional image, like taking a long exposure photograph of a moving car, can sometimes be blurred for all but the most stationary objects. To help overcome this problem, a technique known as line scanning is often used. Line scanning, or line triangulation, is a simple extension of point triangulation. In this case, however, the projected light is a line and an entire strip of the surface is scanned at a time. Although the computational algorithms are somewhat more complex for this method, the time required to scan an object is substantially less.