There are a variety of ways to perform automated, high precision measurement, each with its own strengths. Contact measurement is more effective for measuring specific features—holes for example—to ensure that they are where they belong and of the correct shape and size. When an entire shape needs to be scanned, for example to reverse engineer a part, optical measurement is more effective. Optical technology delivers a complete, detailed picture of a surface. And because optical scanning images cover an entire field of view rather than one point at a time, they can be made very quickly.
Recognizing contour is a matter of judging relative distance from a fixed point, but this cannot be done based solely on a single point of view. As a human, if you close one eye you lose depth perception and cannot effectively judge distance or contour. Our human ability to judge depth is based on seeing the same object through two eyes, each from a different angle. We then mentally “triangulate” to determine relative distance to each point on an object’s surface and, by extension, its contour.