Summary

Straight edges are among the most common features of the modern world, arising in perhaps the majority of manufactured objects and components, not least in the very buildings in which we live. Yet it is arguable whether true straight lines ever arise in the natural state. Possibly the only example of their appearance in virgin outdoor scenes is the horizon—although even this is clearly seen from space as a circular boundary! The surface of water is essentially planar, although it is important to realize that this is a deduction. The fact remains that straight lines seldom appear in completely natural scenes. Be all this as it may, it is vital both in city pictures and in the factory to have effective means of detecting straight edges. This chapter studies available methods for locating these important features.