5.5.1 Introduction

The shapes of common objects such as a notepad or a mobile phone as well as of technical structures such as tunnels can be described by simple basic solids, apart form the "rounded vertices". Why is that?
If a broom is moved straight across a plane floor covered with dust, a rectangular section of the clean floor becomes visible. Geometrically idealised, a rectangle is formed by shifting a line segment (the broom). If the broom is rotated, a circle can be created. In this way, from simple objects more complex objects are constructed that can nevertheless be described easily.