Simple projections

Extract

The simplest way of picturing a three-dimensional object in a plane is by orthogonal projection; that is, as it were, by taking a photograph from a distance. (Perspective, showing its appearance when viewed from nearby, is more accurate and lifelike but much more troublesome.) For technical drawing, it is customary to use a plan and elevation (and sometimes also side elevation). Quite often there are three perpendicular directions naturally associated with the object, such as those of the sides of a rectangular building. We call these the “left-right”, “front-back” and “down-up” axes, and the plan and elevations associated with these directions are usually easy to draw. Unfortunately, technical drawings of plans and elevations often appear rather artificial, and require training and practice to interpret properly.