76 Print Reading for Industry Copyright Goodheart-Willcox Co., Inc. this text. The next few sections of this unit focus on the theory and practice of orthographic projection, which is foundational to the field of engineering graphics. Orthographic Projections of Views Any view of an object can be explained as the pro- jection of an object’s features onto a two-dimensional plane. For a drawing, the plane is often a piece of paper or a computer screen. Simply defined, orthographic projection is a system wherein parallel lines, called projectors, are used to project the points of a 3D object onto a 2D projection plane. The projectors are always perpendicular to the projection plane, resulting in an exact and very precise view. If more than one projec- tion plane is used, the result is a multiview projection. In general terms, a multiview drawing is a drawing based on the principles of orthographic projection. In the drawing, the different views of a multiview drawing must be systematically arranged according to standard practice. This allows anyone “reading” the drawing to “connect” the views together and form a mental picture of the part, Figure 5-1. One way to develop an understanding of the multiview system is to observe how a cardboard box unfolds. Each side of the box is oriented similar to orthographic projection views. The sides are at right angles to each other and have a definite rela- tionship. If the front of the box remains in position, the four adjoining sides unfold similar to how the views of a multiview drawing are arranged. See Figure 5-6. Now think of the cardboard box as made out of glass. Place an object inside of the glass box and imagine that the points of the object are projected Goodheart-Willcox Publisher Figure 5-5. This spatial visualization instrument involves mentally visualizing folding and unfolding paper with punched holes. These exercises help develop spatial visualization skills. See page 86 for solution. Fold A B C Which represents the unfolded paper? D E Fold Punch Goodheart-Willcox Publisher Figure 5-6. Each side of an unfolded cardboard box is oriented similar to orthographic projection views. Top Bottom Right side Front Left side Rear Top Right side Front