g. * Planes*.

As the line projection theory was derived from the point projection

theory, so the plane projection theory follows directly from the line projection

theory. If we consider the following axiom:

This differs from the geometric concept of planes in that it considers a plane a

finite area, that is, an area with known boundaries. Figure 12 gives the front and

top views of plane 1-2-3-4 and asks for the right side view.

FIGURE 12.

PLANE PROJECTION PROBLEM.

Figure 13 (on the following page) shows the solution, which was derived at by the

following:

Step 1.

Identify the lines that define plane 1-2, 2-4, 4-3, and 3-1.

Step 2.

Project the individual points 1, 2, 3, and 4 into the right side view.

Step 3.

Draw in, with object lines, the lines that define the plane.