To cut the converging line coming forward from A, connect the end of the
auxiliary with the opposite D2. This makes A=a=aa, Fig. 4.
Lines drawn from both ends of the auxiliary to the picture plane will give one-half measurement of A, or on the measuring scale, the actual size in feet or inches. This rule will be very helpful when drawing windows and doors which open toward you.
One picture I saw will explain the usefulness of this rule. The window was divided into two parts, being on hinges. These opened toward me, the mistake being that one part was large enough to cover the whole window when closed.
Use this rule to ascertain the length of the converging lines of the chair, Fig. 4, and the table and bureau, Fig. 2.
To obtain the depth of the window, drop lines to the floor converging line.
Place the rungs of the chair according to rule.
The back of the chair slants back slightly. Parallel oblique lines in the air converge to the same point on the prime vertical. In this case they meet below the horizon. If the slant were in the opposite direction, they would meet above the horizon. Obtain the slant of one side of the back, then draw the other side to the same point.
Study Figs. 6 and 7, which show how a circle or an oval can be drawn in perspective. Draw a circle in full view, enclose with a square, cross the square from corner to corner up and down and across through the center, and again up and down and across where the circle meets the cross lines. Continue these cross lines to PS. Place the circle at the junction of these lines on the converging square, Fig. 7; this will give you a vertical ellipse (or a circle in perspective).
A horizontal circle in perspective may be obtained by filling the top converging plane with the same kind of lines. This rule will help you when drawing oval
mirrors, children's hooples, curves on furniture, etc.
Draw an oval mirror on the bureau in Fig. 2. Draw a basket in Fig. 8.
ANGULAR PERSPECTIVE