point where the diagonals cross is the center of the rectangle or square.

This simple rule is invaluable, it enables you to solve problems that are

seemingly unsolvable.

Figure 3-2.

Division

a. At other times it is necessary to divide an area, or a diagonal,

into a number of parts. Here a ruler alone will not suffice. As with most

division of space, the vertical (fig 3-2) or horizontal line (not shown)

parallel to the picture plane is the key. Aspect B of Figure 3-2 shows the

subdivision of a cube, portions removed. For example, to divide a receding

plane into any number of units, divide the left vertical height into the

desired number of parts with a ruler as shown in Figure 3-2.

Draw lines

from the points of division on the vertical line out to the vanishing point.

Then draw a line from corner to corner as shown, and the intersections of

the diagonal and the horizontal lines drawn to the vanishing point are the

correct points to add the other vertical lines.

b. Figure 3-3 shows the correct method of dividing a rectangular area

into uniform rectangular patterns, such as floor tiles.

The width of the

squares are first measured on a horizontal line (A). Two vanishing points

are established and lines are drawn from the divided horizontal line to the

left vanishing point, then the depth is established by drawing lines to the

right vanishing point.

A diagonal line is drawn from corner to corner,

points 1 and 2. Where the diagonal intersects the lines drawn to the left

vanishing point are-the correct points for the receding lines to be drawn to

the right vanishing point.

Notice that the lower drawing is a one-point

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