In Fig. 367, let A B D E be the elevation and K G I O the plan of the pyramid at the base. Project the points B and D into the plan, as shown, locating the points M and P, and draw the sides of the plan at top, each parallel to the corresponding line of the plan at the base. By projection from G or O of the plan draw C F of the elevation, representing O R of the plan and also the straight hight of the frustum.

Before the slant hight or stretchout of a side can be obtained it will be necessary to construct a section on any line crossing the plan of the side at right angles as S T. Therefore extend the top and bottom lines of the elevation, as shown dotted at the right, cutting the vertical line S1 S2, thus making S1 S2 equal to the straight hight of the frustum. Upon the base line extended set of from S1 the distance S1 T1, equal to S T of the plan, and draw S2 T1. Then will S2 T1 be the true profile or slant hight of the frustum.

At right angles to M R of the plan draw S W, making its length equal to the slant hight of the frustum, as shown by S2 T1 of the section. Through W draw N H indefinitely, parallel to K O. At right angles to K O, through the points K and O, draw lines K N and O H, cutting N H in the points N and H, thus establishing its length. Connect M N and

R H. Then M R H N will be the pattern of one of the four sides composing the article.

Fig. 367. - The Envelope of the Frustum of a Pyramid Which is Diamond Shape in Plan.