Elements of descriptive geometry, with applications to isometric projection and othe forms of one-plane projection; a text-book for colleges and ingineering schools by O. E. Randall.

ISOMETRIC PROJECTION

201

To draw the isometric projection of the upper base of the hexagonal prism, make o'-1, o'-m', d'-n', etc., of Fig. 175 equal respectively to O-L, 0-M, D-N, etc., of Fig. 176, and connect the points
thus found by straight lines.
To complete the projection of the prism, find the isometric
projection of the lower base by the process just explained and
connect the corresponding vertices of the two bases.
The shade lines.
The upper base and the three faces L-R, M- U, and N- W are in
the light, locating the shade lines as shown in the drawing.
< r 4 K
-I-C - I I'
/,"s,/' 441. Problem 306. To make
an isometric projection of the
FIG. 177 frustum of an octagonal
pyramid.
Analysis. Imagine the frustum of the pyramid to be inscribed
within a square prism whose base is the circumscribing square of
the larger base of the frustum and whose altitude is the altitude
of the frustum.
Construction. See Figs. 177 and 178. Fig. 178 represents in
plan the two bases of the frustum and their circumscribing squares.
B-G-K-F represents the circumscribing square of the larger base
and L-M-N-P-.. represents the larger base itself.
Q-R-U-W represents the circumscribing square of the smaller
base and 1-2-3-4-.. represents the smaller base itself.