A perspective of the triangular pyramid, Fig. 53, Plate 8, is made in much the same way as the prism of Fig. 52 with a few exceptions. Draw the plan, locate P-P and 5 and then draw G-L and H-L in elevation. Draw the sight lines and drop light lines to the front view as before. Since the object is not rectangular in plan, the perspective may be worked out from the two lines 1-a and 1-b which are drawn at right angles with each other in plan. The direction of 1-a and 1-b will determine the effect of the drawing. Experience and trial will tell just what angle they should make with P-P for the best result. Having drawn these two lines, draw S-v1 and S-v2 parallel to them and locate V1 and V2 as in Fig. 52. Now in plan draw a line parallel to 1-a through apex 4 of the pyramid intersecting P-P at d and a similar line through corner 3 locating point c on P-P. Drop from c and d to G-L at e and f then draw from e toward V2 locating the perspective of corner 8. Corner 1 is of course on G-L. Draw 1-V2 and 1-V1. Draw from the plan of 2 parallel to line 1-b, locating point a on line 1-a. Find the perspective of point a on the perspective line 1-V2 and draw from here toward V1, locating the perspective of corner 2. Connect 1, 2 and 3 for the perspective of the base of the pyramid. Measure up from f to g, a distance equal to the height of the pyramid. Draw from g toward V2, locating the apex 4 in perspective. Connect 4 with 1, 2 and 3. Corner 2 might have been found in the same manner as . corners 3 and 4.
A circle may be drawn in perspective, Fig. 54, Plate 8, by "boxing it in," , drawing the perspective of the "box" or square according to the method of Fig. 52 and then getting the perspective of a number of points on the circle by the method of locating point 3 in Fig. 53.
When the plan is drawn with one face of the object in or parallel to the picture plane as in Fig. 49, Plate 7, or Fig. 55, Plate 8, the drawing will be in parallel perspective. In this we have but one vanishing point and that is in what is known as the center of vision and is on the - horizon line directly opposite the station point. In this figure the sight lines as drawn from S to the plan would cross the front view and so are omitted for a portion of their length. Notice that a part elevation is drawn to the right. By doing this the height of any part can be obtained by simply projecting from the elevation across to the perspective. Since the object here is not touching P-P it is necessary to bring one or more corners forward to P-P so that heights may be measured along them. The vertical edge 1-2 has been brought forward parallel to S-v1 just as d-e was brought to P-P in Fig. 52. From point a on P-P drop to G-L at b. Project over from the elevation at the right and locate the height of the base b-c. Project from b and c toward V1 to locate the perspective of edge 1-2. All edges at right angles to those whose perspective vanishes in V1 will be drawn horizontally or parallel to G-L. Any isolated points such as point 5 may be located by the method of point 4 in Fig. 53. Locate 3-4 similar to 1-2, etc.
On Plate 9 is a perspective drawing of a portion of the Cochran residence. Some of the construction lines are shown and only the methods of the previous plate have been employed in working it out. Notice that the station point has been taken about 6 feet above the ground and just to the left of the walk. This is the way the house would look if the observer were standing just below the terrace and looking toward the front door.
As a matter of interest, compare this mechanical perspective with the photograph given on Plate 6. Even though the station point of the camera was much farther away than that of the opposite drawing, and details of the house were altered somewhat in building, the parallel between the two pictures will be seen to be quite close.
The sketchy effect was obtained by first drawing the perspective mechanically with a soft, sharp pencil and then inking the lines freehand. Notice that the lines of the siding and shingles are not continuous but are just suggested, as are also the bricks of the base course, the muntins of windows, etc.
As an exercise in perspective the student might use first the simple Tuscan entablature of Plate 63, then one of the more complicated Orders and finally draw up a perspective of the residence described by Plates 21 to 30 or some other rather simple building.
It is not always necessary that every little detail of a building be drawn in mechanical perspective. The main lines must of course be located accurately but the draftsman will soon be able to judge as to what should be accurately drawn and what may be drawn by eye.