Drawings will be in angular perspective when the object is placed at an angle with the picture plane as in Figs. 46, 47 and 48, Plate 7, and in parallel perspective when one face or edge is placed parallel to or else in the picture plane as in Fig. 49. The most pleasing presentation of a building is usually in angular perspective while the other method gives good results for interiors.
As a method of study it is suggested that the student follow carefully through the explanation of each figure, understanding fully every statement before proceeding to the next. After he has studied the operation and fixed each step in his mind he should draw the object in perspective to any convenient size.
Since a slight error in draftsmanship would be likely to distort the result badly, great care must be exercised throughout the work. Keep the pencil needle-sharp and make all measurements and locate all intersections with the utmost exactness. After a little practice the student will learn where care is necessary and where it is not so important.
Let the student imagine himself to be looking directly down upon the brick, picture plane and station point shown in Fig. 48 and draw at the desired scale what he sees as in the top view or Plan, Fig. 50, and below this, what he sees when looking straight toward the picture plane as in the front view or Elevation, Fig. 50. In drawing this front view first draw G-L horizontally at a convenient place on the paper. Now if the eye is considered as being 5 feet above the ground, the H-L should be drawn 5 feet above G-L at the scale decided upon and parallel to G-L. The location of the eye or station point 5 must now be fixed at the desired distance in front of P-P in plan and in the desired position laterally. This location must be carefully determined as the result depends largely upon it. Figure 51 shows several perspectives of the same building with the plan in the same position in each case but with S located in various positions. In Fig. 51A the station point is placed toward the left. It is toward the right in B, toward the center and low in c, high in D, at a distance from P-P in E and very close to P-P in f. By making a few quick sketches the position of the plan and station point may be quite accurately determined for the result desired. Thus the designer may imagine himself to be standing at any point about the building and, by drawing a perspective with this station point, he may learn exactly what his design will look like when viewed from this position.
PLATE 7. PERSPECTIVE.
From S, Fig. 50, draw a line parallel to one side of the brick intersecting P-P at v2 and one parallel to the end of the brick touching P-P at v1. These two lines from S must always be 90 degrees apart no matter what the shape of the object may be. From v' and v2 drop vertical lines to H-L which will locate the vanishing points V1 and V2 of the two systems of parallel horizontal lines. Now draw the lines of sight from 5 in plan through P-P to the corners of the brick. Where these lines of sight inter-sect P-P drop light lines to the front view. Point 1 is in G-L because it is on the ground and touching the picture plane. From point 1 draw a line toward V2. Measure up from point 1 a distance equal to the height of the brick, locating point 2 and from here draw toward V2; then draw line 3-4. Similarly draw 1-,5 2-6, and 4-7 toward V1; then draw 5-6, then 6-7 toward V2 and the perspective is complete.
PLATE 8. PERSPECTIVE.
To the object shown in Fig. 50 is added a cubical block, Fig. 52, Plate 8, considering the cube to be the same height as the brick. Draw the sight lines from S to the plan of the cube and from their intersection with P-P drop lines to the front view as before. As the cube does not touch the picture plane, we can not measure its height directly along any of these lines. One way of determining this height is to consider one vertical face of the cube as being brought forward to P-P meeting it at e in plan. In a case like this, line d-e must be brought down parallel to line S-v1 or line S-v2 in plan. Draw from e down to G-L at f. Now line e-f in elevation is in the picture plane and distances may be measured along it. From f measure up the height that point 1 is from the ground, marking it at g and from g measure up the height of the cube to h. Draw from g and h to V1 which will give the perspective of face 1-2-3-4. Now draw 1-5, 2-6, and 3-7 toward V" and then 6-7 toward V1. Any part of an object back of the picture plane may be measured and drawn in this manner.