All of the vertical construction lines have not. been shown in the figure, as this would have made the drawing too confusing. The student should be sure that he understands how every point in the perspective projection has been obtained, and, if necessary, should complete the vertical construction lines with pencil.
63. Having. found the perspective of the vertical walls of the main body of the house, and•of the porch, the next step will be to consider the roof of the main part of the house.
Imagine the horizontal line tze, which forms the ridge of the roof, to be extended until it intersects the picture plane. This is shown on the diagram by the extension of the line tu, until it intersects HPP. From this intersection drop a vertical line, as indicated in the figure. This vertical line may be considered to be the line of measures for an imaginary vertical plane passing through the ridge of the house, as indicated by the dotted lines in the plan and elevations of the house. On this line of meas ures, lay off the distance nm measured from VII, (or VH,), equ'al to the true height of the ridge above the ground as.given by the elevations of the house. A line drawn from the point m, vanish ing at v", will represent the ridge 9f the house, indefinitely ex tended. From the points t and w in the diagram draw visual rays. From the intersections of these visual rays with IIPP drop vertical lines which will establish the positions of tP and wP on the perspective of the ridge of the roof. Lines drawn from tP and toP to the corners of the vertical walls of the house, as in dicated, will complete the perspective of thb roof.
To find the perspective of the porch roof, draw a visual ray through the point y on the diagram, and from its intersection with HPP drop a vertical. Where this vertical crosses the line ev will give yP, one point in the perspective of the ridge of the porch. The perspective of the ridge will be represented by a line through yP, vanishing at ed. The point e in the ridge will be vertically below the intersection of HPP with the visual ray drawn through the point z on the diagram. Lines drawn from yP and e to the corners of the vertical walls of the porch, as indicated, will complete the perspective of the porch roof.
64. The perspective of the chimney must now be found. It will be seen that the chimney is formed by a rectangular block ; and if it is supposed to extend down through the house, and rest upon the ground, it will be a block under exactly the Same con ditions as the one shown in Fig. 21, § 59. In order to find its
perspective, extend its front vertical face, as indicated on the diagram, till it intersects HP?. A vertical line dropped from this intersection will be a line of measures for the front face of the chimney, and the distance ps, laid off on this line from VH, (or will show the true height of the top of the chimney above the ground, as given on the elevation. The distance so, measured from the point s on the line of measures, will be the true vertical height of the face of the chimney that is visible above the roof. Lines through s and o, vanishing at eb, will represent the hori zontal edges of the front visible face of the chimney. The vertical edges of this face will be found vertically below the points wheie HPP is crossed by the visual rays drawn through the horizontal projections of these edges on the diagram.
Having determined the perspective of the front face of the chimney, the perspectives of the remaining edges may be found as in the cases of the rectangular blocks already discussed. From the point r in the diagram, where the ridge of the roof intersects the left hand vertical face of the chimney, draw a visual ray intersecting HPP, and from this intersection drop a vertical line to the perspective of the ridge of the house, giving the perspec tive (re) of the point where the ridge intersects the left hand face of the chimney. A line drawn from rP to the nearest lower corner of the front _face of the chimney will be the perspective of the intersection of the plane of the roof with the left hand face of the chimney.
65. The problem of finding the perspectives of the windows and door is exactly similar to that of finding the perspective of the square hgkl on the surface of the block shown in Fig. 20.
It will be noticed that the intersection with the picture plane of the left hand vertical face of the porch gives a line of meas ures (§ 55 and § 59, note) for this face. This line may be used conveniently in establishing the height of the window in the porch.
At this point in the course the student should solve Plate III.