File:Perspective and geometrical drawing adapted to the use of candidates for second and third-class teachers' certificates (1887) (14760134696).jpg

Identifier: perspectivegeome01mcgu (find matches)
Title: Perspective and geometrical drawing adapted to the use of candidates for second and third-class teachers' certificates
Year: 1887 (1880s)
Authors: McGuirl, Thomas H. (from old catalog)
Subjects: Geometrical drawing Perspective
Publisher: Toronto, W. Briggs
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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Text Appearing Before Image:
ase of pictureplane, 4 feet to right. 2. Find a point 3 feet above G.P., 4 feet to right, andtouching P.P. 3. Find a point directly in front touching P.P., and 6 feetabove it. 4. Find position of a point 3 feet under G.P., 3 feet toright in P.P. produced. (In foregoing examples assume spectators height to be sixfeet.) All lines at Hght angles with the base line (B.L.)., or,parallel with the direction we are looking (L.D) will vanishat the centre of vision (C.Y.); but lines parallel with thebase line (B.L.) or horizon (H.L.) will never vanish, butalways appear parallel. This is an important rule. To find the distance of a point within the plane. In fig. 6, let AB DC represent the face of a cube lestmg on the ground, and let the given face touch the picture plane. The near lower edge will then coincide with base line AB. Now, if we suppose the cube placed to the left of the spec- THE POINT. 17 tator, he will be able to see the side BD FE, or the top, if he3 as HL he as high as the cube.
Text Appearing After Image:
We have said that all lines at right angles to AB willvanish at point C. Y.; and since all angles of a cube are right 18 DRAWING. angles, the line BE, if produced, will reach C.V., andso will line DF, for the same reason. But we want to findthe position of E, the extremity of the line BE. Draw a line from C.Y. perpendicular to AB, and produceit indefinitely. A spectator stationed at N would see theedge BE represented in size by the dotted line Be perpen-dicular from B on EN. If he were placed at O, BE wouldappear as B6, perpendicular to EG from B; also, if placed atP, BE would appear as Ba / and it will be noticed that, asthe spectator recedes, the apparent size of BE decreases, ?*.e.,Ba is less than B6, and B6 less than Be, and so on. (Fig. 6.) Now from B measure lengths of Be, B^, Ba on BE: thus,B/= Be, Be = Bb, Bd = Ba, etc. Take a point M on base line at a distance from B equal torequired length of BE; this point may be on either side of B. In given case, since BE = AB or BD, make

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