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When the observer shifts his attention to the structure, the railroad ties and black lines become oblique to the picture plane, as do the rails and the fancy lines of the structure, in another direction. In the top view, the observer's right hand points to the vanishing point of the first set of lines, while his left hand points to the vanishing point of the second. Now consider the suitcase: one horizontal set of lines has become perpendicular to the picture plane. Therefore the central visual ray points to its vanishing point, which must be in the center of the picture. The other set of suitcase lines is parallel to the picture plane; so the lines remain parallel in the drawing. The one- and two-point perspectives have been transposed.
Chapter 7: "ONE-POINT" AND "TWO-POINT" PERSPECTIVE
WHEN AND WHY?
Floating Houses, Lake George, N. Y. D'Amelio & Hohauser, Architects. An example of "one-point" perspective with the point correctly placed at the center of picture. Rendering by Sanford Hohauser
 Distorted And Correct One-Point Perspective
Many books state categorically that when the vanishing point of one set of horizontal lines of a rectangular subject (such as a railroad track, a cube, etc.) falls within the picture then the other set of lines (at right angles) does not converge and the lines remain parallel and horizontal. The picture above is based on this arbitrary rule.
Note that the rails and the fancy lines converge to their correct vanishing point but that the cross-ties and black lines, which are also oblique to the picture plane (see top view) and should converge to the vanishing point indicated by the observer's right arm, do not. What about the suitcase? Its receding set of lines correctly vanishes to the point indicated by the central visual ray, while the set parallel to the picture plane remains, also correctly, horizontal and non-convergent. The result is that the front edge of the suitcase comes out parallel to the cross-ties. This surely is wrong! Also, it's obvious that objects at the far right suffer from distortion. In other words this rule is contrary to basic perspective drawing principles and results in a variety of distortions and inaccuracies.
The reason this rule prevails is that it eliminates the difficulty of working with distant vanishing points. But while this difficulty may complicate T-square and triangle perspective, it surely is no problem in freehand work.
Therefore, when the vanishing point of one set of lines of a rectangular object is placed at the vertical center of a drawing then the other set of lines (at right angles) should appear parallel and horizontal. (E.g., top picture previous page.) But when this one vanishing point shifts away from the center, indicating that the observer is shifting his viewpoint, the other set of lines should begin to converge to a distant vanishing point. (E.g., bottom picture previous page and picture below.)
Long Island Savings Bank, D'Amelio & Hohauser, Architects. Rendering by Joseph D'Amelio
Chapter 8: MORE ON LOOKING UP, DOWN,
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