Now suppose we held the book this way (if it were possible) so that both the "top" and "bottom" (here, left and right) edges of the pages are now bounded by vertical, rather than horizontal, parallel planes. As above, these two parallel planes, and all the lines that lie on them, will converge to one vanishing line. But in this case the vanishing line is vertical. Where is it located? As in the case above, it is situated on a plane through the observer's eyes and parallel to the planes in question (see top views).
In the diagram at far right, the left and right edges of the pages, and hence the plane through observer's eye, point to the right, therefore the vertical vanishing line shifts to the right.
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