
The Role of Perspective in Shaping the Renaissance
3. The viewer’s angle to any pair of vanishing points is the same
as the angle between the generating parallels in space. In particular, the
vanishing points for any 90º angle in space form a 90º angle at
the viewer's eye (Fig. 5). However the angle is rotated in space (even to
complete foreshortening), the vanishing points will nonetheless hold to
a 90º angle at the viewer's eye. The physical distance between the
vanishing points depends on the intended viewing distance, but a good rule
of thumb is at least twice the width of the picture. Leonardo da Vinci recommended
10  20 times the height of the largest objects depicted.

Fig. 5. Viewing geometry for perspective constructions. The viewer’s
angle to the vanishing points is 90º, matching the angle between
the edges of the cube that generated the vanishing points.


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