The Role of Perspective in Shaping the Renaissance
1. In geometric perspective, all straight lines in space project to straight
lines (or points, if end on) in the picture plane. Rotating the line within
the plane of projection will not introduce any curvature, just a change
in its extent within the line of projection. In the limit when the line
is viewed head on, the projected line will contract to a point in the picture
plane.
Humans actually view scenes with two eyes, but the straightline
projections for each eye are both straight lines (Fig. 2 L & R). The
average, or binocularlyfused, projection is the combination of two straight
lines and is therefore also a straight line (Fig. 2B). No curvature is introduced
by the geometry of binocular combination.

Fig. 2. Binocular perspective.
The different left (L) and right (R) eye views of the three parallel
lines projecting onto the picture plane of Fig. 2. The two straight
lines from each eye are combined in the brain combine by binocular
fusion into the straight lines of fused image, B, whatever their geometric
relationships.

