In article ,
says...


Do you still want to debate this subject?


Not particularly.
I do maintain that you are mistaken about the application of parallax to
illusions related to apparent motion. Parallax, by definiton, requires two
distinct points of view. Thus, the distance between our two eyes would create
two slightly different views, and if we could measure it, we could use this
parallax to measure the distance to the object.

Nevertheless, parallax is not conventionally used to describe perceptions
related to motion. In the photogrammetric model, two views of the same subject
are taken and compared through a stereoscope to produce a pseudo-stereographic
image. Though the two images were taken over time, because of the movement of
the airplane, the information conveyed is considered to represent a geometric
offset, and not an expression of the airplane's movement. The same image could
have been created in the same instant by one, very large airplane, with a
camera at each extremity.

Parallax, is a term used to describe geometric differences in an observed
object from two differing viewpoints. It is not intended, nor is it
sufficient, to describe psychological illusions (expectations) or observations
or illusions related to motion (evolution of geometry over time) except
indirectly, when time is required to obtain two different views, as in the
photogrammetric example above. Definitions of parallax do not include time
constants - only geometric relationships.

Therefore, I maintain that the use of the term "parallax" to describe the
illusion discussed in this thread is imprecise at best.

G Faris