2-D images of 3-D objects

From: Taylor, Karl (krt196@soton.ac.uk)
Date: Mon Mar 03 1997 - 19:49:32 GMT

> From: Harnad, Stevan <harnad@cogsci.soton.ac.uk>
> Date: Fri, 28 Feb 97 19:54:11 GMT
> Subject: Chapter 4 Lecture Notes
> To: PY 104 class discussion list <py104@psy.soton.ac.uk>
> According to a theorem in solid geometry, if you mark three points on
> the surface of a 3-D object, and look at the shadow it casts in 2D,
> then the whole shape of the object can be recovered from just 2
> different 2-D views. This is a view-based invariance. It means that your
> visual system (or a machine's) could tell what the shape of a 3-D object
> was from just two views of it.

I understand that this theory says my visual system can
recover the shape of an object from two different 2-D views.

Does this mean that the two (slightly) different 2-D views
that I receive (one in each eye) when I look at an object
are enough? Or do the views need to be more different or
less different under different circumstances?

e.g. if I look at my fingernail with my hand up close to my
eye the two images I get of it are quite different. But if I
look at the side of a house from a few feet away the two
images I get are virtually the same.

Does that mean the difference necessary is related to
some external things (like the distance between my eyes, the
size of the object, my distance from it)?

Oh dear, this sounds a bit dull.

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