Re: Stereo Window and Convergence Examples

[P3D <Gregg_Podnar@xxxxxxxxxxxxxxxxx>]

I appologise for providing limited explanation with the ASCII examples.  I'd
hoped  that having a common set to look at while considering some of the 
discussion here might be helpful.  (It was late and the ASCII was mind-
numbing.)  Criticisms of the imagery not being realistic and differences in 
perception of a real scene are certanly valid.  If most of us can see 
the different effects in these overly-simplified images, then it is not hard
to believe the effect generalizes to more real-world images.

P3D Gabriel Jacob <jacob@xxxxxxxxxxxxxx> provided a modified example in 
Realist-like mounting (which is perhaps a better analogy than the one I 
chose).  I agree that moving the chip and window simultaneously does not as 
strongly appear to change the distance of the window (especially if one 
ignores the infinity dot), but the apparent distance of the subject from the 
window does change (in my eye anyway) which is attributable primarily to a 
change in convergence.

> ------------------------------------------
>|   -------------          -------------   |  Window at screen level.
>|  |    .        |        |        .    |  |  Scene behind window.
>|  | Move chip   |        |  Move chip  |  |  (same as example above)
>|  | and window  |        |  and window |  |
>|  | together    |        |  together   |  |
>|   -------------          -------------   |
> ------------------------------------------
>
> ------------------------------------------
>|  -------------            -------------  |  Window still at screen level.
>| |     .       |          |       .     | |  Scene behind window.
>| | Move chip   |          |  Move chip  | |  p.s. window will appear behind
>| | and window  |          |  and window | |  screen level when viewing top
>| | together    |          |  together   | |  AND bottom mounts.
>|  -------------            -------------  |
> ------------------------------------------
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(To me this text appears further behind the window than the example above.)

It may be appropriate to note that unlike retinal disparity, convergence is
sensed from the eye muscle positions.  As this sensory mechanism is adaptive,
when an unnatural convergence is required (i.e. setting the infinity point
wider than interocular spacing), the muscles/nerves compensate.  This accounts
for an inability to sense window distance when other cues (like the edges of 
the screen) are not visible.
							Gregg


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