T3D How I done it

[john bercovitz <bercov@xxxxxxxxxxx>]

Not that anyone asked but I'm going to tell you anyhow.  8-)

>From P3D:

> Ref: closeup images at http://starosta.com/3dshowcase/igem.html 
> 
> Going by the size of the index finger's nail, I'm going to say
> that the 80 mm wide image on my screen is about 3/4 life size.
> That means I must view the screen from 3/4 of the distance to
> the reconstructed object.
> 
> Next I'm going to say there is about 6" (150 mm) of depth from 
> the middle joint of the model's little finger to the bead of her 
> necklace which is at the same elevation in the image as this
> joint.
> 
> The stereo disparity between the left and right images from the 
> middle joint to that bead is 7 mm.
> 
> If you combine these three pieces of information, you have 
> enough to lock out ambiguity and you find the distance to the 
> screen should be about 750 mm or about 10X the image width.  
> 
> I used Boris' figure of 70 mm for the separation of the two 
> viewpoints (the stereobase).

OK, here's what you do.  On the figure below, connect the dots 
so as to draw lines from the right eye to each end of the "want 
150" dimension.  Now all you do is change X while letting the 
7 mm float left and right on the face of the screen until "want 
150" becomes 150 mm.  X/3 has to stay at 1/3 of X so that the 
screen is always 3/4 of the way to the near object (at the near 
end of the "want 150" dimension).  OK, so it isn't strictly 
rigorous on the 3/4 bit but it could be made so and this is a 
little less complicated.

John B


_ _  .
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want |
150  |
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_|_  .   
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gvn  | 
X/3  |      
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 |   |   ->| |<-- 7 mm
_|_  |_____|_|___________ face of screen
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chng |        
 X   |
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_|_  |

     O                  O
   left               right
    eye                eye


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End of TECH-3D Digest 241
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