[Lab] Depth Perception

[Jason Cobill]

   Very clever Paul! :) Tycho Brahe had the same brainwave! Indeed -
stereoscopic images are used in astronomy. Between winter and summer, the
earth's orbit takes it 150 million km on either side of the sun, so you get
a 300 million km ocular distance between two photos taken 6 months apart. :)

   Unfortunately, you're right that even then the depth is pretty
imperceptible except to sensitive instruments.
   From Wikipedia: The nearest star to the Sun (and thus the star with the
largest parallax), Proxima Centauri, has a parallax of 0.7687 ± 0.0003
arcsec. This angle is approximately that subtended by an object 2
centimeters in diameter located 5.3 kilometers away
   http://en.wikipedia.org/wiki/Parallax#Stellar_parallax

   These people have gone ahead an exaggerated some illustrations to make
the depth visible to human depth perception.
   http://www.nightscapes.net/photos/stereo/index.html

   I've seen some computer renderings of relative star positions in our
local cluster that you can view crosseyed - but I've never seen a "real"
photo pair that's shown depth. Maybe with really distant probes taking star
shots Nasa's got something?

   -Jason Cobill



On Mon, Aug 22, 2011 at 4:24 PM, Paul & Andrea Mumby <themumbys at gmail.com>wrote:

> Too bad stars are so far away that even with several kilometers of
> stereo separation you likely won't get depth out of the starfield. Because
> that would be damn cool...
>
> - Paul
>
>
> On Mon, Aug 22, 2011 at 4:21 PM, Darcy Whyte <darcy at siteware.com> wrote:
>
>> Ah, I see, the eyes can can change their alignment to snap on to the 3d
>> experience automatically.
>>
>> So the easiest solution is to just have the cameras stationary, perhaps
>> converged a couple km out.
>>
>> Once adjusted you can see the clouds go by in 3d.
>>
>> I guess time lapse would be a great way to capture the material. Then you
>> could play it back whenever you want and the motion would make it cooler.
>>
>> But if you wanted to go real time an pan, you'd need to make sure the pan
>> rates are well match or it would "un-snap" you from the 3d experience.
>>
>> I bet you could get a nice 3d effect even if the cameras were only like a
>> few meters apart.
>>
>>
>>
>>
>>
>>
>>
>> On Mon, Aug 22, 2011 at 4:01 PM, Jason Cobill <jason.cobill at gmail.com>wrote:
>>
>>>
>>>    Alignment's not too tricky - generally, 3D movies aim the cameras
>>> parallel to eachother and let your brain do the tricky work of converging
>>> the images. They don't need to be exactly parallel for this to work, and
>>> this is the reason some people get wicked migraines watching Avatar.
>>>
>>>    You can get the same effect as the XKCD experiment (and Avatar) with a
>>> highly simplified process:
>>>    - Find a point on the horizon and take a picture of it.
>>>    - Walk a few feet.
>>>    - Take a picture aimed at the same point on the horizon
>>>    - Bring the two images together side-by-side on the computer
>>> (preferably without border lines between them)
>>>    - Cross your eyes really hard like you're looking at a "magic eye"
>>> image, and they'll converge and you can see your clouds in 3d.
>>>
>>>    Or save yourself the effort of going outside and look at these:
>>>    http://phereo.com/   (Be sure to click "Mode" and select "Crossed" if
>>> you don't want to use special glasses)
>>>
>>>    The technique is really old - I have a number of friends with
>>> collections of stereoscopic images from the mid 1800's! It was a fun party
>>> toy for Victorians.
>>>    You can find out a bit more here:
>>>    http://en.wikipedia.org/wiki/Stereoscopy
>>>
>>>    Also worth noting that stereo pairs are extensively used in aerial
>>> surveys - a plane takes two photos in succession and the pair can be
>>> converged to get a 3d view. I've often spotted clouds, boats, and even other
>>> planes in high-altitude aerial surveys. I should mention that the effect is
>>> a little less exciting than the XKCD comic paints it to be. Having a pair of
>>> stereo glasses definitely relieves the stress of staring crosswise and lets
>>> you feel a bit more immersed in the image.
>>>
>>>    -Jason Cobill
>>>
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>>>
>>
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