[Lab] Depth Perception

Jason Cobill jason.cobill at gmail.com
Mon Aug 22 16:47:52 EDT 2011

   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

   These people have gone ahead an exaggerated some illustrations to make
the depth visible to human depth perception.

   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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