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<p>HackADay has a discussion about this cartoon also.</p>
<p>http://hackaday.com/2011/08/23/we-dont-need-to-brainstorm-projects-xkcd-does-that-for-us/#comments</p>
<p>The last comment was interesting about taking 2 photos of the starry sky... separated 1/2 year each other, effectively using earths orbit around the sun to create a huge separation. Still not enough to make stars 3D, but an interesting experiment regardless!</p>
<p>Aaron</p>
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<p>On Mon, 22 Aug 2011 16:47:52 -0400, Jason Cobill wrote:</p>
<blockquote type="cite" style="padding-left:5px; border-left:#1010ff 2px solid; margin-left:5px; width:100%"><!-- html ignored --><!-- head ignored --><!-- meta ignored --><br /> 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. :)<br /> <br /> Unfortunately, you're right that even then the depth is pretty imperceptible except to sensitive instruments.<br /> 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<br /> <a href="http://en.wikipedia.org/wiki/Parallax#Stellar_parallax">http://en.wikipedia.org/wiki/Parallax#Stellar_parallax</a><br /><br /> These people have gone ahead an exaggerated some illustrations to make the depth visible to human depth perception.<br /> <a href="http://www.nightscapes.net/photos/stereo/index.html">http://www.nightscapes.net/photos/stereo/index.html</a><br /><br /> 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?<br /><br /> -Jason Cobill<br /><br /><br /><br />
<div class="gmail_quote">On Mon, Aug 22, 2011 at 4:24 PM, Paul & Andrea Mumby <span><<a href="mailto:themumbys@gmail.com">themumbys@gmail.com</a>></span> wrote:<br />
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid #cccccc; padding-left: 1ex;">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...
<div><span style="color: #888888;">- Paul</span>
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<div class="gmail_quote">On Mon, Aug 22, 2011 at 4:21 PM, Darcy Whyte <span><<a href="mailto:darcy@siteware.com">darcy@siteware.com</a>></span> wrote:<br />
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<div>Ah, I see, the eyes can can change their alignment to snap on to the 3d experience automatically.</div>
<div>So the easiest solution is to just have the cameras stationary, perhaps converged a couple km out.</div>
<div>Once adjusted you can see the clouds go by in 3d. </div>
<div>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.</div>
<div>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. </div>
<div>I bet you could get a nice 3d effect even if the cameras were only like a few meters apart. </div>
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<div>On Mon, Aug 22, 2011 at 4:01 PM, Jason Cobill <span><<a href="mailto:jason.cobill@gmail.com">jason.cobill@gmail.com</a>></span> wrote:</div>
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<div><br /> 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.<br /><br /> You can get the same effect as the XKCD experiment (and Avatar) with a highly simplified process:<br /> - Find a point on the horizon and take a picture of it.<br /> - Walk a few feet.<br /> - Take a picture aimed at the same point on the horizon<br /> - Bring the two images together side-by-side on the computer (preferably without border lines between them)<br /> - 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.<br /><br /> Or save yourself the effort of going outside and look at these:<br /> <a href="http://phereo.com/">http://phereo.com/</a> (Be sure to click "Mode" and select "Crossed" if you don't want to use special glasses)<br /><br /> 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.<br /> You can find out a bit more here:<br /> <a href="http://en.wikipedia.org/wiki/Stereoscopy">http://en.wikipedia.org/wiki/Stereoscopy</a><br /><br /> 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.<br /><span style="color: #888888;"> <br /> -Jason Cobill<br /></span></div>
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