941: Depth Perception

Explain xkcd: It's 'cause you're dumb.
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Depth Perception
I've looked at clouds from both sides now.
Title text: I've looked at clouds from both sides now.


This comic is very self-explanatory as it explains what he is doing every step of the way. This is one of those xkcd's that is all about emotion and feeling for both Cueball and the reader.

Ancient stargazers thought the sky was simply a domed ceiling like the 2nd frame on the top line.

In the first frame of the 2nd line, Cueball puts HD webcams on the tops of football uprights, so "hundreds of feet" apart would be 120 yards (360 feet) apart exactly.

Cueball uses strong reading glasses and reversed webcam images to greatly expand his Depth perception using the principle of Parallax.

The title text is a line from "Both Sides Now" by Joni Mitchell.


[The comic is narrated by an unspecified person. All dialog is shown in boxes overlaid on the comic panels.]
[The panel background looks like a cloudy sky, with the clouds all running together and appearing as a blue
grey smear.]
I've always had trouble with the size of clouds.
I know they're huge. I can see their shapes.
But I don't really see them as objects on the same scale as trees and buildings.
They're a backdrop.
[A person stands on a flat disk inside a hemispherical dome with the front half cut away. The dome is labelled "Sky", and the disk is labelled "Ground". The dome is about twice as tall as the person.]
Stars are the same way.
I know they're scattered through and endless ocean, but my gut insists they're a painting on a domed ceiling.
((The next two lines of dialog are stretched over the following three panels.))
[A person stands on a curved surface, looking up.]
If I try hard enough, I get a glimmer of depth, a dizzying sense of space,
[The perspective of the scene shifts, suddenly the surface the person was standing on is in the top left of the panel. The person is now looking down, leaning back, and waving their arms trying to regain balance.]
But then everything snaps back.
[The perspective of the scene returns to normal, the person is now semi-crouched, staring at the ground with legs spaced apart to help them balance.]
[An American football field is shown, with sections at the tips of the goal posts highlighted and shown as a zoomed view in an insert box. The goal posts each have a webcam mounted on top of them.]
So one summer afternoon
I set up two HD webcams hundreds of feet apart,
Pointed them at the sky,
[The next two lines of dialog are stretched over two panels each.]
[The first panel shows a pair of glasses with the note "Very strong reading glasses." and a smartphone with an attachment designed to clip onto the glasses. The smartphone screen is setup to display two images side by side such that one camera is visible in the left half of the screen, and the other camera is visible in the right half of the screen.]
And fed one stream to each of my eyes.
[The next panel shows the completed phone glasses assembly.]
The parallax expanded my depth perception by a thousand times,
[The person stands wearing the phone glasses assembly, staring into the sky.]
And I stood in my living room
At the bottom of an abyss
[The person now stands on the shore of an unidentified coastline (possibly Boston?), a city is near their right foot and the tallest skyscraper appears ankle high. A mountain range is behind them that is also barely ankle high. The person is standing with their head well above cloud level as clouds swim around them.]
Watching mountains drift by.

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Somebody needs to try this. Couldn't be that hard. 21:27, 22 October 2012 (UTC)

Those must have been some tall goalposts if his point of view is above the clouds! -- mwburden 13:16, 10 December 2012 (UTC)

Also, the cameras should be mounted on servos so that when the phone is moved or tilted the cameras can follow, so your viewpoint isn't fixed in one direction. -- mwburden 13:18, 10 December 2012 (UTC)

That wouldn't work. The entire football field would have to swivel, or else he'd get some wicked image shearing... 01:42, 7 August 2013 (UTC)
actually, it might be possible to correct for that, using bipolar geometry. Essentially, you can derive a 3d model from 2 images from different view points. Here is a (very geeky) demontration of what can be done. Watch the end, where they construct a fly-around video from two images of the opera house in sidney. -- 21:10, 19 January 2015 (UTC)
Interesting link, thanks, but I don't think the video was generated from only 2 images, there isn't enough information. If you select "Download the Opera House sequence" you can download the original 43 photographs used. 14:05, 19 March 2015 (UTC)
You're right. But of course you wouldn't need a 90-degree flyby for this. 16:56, 8 July 2015 (UTC)

An updated solution would be to put the two stabilised cameras on quadracopters which are coded to remain a set distance apart. When you want to look left/right it would take a while for the pair of drones to rotate around their centre point but not too long..... Then you could also get a perspective from the height of a giant (drones can go to any height) and with their degree of parallax (from whatever value of height and eye spacing you choose). (talk) (please sign your comments with ~~~~)

This is a very cool project indeed! Some hardcore image stabilizing software would be required too, since you would get nauseous if the two images weren't perfectly aligned at all times. But this setup is the only one I could think of that would enable you to perceive the view from the last frame. Mumiemonstret (talk) 08:44, 17 December 2014 (UTC)

Look at this in stereo mode: http://www.fourmilab.ch/cgi-bin/Solar and cross your eyes so you see three images, then hold your hands up so you only see the one, then... I forget...

I used Google News BEFORE it was clickbait (talk) 12:44, 23 January 2015 (UTC)

I used to do that all the time at one time ... until I got a l...ot of things different to do..

I used Google News BEFORE it was clickbait (talk) 12:44, 23 January 2015 (UTC)

Stereo aerial pairs of clouds do exist see the Google search: https://www.google.co.uk/search?q=stereoscopic+aerial+photos+clouds 07:33, 19 August 2015 (UTC)

Or you could ride in an airplane. Or stand on a mountain. 19:58, 5 September 2015 (UTC)

That would defeat the point entirely. The distance between the two viewpoints is what provides the increased perspective, not the height of the observer. 21:55, 16 November 2015 (UTC)
using a plane isn't a substitute for this, but there's no reason adding the element of flight has to defeat it entirely: you could put one cam on each wing tip & get maybe the coolest effect of all..

Likely the reason the right image is shown on the left and vise versa is that there are two ways to fuse stereo images. Either Walleyed, right-to-rght, or Crosseyed, right-to-left. Doing it the wrong way may result in concave faces and other aberrations. 15:20, 30 March 2016 (UTC)

Clouds are fractal, small ones up close look the same as big ones far away. So I don't think this would look as spectacular as imagined. (talk) (please sign your comments with ~~~~)

The thing is that our brains only associate the binocular/3D effect with items that are relatively close, and tend to judge sizes accordingly. If something appears 3D to us, we judge it to be a certain distance away (a key function of binocular vision) and from that we also get a rough estimate of its size. That's why if you see something like a star destroyer in 3D in the movie theater, it looks like something the size of a bus hanging up in the general vicinity of the screen. It doesn't look like something miles long, because big things look flat when they look that size. I believe this way of looking at clouds would give a similar effect. The clouds might look 3D, but they'd also just seem closer and smaller, rather than giving you a real sense of their size. (talk) (please sign your comments with ~~~~)