5 ms·
VR optics and why IPD means too many things (2019)
- EarthLaunch 3y agoWow, what a fun and knowledge-filled article. It felt like reading Feynman. Just casually browsing HN, this solves a problem that's been bugging me for months in my game: The world is scaled in feet/inches, while WebXR uses meters/cm to set ICD (virtual camera distance)! I think- based on my getting unusually nauseous. I thought the solution was to scale the world, but there's more to it - and I think the solution is to reduce camera translation motion by the scale difference: > Specifically if you translate your head sideways by the distance of your IOD, your left eyeball should now be seeing what your right eyeball was seeing. If it doesn't, the brain worries that something bad has happened, and makes you feel bad about it. > Note that if you scale BOTH – you move the virtual cameras closer together, AND you reduce the in-game motion of the cameras due to head motion – everything is totally fine! The world just grew or shrank magically, but it all still works and you don't get nausea. You may wonder why in hells a programmer would use imperial units instead of metric. It's to give the game a sense of being human-scale and pre-civilization. Why not just use metric and then convert everything to imperial for display purposes? Because then during debugging, units in logs constantly have to be converted to units shown, and the conversion isn't identical. It never bit me until VR!
- teddyh 3y agoImperial units are not “human scale” any more, or less, than metric: https://xkcd.com/526/ https://xkcd.com/526/
- contrarian1234 3y agoA 1 foot sandwich can be easily shared with 2, 3, 4 or 6 friends. And nobody has 5 friends anyway. There are no meter long sandwiches .. and if there were, you couldn't split it between 3 people. It's impractical. It's like if there were 100 degrees in a a circle.. You'd go nuts Metric is for when you've made a mess of things and have completely given up on having nice round integer values EDIT: This comment has been timed to coincide with when Americans wake up to defend me :) ~ USA! USA!
- pavlov 3y agoSplitting a meter-long sandwich between three people is easy. You give each person a footlong slice, and the remaining 8.6 cm to the dog.
- cassianoleal 3y agoOr, you know... You look at it, more or less find the one third point from the tip, cut it there, then cut the remaining larger part in half. Which is probably the same way you'd do it if it was a 3.28ft-long sandwich instead.
- pavlov 3y agoImpossible. Ever since Hercules accidentally stepped on his lunch sandwich in the stables of Augeas, his 12-inch foot has been the standard measurement for Ideal Sandwich.
- deleted 3y ago[deleted]
- the-dude 3y agoIn The Netherlands you can order beer in meters.
- interestica 3y agoI never understood why we never popularized a comparable metric measurement. A quarter-meter perhaps?
- snovv_crash 3y agoA decimeter is about 5 inches, which is the height of a cup, diameter of a burger, span across a hand, etc. To me that's a lot more human-friendly than a 'foot' being 12 inches.
- teddyh 3y ago“Hand” is already a historical unit, equalling almost exactly 10cm; i.e. 1dm. Horses are measured in hands. <https://en.wikipedia.org/wiki/Hand_(unit) https://en.wikipedia.org/wiki/Hand_(unit)>
- blululu 3y agoYou are citing a cartoon with a dick joke and a mom joke to say that metric is just as human oriented as imperial. Seriously: Imperial: 1 Foot ~ the length of some guy's foot. 1 Second - the duration of one heart beat. Metric: 1 Meter - some 1/10000 of 1/4 of an mis-measurement of the circumference of the Earth. 1 Second - stolen from the Imperial system cause 86 microdays did not easily divide by 10, 7, 24, 60, 30, 31 or 29.
- Lapha 3y agoThe first mechanical clock that could accurately and reliably measure seconds was a pendulum clock with a length of one metre. Seconds and metres go hand in hand with the metric system.
- taeric 3y agoI mean, sorta? First, arbitrary numbers are arbitrary. But I can point to my foot and say that is about a foot in size. An inch is roughly one of my knuckles. A yard is roughly a step. Even that comic you linked drives this home. None of them are referenced to humans. They are things we mostly know, sure. But they aren't based on a human. (Well, I suppose the mass ones have an amusing set of people listed.) And this avoids the measures that, for my memory, just haven't made it to metric yet. Acre, Astrological Unit, Knot, etc.
- IYasha 3y ago"3 L - TWO-LITER BOTTLE" Um, okay...
- HPsquared 3y agoAs computer specialists, we should advocate a return of the Imperial system using fractions of an inch for measurements. This is because it fits perfectly into the binary floating-point system. There are no more problems relating to 0.1 being an irrational number in binary. It's all broken down into 1/2, 1/4, 1/8, 1/16 etc which in binary is 0b0.1, 0b0.01, 0b0.001, 0b0.0001
- h2odragon 3y agoHow is it that there's any actual science left to be done here; when the "VR world" has been spending money in occasional waves since the 90s? Shouldn't all this research have been done, and published, already? And re-verified, folded, spindled, mutilated, then recycled as firelighters. It's been 30 years and should mostly be adapting numbers optometrists know already.
- teddyh 3y agoThe first big VR wave was so early it was almost pre-Internet, so I assume most research was done in corporate silos, like Disney. Those silos are black holes from which no information can escape, so everybody has to re-invent everything.
- h2odragon 3y ago1991; I spent a week manning a booth at a construction trade show. We were beside the Autodesk booth, where they had a big show of "VR walk through of the Denver Airport". Several times every day, all week, people would stagger out of the demo and yak into the trash can provided for the purpose... which was just behind us. I think that really showed me the potential of the VR business and the spirit with which it would be pursued.
- LegitShady 3y ago[flagged]
- addaon 3y ago1968 was significantly pre-internet [1], even beating out the first of ARPAnet by a few months. [1] https://www.historyofinformation.com/detail.php?id=861 https://www.historyofinformation.com/detail.php?id=861
- thebigwinning 3y agoSince we have a lot of theoretical science, it's easy to imagine everything is solved in engineering. But when you dig into a new application you learn there are tons of gaps in knowledge. There is theory to draw on, but you need to combine and resynthesize to make it into something that works. I have had experiences translating a professional model (similar to optometry prescriptions) and learn the model isn't described well enough to write in software.
- pavlov 3y agoReally great article. I’ve never heard before that VR headsets produce collimated-light images, but the explanation makes a ton of sense.
- intrasight 3y agoI found the explanation lacking. It just states that collimation is the case without explaining why. The why is the limited optics of HMDs. In the physical world that those optics are trying to simulate, photons can leave from any point in space at any angle.
- lamename 3y agoIs there a graphical explanation of the perceptual phenomenon the author is describing? I think I understand the physical stimulus he describes, based on diagrams in papers, but I havent found anything explaining this part: > So translating the pupil around doesn't change the angle of the light rays, which means the image doesn't move.
- two_handfuls 3y agoThink of the sun. Sun rays are collimated, yet when you look up the sun doesn’t fill the whole sky. That’s because where in your visual field a light will end up depends on its angle, not on where it hits the outer surface of your eye.
- twic 3y ago> photons can leave from any point in space at any angle Not really. They can leave from any point on a surface at any angle. Once they're on their way, they don't change direction. If a surface is an infinite distance away, then by the time they reach your face, the photons from that surface are all travelling parallel to each other. That's what collimation is simulating: looking at objects an infinite distance away. Why? As the article says: "But try this experiment. If you can find a fixed test pattern, put that on the HMD's screen, then pull the HMD away from your face a little, and move it side to side by an inch or so (don't rotate it, just translate it). The image stays fixed in space! It’s a really strange thing – you’re moving the physical box, but the image inside it doesn’t move. That’s the power of collimated-light images, and it's still very unintuitive to me even though I understand the physics and maths very well." Just how, when you look at a surface a great distance away, its appearance doesn't change if you move your head a few millimetres from side to side. "Of course real VR lenses are not perfectly collimated for various reasons. But they're close enough that getting the IAD (optical axis separation) adjustment perfectly right is not as important as it appears at first." Collimation means that the device is robust to the exact distance between the user's eyes. That is very useful.
- bullen 3y agoWhen I built my VR MMO in 2014 I experimented with very wide camera separation, it's very particular; makes things look very small and distant but they pop out much more. Like 3D on steroids + tilt shift. I also experimented with twice the rendering speed to get as recent as possible sensor reading before the Valve/Oculus warping became standard and it was VERY good for nausea. So 120/150 FPS respectively on DK1/2. I'm looking forward to pancake lenses, if they remove godrays so I can play my game again: http://aeonalpha.com http://aeonalpha.com But I read there are a lot of tradeoffs with them too. So far DK1/2 lenses with cups that you could change and adapt to your diopter where the best optics VR has had (but I got lucky with IPD and one cup on DK1 being my exact diopter!) I wish one actor made super tiny glass lenses just so we could see how that would work!? Here is some more experiments: http://aeonalpha.com/fov.html http://aeonalpha.com/fov.html
- nrp 3y agoWe had a somewhat undocumented 120Hz mode on DK2 where both eyes would get the same image (meaning everything was at infinity distance), but I’m not sure if any developers used it.
- bullen 3y agoBut then you get no depth perception?!
- nrp 3y agoYes, that’s why nobody used it. The plausible use case was something like watching 24hz, 30hz, or 60hz video content without juddering that 75Hz would have, and where depth didn’t matter.
- syrrim 3y agoCould you render very close objects twice, far objects once, then composite the image for each eye?
- moron4hire 3y ago
- two_handfuls 3y agoI really like the suggestion of looking at the HMD’s faceplate and having it measure your IPD. I think that’s a great idea! As they say, it’s hard to adjust it optically by moving the lenses because there’s a wide range of values that give a focused image - but the wrong values will result in nausea over time.
- javchz 3y agoI recently went from a quest 2 (limited 3 IPD settings) to a pico 4 (that has gradual fine adjustment) and makes a huge difference. Specially in the headache and nausea department. Even with pancake optic artifacts, just that setting alone makes a huge difference in don't feeling dizzy in rapid movements.
- thendrill 3y agoThe varjo xr headsets use the eye trackers to auto adjust the IPD mechanically the moment you put the headset on. The problem is it takes a second or two and it fails.... Often, so you need to repeat the (take on and off). It makes development and multi person demos into a pain of "put it in and off again it will work"
- nomel 3y agoThe Quest Pro does the same, with the fit adjustment app.
- two_handfuls 3y agoYes I agree something like this is probably the future, once it’s more reliable and more affordable. For now only expensive headsets have the hardware for this. The solution proposed in the article works with the hardware in more affordable headsets which makes it intriguing.