[HN Gopher] VR optics and why IPD means too many things (2019)
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VR optics and why IPD means too many things (2019)
Author : luu
Score : 105 points
Date : 2023-05-27 17:41 UTC (3 days ago)
(HTM) web link (tomforsyth1000.github.io)
(TXT) w3m dump (tomforsyth1000.github.io)
| h2odragon wrote:
| How 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.
| thebigwinning wrote:
| Since 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.
| teddyh wrote:
| The 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 wrote:
| 1991; 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 wrote:
| [flagged]
| addaon wrote:
| 1968 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
| jayd16 wrote:
| Do you expect everything that existed in the 90s to be
| "complete" or just VR?
| krisoft wrote:
| Good question. As a comparison we have been piling up dirt
| significantly longer than VR has been around and yet the
| physics of granular materials is still actively researched.
| h2odragon wrote:
| the software I was selling at the construction show in 1991
| was essentially about piling up dirt.
|
| The reason I was there to sell it was that my software had
| a round up / "fudge factor" applied to the models, based on
| real world experience; where as the competition
| consistently under estimated things because they used the
| nice clean textbook formulas.
|
| Just because a machine has a 2.6 yd^2 capacity doesn't mean
| it will move that much dirt per load. And so on.
|
| Applying back to the original discussion of VR; I expect
| there's been enough time and enough experience with the
| things like head mounted displays that there shouldn't need
| to be much original research into "how to do the optics" of
| same. I'm ignorant of optics generally (and much else) but
| there should be textbooks and people arguing over where
| those are wrong and such; by now. For _this specialized_
| purpose even. See the amount of literature on LCD displays
| by comparison; the basic optics there are known, right?
| moron4hire wrote:
| We did just have a major breakthrough in HMD optics not
| more than 10 years ago with "pancake optics" that have
| only started making it into devices you can actually buy
| within the last year or two.
| washadjeffmad wrote:
| Translation into products requires a study of humans that most
| companies are ill-equipped to apply. For example, the
| Oculus/Meta Quest 2 headset only has 3 "IPD" settings, and the
| face plate was designed to fit a somewhat particular skeletal
| structure.
|
| Notably, while it fits comfortably on my Western friends'
| faces, none of my East Asian friends or family, including any
| women, found it bearable (too tight on forehead, tilted
| downward, light leaking from around nose) or were able to focus
| it cleanly and assumed "VR was not for them".
|
| However, a Japanese headset, often reviewed in English as being
| too small or uncomfortable, fit me perfectly, and the optics
| were clearer despite having lower technical specs. How
| illuminating!
|
| I do wish that companies that designed wearables would either
| disclose the dimensions of their testers or provide what
| dimensions matter. I'm larger than 50% of the people on the
| planet, and I fall within a standard deviation of the mean in
| the United States. However, no product designed by a US tech
| company has ever fit me.
|
| The real answer is probably the same as the Alf Landon election
| prediction by Literary Digest in 1936. Because they only sent
| out ballots to addresses of registered car owners and people
| listed in the relatively new telephone directory, the poll
| results skewed wealthy, urban, and conservative - class bias in
| action.
|
| Are tech companies in the US making the same mistake?
| reaperman wrote:
| > Are tech companies in the US making the same mistake?
|
| Yes, but slightly different, because they're missing less of
| their "addressable market" than the Landon prediction was.
| Their addressable market generally being people outside of
| Asia who have lots of disposable income. People in Asia tend
| to buy homegrown products which approach or exceed the
| quality, are easier to get, and cheaper. People with
| disposable income outside of Asia still trend toward the
| Westerner morphology. Still it's amazing with all the East
| Asians in big tech companies, that so many domestic products
| seem ill-designed to fit them.
|
| Meanwhile tons of my furniture and other items that are
| designed and manufactured in Asia and then shipped to the USA
| seem to be shrinking and I don't fit in so many of them
| anymore. Not sure if that's just selling cheap things that
| have less material/shipping cost, or if it's matching the
| optimal sizes for East Asians.
| washadjeffmad wrote:
| > Meanwhile tons of my furniture and other items that are
| designed and manufactured in Asia and then shipped to the
| USA seem to be shrinking and I don't fit in so many of them
| anymore.
|
| I based my recent purchase of a office chair on its copious
| complaints from very tall people after I found I couldn't
| sit back on a couch I ordered from Costco without my feet
| dangling in the air.
|
| If we were neighbors, I'd offer to trade you!
| thendrill wrote:
| VR AR researcher here.
|
| It is scary once you see what the actual VR research landscape
| looks like.....
|
| There is a clear disconnect between users of vr and vr
| researchers.
|
| I don't know even where to begin. Too much incompetence. Too
| much disinterest. Too much bullshit just to get grant money.
| And nobody has any clear idea of what VRs application should
| be.
|
| So far even for me there are very few applications where vr
| gives an actual advantage for anything.
|
| Take it situational awareness, overview, ux, visual quality
| etc. Most of the vr apps I have seen have no reason to be in
| vr.
| Darkphibre wrote:
| I hear ya! One of my hobbies is to be a _somewhat_ known
| stage & exotic dancer / dance instructor in VR using 5-11pt
| tracking (depending on my mood and production quality). The
| number of "features" that get in the way, and lack of
| representation for VR dancers and performers has been
| frustrating, especially as the world moves more and more
| towards 3-point robot avatars.
|
| Actually had a chance to provide my perspective to a FAANG
| Research Group, but I was laid off (and they were disbanded).
| burnte wrote:
| Replace "VR with "cars", and say all this in 1923. Same thing.
| There's a lot to be done, few domains of knowledge are
| completely mined in 30 years.
| h2odragon wrote:
| 1923 cars had about the same wheelbase, and steering gear
| variety, and differentials... the basics were all worked out
| and agreed on.
| bullen wrote:
| When 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
|
| 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
| nrp wrote:
| We 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.
| syrrim wrote:
| Could you render very close objects twice, far objects once,
| then composite the image for each eye?
| moron4hire wrote:
| Theoretically, yes, but there will be a lot of overhead for
| Z-sorting objects as well as performing a multi-stage
| render like that. I am only guessing, I certainly have
| never tried, but I bet it comes out to a wash, at best.
| It'd be better to keep the rendering pipeline simple, if
| that were the case. Large-scale worlds will have LOD for
| models and terrain at distance, which will help with the
| rendering complexity of far objects.
|
| You can also pre-process it and apply super-far details as
| a skybox image. A 2- or 3-block radius of real, 3D city
| buildings with a cityscape skybox looks pretty good. A
| forest scene can use object instancing to really clutter up
| the medium field and leave even a generic landscape skybox
| for great results.
| bullen wrote:
| But then you get no depth perception?!
| nrp wrote:
| Yes, 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.
| moron4hire wrote:
| It's funny. In my experience, stereo rendering is not a make-
| or-break issue in VR. I mean, it depends on the app design,
| of course, but a lot of apps can get away with monoscopic
| without most people noticing.
|
| I had a regression in an app I was building where it was
| rendering in a monoscopic mode and it actually took me a long
| time to figure out what was "wrong" with the app, but
| apparently, I was the only one who thought it was wrong. It
| went for at least a month before I noticed a problem and
| another month before I eventually had the time to diagnose
| it. All during that time, nobody made any comment about it,
| people were enjoying the app.
|
| I eventually figured out that you really only notice stereo
| rendering in modern VR headsets if you have a lot of near-
| field objects with which to interact _and_ you interact with
| them with direct hand gestures (either hand tracking or
| controller bumping). So, you need stuff to be within a meter
| of the user for them to really notice "this isn't right".
|
| There is a gap past a meter and before 10 meters where it's
| hit or miss if anyone is going to notice the lack of stereo
| rendering. The more the user is moving around, the less
| likely they are to notice.
|
| And then, anything past 15 meters, I don't think there are
| any VR headsets on the market (other than maybe the Varjo
| VR-1, but I've never seen one myself) with fine enough pixel
| pitch that anybody is going to notice the lack of stereo
| rendering.
|
| Now, that's just "where does stereo rendering take effect"?
| Part of what I think makes VR good is the ability to get up
| close and personal with the environment, to manipulate things
| in your hands, so typically I think "good" VR apps are going
| to need stereo rendering, but it was still surprising to see
| that it's not a universal issue.
| wccrawford wrote:
| I think 10 meters is also the point in real life where 3d
| stops being noticeable, too, so I'm not surprised your
| ended up with that number. (I just searched and found
| numbers between 18 ft and 20 meters.)
|
| I don't think the pixel pitch is the limiting factor
| anyhow, because movement of the head means that sub-pixel
| accuracy is achieved by the brain anyhow. It's amazing what
| the human brain lies about in regards to vision.
| jerf wrote:
| This is a "you may not be able to unsee" thing once you
| read this, but... one of the major problems I have with
| 3D movies is precisely that 3D based on image separation
| extends out _way_ less than people think it does, because
| the brain naturally picks up with heuristics and prior
| knowledge and a lot of other things. So if you 're on a
| closeup of someone's face or something, sure, it can be
| in 3D. But if you've got a big action scene with, say,
| helicopters flying around and shooting at people on the
| ground, the camera is likely to be farther than 20 meters
| away. If you can see _any_ "3D" at all, it's wrong. It
| should all be at the plane-at-infinity for you. Which
| means that if you can see "3D", rather than being an epic
| fight to save the world or whatever, you've got a fight
| taking place on a diorama in front of you, about the size
| of a large table or something.
|
| Even something just as the scale like the Transformers
| being about a block away from you brawling with each
| other should all be on the plane-at-infinity to you.
|
| It kinda takes the drama out of 3D action. Technically,
| the 2D version of the movie is probably more actually
| _accurate_ at the important times in a lot of genres.
| Darkphibre wrote:
| Thanks for the warning, genuinely appreciated!! I
| actually opted not to read this comment, I enjoy the
| immersion.
| jasonwatkinspdx wrote:
| Yeah, the vast majority of 3D movies have always had that
| diorama effect to me, though I tend to discount my
| personal experience with anything stereoscopic because I
| had lazy eye as a kid, ultimately corrected by surgery,
| but late enough that my brain mostly ignores the
| information from that eye. Not totally but mostly.
|
| In any case, I don't find the effect unpleasant or
| pulling me out of immersion, because frankly I don't feel
| that immersed in AAA cg heavy action movies anyhow. To me
| it's like watching a fun demoscene with a neat effect.
|
| The only time I recall it being a bit tiresome is when
| friends dragged me to a few horror movies where the 3d
| was obviously low effort crank it to 11 for this jump
| scare stuff.
| moron4hire wrote:
| Yeah, I haven't done the math, so I don't know what the
| exact boundary would be. Supposedly Quest 2's tracking is
| precise down to ~7mm, SteamVR to 75mm, so depending on
| the system, micro head movements may not be larger than
| IOD. Assuming we discount micro head movements, then the
| ICD is the only stereo cue. I _think_ I remember seeing
| someone do the math once and said devices like the Oculus
| DK2 couldn 't show anything beyond 10m for 0.07m
| displacement. Or something like that. Notionally, for
| _some_ pixel size S, you will not be able to see a
| discernable difference at Z distance for X view
| displacement; the left and right eyes will resolve
| objects to the same pixels.
| pavlov wrote:
| Really great article. I've never heard before that VR headsets
| produce collimated-light images, but the explanation makes a ton
| of sense.
| intrasight wrote:
| I 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.
| twic wrote:
| > 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.
| lamename wrote:
| Is 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 wrote:
| Think 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.
| two_handfuls wrote:
| I 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.
| thendrill wrote:
| The 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"
| two_handfuls wrote:
| Yes 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.
| nomel wrote:
| The Quest Pro does the same, with the fit adjustment app.
| javchz wrote:
| I 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.
| EarthLaunch wrote:
| Wow, 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 wrote:
| Imperial units are not "human scale" any more, or less, than
| metric: https://xkcd.com/526/
| IYasha wrote:
| "3 L - TWO-LITER BOTTLE"
|
| Um, okay...
| taeric wrote:
| I 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.
| contrarian1234 wrote:
| A 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!
| teddyh wrote:
| Depends on how thick it is, doesn't it? Why the insistence
| on measuring the _length_? Couldn't you just as easily talk
| about 1kg sandwiches?
| vGPU wrote:
| I could down a meter long sub by myself, and I'm fairly
| certain my dog could too. No need to share.
| regularfry wrote:
| > It's like if there were 100 degrees in a a circle
|
| There are 100 gradians in 90 degrees, does that count?
| They're probably supported on your calculator.
| https://en.wikipedia.org/wiki/Gradian
| HPsquared wrote:
| It's a similar kind of thing to decimal time:
| https://en.wikipedia.org/wiki/Decimal_time
| pavlov wrote:
| Splitting 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 wrote:
| Or, 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 wrote:
| Impossible. 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]
| Symmetry wrote:
| I dunno, a quarter meter sandwich seems just as natural as
| a quarter pound burger.
| the-dude wrote:
| In The Netherlands you can order beer in meters.
| dylan604 wrote:
| At any spring break resort or in Vegas, you can order
| beer by the yard
|
| Edit: mustn't forget the French Quarter either
| the-dude wrote:
| Obviously a meter of beer is better than a yard of beer.
| dylan604 wrote:
| Those last 3" (76.2mm) would just be foam anyways
| the-dude wrote:
| Foam is measured in fingers.
| blululu wrote:
| You 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 wrote:
| The 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.
| interestica wrote:
| I never understood why we never popularized a comparable
| metric measurement. A quarter-meter perhaps?
| snovv_crash wrote:
| A 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.
| HPsquared wrote:
| As 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
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