From: Craig Hubley Subject: Re: half silvered lenses (was Re: Direct Neural Input (Was Re: Date: Thu, 7 Nov 1991 21:16:45 -0500 Organization: UTCS Public Access In article <1991Nov5.033024.17522@watserv1.waterloo.edu> dstamp@watserv1. waterloo.edu (Dave Stampe-Psy+Eng) writes: >uselton@nas.nasa.gov (Samuel P. Uselton) writes: > >>>> The first Chapel Hill system also used temple bar mounted CRT's >>>> and 1/2 silvered lenses, superimposing wireframe images on the >>>> real world. >>>> >>>> The images look "ghostly" because you do see the world "through" >>>> things rendered. I don't know how satisfactory that would be, >>>> or how to avoid it. (The other option, of course, is to digitize >>>> the "real world" and include it in the virtual environment.) Would require small CCD video cameras of the kind used on David Letterman and dropped into sinks, strapped onto monkeys, robot arms, pencils, etc... cost about $11k each last I looked, and dropping fast. Of course then you blow the resolution of reality, but it's a good way to prototype a system. >There HAS to be magnification, unless the display element (CRT, LCD panel, >etc.) is as big as the mirror. You are increasing the apparent size of the >display to put it at an apparent distance of 100 cm or more, while increasing >the field of view. I must be missing something... how close was all this to the eye ? And how small can you make LCD panels or CRTs ? >In optical systems like this, motions of the viewpoint (the pupils of the >eyes) in relation to the mirror will cause shifts in image position much >as if the display element moved in relation to the mirror. The pupils of >eyes move through about 12 mm during normal eye movements, but this can >be compensated for in the optical design (just have the viewpoint be at >the eye's center of rotation, 12 mm behind the cornea). However, shifts OK, but how does this work for odd-shaped (e.g. myopic) eyeballs ? We are talking about fully 60% of the world's population here... >in the helmet or headmount with relation to the eyes are more difficult >to fix. Having just finished a head-mounted gaze tracking system, I can >say that these shifts DO exist, and the problem increases with the mass >(rotational inertia) of the headmount. Movements of facial muscles are >a problem even if the headmount is tightly fastened to the head. So you need this to be light and you lack a fixed point of connection unless people want holes drilled in their skulls... maybe the headmount needs to compensate for this a la Steadicam, either physically or by telling the renderer where it is going to bounce in the next 1/60th second. >Perhaps I'm overrating the problem here, but I do beleive that this problem >will limit the magnification usable for the mirror, setting a minimum size >for the CRT or display element. How big ? >>>- delay between the video and the real world meant that if, say, you >>>were moving your hands to manipulate virtual objects, the objects would >>>lag behind your hand movements: VERY disconcerting! >> >>This is a problem with (1) the tracking technology and (2) the compute >>power to re-render your scene. This method is independent of (1) and >>(2) should make (2) easier than raster systems. > >Time delays ARE a problem, even in complete VR worlds, including represent- >ations of the user's hands, etc. The reason is that the human motor system Time delays are a problem in all interfaces. >does NOT use negative feedback directly, due to long neural delays (>100mS). >Instead, it relies on Kalman-type filters and task-specific motor programs >learned through practice. Any large change in motion-to-visual feedback >delays requires a recalibration of the system at best, and relearning of >fine control for a task at worst. To say nothing of motion sickness Are these constant for an individual ? Can it be calibrated for one person ? >brought on by changing head-motion-to-scene-motion delays, which has NOT >been covered well in VR literature, but exists nonetheless. Any references to these issues would be appreciated. >>>If these objections can be overcome, this system of half-silvered glasses >>>has BIG advanteges for the user, as eye-hand coordination is unaffected >>>by system delays, and real as well as virtual objects can be worked with. >>>Needs a lot less computer power, too. >> >>Of course it depends on the application. They even tried filled polygon >>rendering and half silvered lenses. Then the objects *really* look ghostly. >> >>If you want a substitute reality, this doesn't work too well. If you >>want to add some ghosts to this reality, then it will work. n I think this has an immense number of applications. In fact, I know it does, because I listed a few dozen of them once and gave up when I realized you could replace almost any physical information-bearing object.. not to mention save a lot of trees... >Yes, exactly. What I was proposing involved being able to interact with >virtual *objects*, while letting the user see his hands, the computer >keyboard, etc. This solves a LOT of the psychophysical and kinesthetic >problems. But the time delay problem kills it, for now at least. (sigh). I don't understand why. Seems to me that the answer is practice, practice, practice, which is absolutely justifiable if you are going to provide such a useful device. I don't find it all that easy to walk around in VR anyway... >Again, this approach should not be discarded, but problems should be kept >in mind. If you have references for these phenomena, I for one am interested. Craig Hubley -- Consultants in object-oriented technology & techniques, -- Craig Hubley & Associates -- user interface design & user productivity -- craig@gpu.utcs.Utoronto.CA UUNET!utai!utgpu!craig craig@utorgpu.BITNET craig@gpu.utcs.toronto.EDU {allegra,bnr-vpa,decvax}!utcsri!utgpu!craig 28 First Avenue, Toronto, Ontario M4M 1W8 Canada (US TC) call 416-466-4097