Localized Positional Tracking, in Similar fashion to GPS.

There are RF and magnetic based tracking systems, and optical tracking systems, and acoustic tracking systems, and intertial tracking systems, and perhaps other methods.

GPS (global positioning satellite) provides high accuracy low precision positional tracking that is not precise enough for for head tracking, although it can be use to provide periodic corrections to body position obtained by other means that have more local precision but less absolute accuracy.

EDIT: For those who do not understand the difference between precision and accuracy, precision determines how closely you can repeatedly return to the same location, whereas accuracy determines how well your measured position maps to the real world. Take for example the Razer Hydra, which can measure your position with a precision of 1mm, but which may have absolute positioning accuracy that does not well match the real world (your hands are not where you think they should be when drawn in VR). Such accuracy errors can be compensated in software with a calibrated translation map (i.e. displacement map tuned to Hydra base position and orientation, and environmental distortions).

I understand the downfalls of GPS, what I am suggesting is a similar system, but using local sensors within about ten feet of the user. By combining head orientation and tracking backward/forward/sidetoside position, the height and orientation of the body could be accurately tracked. Obviously it requires a more accurate set of sensors, and not standard GPS.

"jngdwe" wrote:
I understand the downfalls of GPS, what I am suggesting is a similar system, but using local sensors within about ten feet of the user. By combining head orientation and tracking backward/forward/sidetoside position, the height and orientation of the body could be accurately tracked. Obviously it requires a more accurate set of sensors, and not standard GPS.

That is what I meant by "RF tracking system", and this is what I had in mind when I posted that:
viewtopic.php?f=25&t=787

Ten feet is probably not a big enough distance. GPS satellites are really far away, so the speed of light calculations don't need to be super precise (because the signal transmission time is over a hundred milliseconds). Shorten that distance, though, and (like the guy in the video mentions) you've got to deal with differences of just a few nanoseconds. It would be hard to get very precise from that, and his video demonstrates that the positional accuracy of his system isn't great. Probably good enough for many things, but HMD positioning would need to be pretty precise to capture subtle head movements.

There's also the spectrum availability problem. The guy is using a 4 GHz signal. The entire 4-5 GHz part of the spectrum is outside any ISM bands, so using it without a license would be illegal. If you did try to use the ISM bands, there'd be so much interference as to render this sort of system useless...

"Differential GPS" might be able to do what we are talking about here. dGPS is when you have one receiver in a fixed location and the other is mobile. The receiver in the fixed location will always appear to drift, mostly due to atmospheric disturbances, so since you actually know its real location you can always subtract that difference from the location that the mobile receiver reports. This way you can get a reliable accuracy of 1m from GPS. Systems which also use the Russian Glonass, the Chinese version, and the European version of GPS are reported to provide accuracy down to 10cm.

These systems currently start at ~10 000 eurodollars. If you can code a little and your update rate doesn't need to be quicker than about 1s or so you can get in the ballpark with a USB dongle. It can definitely be done at consumer price ranges.

IIRC something about GPS meant that there was a limited update frequency that was barely usable for tracking the motion of a single person. It doesn't look like one can rely on GPS alone for AR & VR translation.

"geekmaster" wrote:
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Appears functional... But I wonder if this guy knows that a fluctuating magnetic field creates a radio wave as it transitions to the far field of that frequency... Probably not. Near field and far field magnetic/electric stuff is pretty esoteric and doesn't get covered in hardly any engineering literature. This is possibly because you are not supposed to rely on such a liminal condition even though it is perfectly linear, as energy evens out between the magnetic and electric components of EM as a function of frequency...
They didn't tell you how photons work either. You're apparently supposed to figure that out from the sine & cosine of AC current and somehow magically intuit the perpendicular geometry of the magnetic and electric field. It's not long ago that Wikipedia added this info. It's like it was just forgotten from public consciousness and later recalled.

...Did you know that a single photon can be as big as a city, and even bigger? Ask a professor about this and I guarantee you he will absolutely vomit circular reasoning and academic vitriol on you in order not to change his perception. At least, that's the response I got when I asked about it over a decade ago.

Centimeter accurate GPS for $500:
http://hackaday.com/2013/08/05/centimeter-level-precision-gps-for-500/