Hmm, the municipality I work with has 6 fixed recievers scattered around the city limits and the best we can get is Cm.. at the mm level we get too much "wiggle" (yes you can actually see the reading wobble and wiggle) but we are using "El-cheapo" units. each survey mobile unit is a laptop and a reciever with a plastic cross hair glued on the unit at the appropiate location for that unit. DGPS is very cheap to impliment, and I have done it for my own uses (I get 1m accuracy with 1 fixed station for a 10mile radius, good enough for me and 98% of all people out there) although 5 miles away the accuracy does drop to 10M due to time lag and building reflections. A university can impliment this via ham radio easily for it's wearable community and the usesr dont have to be ham's as the signal from the fixed location is recieve only. On Mon, 22 Jun 1998, Zeller, Eric (NLC-EX) wrote: > Actually I've seen pictures of GPS units that have crosshairs on the > Antenna, so you can position the antenna down to millimeter level, but we > ain't talking cheap, I think it was in the neighborhood of 80 to 100 grand. > > I'm pretty sure DGPS only needs one fixed receiver to transmit to many > mobile units. I'm not sure of how accuract decreases over range, but I > wouldn't be surprised if you could depend on millimeter accuracy over 10 > mile radius. You have three things working against your accuracy, (1) > Intentional errors introduced by the DoD. By it's very nature of how it > works, DGPS can ignore those. (2) Atmospheric Disturbances, hopefully any > atmospheric phenomenon would be spread out and give the same errors over a > wide area, though I wouldn't depend on millimeter accuracy in a tornado or > hurricane. and last and least (3), differences in the Satelites, though they > claim the satelites are all the same, I would still feel better if the fixed > GPS station was locked into the same satelites that I was. > > Here in the SF Bay Area, the Coast Guard maintains a DGPS transmitter, don't > have the freq's though > (yes, one branch of the military does an end run around the security that > another branch of the military setup). > > And I am also hearing rumours that the DoD will disable the security at the > request of congress, so even our cheapo civilian units can get about 30 foot > accuracy. > > But all this talk is counter to what our friend originally asked for, which > is fine-grained immediate tracking system for use ala Head mounted Tracking > in a small room, which, correct me if I'm wrong, is still the strong point > of Sonar.. Polhemus used to make good, reliable tracking systems, I've been > sort of been out of touch of the VR industry for the past four years so > probably everythings been turned upside down since my last SIGGRAPH show.... > > > ---------- > > From: Timothy D. Gray[SMTP:] > > Sent: Monday, June 22, 1998 4:06 PM > > To: Felix S. Gallo > > Cc:
> > Subject: Re: local area fine positioning with wearables > > > > GPS will do, you just have to go differential GPS. I.E. minimum of 2 > > recievers. more recievers in permanent locations give better accuracy, you > > can get down to 1cm accuracy, (A GPS based transit company brags they can > > give you 1mm but I think that is bull. but the accuracy effect drops > > exponentially as you get outside and farther from the fixed locations. > > > > On Mon, 22 Jun 1998, Felix S. Gallo wrote: > > > > > Does anyone here have any experience with > > > fine-grained local area positioning equipment, > > > especially vis-a-vis 'augmented' reality? I've > > > been trying to figure out how to provide a > > > 'marked up' view of the outside world without > > > it, and have determined that it would be a royal > > > pain in the ass. > > > > > > As others are currently discussing, GPS won't > > > do. For my purposes, constraining the space to > > > one area with arbitrary nontethered equipment > > > would be fine. Any thoughts? Anyone used, eg., > > > Flock of Birds? > > > > > > Felix > > > > > > > >
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