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Index of Subjects Sounds like the Accuracy versus Precision distinction. Presumably the intrinsic accuracy of the system is only ± 2 meters (a guess) at any one ideal site with an ideal number of satellites within range. But the hand-held instrument happens to report a number in meters with a precision of one decimal place, to 10 cm. When the averaging function is on, the hand-held is able to average out internal noise in its circuitry, to get numbers that are known precisely to the nearest 0.1 meter, but these are only accurate to within +/- 2 meters (or whatever the quoted accuracy is). The reverse would be more interesting (to me), if the intrinsic accuracy of the overall system actually were +/- 0.1 meter but that this is not achieved immediately because of noise somewhere out there, say in disagreements (noise) between the satellites. In that unlikely case, repeated determinations and averaging of the initially imprecise numbers could end up approaching the intrinsic accuracy. Presumably, the GPS coordinates of certain highly specific locations on the ground like the major surveying points indicated on maps have been published with high accuracy (??), so if you went and stood exactly on top of one of these for a while with your unit turned on you could check which it is, +/-0.1 m or +/-2 m ? Or, standing on flat ground in the open, you could make a series of measurements exactly 10 m apart all along a straight line. Surely somebody of a curious disposition must have done this. The reason for asking originally was that at one point I fancied using one of these units to try to map out the stability or otherwise of insect colonies along Bay of Fundy cliffs effortlessly, but at the time the quoted specs looked a bit too coarse to do the job and I never bought one. I vaguely remember, though, that there was some touted extra system available on the more expensive units that used additional ground-based stations as well as satellites, called WAIS or WAITS or something like that. This was supposed to increase accuracy further. Is this correct and is it still available? I guess I ought to go and look at the Garmin web site -- too late for Santa this year. Steve ********************************** Quoting Randy Lauff <randy.lauff@gmail.com>: > Yes, I routinely use the averaging function...I watch the tenths-of-metres > tick down, and when that levels off, I save the waypoint. The unit reports > tenths-of-metres, I wonder if the implication is that it can differentiate > 10 cm (4 inches)? Somehow, I think not. > > Randy > 2008/12/23 Phil Schappert <philjs@eastlink.ca> > >> At 09:37 AM 12/23/2008, you wrote: >> >>> Interesting - that's the unit I use and I've never had better than 2 m >>> accuracy, rarely better than 3 (these values according to the unit itself). >>> I'll have to try it out in the open to see what it says...the vast majority >>> of my GPS work is in the woods. >>> >> >> My guess is that anything between 4 and 6 feet would register as 2m in >> metric, Randy. Unfortunately, there doesn't seem to be any way to get it to >> show cm. It's likely also important that I generally spend more than a >> couple of minutes in any one location, usually on the order of 10 to 15 >> minutes (minimum) and location accuracy often increases with time...do you >> use the averaging function? >> >> >> Phil >> >> -- >> >> Dr. Phil Schappert >> >> 27 Clovis Ave. >> Halifax, NS Canada, B3P 1J3 >> Home: 902-404-5679 >> Cell: 902-460-8343 >> >> www.philschappert.com >> www.aworldforbutterflies.com >> >> "Just let imagination lead, reality will follow through..." >> Michael Hedges > _________________________________ > RF Lauff > Way in the boonies of > Antigonish County, NS. >
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