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## Re: Accuracy of radio/GPS-like system?

 Subject: Re: Accuracy of radio/GPS-like system? Jasen Betts Mon, 10 Oct 2005 00:14:00 +1300 sci.electronics.basics
 ```On 2005-10-08, Wildepad wrote: > How accurate could something like this be: > > Three antennae on ten foot towers are set up about 100 yards apart. > > A handheld unit, no larger than about eight inches square and an inch > or so thick, uses signals from those to determine its position within > the triangle (the unit will usually be held fairly parallel to the > ground, rarely at greater than a 45 degree angle). > Now it can't just figure out it's basic spot but also what angle it is > to a baseline -- that is, it isn't enough to say that it's 83 feet > from tower #1, 212 feet from tower #2, etc., it also has to read out > that it is 18.42 degrees to the line between towers 1 and 2. it needs to knows how far off the ground it is, or it needs a fourth transmitter. > In other words, on a map with the towers plotted, it must be possible > to determine exactly where the unit is _and_ where it is pointing. > > 'Absolute' accuracy is not as important as repeatable and relational > accuracy -- that is, it can read 83 feet from tower #1 when it is > actually 82.4 feet, as long as it always reads the same thing at that > point and it reads 41.5 feet from that tower when it is exactly half > as far away (when it is actually 41.2 feet away). ((Does that make > sense?)) > > The complete unit has to be no more than \$1500, and the towers with > transmitters no more than \$500 each (these do not have to be > weatherproof -- they will be taken down after each day's use -- pipe > towers whose 'feet' slip into pipes driven into the ground are > probably best). > > What accuracy could be reasonably reached? > Within a yard, within a foot, within an 1/8 of an inch? > > Perhaps more importantly, what accuracy in the direction it's pointing > could be reached? (i.e. if there were two such units, and you plotted > their readings on a map in a computer, could you determine whether > laser pointers attached to them will cross 250 yards outside the > triangle?) that depends how close they are to each other. > > Any constructive answers appreciated. differential GPS will give you centimetre precision (or better) with just one tower. - should be uner \$1000 for the tower. angle is harder to do, I know there are inertial angle sensors I have no idea of their cost, precision or operating requirements. Bye. Jasen ```
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