Yes, 5 - 10 meters for regular consumer units is the simple answer. In reality it varies depending on a few things:
1. Clear view of sky from all angles. If satellites are visible from only one portion of sky then the triangulation does not work so well and you get a high dilution of precision (see this article in Wikipedia: http://en.wikipedia.org/wiki/Dilution_of_precision_(GPS) ) 2. Solution from 4 or more satellites. The more the better. The unit can make do with just 3 satellites if it guestimates your altitude: but if the guess is wrong you can be off by whatever distance the altitude is off. In one case I had my GPS on while in the air, then switched it on while on the ground. I was off by several km until the unit got a full 3D fix with 4+ satellites. 3. Reflections of signals off buildings in urban areas causing errors in the solution. I think modern units are good at mitigating that problem. The reply below mentions deliberate error. Yes, that did exist once. It was called SA (Selective Availability). Deliberate errors were introduced into the clock signals and orbital parameters which ensured an uncertainty of approx +/- 100m for civilian units. President Bill Clinton ordered it switched off permanently in 2000. I caught the moment in this graph: http://www.wombat.ie/gps/index.shtml (Ironically SA was temporarily switched *off* in 1990 during Gulf War I, because the military did not have enough military units). Timing is mentioned in the post below. GPS is excellent for getting good time (+/- 1 microsecond of UTC is easily achievable with cheap hardware). Time sync is such an important application of GPS that even during the SA era, one satellite (# 13 if memory serves me correctly) was guaranteed to have accurate timing signals at all times. Joe. On Aug 17, 3:32 pm, _AM_ <[email protected]> wrote: > Hi, > > 5-10 miters is accuracy of GPS. Do not expect too much... > > According to conspiracy theory this is done specially by USA > military :) they each day set new deltas into GPS system to prevent it > use for rockets navigation by other countries... > > In reality I think GPS internal timing is not very good for making > more accurate positioning. > > On Aug 16, 5:38 pm, Lorenz <[email protected]> wrote: > > > > > How much accurate are the coordinates received by the GPS antenna in > > the reality?I'm using the emulator but it doesn't work well with > > coordinates too much close...is there nobody that have tested an > > application based on the package "Location" in a real device(I don't > > have a real one yet..) and knows how to answer me?.. > > Lorenz > > > thanks! --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -~----------~----~----~----~------~----~------~--~---
