• What is the GPS?

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    Our phone's GPS location, is a conventional term for satellite positioning, satellite's full name should be called GNSS (Global Navigation Satellite System) location. GPS is an GNSS, is the United States to deploy a global satellite system. This system gives a simple description, is


    There are 24 satellites constantly orbiting the Earth campaign




    Each satellite continuously sends "who I am, where I am" signal


    Receiver (such as phone GPS chip) received such signals from several satellites, calculate the distance from the satellite signal propagation time, then work out the receiver's own position, by the way you can getthe current time.



    Basic principles on the GPS question-and-answer


    If a little ponder on this principle, it is easy to be understood, such as:


    Someone asked, why can we can guarantee every position it? if the two satellites in the sky, how can only calculate device locations? that's the reason why the deployment of 24 satellites in the sky, this deployment will ensure whenever the sky is >=4 satellite signal was received.


    Someone asked, solve 3D coordinates as long as the three satellites will be enough, why four? the problem lies in the receiver (mobile) clockand the clock there is a time gap of the satellite, we need to calculate both the real time clock, we cannot calculate the propagation time, they cannot be spread to calculate distances, eventually was unable to locate. In other words, we going to unknowns, not three, but four.


    Was asked, since satellite signal in satellite positioning success Hou, each seconds will positioning once, this enough to description signal spread is no obstacles of, so why to spent so long of time to found star? this is a good problem, but this problem is complex, a statements cover of is most main of time with in has "waiting for message" Shang, so-called message is satellite used to cycle broadcast current location of signal (here clarified Xia, satellite is not as we wants to of such, each seconds broadcast once current of location, But send a signal in a continuous loop, otherwise there is no receiver can achieve dozens of times per second GPS positioning), the signal is broadcast for 30 seconds, thus cold start of GPS in General, at least 30 seconds to complete.



    Was asked, why in car of navigation Shang see GPS of track movement very continuous smooth, and phone Shang is is each seconds jumped once, phone can each seconds positioning n times? this to points two aspects said, first this certainly is can do of, because GPS satellite launches of signal is continuous of, he not each seconds broadcast a satellite location, but transmission a track parameter, based on this information, on can heavy frame satellite of full flight track, to as long as received party willing to, it can do each seconds solutions is dozens of times location; Second so far, cell phone GPS module for compromise between cost and benefit, designed to position once per second, basic but adequate. Of course, as a perfect mobile APP developer, if you really dislike of beats per second, can also be based on one time per second, use filtering for smoother projection, Visual effects are very smooth, looks can be deceptive.

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