Monday, July 13, 2015

cell phone locator

Ionosphere and layer delays - The satellite signal slows because it passes through the atmosphere. The GPS system uses a intrinsic  model that calculates a mean quantity of delay to partly correct for this sort of error.

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Signal multipath - this happens once the GPS signal is mirrored off objects like tall buildings or giant rock surfaces before it reaches the receiver. This will increase the period of the signal, thereby inflicting errors.
Receiver clock errors - A receiver's intrinsic  clock isn't as correct because the atomic clocks aboard the GPS satellites. Therefore, it should have terribly slight temporal arrangement errors.
Orbital errors - conjointly referred to as annual errors, these ar inaccuracies of the satellite's reportable location.
Number of satellites visible - The a lot of satellites a GPS receiver will "see," the higher the accuracy. Buildings, terrain, electronic interference, or generally even dense foliage will block signal reception, inflicting position errors or probably no position reading the least bit. GPS units usually won't work inside, underwater or underground.
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Satellite geometry/shading - This refers to the relative position of the satellites at any given time. Ideal satellite pure mathematics exists once the satellites ar settled at wide angles relative to every different. Poor pure mathematics results once the satellites ar settled in an exceedingly line or in an exceedingly tight grouping.
Intentional degradation of the satellite signal - Selective convenience (SA) is associate degree intentional degradation of the signal once obligatory by the U.S. Department of Defense. Sturmarbeiteilung was meant to forestall military adversaries from mistreatment the extremely correct GPS signals. the govt turned off Sturmarbeiteilung in might 2000, that considerably improved the accuracy of civilian GPS receivers.
GPS satellites transmit 2 low power radio signals, selected L1 and L2. Civilian GPS uses the L1 frequency of 1575.42 rate within the ultrahigh frequency band. The signals travel line of sight, that means they'll experience clouds, glass and plastic however won't undergo most solid objects like buildings and mountains.
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A GPS signal contains 3 completely different bits of data - a pseudorandom code, annual knowledge and almanac knowledge. The pseudorandom code is just associate degree I.D. code that identifies that satellite is transmittal data. you'll read this range on your Garmin GPS unit's satellite page, because it identifies that satellites it's receiving.
Ephemeris knowledge, that is consistently transmitted by every satellite, contains necessary data concerning the standing of the satellite (healthy or unhealthy), current date and time. This a part of the signal is important for determinative an edge.

The almanac knowledge tells the GPS receiver wherever every GPS satellite ought to be at any time throughout the day. every satellite transmits almanac knowledge showing the orbital data for that satellite and for each different satellite within the system.