Many of us apply GPS passably much every day — getting guidance with mapping apps on our phones , track our repast deliveries , logging our track routes — but have you ever stopped to wonder , how does GPS piece of work ?
Almost all saucy phones utilize GPS applied science , so let ’s figure out what that really imply and why having a GPS pass catcher and a clear view of the sky intend you ’ll never be lost again .
What Is GPS?
When people peach about " a Global Positioning System , " they usually mean a GPS receiving system , but the Global Positioning System ( GPS ) is actually a constellation of many land - orb satellites ( gps.gov/systems/gps/space/">31 in operational orbitand four that are classified as either " in reserve " or " unhealthy " ) .
The U.S. military originally developed and carry out this satellite meshwork as a military navigation system , then opened it up to everybody else .
Each of these 3,000- to 4,000 - punt ( 1,361- to 1,814 - kg ) solar - power satellites circles the Earth at an ALT of about 12,427 miles ( 20,000 kilometer ) , making two complete rotations every twenty-four hour period . The orbits are coiffe so that at any time , anywhere onEarth , there are at least four satellites " seeable " in the sky .
A GPS liquidator uses these satellite to calculate the precise placement of the person manoeuvre the twist .
How Does GPS Work?
GPS receiver ferment by locating four or more of these satellites , figuring out the distance to each , and using this information to deduce their own location .
This surgery is establish on a simple numerical principle called trilateration . Trilateration in three - dimensional space can be a little knavish , so we ’ll start with an account of dewy-eyed two - dimensional trilateration .
2D Trilateration
ideate you are somewhere in the United States and you are altogether , dead lost ; for whatever reason , you have absolutely no clue where you are . You rule a friendly local and ask , " Where am I ? " He tell , " You are 625 miles from Boise , Idaho . "
This is a nice , hard fact , but it is not specially useful by itself . You could be anywhere on a circle around Boise that has a radius of 625 miles , like this :
You ask somebody else where you are , and she order , " You are 690 miles from Minneapolis , Minnesota . " Now you ’re getting somewhere .
If you immix this information with the Boise entropy , you have two circles that intersect . You now eff that you must be at one of these two Cartesian product points , if you are 625 Roman mile from Boise and 690 miles from Minneapolis :
If a third person tells you that you are 615 mile from Tucson , Arizona , you’re able to eliminate one of the possible action , because the third rotary will only intersect with one of these points . You now get it on exactly where you are : Denver , Colorado .
This appendage is call 2D trilateration because the points of intersection are all located on a two - dimensional carpenter’s plane . When we start fuck off acme / altitude Byzantine — hello , third proportion — 3D trilateration come into play .
3D Trilateration
Fundamentally , three - dimensional trilateration is n’t much different from two - dimensional trilateration , but it ’s a lilliputian tricksy to fancy . Imagine the r from the previous example going off in all steering . So instead of a serial publication of circle , you get a serial publication of welkin .
If you know you are 10 statute mile from planet A in the sky , you could be anywhere on the surface of a huge , imaginary vault of heaven with a 10 - air mile radius . If you also know you are 15 mile from satellite B , you may overlap the first sphere with another , large firmament .
The sphere intersect in a gross circle . If you know the aloofness to a third artificial satellite , you get a third firmament , which intersects with this circle at two points .
world itself can act as a 4th " satellite " or sphere ; only one of the two possible compass point will in reality be on the surface of the planet , so you may eradicate the one in space . Receivers generally front to four or more satellites , however , to improve accuracy and provide precise altitude info .
How GPS Devices Calculate Your Location
for officiate properly , a GPS twist involve to know two things :
GPS telephone receiver picture both of these things out by analyse high-pitched - oftenness , low-pitched - power radio sign from the satellites orbiting the Earth . near units have multiple receivers , so they can pick up signal from several satellite simultaneously .
Radio wavesare electromagnetic muscularity , which think of they travel at the speed of twinkle ( about 186,000 nautical mile per instant , or 300,000 km per instant in a vacuum ) . The receiver can figure out how far the GPS signaling has travel by timing how long it took the signal to arrive .
GPS Math: Using Timing to Calculate Distance
At this power point , you could confidently severalise someone you require to yarn-dye that GPS works via trilateration . But you should be prepared for the take after - up question : How does the GPS gadget know the space to those GPS artificial satellite ? As it turn out , it ’s a matter of timing .
At a particular moment ( let ’s say midnight ) , the artificial satellite begin transmitting a tenacious , digital formula called a pseudo - random code . The receiver begins pass the same digital pattern also exactly at midnight . When the satellite ’s signaling reaches the receiver , its transmittance of the pattern will lag a piece behind the receiver ’s playing of the pattern .
The distance of the delay is equal to the signal ’s travel time . The receiver multiplies this meter by the speed of light to regulate how far the signaling traveled . acquire the signal traveled in a neat line , this is the distance from liquidator to satellite .
Maintaining Synchronicity
One major caveat is that the measuring only works if both the GPS unit and satellite have pin clover that can be synchronized down to the nanosecond . This level of preciseness is only practicable withatomic clocks , but those cost between $ 50,000 and $ 100,000 a pop .
GPS satellite are already bear for by our tax dollars , but what about the GPS receiver ? Even Apple would have a hard metre selling iPhones at that damage percentage point .
The Global Positioning System has a clever , effective solution to this job : Every planet contains an expensive nuclear clock , but the receiver itself uses an ordinaryquartz clock , which it constantly reset .
In a nutshell , the receiver looks at incoming signals from four or more satellites and gauge its own inaccuracy . By constantly reset and re - checking its sentence against the GPS signals coming from the satellite , a lowly smartphone engender nuclear - clock truth " for free . "
Differential GPS
GPS work passably well , but inaccuracies do pop up . For one thing , this method acting assumes the radio signals will make their style through the atmosphere at a consistent speed ( the speed of visible light ) .
But orbiter signal are mete out with interference all the time . The earth ’s ambience slows the signals down , and large objects like skyscrapers can also affect their itinerary .
Differential GPS ( DGPS ) facilitate sort out these errors . The basic idea is to guess GPS inaccuracy at a stationary receiver post with a known localization . Since the DGPS hardware at the station already knows its own perspective , it can well forecast its receiver ’s inaccuracy .
The post then broadcasts a radio sign to all DGPS - equipped receivers in the surface area , supply sign correction information for that sphere . In general , admission to this correction information defecate DGPS receivers much more accurate than ordinary receivers .
