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Gps Navigation System


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Gps Navigation System

  1. 1. GPS Navigation Systems By: Amit ChaudharyAbstract distance to each, and use this information to deduce its own location. This operation isArtificial Intelligence in GPS Navigation based on a simple mathematical principleSystems helps user to reach the destination called trilateration.he set before leaving the current position. Itintegrates the surrounding environmental Imagine you are somewhere in Gandhinagarvalues with the data stored somewhere to (Gujarat, India) and you are totally lost forprovide the optimum path which not only whatever reason; you have absolutely nosaves the time but also the costs associated clue where you are. You find a friendly localwith different routes and proactively warns and ask, “Where am I?” He says, “You aredrivers about potential traffic jams or 1km from Sector-4, Gandhinagar.”suggests alternate commutes that are more This is a nice, hard fact, but is notfuel efficient. After implementing many particularly useful by itself. You could bealgorithms it decides actual measurements anywhere on circle around Sector-4 that hasto improve future routes based on the a radius of 1km like this:information of time it took the last time.IntroductionArtificial Intelligence doesn’t just work onthe software but also needs a bunch ofhardware components that collect the datafrom the outside world to make everythinghappen as per user’s expectations. GPS too,is solely dependent on the GPS receiversthat receive the data sent by satellites. TheGlobal Positioning System is actually a You ask somebody else where you are, andconstellation of 27 Earth-orbiting satellites she says, “You are 1.5km from Sector-1,(24 in operation and 3 extras in case one Gandhinagar.” Now you are gettingfails). somewhere. If you combine thisHow it works information with the Sector-4 information, you have two circles that intersect. You nowA GPS receiver’s job is to locate four or know that you must be at one of these twomore of these satellites, figure out the 1
  2. 2. intersection points, if you are 1km from  The location of at least threeSector-4 and 1.5km from Sector-1. satellites above you  The distance between you and each of those satellites The GPS receiver figures out of these things out by analyzing high-frequency, low-power radio signals from the GPS satellites. Radio waves are electromagnetic energy, which means they travel at the speed of light (about 1,86,000 miles per second). The receiver can figure out how far the signal has travelled by timing how long it took the signal to arrive. At a particular time (let’sIf a third person tells you that you are say midnight), the satellite begins0.90km from Sector-6, Gandhinagar, you transmitting a long, digital pattern called acan eliminate one of the possibilities, pseudo-random code. The receiver beginsbecause the third circle will only intersect running the same digital pattern alsowith one of these points. You now know exactly at midnight. When the satellite’sexactly where you are – Sector-3, signal reaches the receiver, its transmissionGandhinagar. of the pattern will lag a bit behind the receiver’s playing of the pattern. The length of the delay is equal to the signal’s travel time. The receiver multiplies this time by the speed of light to determine how far the signal has travelled. Assuming the signal travelled in a straight line, this is the distance from receiver to satellite. In order to make this measurement, the receiver and satellite both needs clocks that can be synchronized down to the nanosecond. To make a satellite positioning system using only synchronized clocks, you would need to have atomic clocks not only on all the satellites, but also in the receiverIn order to make this simple calculation, the itself. But atomic clocks cost somewhereGPS receiver has to know two things: between $50,000 and $100,000, which 2
  3. 3. makes them a just bit too expensive for method assumes the radio signals will makeeveryday consumer use. their way through the atmosphere at a consistent speed (the speed of light). InThe GPS has a clever, effective solution to fact, the Earth’s atmosphere slows thethis problem. Every satellite contains an electromagnetic energy down somewhat,expensive atomic clock, but the receiver particularly as it goes through theitself uses an ordinary quartz clock, which it ionosphere and troposphere. The delayconstantly resets. In a nutshell, the receiver varies depending on where you are onlooks at incoming signals from four or more Earth, which means it’s difficult tosatellites and gauges its own accuracy. In accurately factor this into the distanceother words, there is only one value for the calculations. Problems can also occur whencurrent time that the receiver can use. The radio signals bounce off large objects, suchcorrect time will cause all of the signals that as skyscrapers, giving a receiver thereceiver is using to align at a single point in impression that a satellite is farther awayspace. That time value is the time value than it actually is. On top of all that,held by the atomic clocks in all of the satellites sometimes just send out badsatellites. So the receiver sets its clock to almanac data, misreporting their ownthat time value, and it then has the same position.time value that all the atomic clocks in all ofthe satellites have. The GPS receiver gets Differential GPS (DGPS) helps correct theseatomic clock accuracy for free. errors. The basic idea is to gauge GPS inaccuracy at a stationary receiver stationIn order for the distance information to be with a known location. Since the DGPSof any use, the receiver also has to know hardware at the station already knows itswhere the satellites actually are. This isn’t own position, it can easily calculate itsparticularly difficult because the satellites receiver’s inaccuracy. The station thentravel in very high and predictable orbits. broadcasts a radio signal to all DGPS-The GPS receiver simply stores an almanac equipped receivers in the area, providingthat tells it where every satellite should be signal correction information for that any given time. Things like the pull of the In general, access to this correctionmoon and the sun do change the satellites’ information makes DGPS receivers muchorbits very slightly, but the Department of more accurate than ordinary receivers.Defense constantly monitors their exactpositions and transmits any adjustments to Based on the calculations, the algorithm toall GPS receivers as part of the satellites’ find out the user’s position can easily knowsignals. the longitude, latitude and altitude of its current position. To make the navigationThese calculations work pretty well, but more user-friendly, most receivers plug thisinaccuracies do pop up. For one thing, this raw data into map files stored in memory. A 3
  4. 4. standard GPS receiver will not place you ona map at any particular location (in our caseSector-3), but will also trace your pathacross a map as you move. If you leave your Sourcereceiver on, it can stay in constant (Sector-3)communication with GPS satellites to seehow your location is changing. With thisinformation and its built-in clock, thereceiver can give you several pieces ofvaluable information:  How far you’ve travelled  How long you’ve been travelling  Your current speed  Your average speed  A bread crumb trail showing you exactly where you have travelled on the map  The estimated time of arrival at your destination if you maintain your current speedAs we have now seen how to infer thecorrect position of any source, in the sameway we can obtain the destination point byabove computations. But the problem is notfinding the path between the source(Sector-3) and destination (for instance,Sector-21), but is to find optimum path. Tosee the practical of it, you can have a lookat the screenshots to reach Sector-21considering that efficient algorithms areimplemented. Destination (Sector-21) 4
  5. 5. Select the source as Sector-3 anddestination Sector-21 The path shown in blue color is the optimum path provided by Google with the total distance (5.8km from Sector-3 to Sector-21) and the approximate time (10 minutes). Conclusion To search the optimum path, the algorithms are fully dependent on the data. The more the data, the better the results are. We may need heuristics techniques, to select the best possible path or use DFS (Depth-First- Search) algorithm to reach the destination, and once it is reached, there is no need to look up other solutions unlike BFS (Breadth- First-Search). 5
  6. 6. References: 1. 2. http://howstuffworks 3. 6