GPS basics u blox en

GPS mới nhất

   GPS Basics Introduction to the system Application overview              GPS Basics GPSBasics  u-bloxag GPS-X-02007  Page2  Title GPS Basics Doc Type BOOK  Doc Id GPS-X-02007 Author: Jean-MarieZogg Date: 26/03/2002 Formostrecentdocuments,pleasevisitwww.u-blox.com Wereserveallrightsinthisdocumentandintheinformationcontainedtherein.Reproduction,useordisclosuretothirdpartieswithoutexpressauthorityisstrictlyforbidden.                                      Alltrademarksmentionedinthisdocumentarepropertyoftheirrespectiveowners. Copyright©2002,u-bloxag        T HIS B OOKISSUBJECTTOCHANGSEATU - BLOX ' DISCRETION . U - BLOXASSUMESNORESPONSIBILITYFORANYCLAIMSORDAMAGESARISINGOUTOFTHEUSEOFTHIS BOOK , INCLUDING BUT NOT LIMITED TO CLAIMS OR DAMAGES BASED ON INFRINGEMENT OF PATENTS , COPYRIGHTS OR OTHER INTELLECTUAL PROPERTY RIGHTS . U - BLOXMAKESNOWARRANTIES , EITHEREXPRESSEDORIMPLIEDWITHRESPECTTOTHEINFORMATIONANDSPECIFICATIONSCONTAINEDINTHISBOOK .P ERFORMANCE CHARACTERISTICSLISTEDINTHISBOOKAREESTIMATESONLYANDDONOTCONSTITUTEAWARRANTYORGUARANTEEOFPRODUCTPERFORMANCE . GPSBasics  u-bloxag GPS-X-02007  Page3 GPS Basics • Introductiontothesystem • Applicationoverview  u-blox ag Zuercherstrasse68 CH-8800Thalwil Switzerland  Phone: +4117227444 Fax: +4117227447  Internet:www.u-blox.com  GPSBasics  u-bloxag GPS-X-02007  Page4 Preface by the author   Jean-MarieZogg My Way In1990,IwastravellingbytrainfromChurtoBrigintheSwisscantonofValais.Inordertopassthetimeduring thejourney,Ihadbroughtafewtradejournalswithme.WhilstthumbingthroughanAmericanpublication,I cameacrossaspecialistarticleaboutsatellitesthatdescribedanewpositioningandnavigationalsystem.Usinga fewUSsatellites,thisparticularsystem,knownasaGlobalPositioningSystemorGPS,wasabletodeterminea positionanywhereintheworldtowithinanaccuracyofabout100m(*). Asakeensportsmanandmountaintrekker,Ihadendeduponmanyanoccasioninprecarioussituationsdueto alackoflocalknowledgeandIwasthereforefascinatedbytheprospectofbeingabletodeterminemyposition infogoratnightbyusingarevolutionaryprocessinvolvingaGPSreceiver.AfterreadingthearticleIwassmitten bytheGPSbug. IthenbegantodelvedeeperintotheGlobalPositioningSystem.Iarousedalotofenthusiasmamongststudents atmyuniversityforthisparticularuseofGPS,andasaresult,producedvariousitemsofcourseworkaswellas degreepapersonthesubject.FeelingthatIwasatrueGPSexpert,Iconsideredmyselfqualifiedtospreadthe ‘navigationmessage’andcompiledspecialistarticlesaboutGPSforvariousmagazinesandnewspapers.Asmy specialistknowledgegrew,sodidmyenthusiasmforthesystemandthedegreetowhichIbecamehookedon thesubject.  Why read this book? Basically, a GPS receiver determines just four variables: longitude, latitude, height and time. Additional information(e.g.speed,directionetc.)canbederivedfromthesefourcomponents.Anappreciationoftheway in which the GPS system functions is necessary, in order to develop new, fascinating applications. If one is familiarwith thetechnicalbackgroundto theGPSsystem,itthen becomespossible to develop and use new positioningandnavigationalequipment.Thisbookalsodescribesthelimitationsofthesystem,sothatpeopledo notexpecttoomuchfromit. Beforeyoudecidetoembarkonthistext,IwouldliketowarnyouthatthereisnoknowncurefortheGPSbug andthatyouproceedatyourownperil!  GPSBasics  u-bloxag GPS-X-02007  Page5 How did this book come about? Two years ago, I decided to reduce the amount of time I spent lecturing at the university, in order to take anotherlookatindustry.MyaimwastoworkforacompanyprofessionallyinvolvedwithGPSandu-bloxag received me with open arms. Thecompany wanted meto produce a brochure that theycould give to their customers.Thispresentsynopsisisthereforetheresultofearlierarticlesandnewlycompiledchapters.  A heartfelt wish IwishyoueverysuccesswithyourworkwithintheextensiveGPScommunityandtrustthatyouwillsuccessfully navigateyourwaythroughthisfascinatingtechnicalfield.Enjoyyourread!    Jean-MarieZogg October2001     (*):thatwasin1990,positionaldataisnowaccuratetowithinabout10m! GPSBasics  u-bloxag GPS-X-02007  Page6 Table of contents  1 INTRODUCTION .9 2 GPS made simple 11 2.1 Theprincipleofmeasuringsignaltransittime 11 2.1.1 GeneratingGPSsignaltransittime .12 2.1.2 Determiningapositiononaplane 13 2.1.3 Theeffectandcorrectionoftimeerror .14 2.1.4 Determiningapositionin3-Dspace .15 3 GPS, THE TECHNOLOGY .16 3.1 Descriptionoftheentiresystem 16 3.2 Spacesegment .17 3.2.1 Satellitemovement 17 3.2.2 TheGPSsatellites 19 3.2.3 Generatingthesatellitesignal 20 3.3 Controlsegment 23 3.4 Usersegment .23 4 THE GPS NAVIGATION MESSAGE 25 4.1 Introduction .25 4.2 Structureofthenavigationmessage 26 4.2.1 Informationcontainedinthesubframes .26 4.2.2 TLMandHOW 27 4.2.3 Subdivisionofthe25pages .27 4.2.4 Comparisonbetweenephemerisandalmanacdata .28 5 Calculating position .29 5.1 Introduction .29 5.2 Calculatingaposition .29 5.2.1 Theprincipleofmeasuringsignaltransittime(evaluationofpseudo-range) 29 5.2.2 Linearisationoftheequation 32 5.2.3 Solvingtheequation 33 5.2.4 Summary 34 5.2.5 Errorconsiderationandsatellitesignal 35 6 Co-ordinate systems .38 6.1 Introduction .38 6.2 Geoids .38 6.3 Ellipsoidanddatum 39 6.3.1 Spheroid .39 6.3.2 Customisedlocalreferenceellipsoidsanddatum .40 6.3.3 Nationalreferencesystems .41 6.3.4 WorldwidereferenceellipsoidWGS-84 .41 6.3.5 Transformationfromlocaltoworldwidereferenceellipsoid .42 6.3.6 Convertingco-ordinatesystems .44 6.4 Planarlandsurveyco-ordinates,projection 45 6.4.1 ProjectionsystemforGermanyandAustria .45 GPSBasics  u-bloxag GPS-X-02007  Page7 6.4.2 Swissprojectionsystem(conformaldoubleprojection) 46 6.4.3 Worldwideco-ordinateconversion .47 7 Differential-GPS (DGPS) .48 7.1 Introduction .48 7.2 DGPSbasedonthemeasurementofsignaltransittime 48 7.2.1 DetailedDGPSmethodofoperation .49 7.3 DGPSbasedoncarrierphasemeasurement .50 8 DATA FORMATS AND HARDWARE interfaces 52 8.1 Introduction .52 8.2 Datainterfaces .52 8.2.1 TheNMEA-0183datainterface 52 8.2.2 TheDGPScorrectiondata(RTCMSC-104) 63 8.3 Hardwareinterfaces .66 8.3.1 Antenna .66 8.3.2 Supply 67 8.3.3 Timepulse:1PPSandtimesystems .67 8.3.4 ConvertingtheTTLleveltoRS-232 .68 9 GPS RECEIVERS .71 9.1 BasicsofGPShandheldreceivers .71 9.2 GPSreceivermodules .73 9.2.1 BasicdesignofaGPSmodule 73 10 GPS APPLICATIONS 74 10.1 Introduction .74 10.2 Descriptionofthevariousapplications .75 10.2.1 Scienceandresearch .75 10.2.2 Commerceandindustry .76 10.2.3 Agricultureandforestry .77 10.2.4 Communicationstechnology 78 10.2.5 Tourism/sport 78 10.2.6 Military .78 10.2.7 Timemeasurement 78 APPENDIX 79 A.1 DGPSservices .79 A.1.1 Introduction 79 A.1.2 Swipos-NAV(RDSorGSM) 79 A.1.3 AMDS .79 A.1.4 SAPOS 80 A.1.5 ALF .80 A.1.6 dGPS 80 A.1.7 RadioBeacons .81 A.1.8 OmnistarandLandstar 81 A.1.9 EGNOS .81 A.1.10 WAAS 81 A.2 Proprietarydatainterfaces 82 A.2.1 Introduction 82 A.2.2 SiRFBinaryprotocol .82 GPSBasics  u-bloxag GPS-X-02007  Page8 A.2.3 Motorola:binaryformat 85 A.2.4 Trimbleproprietaryprotocol .86 A.2.5 NMEAorproprietarydatasets? 86 Resources on the World Wide Web 88 Generaloverviewsandfurtherlinks .88 DifferentialGPS 88 GPSinstitutes .89 GPSantennae .89 GPSnewsgroupsandspecialistjournals .89 List of tables .90 List of illustrations 91 SOURCES .93  GPSBasics  u-bloxag GPS-X-02007  Page9 1 INTRODUCTION  UsingtheGlobalPositioningSystem(GPS,aprocessusedtoestablishapositionatanypointontheglobe)the followingtwovaluescanbedeterminedanywhereonEarth(Figure1): 1. One’sexact location (longitude, latitude and height co-ordinates) accurateto within a range of 20 m to approx.1mm. 2. Theprecisetime(UniversalTimeCoordinated,UTC)accuratetowithinarangeof60nstoapprox.5ns. Speed and direction of travel (course) can be derived from these co-ordinates as well as the time. The co- ordinatesandtimevaluesaredeterminedby28satellitesorbitingtheEarth. Longitude: 9°24'23,43'' Latitude: 46°48'37,20'' Altitude: 709,1m Time: 12h33'07''  Figure 1: The basic function of GPS GPS receivers are used for positioning, locating, navigating, surveying and determining the time and are employedbothbyprivateindividuals(e.g.forleisureactivities,suchastrekking,balloonflightsandcross-country skiingetc.)andcompanies(surveying,determiningthetime,navigation,vehiclemonitoringetc.). GPS(thefulldescriptionis:NAVigationSystemwithTimingAndRangingGlobalPositioningSystem,NAVSTAR- GPS)wasdevelopedbytheU.S.DepartmentofDefense(DoD)andcanbeusedbothbyciviliansandmilitary personnel.ThecivilsignalSPS(Standard PositioningService)canbeusedfreelybythegeneralpublic,whilstthe militarysignal PPS(PrecisePositioning Service)canonlybe used byauthorised governmentagencies.The first satellitewasplacedinorbiton22 nd February1978,andtherearecurrently28operationalsatellitesorbitingthe Earthat a height of 20,180 km on 6 differentorbital planes.Their orbits are inclined at 55° tothe equator, ensuringthataleast4satellitesareinradiocommunicationwithanypointontheplanet.Eachsatelliteorbits theEarthinapproximately12hoursandhasfouratomicclocksonboard. DuringthedevelopmentoftheGPSsystem,particularemphasiswasplacedonthefollowingthreeaspects: 1. Ithadtoprovideuserswiththecapabilityofdeterminingposition,speedandtime,whetherinmotion oratrest. 2. Ithadtohaveacontinuous,global,3-dimensionalpositioningcapabilitywithahighdegreeofaccuracy, irrespectiveoftheweather. 3. Ithadtoofferpotentialforcivilianuse.  GPSBasics  u-bloxag GPS-X-02007  Page10 TheaimofthisbookistoprovideacomprehensiveoverviewofthewayinwhichtheGPSsystemfunctionsand theapplicationstowhichitcanbeput.Thebookisstructuredinsuchawaythatthereadercangraduatefrom simple facts to more complex theory. Important aspects of GPS such as differential GPS and equipment interfacesaswellasdataformatarediscussedinseparatesections.Inaddition,thebookisdesignedtoactasan aidinunderstandingthetechnologythatgoesintoGPSappliances,modulesandICs.Frommyownexperience,I knowthatacquiringanunderstandingofthevariouscurrentco-ordinatesystemswhenusingGPSequipment canoftenbeadifficulttask.Aseparatechapteristhereforedevotedtotheintroductionofcartography. Thisbookisaimedatusersinterestedintechnology,andspecialistsinvolvedinGPSapplications. . IthenbegantodelvedeeperintotheGlobalPositioningSystem.Iarousedalotofenthusiasmamongststudents atmyuniversityforthisparticularuseof GPS, andasaresult,producedvariousitemsofcourseworkaswellas. aidinunderstandingthetechnologythatgoesinto GPS appliances,modulesandICs.Frommyownexperience,I knowthatacquiringanunderstandingofthevariouscurrentco-ordinatesystemswhenusing GPS equipment canoftenbeadifficulttask.Aseparatechapteristhereforedevotedtotheintroductionofcartography.