搜索
TheNationalGeodeticSurveyStandardGPSFormatSP3PaulR.SpoffordNationalGeodeticSurveyNationalOceanService,NOAASilverSpring,MD20910-3282,USAandBenjaminW.Remondi,PhDP.O.Box37Dickerson,Maryland20842,USAINTRODUCTIONWhydoweneedstandardizedorbitformats?Standardorbitformatsprovidemanyadvantages,themostobviousbeingorbitexchange.ASCIIandbinaryformatsbothsatisfythisfunction,butASCIIdoesitwithgreatergeneralitybecausebinaryformatsarecomputeroperatingsystemdependent.TheNGSstandardGPSorbitformatSP1wasintroducedinRemondi(1985).Afterafewyearsofuse,itwasrealizedthatenhancementswouldeventuallyberequired.Theorbittype,thecoordinatesystem,andtheGPSweekassociatedwiththefirstepochoftheephemerisfilewereaddedinamannerthatdidnotimpacttheformatsandexistingsoftware.AmoreseriousomissionoftheinitialNGSorbitformatwasthesatelliteclockcorrections.Thisomissionreflectedanearlierbeliefthatallgeodeticapplicationscouldbeaccomplishedindifferentialmode.Todaywerealizethatstandardformatsserveawidercommunityandincludethosewhofinditinconvenienttooperateinadifferentialmode.Ausercanoperateinsingle-receiverornavigationmodebasedonthebroadcastmessage.However,theusercangetmoreaccurate(post-processed)resultsifthepreciseorbitaldataandtheassociatedsatelliteclockcorrections,whichweredeterminedsimultaneouslywiththosepreciseorbits,areavailable.Thisbecomesevenmorevaluablewhenthebroadcastorbitandclockinformationareintentionallydegraded.Thus,anewNGSorbitformatwasproposedinRemondi(1989),andmodifiedandadoptedinRemondi(1991).ThisformatissimilartotheoriginalNGSorbitformat,butcomprisespositionalandsatelliteclockcorrectiondata.Furthermore,otherchangeswereproposedwhichallowmoreflexibilitywithregardtoenhancements.ThissummarydocumentcombinesthespecificationsandenhancementsdiscussedinRemondi(1989)andRemondi(1991),withexamplesforthebenefitoftheuser.SP3InthisdocumenttheNGSorbitalformatSP3(StandardProduct#3)forGlobalPositioningSystem(GPS)satellitesisdiscussed(seeexamples1and2).Themajoradditiontoearlierformatsisthesatelliteclockcorrectioninformationwhichiscomputedsimultaneouslywiththeorbits.Thebasicformatisapositionandclockrecord;asecond,optional,recordcontainsvelocitiesandclockrates-of-change.ThePositionRecordFlag,P,inlineoneindicatesthatnovelocitiesareincluded.TheVelocityRecordFlag,V,inlineoneindicatesthatateachepoch,andforeachsatellite,asatellitevelocityandclockrate-of-changehasbeencomputed.TheSP3formathasbeendesignedsuchthatsatellitesotherthanGPScouldbedescribedaswell.Note:AlltimesreferredtointhisdocumentareGPStimes,evenwhentheyarerepresentedasGregorianorModifiedJulianDates.Thus,informationforconversionofGPStimetoCoordinatedUniversalTime(UTC)isnotprovidedaspartoftheSP3format.!StandardProduct#3ASCIISP3FormatVersiona(refertoexamplegiveninfigure1)SP3FirstLineColumns1-2VersionSymbol#aColumn3PosorVelFlagPorVColumns4-7YearStart1994Column8Unused_Columns9-10MonthStart12Column11Unused_Columns12-13DayofMonthSt17Column14Unused_Columns15-16HourStart_0Column17Unused_Columns18-19MinuteStart_0Column20Unused_Columns21-31SecondStart_0.00000000Column32Unused_Columns33-39NumberofEpochs_____96Column40Unused_Columns41-45DataUsed____dColumn46Unused_Columns47-51CoordinateSysITR92Column52Unused_Columns53-55OrbitTypeFITColumn56Unused_Columns57-60Agency_NGSSP3LineTwoColumns1-2Symbols##Column3Unused_Columns4-7GPSWeek_779Column8Unused_Columns9-23SecondsofWeek518400.00000000Column24Unused_Columns25-38EpochInterval__900.00000000Column39Unused_Columns40-44ModJulDaySt49703Column45Unused_Columns46-60FractionalDay0.0000000000000SP3LineThreeColumns1-2Symbols+_Column3-4Unused__Columns5-6NumberofSats25Column7-9Unused__Columns10-12Sat#1Id__1Column13-15Sat#2Id__2***Columns58-60Sat#17Id_22SP3LineFourColumns1-2Symbols+_Columns3-9Unused_______Columns10-12Sat#18Id_23Columns13-15Sat#19Id_24***Columns58-60Sat#34Id__0SP3LineFiveColumns1-2Symbols+_Columns3-9Unused_______Columns10-12Sat#35Id__0Columns13-15Sat#36Id__0***Columns58-60Sat#51Id__0SP3LineSixColumns1-2Symbols+_Columns3-9Unused_______Columns10-12Sat#52Id__0Columns13-15Sat#53Id__0***Columns58-60Sat#68Id__0SP3LineSevenColumns1-2Symbols+_Columns3-9Unused_______Columns10-12Sat#69Id__0Columns13-15Sat#70Id__0***Columns58-60Sat#85Id__0SP3LineEightColumns1-2Symbols++Columns3-9Unused_______Columns10-12Sat#1Accuracy__7Columns13-15Sat#2Accuracy__6***Columns58-60Sat#17Accuracy__5SP3LineNineColumns1-2Symbols++Columns3-9Unused_______Columns10-12Sat#18Accuracy__5Columns13-15Sat#19Accuracy__5***Columns58-60Sat#34Accuracy__0SP3LineTenColumns1-2Symbols++Columns3-9Unused_______Columns10-12Sat#35Accuracy__0Columns13-15Sat#36Accuracy__0***Columns58-60Sat#51Accuracy__0SP3LineElevenColumns1-2Symbols++Columns3-9Unused_______Columns10-12Sat#52Accuracy__0Columns13-15Sat#53Accuracy__0***Columns58-60Sat#68Accuracy__0SP3LineTwelveColumns1-2Symbols++Columns3-9Unused_______Columns10-12Sat#69Accuracy__0Columns13-15Sat#70Accuracy__0***Columns58-60Sat#85Accuracy__0SP3LinesThirteenandFourteenColumns1-2Symbols%cColumn3Unused_Columns4-52charactersccColumn6Unused_Columns7-82charactersccColumn9Unused_Colu