衛(wèi)星定位理論與方法測量與導(dǎo)航工程系導(dǎo)航與定位教研室陳明劍第14次課精度評定上次課內(nèi)容取接收機(jī)某一初值（X0、Y0、Z0），有：其中

e為方向余弦XρSPXj-X當(dāng)觀測有4顆衛(wèi)星時，j=1~4，有：

當(dāng)衛(wèi)星多于4顆時，可以有最小二乘解算采用迭代法求解，一般二次解得誤差方程法方程未知參數(shù)解未知參數(shù)的權(quán)逆陣m為偽距觀測精度，qii是QX的第i行i列元素其中未知參數(shù)精度（中誤差）參數(shù)精度mX取決于觀測精度m和系數(shù)陣A，而A只與衛(wèi)星和接收機(jī)幾何位置有關(guān)，同一類接收機(jī)m是不變的，不同地區(qū)、不同時間、不同衛(wèi)星的導(dǎo)航解精度也不同，需有一技術(shù)指標(biāo)衡量導(dǎo)航解的精度觀測值等權(quán)：協(xié)方差矩陣：估值精度有兩部分構(gòu)成：1、觀測值等效誤差(UERE：userequivalentrangeerror)UERE=URE(UserRangeError)+UEE(UserEquipmentError)SPS:SAon:URER25米SAoff:URER5米2、衛(wèi)星幾何結(jié)構(gòu)有關(guān)(GDOP:geometricdilutionofprecision)GPSexhibitsstatisticalaccuracydistributionsbecauseUEREandGDOParecontinuouslyvariable.UERE(UserEquivalentRangeError)isameasureoftheerrorintherangemeasurementtoeachsatelliteasseenbythereceiver.GDOPisameasureoftheerrorcontributedbythegeometricrelationshipofthesatellitesasseenbythereceiver.PositionAccuracyUERE=URE+UEEURE(UserRangeError)istheportionoftheUEREallocatedtotheSpaceandControlsegment.UEE(UserEquipmentError)istheportionoftheUEREallocatedtotheuserequipment.Therefore,receiverpositionaccuracymustbespecifiedforconditionsofDOPandURE.Dynamicpositioningaccuracyrequirementsmusttakeintoaccounttheeffectofvehiclemotionaswell.GeneralDOPconditionsPDOP<6,HDOP<4,VDOP<4.5,andTDOP<2.解的誤差協(xié)方差陣為：在導(dǎo)航中，經(jīng)常用到精度衰減因子DOP（DilutionofPrecision）來表示衛(wèi)星空間圖形的貢獻(xiàn)。空間精度衰減因子GDOP(GeometricalDOP):

位置精度衰減因子PDOP(PositionDOP):平面精度衰減因子HDOP(HorizontalDOP):垂直精度衰減因子VDOP(VerticalDOP):時間精度衰減因子TDOP(TimeDOP):定義及協(xié)方差陣和誤差間的關(guān)系，有下列關(guān)系式：由上面的可知：定位精度若要越高，定位誤差越小，DOP值就要越小，即定位精度和DOP值成正比，一般規(guī)定GDOP值應(yīng)小于6。-

Wanttetrahedronaslargeaspossible- WantindexaslowaspossiblePDOP

PositionDilutionofPrecisionGarminsViewofMappingTypicalMappingGradeGPSSettings-PDOP=99-SNR=2-MaskAngle=5oPDOP=6SNR=6MaskAngle=15oPDOPof6orLess-GoodDOPof3orLess-GoodPDOP/DOP

PositionDilutionofPrecisionGarminonlyShowsDOPThat’s1/2ofPDOPDilutionofPrecision(DOP)

DOPisafunctionexpressingthemathematicalqualityofsolutionsbasedonthegeometryofthesatellites.Ithasabestcasevalueof1,highernumbersbeingworse.DilutionofPrecision(DOP)3.GPS導(dǎo)航精度評定指標(biāo)HDOP：水平精度衰減因子VDOP：垂直精度衰減因子PDOP：位置精度衰減因子TDOP：時間精度衰減因子GDOP：幾何精度衰減因子六面體的體積越大，所測衛(wèi)星的空間分布范圍也越大，反之越小，GDOP值越大。

DilutionOfPrecision(3)PDOP=PositionDilutionOfPrecision(MostCommonlyUsed)VDOP=VerticalDilutionOfPrecisionGDOP=GeometricDilutionOfPrecisionHDOP=HorizontalDilutionOfPrecisionTDOP=TimeDilutionOfPrecisionQUALITY DOPVeryGood 1-3Good 4-5Fair 6Suspect >6MissionPlanningIsCriticaltoObtainGoodDOPIntuitiveConceptsofXDOP3.GPS導(dǎo)航精度評定指標(biāo)DilutionOfPrecision(DOP)AMeasureofTheGeometryOfTheVisibleGPSConstellationGoodDOPPoorDOPPoorGDOPResultswhenanglesfromreceivertothesetofSVsusedaresimilarGoodGDOPAnglesfromreceivertoSVsaredifferentGDOP作用：1、衡量衛(wèi)星幾何結(jié)構(gòu)對精度的影響GDOP變化比URER快2、最佳選星GeneralDOPconditionsPDOP<6,HDOP<4,VDOP<4.5,andTDOP<2.Howdoessatellitegeometryinfluenceaccuracy?Atelemetryexample(2D):90oShapeofareawhichmaycontaintransmitter30oShapeofareawhichmaycontaintransmitterReceiverWithoutcorrectingfortheseerrors,wecanachieveabouta5maccuracywithparalleltrackingunits(goodones),or10mwithserialtrackingunits(cheapones).Severalsourcesoferrorareverydifficulttocorrectfor.Fortunately,thelargesterrorsourcescanbecorrectedforusingdifferentialprocessing.Withdifferentialprocessing,wecanachieveaccuraciesof<1m,andevencentimeteraccuracywiththerightreceiver.GPSAccuracyRelationshipPOSITIONERROR=PDOPXUERE-DependsonGeometry-Dependsonsatellitepositionerrors,propagationerrors,andinstrumentationerrorsCodeRangeResultsAutonomousPosition+/-10m(30ft)error(horizontal)+/-15m(45ft)error(vertical)CarrierPhaseResultsMeasuredReducedBaselineorVector(cmprecision)Azimuth=212o42’49.8244”Distance=557.05307mDeltaEle