GPSIntroduction,NSSDA• LearnGPSuse,accuracyviaNSSDA
• CollectdatafromNGSpoint(s)
• TransferthetestdatatoLabcomputers
• Differentiallycorrectyourtestdata
• Exportyourtestdataasashapefileorgeodatabase
• Extractx,yvaluesfromthelayer
• CompleteNSSDAspreadsheet
GNSS,GlobalNavigationSatelliteSystem,e.g.GPSbutalsoGalileo,GLONASS,COMPASS
Positionisestimatedbasedonrangemeasurements
Range = speed of light x travel time Range = c(t1 – t2)
Measurementstomultiplesatellitesdetermineposition
5
LowHorizonAngles-AtmosphericDelays,SetMask,RejectSatellitesBelow15o
AccuracyDeclinesintheMountains,Forests,orCities(blockage)
PDOPs–PositionDilutionofPrecisionLowerPDOPSarebetter
GPS-Differen,alCorrec,onUsingtwounitstoimproveaccuracySta,onsetupoverknownposi,on(Base).1. Sta,onsetupatunknownpoint.2. Collectdatasimultaneously.4. CalculatenewpointsfromknownBaseSta,onanddifference.
Afterdifferentialcorrection
Thedatumisinherentlythatofthebasestation
MostCORSstationsarereferencedtoITRF00,ortoNAD83(96)
MNDOTare(usually)referencedtoNAD83
Ifyourequipmentandaccuracyrequirementsarebetterthanthedatumshift,itmatters
Weneedtheproperdatumtransformation,asshowninpfinderofficevideos
Field Part
• Pair GPS receiver with handheld logger using bluetooth (careful with classmate’s loggers, phones, etc.)
• Open Terrasync, make sure settings are correct (non-real time, coordinate system, etc.)
• Wait for sufficient satellites, open Data, then a file, then collect feature, close file.
Lab Part • Download data start pathfinder office • Import from logger/chip to computer • Differentially correct files, in correct coordinate system • Export files • Start ArcMap, extract XY from files • Complete NSSDA calculations