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