Accessing and Processing Real-Time GPSCorrections for Precise Point Positioning– Some User Considerations

摘要

Natural Resources Canada makes its GPS Correctionsrn(GPS·C) available in real-time through the Canada-widernDifferential GPS Service. These corrections have alsornrecently become available over the Internet usingrnprototype UDP and TCP servers. The latter uses thernNTRIP model of data transfer to allow, in part, for therncreation of Virtual Reference Stations and the productionrnof RTCM-SC104 local-area corrections for DifferentialrnGPS. In addition, both servers provide high-precisionrnwide-area corrections in a modified RTCA-SC159 formatrnto provide the necessary precision to eventually realizernreal-time Precise Point Positioning (PPP) to the subdecimetrernlevel.rnObtaining the highest possible accuracy from GPSrncorrections requires an awareness of the clock reference,rnor datum, to which they refer. The pseudorangernmeasurements selected for the correction computationrndetermine the clock reference for those corrections. ThernGPS·C corrections are currently referenced to the C/Arn(C1) and P2′ (C1+P2?P1) pseudorange observables andrnusers must match these to achieve the best possiblernaccuracy. Failure to do so can degrade positioningrnprecision by up to a factor of three or more.