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RTN Methodologies & Best Practices

RTN Methodologies & Best Practices. Neil D. Weston National Geodetic Survey, NOS, NOAA. Silver Spring, MD March 20, 2014. RTN Basics. City limits. City limits. 100. Ref. Ref. 100. Ref. *. *. Northing (km). Northing (km). Ref. Ref. 0. 0. Easting (km). 0. Easting (km). 100.

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RTN Methodologies & Best Practices

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  1. RTN Methodologies & Best Practices Neil D. Weston National Geodetic Survey, NOS, NOAA Silver Spring, MD March 20, 2014

  2. RTN Basics City limits City limits 100 Ref. Ref. 100 Ref. * * Northing (km) Northing (km) Ref. Ref. 0 0 Easting (km) 0 Easting (km) 100 0 100 Single baseline approach Network approach

  3. RTN Basics • Reference frame – adopt latest realization of NAD 83 (NAD 83 2011 epoch 2010.00) • CORS + RTN – include a few CORS in the RTN • Adjustments • Constrain CORS that are included • Base station monitoring • Process data periodically • Monitor coordinates over time • Base station information • Coordinates, velocities, epoch

  4. RTN Basics and Formats • Receiver collection rate – minimum 1Hz • Data formats • Propriety • Open standard • Compatibility • RTCM SC-104 • Only true ‘open’ protocol • RTCM-2.1 Added RTK messages for dm levels at short distances • RTCM-2.2 Expanded for differential operations with GLONASS

  5. RTCM Formats • RTCM-2.2, 2.3 RTK operations providing cm- level performance at short distances • RTCM-3.x More efficient; support RTK operations (GPS+GLONASS); network correction message • Common message types 2.x • Type 18, 20 – RTK uncorrected carrier phase data and carrier phase corrections • Type 19, 21 – RTK uncorrected pseudo-range measurements and appropriate range corrections • Common message types 3.x • 1004 – full observables • 1005 – reference station coordinates • 1007 – antenna description

  6. RTCM Formats

  7. Network Messages

  8. Network RTK Processing Techniques & Applications • Virtual Reference Station – VRS • Area-Parameter Correction – FKP • Master-Auxiliary Concept – MAC • Grading, utilities, pipelines, roads • Landscaping, cadastral surveys, mapping

  9. Area Correction Parameters - FKP • Network described using coefficients for a surface • Parallel surface with baselines less than 100 km • Reference station at the center of the “surface” • Software in rover receiver does the interpolation of corrections • Error information is provided for quality control and analysis • Single and bi-directional communications

  10. Virtual Reference Station - VRS • VRS techniques is currently the most popular • Requires bi-directional communications • VRS observations constructed • Rover approx. position to NRTK center • Rover solution based on range between VRS and rover • VRS kept to preserve ambiguities

  11. Virtual Reference Station - VRS Ref Sta. NRTK Center Ref Sta. j Rover VRS Sta. i Ref Sta.

  12. Master Auxiliary Concept - MAC • Rover position (NMEA) to processing center • Processing center chooses a master station – usually closest ref. station • Auxiliary stations are chosen from a 70 km catch circle • Rover receives MAC corrections via RTCM • Rover decides on method of interpolation of corrections and how the position is determined – double difference, for example

  13. Master Auxiliary Concept - MAC Aux k4 Auxiliary k1 Master j Rover 70 km Aux k2 Aux k3

  14. RTK Processing Network RTK Processes Correction Generation Correction Interpolation Correction Transmission Network Ambiguities Network Corrections Linear Interpolation Surface Modeling Grid-based Parameters One way Comms. Two way Comms. FKP VRS State Space Observation Space Linear Combination Least Squares Co-location MAC Net Adjust

  15. Thank You Neil D. Weston Deputy Director National Geodetic Survey 301-713-3222 Neil.d.weston@noaa.gov

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