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RTN Methodologies & Best Practices. Neil D. Weston National Geodetic Survey, NOS, NOAA. Silver Spring, MD July 31, 2013. 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.

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RTN Methodologies & Best Practices

Neil D. Weston

National Geodetic Survey, NOS, NOAA

Silver Spring, MD July 31, 2013


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


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


RTN Basics and Formats

  • Receiver collection rate – minimum 1Hz

  • Data formats

    • Proprietary

    • 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


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




  • 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


    Area correction parameters fkp
    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


    Virtual reference station vrs
    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


    Virtual reference station vrs1
    Virtual Reference Station - VRS

    Ref Sta.

    NRTK

    Center

    Ref Sta. j

    Rover

    VRS Sta. i

    Ref Sta.


    Master auxiliary concept mac
    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


    Master auxiliary concept mac1
    Master Auxiliary Concept - MAC

    Aux k4

    Auxiliary k1

    Master j

    Rover

    70 km

    Aux k2

    Aux k3


    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


    Thank You

    Neil D. Weston

    Chief – Spatial Reference System Division

    301-713-3191 x 103

    [email protected]


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