RTN Methodologies &amp; Best Practices

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RTN Methodologies &amp; 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
• 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
• Landscaping, cadastral surveys, mapping
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
• 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 - VRS

Ref Sta.

NRTK

Center

Ref Sta. j

Rover

VRS Sta. i

Ref Sta.

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 - 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