Lewis Lapine, SCB&CB Chief, South Carolina Geodetic Survey

Transcription

1 The SC VRS Network Matt Wellslager Project Manager Lewis Lapine, SCB&CB Chief, South Carolina Geodetic Survey

2 South Carolina Geodetic Survey Geodetic and Mapping Services works cooperatively to provide current geodetic information and modern land information systems. The primary mission of the Geodetic Survey is to establish horizontal and vertical geodetic control throughout the state to allow land and land-related items to be referenced to the national horizontal and vertical coordinate system, to ensure the integrity of new geodetic data, and to maintain geodetic files. Mapping Coordination supports the development of an accurate, uniform statewide mapping system on a county-by-county base. These mapping systems will provide a large-scale map base for county and state land information systems that will enhance land records, engineering, land planning and economic development.

3 Centimeter Real Time Positioning Accuracy Using GPS 7 Years Ago Not Possible! Then there was RTK Expensive and Restrictive Use Now there is VRS Less expensive, Labor Efficient, Very Accurate

4 Before Virtual Reference Station (VRS) Real Time Kinematic All components must be present at the Base and Rover! GPS Antenna Data Link or Radio Modem and Radio Antenna Batteries GPS Receiver Data Collector

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6 Technology

7 VRS Conventional State of the Art

8 SC - VRS Network Design -

9 Conceptual Layout of the SCVRS

10 Antenna Hardware Tamper-Proof Leveling Head Self Supporting 24 Foot Tower Stainless Steel Mount For Masonry Buildings

11 The NetR5 and HTTP Interface

12 Server Interface in GPSNet

13 Components of the state vector ambiguity (meters) multipath (centimeters) ionosphere parameters :30 15: : : :30 15:00 differences between ambiguities are constant Japan, day 1 Japan, day 2 (shifted by 4 minutes) uncorrelated between stations days activity of ionosphere about to decline Use double differences together with code measurement and tropo model to resolve the ambiguity (FAMCAR)

14 Summary Model ionospheric phase advance in terms of a first order approximation across local area network Extract ionospheric parameters, multipath and double differenced ambiguities by means of a Kalman filter Obtain increased availability of network corrections and reliability for small to intermediate network sizes together with a physical picture of the evolution of the ionosphere

15 NC CORS Sites

16 Equipment Required to use the SCVRS 1. Dual Frequency GNSS Receiver - Capable of tracking multiple constellations. 2. Cellular Device 3. Cellular Carrier Service Digital Service required for data. Verizon, Alltel, Cingular 4. Data Collector collection software must be capable of broadcasting a GPS coordinate. 5. Adjustable or Fixed height Pole good if pole has a locking mechanism to prevent slippage.

17 The required components to use the VRS

18 Roving receiver sends an NMEA string back to server using cellular modem. Virtual Reference Station position is established. VRS VRS RTK

19 SC Prototype VRS Network

20 VRS Absolute Accuracy Comparison of VRS and NGS Height Mod Control Absolute Accuracy Meters Time (sec) Horizontal (cm) Vertical (cm) Allowable 2-D RMSE r 95% = * RMSE r = (2.0* * *1.2) 1/2 = 2.4 cm* Allowable 1-D RMSE v 95% = *RMSE v = (2.0* * *2.4) 1/2 = 3.1 cm* *(Local Accuracy 2 + Eccentricty 2 + System Design 2 ) 1/2

21 Users of the SCVRS 1. SCDOT Originators for the network. Provided the money to get things started. 2. General Contractors for the SCDOT. Use the real time service for automated heavy machinery and earth moving. Envision as many as 50 bulldozers operating with VRS Service 3. The SC Society of Professional Land Surveyors 4. Academic Institutions that include: USC, Clemson, College of Charleston, the Citadel, Greenville Tech. and Midlands Tech. 5. Other State, County and Municipal organizations.

22 Practical Applications

23 Mean/SDV 0.001/0.008 Tidal Datum Transfer VRS Elevation (ft) Leveling (ft) Difference mile transfer 0.05 ft uncertainty

24 Trimble Integrity Manager

25 Test of VRS Vertical Accuracy Using 60 Second Sample NGS Elevation - VRS Elevation # of differences (m) 94% within 5cm (.164 ft)

26 Classical Leveling vs VRS 1 st Order Class 2 Leveling 4 Surveyors 4 days 5.5km 6mm 1 Surveyor 4 hours 12mm comparison

27 What needs to be done to improve results? 1. Attempt to separate the antenna from the receiver. 2. Use a geodetic grade antenna with ground plane. 3. Update roaming capabilities of cell phone. 4. Conduct a preplanned survey of points for optimal times of observations.

28 Advantages of the VRS Significantly reduces systematic errors Extended operating range with improved initialization and accuracy Increased productivity Single person surveying Eliminates need to establish reference station Set-up, power, physical security become non-issues

29 Advantages of VRS Eliminates dependency on single reference station Graceful degradation should a R.S. fail Uses established communications Establishes a single coordinate system

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31 Thank-you