Published on April 16, 2008
Slide 1: South Carolina Geodetic Survey SOUTH SURVEY GEODETIC CAROLINA Marine Transportation Highway Construction Obstruction Charting Utilities Surveying Engineering GIS Mapping Infrastructure Slide 2: 3.) User Segment 1.) Control Segment Master Control Station Colorado Springs Control Segment Monitor Stations Diego Garcia Ascension Is. Kwajalein Hawaii 2.) Space Segment Three Segments The Global Positioning System Slide 3: Space Segment 29 Satellites 6 orbital planes inclined 55 degrees to equator 4 or 5 SVs in each plane 20,200 Km high orbits (12,550 Miles) Orbit twice daily (11 hr 58 min) Slide 4: Typical South Carolina Land Surveyor At WorkUser Segment Slide 5: One measurement narrows down our position to the surface of a sphere Calculate your position Slide 6: Second measurement narrows it down to intersection of two spheres Calculate your position, cont’d Slide 7: Third measurement narrows to just two points In practice 3 measurements are enough to determine a position. We can usually discard one point because it will be a ridiculous answer, either out in space or moving at high speed. Calculate your position, cont’d Slide 8: Fourth measurement will decide between the two points The fourth measurement allows us to solve for the receiver clock bias. Fourth measurement will only go through one of the two points Calculate your position, cont’d Slide 9: Determined 33o 23’ 30.195065” N 079o 02’ 33.948394” W -12.445 m Known 33o 23’ 28.607434” N 079o 02’ 41.161474” W -12.637 m GPS Post Processed or RTK Uses Baselines From A Known Position Slide 10: = First Partial Wavelength N N = Integer Ambiguity D Distance D = N + Integer Ambiguity Resolution Yields Survey Quality Baselines Slide 11: Continuous Carrier Phase Measurement Initialization From The Phase Measurements Slide 12: Overview of RTK Slide 13: Ambiguity Resolution for RTK Slide 14: RTK Example OTF Initialization Loss of Lock! Slide 15: RTK Example Known Point Initialization Slide 16: Limited range from single reference station Potential gross error in establishing reference station No integrity monitoring Dependency on single reference station Productivity loss Security Communications Power supply Limitations of Classical RTK Survey Slide 17: RTK PPM Error vs. Baseline Length Slide 19: Permanently EstablishedRTK Reference Stationsaka CORS Slide 20: What is a CORS? Slide 21: Reference Stations…defined Located at a precisely known position Records GPS data for later use Post Processing Generates GPS corrections for immediate use Real - time, broadcast or dial - in Results degrade with distance from Reference Station Useable range can be from 10 km to 500 km (RTK vs DGPS) Slide 22: Monumentation Components of a CORS site Hardware Communications Software Photo Courtesy UNAVCO Slide 23: The South Carolina Virtual Reference StationNetwork Slide 24: RTKNet VRS - Data Flow Reference Station data streams back to server through LAN or Internet Slide 25: RTKNet VRS - Data Flow Roving receiver sends an NMEA string back to server using cellular modem - VRS position is established NMEA - GGA VRS Slide 26: RTKNet VRS - Data Flow Server uses VRS position to create corrected observables and broadcasts to rover RTCM or CMR+ VRS Slide 27: RTKNet VRS - Data Flow Rover surveys as in normal RTK survey but getting data as if coming from the VRS VRS Slide 28: Network Multiple Base Station Solution B1 B2 B3 R Let B1, B2 B3 be base stations, R be the rover The indexes r = 1,2,3 are for bases, r=0 stands for the rover Four RTK engines run simultaneously: (1,2) (2,3) (3,1) (1,0)+(2.0)+(3,0) Slide 29: Field Test Results Time (secs) Probability of Certainty Slide 30: The origin of the ionosphere schematic, not to scale Slide 31: A global VTEC map, calm ionosphere Vertical Total Electron Content on a global map, as derived from GPS base station observations Slide 32: Modeling gradients of the ionosphere Reference Stations Changes of satellite geometry lead to changes in mapping functionChanges of piercing coordinates and dynamical changes in ionosphere lead to time dependence of expansion parameters Gradients Slide 33: Modeling gradients of the ionosphere Changes of satellite geometry lead to changes in mapping functionChanges of piercing coordinates and dynamical changes in ionosphere lead to time dependence of expansion parameters Gradients Ionosphere Reference Stations Slide 34: Components of the state vector Slide 35: Quality Control RS Data BAD! USERS Quality Control Slide 36: 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 Slide 37: SC - VRS Network Design VRS Is Not Built In a Day! There Are Many Stakeholders!! They Are ALL Critical To Your Success Slide 38: Antenna Hardware Stainless Steel Mount For Masonry Buildings Self Supporting 24 Foot Tower Tamper-Proof Leveling Head Slide 39: Server Network Design Should IT Be a Shareholder? 5 6 7 Slide 40: Modeling ??? I(λ,φ) = I0 +aλ∆λ + aφ∆φ 1 cm -1 cm 2 – 12hr Multipath Plots Areal Variant Ionospheric Model The solution of Integer Ambiguity is influenced by external variables Atmosphere - Tropo, Ion Clock Error - SV and Receiver SV Orbit Error Multipath Separation of Base and Rover Slide 41: Test Network 11 Counties, 6700 Sq Mi, 10 VRS Base Stations, 50 Control Pts Slide 42: VRS Absolute Accuracy Comparison of VRS and NGS Height Mod Control Absolute Accuracy Meters Allowable 2-D RMSEr 95% = 1.7308 * RMSEr = (2.0*2.0 + 0.3*0.3 + 1.2*1.2)1/2 = 2.4 cm* Allowable 1-D RMSEv 95% = 1.9600* RMSEv = (2.0*2.0 + 0.3*0.3 + 2.4*2.4)1/2 = 3.1 cm* *(Local Accuracy2 + Eccentricty2 + System Design2)1/2 Slide 43: Comparison of VRS to Total StationRelative Accuracy Grid Brg Angle Rt Grd Dist TPT1 SURVEY 068/00/55 TPT1 TPT2 207/30/58 220/29/57 544.669 VRS 220/29/55.2 544.678 Total Station 139/30/03 Interior Angle TPT2 TPT1 027/30/58 TPT2 TPT3 198/49/59 188/40/59 957.778 VRS 188/40/57.2 957.769 Total Station 171/19/01 Interior Angle TPT3 TPT2 018/49/59 TPT3 SURVEY 038/08/33 340/41/26 2165.470 VRS 340/41/27.5 2165.441 Total Station 019/18/34 Interior Angle SURVEY TPT1 248/00/55 837.523 VRS 837.500 Total Station SURVEY TPT3 218/08/33 029/52/22 Interior Angle 029/52/21.0 360/00/00 VRS 359/59/59.1 Total Station Slide 44: Network Integrity 6 cm Vert. 9 cm Horiz. Slide 45: Practical Applications Slide 46: Tidal Datum Transfer 2 mile transfer 0.05 ft uncertainty Slide 47: Classical Leveling vs VRS 1st Order Class 2 Leveling 4 Surveyors 4 days 5.5km – 6mm 1 Surveyor 4 hours 12mm comparison Slide 48: Concluding Remarks Number of Registered Users Maintenance Plan Replacement Plan Integrity Monitoring Cost Subscription Fee Questions? Slide 49: Questions
The SC VRS Network Matt ... • The primary mission of the Geodetic Survey is ... Envision as many as 50 bulldozers operating with VRS Service • 3. The ...
South Carolina Geodetic Survey SOUTH SURVEY ... SC Real Time Network ... Test Network 11 Counties, 6700 Sq Mi, 10 VRS Base Stations, 50 NGS Ht Mod Control Pts.