Introduction into Real-Time Network Adjustment with Geo++ GNSMART Andreas Bagge Gerhard Wübbena, Martin Schmitz Geo++ GmbH D-30827 Garbsen, Germany www.geopp.de GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 1 2004 Geo++ GmbH
Content Introduction GNSS Basic Principle Error sources, Absolute Accuracy Differential GNSS Spatial Variations, Distance dependent errors GNSMART Networks Ambiguity Problem State Monitoring, Modelling of error sources Representation, FKP, VRS,... Communication Issues GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 2 2004 Geo++ GmbH
Introduction GNSS-SMART = Global Navigation Satellite System State Monitoring And Representation Technique = Technique to determine (State Monitoring) and to represent (Representation) the system status of GNSS Systems GNSMART = Geo++ Software implementation of GNSS-SMART GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 3 2004 Geo++ GmbH
GNSS Principle GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 4 2004 Geo++ GmbH
Range Observation Range Measurement R to 1 Satellite R Receiver must be somewhere on the surface of sphere GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 5 2004 Geo++ GmbH
Geometric Position from Range Observations Range Measurements to 2 Satellites R2 R1 Receiver must be somewhere on the intersection circle of both spheres GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 6 2004 Geo++ GmbH
Absolute Positioning Position determination of a single ( Stand-Alone ) GNSS receiver in system of GNSS Accuracy with GPS/GLONASS 5 20 m for many applications not sufficient! full influence of all error sources GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 7 2004 Geo++ GmbH
Error Sources GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 8 2004 Geo++ GmbH
GNSS Error Sources Satellite clock error Satellite orbit error Ionosphere Troposphere X Z Y WGS84 Multipath Antenna (PCV) Receiver clock error GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 9 2004 Geo++ GmbH
Magnitude of Error Sources Error Source Satellite Orbit Satellite Clock Ionosphere Troposphere Multipath Code Multipath Phase Antenna Absolute Influence 2... 50m 2... 100m 0.5... >100 m 0.01... 0.5 m m mm... cm mm... cm -> total: 5... 20 m GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 10 2004 Geo++ GmbH
Differential GNSS GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 11 2004 Geo++ GmbH
Differential ( DGNSS ) Positioning Determine all error influences on a known station Corrections Transmit corrections to the rover Apply corrections reduce error influence Compute position with code ( DGNSS ) or with carrier phase ( RTK ) GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 12 2004 Geo++ GmbH
DGNSS Error Sources Spatial Variations GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 13 2004 Geo++ GmbH
DGNSS/RTK Distance Dependency PRC true error influence broadcast correction distance dependent error (degrades quality with increasing distance) Reference Rover Distance GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 14 2004 Geo++ GmbH
Magnitude of Error Sources Error source Absolute influence Relative influence Satellite Orbit 2... 50m 0.1... 2 ppm Satellite Clock 2... 100m 0.0 ppm Ionosphere 0.5... >100 m 1... 50 ppm Troposphere 0.01... 0.5 m 0... 3 ppm Multipath Code m m Multipath Phase mm... cm mm... cm Antenna mm... cm mm... cm -> total: 1...2 cm + 1...20 ppm High spatial correlation Local (Calibration) GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 15 2004 Geo++ GmbH
Geo++ Absolute Antenna Calibration orientation changes of antenna required robot to rotate and tilt the antenna dynamic robot guidance automatic operational procedure real-time Old Relative Calibration Geo++ Absolute Calibration GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 16 2004 Geo++ GmbH
RTK: Accuracy, Reliability, Availability 100 % Availability, Reliability Accuracy 1 cm Distance from Reference GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 17 2004 Geo++ GmbH
RTK-Limits from Distance Dependency PRC RTK Limits max. acceptable error for RTK Reference Distance GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 18 2004 Geo++ GmbH
Stand Alone Reference Stations Accuracy, Reliability, Availability Good Bad GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 19 2004 Geo++ GmbH
Stand Alone Reference Stations Accuracy, Reliability, Availability Good Bad GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 20 2004 Geo++ GmbH
Stand Alone Reference Stations Accuracy, Reliability, Availability Good Bad GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 21 2004 Geo++ GmbH
Stand Alone Reference Stations Accuracy, Reliability, Availability Good Bad GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 22 2004 Geo++ GmbH
RTK Networks GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 23 2004 Geo++ GmbH
Distance dependent Errors in RTK Networks PRC true error influence error influence in Ref 1 Interpolated error influence for rover position error influence in Ref 2 Ref 1 Rover Ref 2 Distance GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 24 2004 Geo++ GmbH
GNSS-SMART Network Accuracy, Reliability, Availability Good Bad GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 25 2004 Geo++ GmbH
GNSMART: User View user in the field one way communication link receive all necessary correction/reference data determine absolute RTK position anytime/anywhere 1 cm accuracy 1 cm accuracy - everywhere! GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 26 2004 Geo++ GmbH
Network RTK: Network Tasks primary task (pre-requisite): State Monitoring determine distance (and site) dependent errors carrier phase ambiguity resolution secondary task: Representation represent network information for user distance dependent errors orbit, ionosphere, troposphere reference station dependent errors multipath, antenna, clock using adequate formats (RTCM, FKP, VRS, SSR) GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 27 2004 Geo++ GmbH
Carrier Phase Ambiguity GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 28 2004 Geo++ GmbH
Ambiguty Level Phase correction 2 identical Ambiguity Levels different Ambiguity Level Ref 1 Rover Ref 2 Distance GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 29 2004 Geo++ GmbH
GNSMART State Monitoring GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 30 2004 Geo++ GmbH
GNSMART State Monitoring Complete State Space Model (SSM) for all error sources with carrier phase accuracy Multi-station RT network solution Increased redundancy compared to triangle processing! Increased inter-station distances (sparse networks) Robust against single station/communication failures undifferenced observables Multiple Stations Multiple Signals (L1,L2,P1,P2,C/A) undifferenced ambiguity resolution Low Elevation Ambiguity Fixing GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 31 2004 Geo++ GmbH
GNSMART: State Modeling functional models dynamic processes with temporal and/or spatial stochastic characteristics static parameters stochastical models stochastic processes with temporal and/or spatial characteristics GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 32 2004 Geo++ GmbH
Ambiguity Search GNSS error modelling needs correct ambiguity level -> Ambiguities must be solved Ambiguity search needs accurate observations bias-free observations -> GNSS errors must be modelled GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 33 2004 Geo++ GmbH
GNSMART Representation GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 34 2004 Geo++ GmbH
FKP Representation Phase correction FKP 1 d FKP Representation error 1 FKP M 2 Distance Ref 1 Rover Ref 2 GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 35 2004 Geo++ GmbH
FKP Representation in GNSMART base signal of reference station (corrections) one linear FKP plane for each reference station PRC Φ signal (L i, L 0 ) Satellite optional: higher order polynomials base signal FKP plane Λ GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 36 2004 Geo++ GmbH
Individualized Corrections Virtual Reference Station (VRS) Phase correction Problem 1: transfered tropo model consistent? d VRS Representation error Problem 3: unexpected 1 VRS M Ref V Ref 1 Rover 2 Ref 2 Problem 2: moving (virt.) reference station? Distance GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 37 2004 Geo++ GmbH
Communication GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 38 2004 Geo++ GmbH
GNSS-SMART System structure Central Concept raw data / RTCM RTCM/SSR Sensor network SMART Center Distribution network GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 39 2004 Geo++ GmbH
Communication within Network Reference Station to Network Center Telecommunication lines Modem, ISDN Leased Lines Internet local provider (static IP, data integrity?) Intranet Radio Links directed antenna beacons Mobile Phone data (GSM, GPRS, UMTS) Satellite Communication Data formats receiver specific raw data 19200bps, bi-directional pre-processed data (RTCM, RTCM++) 2400bps, uni-directional GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 40 2004 Geo++ GmbH
Communication Reference/Center to Rover Mobile phone (GSM) bidirectional communication (SSR,OSR (FKP,PRS,VRS) mobile Internet (GPRS, UMTS) bidirectional or uni-directional NTRIP encryption for access control charging Broadcast media VHF, TV, Radio, Satellite communication SSR, FKP no VRS,PRS encryption for access control charging GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 41 2004 Geo++ GmbH
Conclusions GPS positioning is affected by absolute and distance dependent errors DGPS and local RTK systems can only avoid absolute errors lead to limited RTK (and DGPS) distance GNSMART network monitors all errors allowing RTK (and DGPS) applications with homogenous accuracy, reliability and availability GNSMART supports all currently used representation modes FKP, VRS, PRS GNSMART is well prepared for future developments GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 42 2004 Geo++ GmbH
Further Information For general information on GNSMART please refer to the Geo++ home page http://www.geopp.com/gnsmart For background publications refer directly to the Geo++ Publications page http://www.geopp.com/publications/english/lit_e.htm GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 43 2004 Geo++ GmbH