introduction into gnsmart · geoinformation workshop 2004, istanbul kultur university, september...
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GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 1 © 2004 Geo++® GmbH
Introduction into Real-Time Network Adjustment with Geo++ GNSMART
Andreas BaggeGerhard Wübbena, Martin Schmitz
Geo++® GmbHD-30827 Garbsen, Germany
www.geopp.de
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 2 © 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 3 © 2004 Geo++® GmbH
Introduction
GNSS-SMART =Global Navigation Satellite SystemState 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 4 © 2004 Geo++® GmbH
GNSS Principle
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 5 © 2004 Geo++® GmbH
Range Observation
R
Range Measurement Rto 1 Satellite
Receiver must besomewhere on thesurface of sphere
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 6 © 2004 Geo++® GmbH
Geometric Position from Range Observations
R1
R2
Range Measurementsto 2 Satellites
Receiver must besomewhere on theintersection circle of both spheres
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 7 © 2004 Geo++® GmbH
● 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
Absolute Positioning
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 8 © 2004 Geo++® GmbH
Error Sources
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 9 © 2004 Geo++® GmbH
XY
Z
WGS84Receiver clock error
GNSS Error Sources
Antenna (PCV)
Multipath
Troposphere
Ionosphere
Satellite clock error
Satellite orbit error
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 10 © 2004 Geo++® GmbH
Error Source Absolute Influence
Satellite Orbit 2 ... 50mSatellite Clock 2 ... 100mIonosphere 0.5 ... >100 mTroposphere 0.01 ... 0.5 mMultipath Code mMultipath Phase mm ... cmAntenna mm ... cm
Magnitude of Error Sources
-> total: 5 ... 20 m
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 11 © 2004 Geo++® GmbH
Differential GNSS
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 12 © 2004 Geo++® GmbH
Differential („DGNSS“) Positioning
● Determine all error influenceson a known station „Corrections“
● Transmit correctionsto 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 13 © 2004 Geo++® GmbH
Spatial Variations
DGNSS Error Sources
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 14 © 2004 Geo++® GmbH
DGNSS/RTK Distance Dependency
PRC
Distance
Reference Rover
distance dependent error (degrades quality with increasing distance)
broadcast correction
“true” errorinfluence
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 15 © 2004 Geo++® GmbH
Magnitude of Error Sources
High spatial correlation
Error source Absolute influence Relative influence
Satellite Orbit 2 ... 50m 0.1 ... 2 ppmSatellite Clock 2 ... 100m 0.0 ppmIonosphere 0.5 ... >100 m 1 ... 50 ppmTroposphere 0.01 ... 0.5 m 0 ... 3 ppmMultipath Code m mMultipath Phase mm ... cm mm ... cmAntenna mm ... cm mm ... cm
Local (Calibration)
-> total: 1...2 cm + 1...20 ppm
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 16 © 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
Geo++ Absolute CalibrationOld Relative Calibration
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 17 © 2004 Geo++® GmbH
Distance from Reference
AccuracyAvailability, Reliability
100 %
1 cm
RTK: Accuracy, Reliability, Availability
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 18 © 2004 Geo++® GmbH
PRC
DistanceReference
max. acceptableerror for RTK
RTK Limits
RTK-Limits from Distance Dependency
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 19 © 2004 Geo++® GmbH
Stand Alone Reference Stations
Accuracy, Reliability, AvailabilityGood Bad
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 20 © 2004 Geo++® GmbH
Stand Alone Reference Stations
Accuracy, Reliability, AvailabilityGood Bad
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 21 © 2004 Geo++® GmbH
Stand Alone Reference Stations
Accuracy, Reliability, AvailabilityGood Bad
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 22 © 2004 Geo++® GmbH
Stand Alone Reference Stations
Accuracy, Reliability, AvailabilityGood Bad
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RTK Networks
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 24 © 2004 Geo++® GmbH
Distance dependent Errorsin RTK Networks
PRC
DistanceRef 1 Rover Ref 2
„Interpolated“ error influence for rover positionerror influence
in Ref 1
error influencein Ref 2
“true” error influence
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 25 © 2004 Geo++® GmbH
GNSS-SMART Network
Accuracy, Reliability, AvailabilityGood Bad
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GNSMART: User View
1 cm accuracy - everywhere!
● user in the field
❐ one way communication link
❐ receive all necessary correction/reference data
❐ determine absolute RTK position
❐ anytime/anywhere
● 1 cm accuracy
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 27 © 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 28 © 2004 Geo++® GmbH
Carrier Phase Ambiguity
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 29 © 2004 Geo++® GmbH
Phase correction
Distance
2
Ref 1 Rover Ref 2
identicalAmbiguity Levels different
Ambiguity Level
Ambiguty Level
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 30 © 2004 Geo++® GmbH
GNSMART State Monitoring
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 31 © 2004 Geo++® GmbH
GNSMART State Monitoring
● Complete State Space Model (SSM) for all error sourceswith 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 32 © 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 33 © 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 34 © 2004 Geo++® GmbH
GNSMARTRepresentation
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 35 © 2004 Geo++® GmbH
FKP Representation
Phase correction
Distance
Ref 1
1
Rover
M
1
Ref 2
2
FKP
FKP
dFKP
Representation error
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 36 © 2004 Geo++® GmbH
FKP Representationin GNSMART
● base signal of reference station (corrections)
● one linear FKP planefor each❐ reference station❐ signal (Li, L0)
❐ Satellite● optional: higher order
polynomialsΛ
Φ
base signal
FKP plane
PRC
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 37 © 2004 Geo++® GmbH
Individualized CorrectionsVirtual Reference Station (VRS)
Phase correction
Distance
Ref 1
1
Rover
M
Ref 2
2
dVRS
Representation error
VRS
Ref V
Problem 1: transfered tropo model consistent?
Problem 2: moving (virt.) reference station?
Problem 3: unexpected
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 38 © 2004 Geo++® GmbH
Communication
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 39 © 2004 Geo++® GmbH
GNSS-SMART System structureCentral Concept
Sensor network SMART Center
raw data / RTCM
Distribution network
RTCM/SSR
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 40 © 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 41 © 2004 Geo++® GmbH
Communication
● 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
Reference/Center to Rover
GeoInformation Workshop 2004, Istanbul Kultur University, September 20-26, Antalya 42 © 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 43 © 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