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Enabling high precision positioning on Android devices
The French Institute of Science and Technology for Transport,
Development and Networks
Antoine GRENIERCéline RAGOINValérie RENAUDIN
GNSS measurements Taskforce WorkshopPrague, June 26th 2019
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www.ifsttar.fr26/06/2019
Road to PPP-RTK
● Raw measurements○ Validity & quality
● Modelling○ Precise orbits & clocks for satellites○ Tropospheric corrections○ …
● Signal combination○ Allow ionospheric correction (“Iono-free” combination)○ Require multiple frequency acquisition
■ Xiaomi Mi8 with L1 and L5 capacities
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www.ifsttar.fr26/06/2019 3Credits @ Roberto Lee Cortes
Environment c
onstraints
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Environment constraints
● Only 12 GPS satellites with L5 signals○ 4-5 available in open sky ○ Less in an urban canyon -> PPP system unsolvable or non redundant○ Use multiple constellations (GALILEO, BEIDOU, ...)
● Problem○ GALILEO navigation message not available on Xiaomi Mi8
● Solutions:○ SUPL Google○ IGS products (FTP)○ RTCM streams (RTS IGS)
● Radio Technical Comission for Maritime Services (RTCM) Protocol● Stream divided in messages (Observation, Navigation, Corrections...)
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Precise orbits& clocks
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Precise orbits and clocks
● Need precise products in real time○ IGS ultra-rapid products (predicted) using FTP○ RTCM streams from Real Time Service IGS
■ Need identifcation to access, freely available for research purposes
● Streams VS ultra-rapids products○ More accurate satellites clocks estimation [1]○ Available for all constellations○ Easy to implements
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[1] Tomasz Hadas and Jaroslaw Bosy. “IGS RTS precise orbits and clocks verifcation and quality degradation over time” (2014).
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Implementation in Android
● GoGPS Java open-source library ○ Java port of the Matlab code written by Mirko Reguzzoni and Eugenio
Realini (Geomatics Laboratory of Politecnico di Milano, Italy).
● Java toolbox ○ DGNSS-RTK computations, RINEX logging, …○ RTCM streams receiving and decoding capacities
● Problem○ Only observation messages (1004, 1006, …) decoded○ Classes for other messages need to be added
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Implementation in GeolocPVT
● GoGPS added in the source code of the app○ Enhanced for ephemeris/corrections messages
■ GPS (1019/1060)■ GALILEO (1045/1243)
○ Standard binary string decoding, specs in RTCM standards 10403.3 [2]
○ An working example can be found in RTKLIB open source code (C++)
● Log into the IGS-RTS server (www.rt.igs.org) ○ “RTCM3EPH” Mountpoint for ephemeris
■ Message 1019, 1045
○ “CLK93” Mountpoint for orbit/clock corrections■ Message 1060, 1243
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[2] RTCM. RTCM 10403.3, Differential GNSS (Global Navigation Satellite Systems) Services. Radio Technical Commission For Maritime Services. 2016.
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Results
Future developments of GeolocPVT○ Management of internet data resources○ Toward an effcient PPP-RTK solution○ ...
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References
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[1] Tomasz Hadas and Jaroslaw Bosy. “IGS RTS precise orbits and clocks verifcation and quality degradation over time”. In: (2014).[2] RTCM. RTCM 10403.3, Differential GNSS (Global Navigation Satellite Systems) Services. Radio Technical Commission For Maritime Services. 2016.
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Raw measurements
● Validity○ Pseudorange and phase need to be independent from each other
■ Ex: Low cost receivers
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Source: Zhu Ni, GEOLOC/IFSTTAR
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Raw measurements
● Validity - Xiaomi Mi8 results
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Raw measurements
● Quality○ Precise phase measurements○ Fewest cycle slip possible
■ Ambiguity estimation and resolution
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Applying corrections
● Applied on coordinates computed from broadcast ephemeris
● Broadcast ephemeris can be retrieved from streams
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○ IoD (Issue of Data) id of broadcast and corrections need to be similar
Source: Schmitz, 2012 [2]For details see references [2, 3]
[2] Martin Schmitz. RTCM State Space Representation Messages, Status and Plans. Geo++ GmbH, 2012.[3] RTCM. RTCM 10403.3, Differential GNSS (Global Navigation Satellite Systems) Services. Radio Technical Commission For Maritime Services. 2016.