GNSS Precise Point Posi.oning(PPP)
Associate Professor Suelynn Choy
School of Science
RMIT University, Australia
suelynn.choy@rmit.edu.au
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Content
1. GNSS Precise PosiBoning Techniques
2. Theory of Precise Point PosiBoning (PPP)
3. GNSS Online Processing Services
4. Real-Bme PPP System and ApplicaBons
5. *PPP-RTK

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GNSS PosiBoning Techniques

3Real-Time KinemaBc (RTK)• PosiBonal accuracy +/- 2cm (horiz)• Single base soluBon• Range < 10-20 km (accuracy decreases with distance)• Data transfer via UHF radioUHF RadioReferenceUser4

Network RTK• PosiBonal accuracy +/- 2cm (horiz)• Based on CORS network• Range increased up to 70 km between CORS sites• Data transfer via mobile internet

CORS - Continuously
Operating Reference Station

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Thailand’s
CORS network
providing NRTKServices

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Australia’s CORS Network

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Australia’s Mobile ConnecBvity

89Precise Point PosiBoning (PPP)• Precise Point Posi.oning (PPP) allows a single GNSS receiver user
to determine posiBon at the decimetre / cenBmetre error level inkinemaBc / staBc mode using precise satellite orbits and clocks.
Standard Positioning Service
Broadcast orbit and clock
informaBon+
User satellite tracking
informaBon=
m-level user posiBon esBmates

Precise Point Positioning
Precise orbit and clock
informaBon+
User satellite tracking
informaBon+
AddiBonal error modelling=dm- to cm-level user posiBon
esBmates10

InternaBonal GNSS Services (IGS)

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How Does PPP Work?

Diﬀeren.al

PPP

PPP uses state space representation (SSR) correction products suchas precise satellite orbits, clocks and signal biases from either
commercial or/and public (e.g., IGS) that are delivered to the user via
satellite and/or internet.

MathemaBcal Model
Lki − ρik − c( Δti − Δt k ) − α ik Ti + I ik − λ Bik−ε = 0

Pi k − ρik − c( Δti − Δt k ) − α ik Ti − I ik − c(b k + bi ) − ε = 0
Lki , Pi k - undifferenced carrier phase and code observations (meters)

ρ ik - geometric distance (satellite-receiver)Bik - carrier phase bias, where λ Bi = λ ( N i + δ N i ) + c(d + d i )kkkk

N ik , δ N ik - integer carrier phase ambiguity and non-zero initial fractional phaseΔti , Δt k - receiver and satellite clock offsets
Ti - tropospheric total zenith delay

α ik - troposphere mapping function
I ik - slant ionospheric delay
bi , b k ; di , d k - receiver and satellite code and phase hardware delays

λ - corresponding carrier wavelengthc - speed of lightε - random error or residual

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PPP Error Budget

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IGS Orbit and Clock Products

Real-Bme IGSOrbit
Clock< 10 cm0.15 ns

10-20 secs
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PPP Accuracy
Processing ModeEast

RMS (cm)NorthUp

Daily staBc<0.5<0.5<1Hourly staBc
Post-processed kinemaBc
Real-Bme kinemaBc~4~5<10~2~4<10~3~10<20

Note: Based on dual-frequency measurements

16How Good is PPP?

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How Good is PPP?
10 cm

30 min18

MulB-GNSS

GPS(32) + Glonass(24) + Galileo(26) + BeiDou(29) + IRNSS(7) + QZSS(4) + SBAS(13)MarengoSource: UNSWRMIT University

School of Science Spring Lectures 201719

Source:et al (2015)
RMITLiUniversity

School of Science Spring Lectures 201720

Key Points to Remember
PPP• Absolute posiBon• Global coverage• Precise orbits and clocks are indispensable• Iono error is canceled by using iono-freecombinaBon (DF) or esBmated by models (SF)• Cm-dm accuracy but with long convergence Bme

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Beneﬁts and LimitaBons of PPP
Limita.ons

Beneﬁts

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Primary ApplicaBons of PPPEngineering (commercial) and scien.ﬁc applica.ons

PPP is feasible for posiBoning and navigaBon in remote areas or regions oflow GNSS reference sta.ons

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PPP

GNSS Online Processing Services
1. CSRS-PPP: Canadian SpaBal Reference System, NaturalResources Canada
2. MagicGNSS: GMV
3. CenterPoint RTX: Trimble NavigaBon
4. GAPS: University of New Brunswick
5. APPS: Jet Propulsion Laboratory
6. SCOUT: Scripps Orbit and Permanent Array Center (SOPAC),
University of California, San Diego
7. AUSPOS: Geoscience Australia

8. OPUS: U.S. NaBonal GeodeBc Survey’s Online PosiBoning User
Baselines Service24

Work Example
Sta.on Informa.on• CUSV, Bangkok, Thailand• 1 December 2017 (1 day, 24 hours)• Dual-frequency, staBc processing
Online GNSS Processing Service(s)• CSRS-PPP• MagicGNSS• CenterPoint RTX• AUSPOS• GAPS

Compute and compare X, Y, Z coordinates of CUSV

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Work Example: Notes
1. Check RINEX ﬁle(s)• antenna• sampling rate

2. Upload and submit RINEX ﬁle(s)• CSRS-PPP (hops://webapp.geod.nrcan.gc.ca/geod/toolsouBls/ppp.php)• MagicGNSS (hops://magicgnss.gmv.com)• CenterPoint RTX (hop://trimblertx.com)• AUSPOS (hop://www.ga.gov.au/bin/gps.pl)• GAPS (hop://gaps.gge.unb.ca/submitbasic.php)
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Work Example: Notes
3. Assess the reports provided by the processingservices and note any warnings/errors
4. Collate and compare the coordinates• reference frame, e.g., ITRF (year and epoch)• cartesian, geodeBc or local, etc

5. Plot ΔX, ΔY, ΔZ

Make sure the coordinates arein the same reference frame !!

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Real-Bme PPP System
GNSS Satellites

GNSS Satellites

CommunicaBon/GNSS
Satellites

CorrecBons

ObservaBons
CorrecBons

CorrecBons

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Commercial PPP Services
Company

OmniSTARServices

CompanyServices

OmniSTAR HP

NavComStarFire

OmniSTAR G2
OmniSTAR XP

TrimbleC-Nav

C-NavC1

CenterPoint RTX

Apex 2RangePoint RTX

Apex

ViewPoint RTX

Fugro

C-NavC2

Veripos

Ultra 2

Starfix.G2+

Ultra

Starfix.G4

TerraStar-C

Starfix.G2

TerraStar

TerraStar-D

Starfix.XP2

Novatel

CORRECT (PPP)Starfix.HP

HemisphereAtlasNext GeneraBon GNSS/RNSS
Regional/Global Precise Posi.oning Service(s)Next generaBon GNSS/RNSS satellites augmentaBon signals, which
could be used for real-Bme PPP services

GLONASS

L31207.14?
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Real-time PPP Application:
Precision Agriculture•••

Rice farming: Nov 2014 – Feb 2015
Location: Jerilderie, NSW
Funded by Japan Ministry of Internal Affairs
and Communications• Japanese Partners:• Hitachi, Hitachi Zosen,Hitachi Solutions, JAXA,
Hokkaido University,Yanmar• Australian Partners:• CRCSI, Hitachi Australia,
Rice Research Australia,
SmartNet, CRK, PACA,
UNSW, UNE, RMIT

• Aim: Evaluate theperformance of QZSS-PPP

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Real-time PPP Application:
Mining and Construction••••

Mining: Aug 2016 – Sep 2016
LocaBon: Morewell, Victoria
Funded and supported by the CRCSI and JAXA
Australian Partners:– PosiBon Partners, Energy Australia, Victoria
government (DELWP)• Aim: Evaluate QZSS-PPP in mining applicaBons

Loca.on of Morwell coal mine site

Dozer used on mining opera.ons

Dozer opera.on pathReal-time PPP Application:
Auto-Driving Vehicle• Autonomous vehicle: Dec 2017
(on-going)• Location: Melbourne• Funded by the Australian andNew Zealand Governments• International Partners:• Lockheed Martin, Inmarsat andGMV• Local Partners:• Geoscience Australia, CRCSI,Bosch, VicRoads and RMIT

• Aim: Evaluate the performanceof PPP and its suitability forautonomous driving
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Useful References• Kouba J (2009) A Guide to using InternaBonal GNSS Service (IGS)
Products.
hops://kb.igs.org/hc/en-us/arBcles/201271873-A-Guide-to-Using-theIGS-Products.
• Silver M (2013) A Comparison of Free GPS Online Post-Processing
Services. GPS World.
hop://gpsworld.com/a-comparison-of-free-gps-online-postprocessing-services/• Choy S, Bisnath S, Rizos C (2017) Uncovering common misconcepBons
in GNSS Precise Point PosiBoning and its future prospect. Available todownload:
hops://www.ﬁg.net/resources/monthly_arBcles/2016/september_2016/Suelynn_etal_september_2016.pdf• Teunissen PJG, Montenbruck O (2017) Springer handbook of globalnavigaBon satellite systems. Springer handbooks, 1st ediBon. Springer
Berlin Heidelberg, New York.
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The Future?
RTK, NRTK, PPP, PPP-RTK
Commonlyused term
RTK

NRTK

Technically beYerterm

What does itmean?

EliminaBon ofDiﬀerenBal GNSS
most errors
orand
ObservaBon Space
EsBmaBon ofRepresentaBon (OSR)some errors

PPP
PPP-RTK

State Space
RepresentaBon (SSR)

EsBmaBon oferrors

What is thediﬀerence?
Only common
errors are
eliminatedCombinaBon ofeliminaBon andesBmaBon
Only some errors
esBmatedAlmost all errors
esBmated35

The Future?
RTK, NRTK, PPP, PPP-RTKMethod

What istransmiYed?

Ini.alisa.on .meAccuracy (horiz)

RTK/NRTK

CorrecBons persatellite and per(virtual) reference
staBon< 20 s~ 2 cm

PPP

§ Orbits§ Clocks> 40 min for ﬂoat

a few cm

PPP-AR§ Orbits§ Clocks§ Phase biases~ 30 mina few cm

PPP-RTK§ Clocks§ Orbits§ Phase biases§ Troposphere§ Ionosphere< 1 mina few cm36

Advantages• Rapid cm level accuracy like NRTK
• Transmission bandwidth lessdependent on the number ofsatellites (important when 4global systems are available)• Independent from individualreference staBon and satellites• Reduced inﬂuence of local errors,e.g. mulBpath• Scalable accuracy, i.e. diﬀerent
accuracy levels can be realized byusing only parts of the models,e.g., PPP, PPP-AR, PPP-RTK

Bandwidth needed forTransmission

PPP-RTK

Number of Satellites
RTK

PPP

PPP-RTK

Disadvantages• Needs local ground infrastructure asNRTK• Can not be applied globally• Method not yet widely accepted inpracBce• No standardised data formats
available yet (sBll in development)

Comparison NRTK, PPP and PPP-RTK
1Accuracy [m]DGNSS
PPP-RTK0.1

PPP

NRTK
0.01

0.001
0s1s1 min10 minTime to Positioning Solution

1h1d

Useful References• Wübbena G, Schmitz M, Andreas B (2005) PPP-RTK: Precise Point
PosiBoning Using State-Space RepresentaBon in RTK Networks. In: the18th InternaBonal Technical MeeBng of the Satellite Division (IONGNSS), Long Beach, California, 13-16 September. pp 2584-2594• Wübbena G et al (2016) SSR-Technologie für skalierbare GNSS Dienste
Prinzipien, Anwendungen, Standardisierung. In: INTERGEO, Hamburg,Germany, 11 October• Geng J, Teferle FN, Meng X, Dodson AH (2011) Towards PPP-RTK:Ambiguity resoluBon in real-Bme precise point posiBoning Advancesin Space Research 47:1664-1673 doi:10.1016/j.asr.2010.03.030• Choy S, Harima K (2018) Satellite Delivery of High Accuracy GNSS
Precise Point PosiBoning Service: An Overview for Australia. Journal ofSpaBal Science (accepted for publicaBon)
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