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Technical Impact of Multiple GNSS on Applications
Professor Gethin Wyn Roberts
Dr. Lawrence Lau
Dr. Craig Hancock
University of Nottingham
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Overview
• Discrepancy among the GNSS Reference Frames
• Discrepancy among the GNSS Reference Time Systems
• Impact on the Mainstream Applications (i.e., SPP)
• Impact on the Land/Engineering Surveying Applications (i.e., RTK
including NRTK)
• Impact on the Standalone/Remote Precise Positioning Applications (i.e.,
Precise Point Positioning - PPP)
• Summary and Discussion
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Discrepancy between ITRF and GNSS reference frames• Discrepancy between ITRF2000 and WGS84 (G1150): “two reference frames are
essentially identical with differences being statistically insignificant for most applications“
(NGA, 2003), ~1-2cm (Slater, J.A. - NGIA) -> WGS84(G1674): sub-cm?
– Diff. ITRF2000/ITRF2005 < diff. ITRF2000/WGS84
• Discrepancy between ITRF2005 and GTRF: sub-mm
• Discrepancy between ITRF2000 and PZ90.02 (introduced 20 Sept 2007): No
rotation, dX:-36cm, dY: 8 cm, dZ:18cm (Ørpen, 2008)
• Discrepancy between ITRF2000 and CGCS 2000: +/- 3 cm or less (Cheng, et.
al.,2009)?
CHENG P., et. al. (Chinese Academy of Surveying and Mapping), China Geodetic Coordinate System 2000, Eighteenth United Nations Regional Cartographic Conference for Asia and the Pacific Bangkok, 26-29 October 2009
US National Geospatial Intelligence Agency (NGA), Addendum to NIMA TR 8350.2: Implementation of the World Geodetic System 1984 (WGS 84) Reference Frame G1150, 2003.
O. Ørpen (Fugro Seastar), GNSS Status, Havbunnskartlegging og Inspeksjon, Geilo 6-8 Feb. 2008
4 of 23
GNSS Reference Time Systems
• GGTO specified requirement of 5 ns, 2 sigma over 24 hour (Hahn & Powers, 2005) –>
too challenging
• “Error of determining GLONASS Time/GPS Time is no more than 20 ns” (RIRT)
• GPS Time & Beidou Time (BDT) -> GBTO: 20 ns or better?
J. Hahn & E. Powers, 2005, “Implementation of the GPS to Galileo Time Offset (GGTO),” in Proceedings of the 2005 Joint IEEE International Frequency Control Symposium and Precise Time and Time Interval (PTTI) Systems and Applications Meeting, 29-31 August 2005, Vancouver, Canada (IEEE 05CH37664C), pp. 33-212.
Russian Institute of Radionavigation and Time (RIRT), Complementarity of GNSS Regarding System Time Scales, www.oosa.unvienna.org/pdf/icg/2009/workgroupinterop2/08.pdf
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Single Point Positioning (SPP) - Mass Market applications
(X,Y,Z)WGS84
T0GPST
Transit time
(X,Y,Z)WGS84
R RT t→ ∆
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Single Point Positioning/Navigation solution
( ) ( ) ( )
( ) ( ) ( )
( ) ( ) ( )
( ) ( ) ( )
1 1 1
1 1 1
2 2 2
2 2 2
3 3 3
3 3 3
S S S
R R R
S S S
R R R
S S S
R R R
S S S
R R R
S S S
R R R
S S S
R R R
Sn Sn Sn
R R R
Sn Sn Sn
R R R
X X Y Y Z Zc
X X Y Y Z Zc X
YAx lX X Y Y Z Z
Zc
t
X X Y Y Z Zc
ρ ρ ρ
ρ ρ ρ
ρ ρ ρ
ρ ρ ρ
− − − − − −
− − − − − − ∆
∆ = = − − − ∆ − − − ∆
− − − − − −
M M M M
1,( ( ) )
k k k k k k
i i i i i il P t t c I Tρ δ δ ε= − + − + + + X n
7 of 23
Single Point Positioning (SPP) - Mass Market applications
(X,Y,Z)WGS84
T0GPST
Transit time
(X,Y,Z)WGS84
R RT t→ ∆
T0GST
(X,Y,Z)GTR
F
(X,Y,Z)GTR
F
8 of 23
Single Point Positioning (SPP) - Mass Market applications( ) ( ) ( )
( ) ( ) ( )
( ) ( ) ( )
( ) ( ) ( )
( ) ( ) ( )
1 1 1
1 1 1
1 1 1
1 1 1
1 1 1
1 1 1
0 0
0 0
0 0
0 0
0 0
G G G
R R R
G G G
R R R
G n G n G n
R R R
G n G n G n
R R R
E E E
R R R
E E E
R R R
E n E n E n
R R R
E n E n E n
R R R
B B B
R R R
B B B
R R R
X X Y Y Z Zc
X X Y Y Z Zc
X X Y Y Z Zc
A x
X X Y Y Z Zc
X X Y Y Z Zc
ρ ρ ρ
ρ ρ ρ
ρ ρ ρ
ρ ρ ρ
ρ ρ ρ
− − −− − −
− − −− − −
− − −− − −
=
− − −− − −
− − −− − −
M M M M M M
M M M M M M
M M M M M
( ) ( ) ( )
,
,
,
0 0
R
R
R
R G
R E
R B
B n B n B n
R R R
B n B n B n
R R R
X
Y
Z
t
t
t
X X Y Y Z Zc
ρ ρ ρ
∆ ∆ ∆
∆ ∆
∆ − − − − − −
M One freq. only!, more..
1,( )
k k k k k k
i i i i i iP t t c I Tρ δ δ ε= + − + + +
9 of 23
Single Point Positioning (SPP) - Mass Market applications
• GNSS time offsets
– Can be “aligned” by applying the broadcast GxTO
– Estimate in user level
• GNSS reference frames
– Can be neglected
– Can be mitigated by applying given transformation parameters
• Satellite coordinates
• User position
(Recommended!!)
10 of 23
Single Point Positioning (SPP) - Mass Market applications( ) ( ) ( )
( ) ( ) ( )
( ) ( ) ( )
( ) ( ) ( )
( ) ( ) ( )
1 1 1
1 1 1
1 1 1
1 1 1
1 1 1
1 1 1
0 0
0 0
0 0
0 0
0 0
G G G
R R R
G G G
R R R
G n G n G n
R R R
G n G n G n
R R R
E E E
R R R
E E E
R R R
E n E n E n
R R R
E n E n E n
R R R
B B B
R R R
B B B
R R R
X X Y Y Z Zc
X X Y Y Z Zc
X X Y Y Z Zc
A x
X X Y Y Z Zc
X X Y Y Z Zc
ρ ρ ρ
ρ ρ ρ
ρ ρ ρ
ρ ρ ρ
ρ ρ ρ
− − −− − −
− − −− − −
− − −− − −
=
− − −− − −
− − −− − −
M M M M M M
M M M M M M
M M M M M
( ) ( ) ( )
,
,
,
0 0
R
R
R
R G
R E
R B
B n B n B n
R R R
B n B n B n
R R R
X
Y
Z
t
t
t
X X Y Y Z Zc
ρ ρ ρ
∆ ∆ ∆
∆ ∆
∆ − − − − − −
M
1,( ( ) )
k k k k k k
i i i i i il P t t c I Tρ δ δ ε= − + − + + +
User estimates
IFB/ICB?
Use GxTO
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Relative Positioning - Land/Engineering surveying
(X,Y,Z)WGS84
T0GPST
(X,Y,Z)rov,WGS84(X,Y,Z)ref,WGS84
,ref GPSTt∆
,ref GPSTt∆ ,rov GPSTt∆,rov GPST
t∆
12 of 23
Relative Positioning - Land/Engineering surveying
1, 1 1, 1,
kl kl kl kl kl kl
ij ij ij ij ij ijI T Nρ λ εΦ = − + + +
2
2, 1 2 2 2, 2,( / )
kl kl kl kl kl kl
ij ij ij ij ij ijf f I T Nρ λ εΦ = − + + +
2
5, 1 5 5 5, 5,( / )
kl kl kl kl kl kl
ij ij ij ij ij ijf f I T Nρ λ εΦ = − + + +
1 GNSS, 3 Freq.
Medium/Short baselines
1, 1 1, 1,
kl kl kl kl
ij ij ij ijNρ λ εΦ = + +
2, 2 2, 2,
kl kl kl kl
ij ij ij ijNρ λ εΦ = + +
5, 5 5, 5,
kl kl kl kl
ij ij ij ijNρ λ εΦ = + +
1, 1 1, 1,( )
kl kl kl kl
ij ij ij ijl Nρ λ ε= Φ − + +
13 of 23
Relative Positioning - Land/Engineering surveying
(X,Y,Z)WGS84
T0GPST
(X,Y,Z)rov,WGS84?(X,Y,Z)ref,WGS84?
(X,Y,Z)GTRF
T0GST
,ref GSTt∆,rov GSTt∆
,rov GPSTt∆
,ref GPSTt∆
14 of 23
Relative Positioning - Land/Engineering surveying
(X,Y,Z)WGS84
T0GPST
(X,Y,Z)rov,WGS84?(X,Y,Z)ref,WGS84?
(X,Y,Z)GTRF
T0GST T0GPST
(X,Y,Z)WGS84
,ref GPSTt∆
,rov GPSTt∆
,rov GSTt∆,ref GST
t∆
,ref GSTt∆
,rov GSTt∆
,rov GPSTt∆,ref GPSTt∆
T0GST
(X,Y,Z)GTRF
1, 1 1, 1,( )
kl kl kl kl
ij ij ij ijl Nρ λ ε= Φ − + +
Single difference + models
15 of 23
Relative Positioning - Land/Engineering surveying( ) ( ) ( ) ( ) ( ) ( )
( ) ( ) ( ) ( ) ( ) ( )
( ) ( ) ( ) ( )
2 1 2 1 2 1
2 1 2 1 2 1
1 1 1
1 1 1
2 1 2 1
2 1 2
0 0 0 0 0 0
0 0
0 0 0 0 0 0
G G G G G G
R R R R R R
G G G G G G
R R R R R R
Gn G Gn G Gn G
R R R R R R
Gn G Gn G Gn G
R R R R R R
E E E E
R R R R
E E E E
R R R R
X X X X Y Y Y Y Z Z Z Z
X X X X Y Y Y Y Z Z Z Z
X X X X Y Y Y Y
Ax
λρ ρ ρ ρ ρ ρ
λρ ρ ρ ρ ρ ρ
ρ ρ ρ ρ
− − − − − −− − −
− − − − − −− − −
− − − −− −
=
L L
M M M O M O M M O M
L L
( ) ( )
( ) ( ) ( ) ( ) ( ) ( )
( ) ( ) ( ) ( ) ( ) ( )
2 1
1 2 1
1 1 1
1 1 1
2 1 2 1 2 1
2 1 2 1 2 1
0 0 0 0 0 0
0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0
E E
R R
E E
R R
En E En E En E
R R R R R R
En E En E En E
R R R R R R
B B B B B B
R R R R R R
B B B B B B
R R R R R R
Z Z Z Z
X X X X Y Y Y Y Z Z Z Z
X X X X Y Y Y Y Z Z Z Z
X
λρ ρ
λρ ρ ρ ρ ρ ρ
λρ ρ ρ ρ ρ ρ
− −−
− − − − − −− − −
− − − − − −− − −
L L
M M M M O M O M O M
L L
L L
M M M M O M M O M O
( ) ( ) ( ) ( ) ( ) ( )
2 1
1
2 1
1
2 1
1
1 1 1
1 1 10 0 0 0 0 0
R
R
R
G G
R
GnG
R
E E
R
EnE
R
B B
R
BnB
R
Bn B Bn B Bn B
R R R R R R
Bn B Bn B Bn B
R R R R R R
X
Y
Z
N
N
N
N
N
N
X X X Y Y Y Y Z Z Z Zλ
ρ ρ ρ ρ ρ ρ
∆ ∆ ∆ − − − − − − − − −
M
M
M
L L
16 of 23
Relative Positioning - Land/Engineering surveying
Intraplate earthquake and other local deformation such as subsidence and landslides!!
e.g., 10 cm/year
Ref. station
Rover
17 of 23
Relative Positioning - Land/Engineering surveying
Intraplate earthquake and other local deformation such as subsidence and landslides!!
e.g., 10 cm/year
NRTK stations
VRS
Rover
18 of 23
Precise Point Positioning (PPP) Standalone/remote precise positioning applications
(X,Y,Z)ITRF
T0GPST?
(X,Y,Z)ITRF
R RT t→ ∆ + High-precision carrier-phase data
+ Precise ephemeris
19 of 23
Precise Point Positioning (PPP) Standalone/remote precise positioning applications
,( )
k k k k k k
i i i i i i PP t t c I Tρ δ δ ε= + − + + + ,
( )k k k k k k k
i i i i i i it t c I T Nρ δ δ λ ε ΦΦ = + − − + + +
,0
k k k
P i i i P if c t MF ZTD Pρ δ ε= + + + − =�,
0k k k k
i i i i if c t MF ZTD Nρ δ λ εΦ Φ= + + + + − Φ =�
Iono-free Iono-free
20 of 23
Precise Point Positioning (PPP) Standalone/remote precise positioning applications( ) ( ) ( )
( ) ( ) ( )
( ) ( ) ( )
( ) ( ) ( )
1 1 1
1
11 1 1
1
1 1 1
1
11 1 1
0 0 0 0 0
0 0
0 0 0 0 0
0 0 0 0 0
0 0
G G G
R R R G
R LG G G
R R R
Gn Gn Gn
R R R Gn
R LGn Gn Gn
R R R
E E E
R R R E
R LE E E
R R R
En En En
R R R
En En
R R
X X Y Y Z Zc MF
X X Y Y Z Zc MF
X X Y Y Z Zc MF
X X Y Y Z Z
Ax
λρ ρ ρ
λρ ρ ρ
λρ ρ ρ
ρ ρ
− − −− − −
− − −− − −
− − −− − −
− − −− − −
=
L
M M M M M M O M O M
L
L
M M M M M M M O M O
( ) ( ) ( )
( ) ( ) ( )
( ) ( ) ( )
( ) ( )
1
1 1 1
1
1 1 1
1 1 1
1
1 1 1
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
En
R LEn
R
G G G
R R R G
RG G G
R R R
Gn Gn Gn
R R R Gn
RGn Gn Gn
R R R
E E E
R R R E
RE E E
R R R
En En
R R
En
R
c MF
X X Y Y Z Zc MF
X X Y Y Z Zc MF
X X Y Y Z Zc MF
X X Y Y
λρ
ρ ρ ρ
ρ ρ ρ
ρ ρ ρ
ρ ρ
− − −− − −
− − −− − −
− − −− − −
− −− −
L
L L
M M M M M M M O M M O M
L L
L L
M M M M M M M O M M O M
( )
,
,
1
1
0 0 0 0 0
R G
R E
G
R
Gn
R
E
R
En
R
En
R En
REn En
R R
X
Y
Z
t
t
ZTDl
N
N
N
N
Z Zc MF
ρ
∆ ∆ ∆ ∆ ∆ =
− −
M
M
L L
Phase
PR
21 of 23
Precise Point Positioning (PPP) Standalone/remote precise positioning applications
• Site displacement effects
– Solid Earth tides
– Ocean loading
– Sub-daily Earth Rotation Parameters (i.e. Pole position Xp, Yp and UT1-UTC)
• Satellite attitude effects
– Satellite antenna offset
– Phase wind-up correction
• IFB/ICB
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Summary and Discussion
• Transform all GNSS reference frames to a reference frame
• Align all GNSS reference time to a reference time
• Multiple GNSS Benefits and Residuals
– SPP
• Reference frames
• Reference time
– Relative positioning
• Reference frames
• Reference time
– PPP
• Reference frames
• Reference time
23 of 23
END
Thank you for your attention
24 of 23
Local Datum
• Difference to Local Datum
– depends on the time of synchronization with ITRF or other GNSS reference frames
• Tectonic movement of the corresponding plate
• Preferably there is a set of transformation parameters between the national datum and
the selected GNSS reference frame
Recommended