Paris, Marne-La-Vallée, 20th July 2017
Extension of RTKLIB for the calculation and validation of protection levels
Bence TAKÁCS1,2, Zoltán SIKI1,2, Rita MARKOVITS-SOMOGYI3
1Budapest University of Technology and Economics, Department of Geodesy and Surveying
2GeoForAll Lab at Budapest
3Hungarocontrol, Hungarian Air Navigation Service Provider
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Content
● Why?Plans to introduce GPS based flight procedures in Hungary
● Compare RTKLIB to proprietary programs
● Application: flight validation at Debrecen airport
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Rationale
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EGNOS improves GPS over Europe
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EGNOS improves GPS over Europe
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EGNOS improves GPS over Europe
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EGNOS improves GPS over Europe
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EGNOS improves GPS over Europe
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Accuracy
Standalone GPS GPS with EGNOS corrections
EGNOS monitor station at BME
www.agt.bme.hu/egnosAircraft moving in 3D?
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Integrity protection cylinder
Source: http://www.gps.gov/technical/ps/2008-WAAS-performance-standard.pdf
Protection level cylinder: VPL and HPL
Vertical and Horizontal Alert Limit cylinder are defined by the phase of flight
The aircraft's true position: not known
The aircraft's calculated position based on the EGNOS corrections is the center of cylinder
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Protection level (PL) calculation
HPL=K H⋅dmajor
VPL=K V⋅dU
KH=6.00KV=5.33
dmajor=√ deast2
+dnorth2
2+√ deast
2−dnorth
2
2+dEN
2
D=[deast
2 d EN d EU dET
d EN dnorth2 dNU d NT
dEU dNU dU2 dUT
dET d NT dUT dt2 ]=(GT WG)
−1GiT=[
cos(El i)⋅cos (Azi)
cos(El i)⋅sin(Azi)
sin(El i)1
]W−1=[
σ12 0 … 0
0 σ22
… 0⋮ ⋮ ⋱ ⋮
0 0 ⋯ σn2]
Inverse of the weight matrix
variance of ith satellite has 4 components
Geometry matrix
Factor bounding users horizontal / vertical position with a probability of 10-9 / 0.5 x 10-7
Horizontal and vertical protection level
Variance/covariance matrix
Source: RTCA MOPS DO-229-C “Minimum Operational Performance Standards for Global Positioning System/Wide Area Augmentation System airborne equipment”
σi2=σi , flt
2 +σ i ,iono2 +σ i , air
2 +σ i ,tropo2
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Variance includesσi
2=σi , flt2 +σ i ,iono
2 +σ i , air2 +σ i ,tropo
2
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Variance includes
● Fast and long term correction
● Ionospheric delay● Tropospheric
delay● Airborne error
σi2=σi , flt
2 +σ i ,iono2 +σ i , air
2 +σ i ,tropo2
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Software to calculate PL
● Eurocontrol: Pegasus
● GMV: magicGemini
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Open source solution: RTKLIB
● RTKLIB – SBAS positioning mode
– no PL calculation
● Houghton Assoc Inc. fork of RTKLIB– PL calculation available
● Our enhanced version– https://github.com/zsiki/RTKLIB/
tree/rtklib_2.4.3
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PL calculated by different programsRTKLIB-mGemini RTKLIB-pegasus
∆HPL [m]
∆VPL [m]
∆HPL [m]
∆VPL [m]
min -0.86 -1.65 -1.18 -1.85
max +1.68 +1.66 +1.57 +1.40
mean -0.08 -0.14 -0.32 -0.55
std. dev. ±0.18 ±0.24 ±0.21 ±0.28
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What is Cat. I – II – III?
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PL calculated by different programsRTKLIB-mGemini RTKLIB-pegasus
∆HPL [m]
∆VPL [m]
∆HPL [m]
∆VPL [m]
min -0.86 -1.65 -1.18 -1.85
max +1.68 +1.66 +1.57 +1.40
mean -0.08 -0.14 -0.32 -0.55
std. dev. ±0.18 ±0.24 ±0.21 ±0.28
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Data processing scheme
GPS+SBAS raw data
pos and rangeoutput files
gawk scripts CSV filessql scripts
in psql
text files
GNUplot QGISPEGASUSmagicGeminirnx2rtkp(RTKLIB)
output messages trace output
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1st reason: Some of the measurements are filtered out
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2nd reason: Differences of variancesmagicGemini vs.
RTKLIBPegasus vs.
RTKLIB
differences of fast and long term correction variance [m]
minimum -2.14 +0.04
maximum +2.42 +0.29
mean +0.09 +0.13
std. dev. ±0.04 ±0.04
differences of airborne variance [m]
minimum -0.18 0.00
maximum 0.00 0.00
mean -0.15 0.00
std. dev. ±0.04 0.00
differences of ionospheric delay variance [m]
minimum -26.23 -26.23
maximum +10.47 +0.22
mean -0.02 -0.02
std. dev. ±0.41 ±0.38
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Airborne variance
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Largest component: Ionosphere
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Ionosphere grid models
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IPP positions all measurements during a 24 hour session at Budapest
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IPP positions Large ionosphere variance differences!
(RTKLIB vs. mGemini)
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Range and Integrity Monitor Stations (RIMS)
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Flight validation at Debrecen airport
12/1
3th J
uly
2016
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PL during flight validation
On a permanent station close to the airport
On the aircraft
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To sum it up
● Open source SW compared to proprietaryhttps://github.com/zsiki/RTKLIB/tree/rtklib_2.4.3
● Protection levels● Reason behind the differences
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