1) The document discusses extending the open source RTKLIB software to calculate and validate protection levels for GPS-based flight procedures in Hungary. 2) It compares the protection level calculations from RTKLIB to proprietary programs like Pegasus and magicGemini, finding differences due to filtered measurements and variances. 3) As a case study, it describes calculating protection levels during a flight validation at Debrecen airport in Hungary.

1. 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
1
Budapest University of Technology and Economics,
Department of Geodesy and Surveying
2
GeoForAll Lab at Budapest
3
Hungarocontrol, Hungarian Air Navigation Service Provider

2. 2
Content
● Why?
Plans to introduce GPS based flight
procedures in Hungary
● Compare RTKLIB to proprietary
programs
● Application: flight validation at Debrecen
airport

3. 3
Rationale

4. 4
EGNOS improves GPS over Europe

5. 5
EGNOS improves GPS over Europe

6. 6
EGNOS improves GPS over Europe

7. 7
EGNOS improves GPS over Europe

8. 8
EGNOS improves GPS over Europe

9. 9
Accuracy
Standalone GPS GPS with EGNOS corrections
EGNOS monitor station
at BME
www.agt.bme.hu/egnosAircraft moving in 3D?

10. 10
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

11. 11
Protection level (PL) calculation
HPL=K H⋅dmajor
VPL=KV⋅dU
KH =6.00
KV=5.33
dmajor=
√deast
2
+dnorth
2
2
+
√deast
2
−dnorth
2
2
+dEN
2
D=
[
deast
2
dEN dEU dET
dEN dnorth
2
dNU dNT
dEU dNU dU
2
dUT
dET dNT dUT dt
2 ]=(G
T
WG)
−1Gi
T
=
[
cos(Eli)⋅cos( Azi)
cos(Eli)⋅sin( Azi)
sin(Eli)
1
]W−1
=
[
σ1
2
0 … 0
0 σ2
2
… 0
⋮ ⋮ ⋱ ⋮
0 0 ⋯ σn
2]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”
σi
2
=σi, flt
2
+σi,iono
2
+σi, air
2
+σi,tropo
2

12. 12
Variance includes
σi
2
=σi, flt
2
+σi,iono
2
+σi, air
2
+σi,tropo
2

13. 13
Variance includes
● Fast and long
term correction
● Ionospheric delay
● Tropospheric
delay
● Airborne error
σi
2
=σi, flt
2
+σi,iono
2
+σi, air
2
+σi,tropo
2

14. 14
Software to calculate PL
● Eurocontrol: Pegasus
● GMV: magicGemini

15. 15
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

16. 16
PL calculated by different programs
RTKLIB-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

17. 17
What is Cat. I – II – III?

18. 18
PL calculated by different programs
RTKLIB-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

19. 19
Data processing scheme
GPS+SBAS
raw data
pos and range
output files
gawk scripts CSV files
sql scripts
in psql
text files
GNUplot QGISPEGASUSmagicGemini
rnx2rtkp
(RTKLIB)
output
messages
trace output

20. 20
1st
reason: Some of the
measurements are filtered out

21. 21
2nd
reason: Differences of variances
magicGemini vs.
RTKLIB
Pegasus 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

22. 22
Airborne variance

23. 23
Largest component: Ionosphere

24. 24
Ionosphere grid models

25. 25
IPP positions
all measurements during a 24 hour session at Budapest

26. 26
IPP positions
Large ionosphere variance differences!
(RTKLIB vs. mGemini)

27. 27
Range and Integrity Monitor
Stations (RIMS)

28. 28
Flight validation at Debrecen airport
12/13th
July2016

29. 29
PL during flight validation
On a permanent station close
to the airport
On the aircraft

30. 30
To sum it up
● Open source SW compared to proprietary
https://github.com/zsiki/RTKLIB/tree/rtklib_2.4.3
● Protection levels
● Reason behind the differences

31. 31