extension of rtklib for the calculation and validation of

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

2

Content

● Why?Plans to introduce GPS based flight procedures in Hungary

● Compare RTKLIB to proprietary programs

● Application: flight validation at Debrecen airport

3

Rationale

4

EGNOS improves GPS over Europe

5

EGNOS improves GPS over Europe

6

EGNOS improves GPS over Europe

7

EGNOS improves GPS over Europe

8

EGNOS improves GPS over Europe

9

Accuracy

Standalone GPS GPS with EGNOS corrections

EGNOS monitor station at BME

www.agt.bme.hu/egnosAircraft moving in 3D?

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

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

12

Variance includesσi

2=σi , flt2 +σ i ,iono

2 +σ i , air2 +σ i ,tropo

2

13

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

14

Software to calculate PL

● Eurocontrol: Pegasus

● GMV: magicGemini

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

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

17

What is Cat. I – II – III?

18

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

19

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

20

1st reason: Some of the measurements are filtered out

21

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

22

Airborne variance

23

Largest component: Ionosphere

24

Ionosphere grid models

25

IPP positions all measurements during a 24 hour session at Budapest

26

IPP positions Large ionosphere variance differences!

(RTKLIB vs. mGemini)

27

Range and Integrity Monitor Stations (RIMS)

28

Flight validation at Debrecen airport

12/1

3th J

uly

2016

29

PL during flight validation

On a permanent station close to the airport

On the aircraft

30

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

31