RINEX files contain GPS data collected at receiver stations in an open format to allow for processing using different software. There are three main types of RINEX files - observation data files containing GPS measurements, navigation message files containing ephemeris data, and meteorological files. GAMIT and GLOBK are widely used open source software for processing and combining GNSS data. GAMIT analyzes GPS data to estimate parameters like station positions and satellite orbits through least squares estimation. GLOBK combines solutions from different techniques like GPS, SLR, VLBI using their parameter estimates and covariance matrices.

1. GNSS data Processing
Kutubuddin ANSARI
kutubuddin.ansari@ikc.edu.tr
GNSS Surveying, GE 205
Lecture 8, May 17, 2016

2. GNSS data Processing Files

3. 3
RINEX
• Receiver Independent Exchange Format
• Developed by the Astronomical Institute of the
University of Berne in 1989
• For the easy exchange of the GPS data to be collected
• For processing in various software

4. • Consists of 3 ASCII file types available to be
downloaded from Satellite Reference System
File Type
Containing
Information
Observation Data File GPS Measurements
GPS Navigation
Message File
Ephemeris
(Orbit information)
Meteorological Data File
Pressure, Temperature,
Relative Humidity, etc
RINEX

5. RINEX FILES
RINEX is a generic term - it refers to a kind of data format. It is
ALWAYS ascii
o: Observation
d: Observation (compressed)
n: Navigation file
m: Meteorological data file
g: GLONASS Navigation file
h: Geostationary GPS payload nav mess file
b: Geostationary GPS payload broadcast data
c: Clock files

6. Header
Section
RINEX

7. Data
Section
RINEX

8. L1 : Phase measurements on L1
L2 : Phase measurements on L2
P1 : Pseudorange using P-Code on L1
P2 : Pseudorange using P-Code on L2
C1 : Pseudorange using C/A code on L1
S1 and S2: Signal to noise ratio (SNR)
RINEX

9. RINEX
Top line is year, month, day, hour, minute, second

10. Then number of satellites and their names. G means GPS, R is Glonass,
and M is Galileo. If there is no letter, it means it is a GPS satellite.
In this example, there are 9 satellites. They are all GPS satellites.
RINEX

11. These are the data for PRN 29. Remember the first two columns are
phase (L1 and L2) and then P1, P2, and C1. Last are S1 and S2.
RINEX

12. Navigation File
• Data computed for Satellite Position
• Satellite Motion is described by Satellite Orbit
• Satellite Orbit is described by 6 (Keplerian)
Elements

13. • Define satellite position in the satellite orbit – v
• Define size and shape of the satellite orbit - a, e
• Define the orientation of the satellite orbit – ωω
• Define the orbital plane in the equatorial system - ΩΩ, I
v True Anomaly
aa Semi-major axis of ellipse
ee Eccentricity
II Inclination of the orbit
ΩΩ Right ascension of the ascending node
ωω Argument of perigee
Navigation File: Satellite Orbit

14. Satellite
focus
earth
a
e
• semi-major axis, a : Size of Orbit
• eccentricity, e : Shape of Orbit
PerigeeApogee
• position vector, r
r
ν
• true anomaly, ν
Satellite Position
Navigation File: Satellite Orbit

15. Navigation File: Satellite Position

16. Navigation File: Satellite Position

17. i
e Ω
ω
v (mean)
√a
Navigation File

18. GNSS data Processing
Software

19. GAMIT
GPS Analysis at Massachusetts Institute
of Technology

20. Basic framework: GAMIT
GAMIT: Series of programs that analyze GPS phase
data to estimate parameters:
 Station positions (coordinates)
Satellite orbital parameters
Earth orientation parameters (EOP)
Atmospheric delay parameters
Carrier phase ambiguities

21. GAMIT History
• Development started in late 1970s when MIT was
building GPS receivers
• Code derived from 1960-1970 planetary ephemeris
and VLBI software
• Ported to Unix in 1987
• Start of IGS in 1992 prompted development of
automatic processing schemes
• Fully automatic processing mid-1990s including
continuous stations and campaign GPS
measurements

22. Data Types
 L1 and L2 phase
• used for parameter estimation
 P1 and P2 range measurements
• used to help clean phase data
• used to estimate receiver clock offset with
acceptance of 1 microsecond (= 300 m)
 Phase data
• proportional to geometric range
• sensitive to ionospheric delay
• linear combination of L1 and L2

23. Major steps for GAMIT
• Calculates theoretical (modeled) phase
• Partial derivatives of phase w.r.t. parameters
• Cleans GPS data and repairs cycle slips
• Estimates parameters via least squares
• Calculates goodness of fit
• Integrates GPS satellite orbits

24. Files needed for processing
• Broadcast ephemeris from receivers
• Rinex file
• SP3 orbit files from IGS
• Earth Orientation Parameters (EOP) files
• Satellite clock files (J-files)
• Ocean tide files
• Models for GPS antenna phase center
• Satellite information files
• Leap-second file

25.  Moon and Sun ephemerides
• orbit integration
• solid Earth tides
 Information about stations
• prior (approximate) estimates of coordinates
• receiver and antenna types
• antenna heights
Files needed for processing

26. GLOBK
(Global Kalman filtering software)

27. Basic framework: GLOBK
GLOBK combines solutions from GPS, SLR, & VLBI
data via their parameter estimates and full covariance
matrices to estimate other parameters:
– Site velocities
• temporal derivative of position in mm/yr
• requires a time series of measurements
– Satellite orbit adjustments
– EOP parameters
– Others parameters, e.g., co-seismic displacements

28. GLOBK History
• Suite of programs
• Written in mid-1980s to handle combination of VLBI
data
• Extended in 1989 to handle GPS results: GAMIT
modified to output needed files
• 1990's: Extensions to handle SLR data

29. Required files
• binary h-files generated by htoglb from:
– GAMIT h-files (ASCII),
• command files
– very flexible, key-word structure

30. Optional files
• Orbit files
• EOP
• Earthquake/rename definitions
• Apriori coordinate and motion files

31. GLOBK documentation
• Available as PDF, PS and RTF files
• Nearly all modules in GLOBK suite have up-to-date
documentation on-line
• To get help for a command, type its name alone on
the command line.

32. Differences between GAMIT and GLOBK
• GAMIT operations and files are rigid; GLOBK uses
flexible formats and is used in many different ways
• GAMIT tends to stop if a problem is encountered
(less so these days); GLOBK tries to continue as far
as it can by defaulting values
• Pros/Cons: GAMIT stops can be frustrating; GLOBK
may appear to work but might generate erroneous
results.

33. • Basic aim of GAMIT is to generate positions/orbits
for one day of data. Standard product of GAMIT is a
minimally constrained solution
• GLOBK flexibly combines minimally constrained
parameter estimates from one or more measurement
types (GPS, SLR, VLBI, DORIS)
Differences between GAMIT and GLOBK

34. Getting GAMIT/GLOBK
• Free for research/non-commercial license
• Fortran Source code
• Executables for HP, Solaris and Linux