WORK EXAMPLE: ONLINE GNSS PROCESSING SERVICES
1. AIM:
The work example aims to introduce the various online (free) GNSS processing services,which could be used to derive accurate estimates of positions/coordinates on a global
reference frame.

2. DESCRIPTION:
You will be introduced to five (5) free online GNSS processing services to obtain
International Terrestrial Reference Frame (ITRF) 2014 coordinates in Cartesian format, X, Y,and Z.
The online GNSS processing services are:
1. CSRS-PPP: Canadian Spatial Reference System, Natural Resources Canada(https://webapp.geod.nrcan.gc.ca/geod/tools-outils/ppp.php)
2. MagicGNSS: GMV (https://magicgnss.gmv.com/)
3. CenterPoint RTX: Trimble Navigation (http://trimblertx.com)
4. GAPS: The University of New Brunswick (http://gaps.gge.unb.ca/submitbasic.php)
5. AUSPOS: Geoscience Australia (http://www.ga.gov.au/bin/gps.pl)
Follow the guidelines instructions provided online by the GNSS processing service providers.
Note that these services are free but some require registration, e.g., name, password etc.
Once all the details have been entered correctly, you could then submit the data forprocessing. The results will be sent back to you via email.

3. DATA:A sample GNSS RINEX data collected at Chulalongkorn University GNSS station inBangkok Thailand will be provided. The GNSS RINEX data was collected on 1 December
2017 over a one-day period (24 hours). The data was downloaded from the International
GNSS Service (IGS) ftp archive.
The IGS operates and maintains a large permanent network of GNSS CORS receivers which
can be used in geodetic surveys and processing.
RINEX stands for Receiver Independent Exchange Format and is the standard format which
all allows different types of GNSS receivers to be used together and also their data to beprocessed together, in all GNSS software. The RINEX format is particularly useful for GNSS
research and testing and contains important information required to calculate the GNSS
receivers’ position is included, with the exception of the satellite ephemeris.
Figure 1 shows an example of a RINEX (version 2.11) header for an IGS station, i.e.,
Melbourne Observatory. Each GNSS station has a unique 4-char ID. In the case of
Melbourne Observatory, the 4-char ID is MOBS. In the case of Chulalongkorn University
GNSS station, the 4-char ID is CUSV.
Understanding the file naming conventions in GNSS is important. The IGS recommend using
the following naming convention for RINEX files:
ssssdddf.yyt|| | | ||
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file type:
O: Observation file
N: GPS Navigation file
M: Meteorological data file
G: GLONASS Navigation file
L: Future Galileo Navigation file
H: Geostationary GPS payload nav mess file
B: Geo SBAS broadcast data file(separate documentation)
C: Clock file (separate documentation)
S: Summary file (used e.g., by IGS, not a standard!)
two-digit year
file sequence number/character within day
daily file: f = 0
hourly files:
f = a: 1st hour 00h-01h; f = b: 2nd hour 01h-02h;

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+------- ddd:|+----------- ssss:f = x: 24th hour 23h-24h
day of the year of first record
4-character station name designator

As examples, the RINEX file for:§Melbourne Observatory GNSS station on 17 February 2011 will be named as
MOBS0480.11O.

§Chulalongkorn GNSS station on 1 December 2017 will be named as CUSV3350.17O.

You could use interactive GNSS calendars, which are available online, e.g.,
http://www.gnsscalendar.com/, to convert dates in different formats.
Example:Friday, December 1, 2017 (UTC)
Julian Day Number:
Day of Year: 335
GPS Week:
1977
GPS Week Number:

2458088.5

19775

Figure 1: Example of a RINEX Version 2.11 file.

It is worth noting that most, if not all, of the online GNSS processing services accept RINEX
Version 2.11 files. However, the GNSS community is now moving towards RINEX Version
3 to accommodate multi-GNSS data. For more information on the file formats currently usedby the GNSS community, refer to https://igscb.jpl.nasa.gov/components/formats.html