UTOKYO/ICG Training on
Global Navigation Satellite Systems (GNSS)
12-16 February 2024

GNSS Software and Data Formats
Avinab Malla
Institute of Engineering, Tribhuvan University

Software
Receiver Configuration and Logging• U-Center• Septentrio Rxtools
Data Processing• RTKLIB
MADOCA PPP• MAD-WIN

GNSS Sample Data
• StaticData• F9P_181215_static.ubx : Rover raw observation file
• NetR9_181215_static.binex: Base station raw file
• BaseStationPosition.txt : Position of base station• PPP.conf: RTKLIB configuration file for PPP• PPP_correction: Correction data for PPP• DynamicData• ECJ02_base.ubx: Base station raw observation file
• F9P_dynamic_rover.ubx: Rover raw observation file
• RTK.conf: RTKLIB configuration file for RTK• BaseStationPosition.txt : Position of base station

All these sample data are prepared by researchers at TUMSAT (Tokyo University of Marine Science and Technology)

National Marine Electronics Association (NMEA) Format• NMEA 0183 (National Marine Electronics Association) is format to output
measurement data from a sensor in a pre-defined format in ASCII• Contains GNSS Position, velocity, time, accuracy and satellite information• Generally output by Rover devices. Most GNSS Receivers support NMEA output• Can be used as a data processing output format.

NMEA Format$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47
Message Contents
Message Type
Talker ID (GN: GNSS, GP: GPS, GL: GLONASS…)
Different NMEA Message Types contain different types of GNSS information• RMC: 2D Position, Date/Time, Speed, Heading• GGA: 3D Position(Lat/Lon), Time, Fix Quality, DOP, DGPS status• GSA: Active Satellites• GSV: Satellites in view, Azimuth, Elevation, SNR• GST: Estimated accuracy

ChecksumProprietary Receiver Formats• Most receivers can output RAW data in proprietary binary formats.
• Format depends on receiver module manufacturer.
• u-blox: UBX• Septentrio: SBF• Contains many additional information• GNSS Measurements: Pseudorange, Carrier Phase• Navigation messages for computing satellite positions• Computed position, satellite positions and signal strengths• Can be streamed real time or recorded for post-processing• Data format can be openly available or restricted depending on manufacturer• Often mixed with NMEA dataUBX Raw Data File
StaticData/F9P_181215_static.ubx

NMEAu-blox Binary Data

RINEX: Receiver Independent Exchange Format• Exchange format for raw satellite data among different types of receivers.

• Used to process data from receivers made by different manufacturers• Contains raw satellite data (Pseudorange, Carrier phase, Doppler, satellite
orbits). No position data.
• Two types of files in common use• Observation File (*.yyO, *.obs): Contains measurements• Navigation File(*.yyP, *.yyN, *.nav): Contains satellite orbits• Frequently used for post-processing GNSS data

RINEX 3 Mixed Observation FileRINEX Navigation File

RTCM : Radio Technical Commission for Maritime Services• An internationally accepted data transmission standard for base-station datatransmission• The standards are defined and maintained by RTCM SC-104.
• Provides GNSS Raw Data in compressed format that can be used as DGPS or RTKCorrections• Output by GNSS Base stations, must be transmitted to rover device in real-timefor RTK.

RTCM 3 Message Types• MT 1-100 : Experimental Messages• MT 1001 –1230 : GNSS Messages• MT 4001 –4095 : Proprietary Messages

RTCM 3.2 Multi Signal Messages• Developed to support new constellations andfrequencies• MSM1 to MSM7 messages defined to provide
different levels of raw data

RTCM 3.0 Messages• GPS L1 MT: 1001, 1002
• GPS L1/L2 MT: 1003, 1004

• GLONASS L1 MT: 1009, 1010
• GLONASS L1/L2 MT: 1011, 1012

Commonly used MSM messages• MSM1: Pseudorange DGNSS• MSM4: RTK• MSM5: Full RINEX data
• MSM7: Full RINEX data with extended resolution• Station Coordinates MT: 1005,1006• Antenna Description MT: 1007,1008

MSM may not be supported by all receivers.

NTRIP
How to distribute correction data from base stations to rovers?

• Networked Transport of RTCM via Internet Protocol• A protocol used to distribute GNSS data streams, commonly used to distributecorrections in RTCM format.

• Contains three components• Caster: Internet server that receives data and broadcasts to clients• Client: User who takes and applies correction to get high accuracy positioning (RTK Rover)• Server: Base station/CORS receiver that generates and transmits corrections to the caster.

• A caster can have many mountpoints.
• Each mountpoint has one base station (server) and multiple rovers (clients).

NTRIPNTRIP CasterServer
1

Mountpoint 1

Server2

Mountpoint 2

Server3

Mountpoint 3

Client1

Client2
Client3

Client4

Client5

Accessing Data from NTRIP Caster
NTRIP Clients• GNSS receivers with built-in cellular device (SIM Card)• Computer Programs (RTKLIB, u-center, MAD-WIN)• Mobile Applications: RTKDROID, MADROID, SW Maps…
• RTK Drone Remote Controllers
What you need
• Caster Address: Domain name or IP Address• Caster Port: Usually 2101
• Mount Point Name
• Username and Password

RTKLIB: Introduction• RTKLIB is an open source program package for standard and precise positioningwith GNSS.
• Contains several windows applications and command line tools for GNSS datacollection and processing.
Useful tools:• strsvr.exe: communication server, connect to receivers/NTRIP and log/retransmit data
• rtkconv.exe: Convert proprietary receiver raw data to RINEX• rtkpost.exe: Post-process GNSS data
• rtknavi.exe: Real time processing of GNSS data (RTK)• rtkplot.exe: Plotting and visualization toolData Conversion and Processing using RTKLIBSingle Point Positioning

Proprietary DataFormat(UBX, SBF etc.)

RTKCONVRINEX 3OBS, NAV

RTKPOST

Position Output(POS/NMEA/KML)RTKPLOT

Convert RAW to RINEXUse Data from StaticFiles/F9P_181215_static.ubx

1. Select File
2. Select Format (UBX)
3. Output File Names

4. Conversion Options

5. Start Conversion

Single Point Positioning using RTKPOST

1. Select Rover OBS File

2. Select Rover NAV File

4. Single Positioning Mode
5. Solution Output File
6. Execute
3. Setup Processing Options

Plotting using RTKPLOT

Processing Status Display
Open results in RTKPLOT
RTKPLOT (20cm Grid)