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galileo/GPS/GLONASS/BeiDou open source monitoring. GPL3 licensed. (C) AHU Holding BV - -

Live website:

Multi-vendor, with support for U-blox 8 and 9 chipsets and many Septentrio devices. Navilock NL-8012U receiver works really well, as does the U-blox evaluation kit for the 8MT. In addition, many stations have reported success with this very cheap AliExpress sourced device.

For ublox, there is good support for the F9P, several of us use the ArdusimpleRTK2B board. It adds the Galileo E5b band.

Septentrio devices support even more bands.

An annotated presentation about our project aimed at GNSS professionals can be found here.

NOTE: One of our programs is called 'ubxtool'. Sadly, we did not do our research, and there is another 'ubxtool' already, part of gpsd. You might have ended up on our page by mistake. Sorry!

To deliver data to the project, please read The Galmon GNSS Monitoring Project and consult the rules outlined in the operator guidelines.


  • Support for Septentrio and U-blox.
  • Processes raw frames/strings/words from GPS, GLONASS, BeiDou and Galileo
  • All-band support (E1, E5a, E5b, B1I, B2I, Glonass L1, Glonass L2, GPS L1C/A) so far.
  • Calculate ephemeris positions
  • Comparison of ephemerides to independent SP3 data to determine SISE
    • Globally, locally, worst user location
  • Record discontinuities between subsequent ephemerides (in time and space)
  • Compare doppler shift as reported by receiver with that expected from ephemeris
  • Track atomic clock & report jumps
  • Coverage maps (number of satellites >5, >10, >20 elevation)
  • Compare orbit to TLE, match up to best matching satellite
  • Tear out every bit that tells us how well an SV is doing
  • Full almanac processing to see what should be transmitting
  • Distributed receivers, combined into a single source of all messages
  • Ready to detect/report spoofing/jamming

Data is made available as JSON, as a user-friendly website and as a time-series database. This time-series database is easily mated to the industry standard Matplotlib/Pandas/Jupyter combination (details here.

There is also tooling to extract raw frames/strings/words from specific timeframes.


  1. Support multiple wildly distributed receivers
  2. Combine these into a forensic archive of all Galileo/GPS NAV messages
  3. Make this archive available, offline and as a stream
  4. Consume this stream and turn it into an attractive live website ( As part of this, perform higher-level calculations to determine ephemeris discontinuities, live gst/gps/galileo time offsets, atomic clock jumps etc.
  5. Populate an InfluxDB timeseries database with raw measurements and higher order calculations

Works on Linux (including Raspbian Buster on Pi Zero W), OSX and OpenBSD.

Build locally (Linux, Debian, Ubuntu)

To get started, make sure you have a C++17 compiler (like g++ 8 or higher), git, protobuf-compiler. Then run 'make ubxtool navdump' to build the receiver-only tools.

To build everything, including the webserver, try:

apt-get install protobuf-compiler libh2o-dev libcurl4-openssl-dev libssl-dev libprotobuf-dev \
libh2o-evloop-dev libwslay-dev libncurses5-dev libeigen3-dev libzstd-dev g++
git clone --recursive
cd galmon

If this doesn't succeed with an error about h2o, make sure you have this library installed. If you get an error about 'wslay', do the following, and run make again:

echo WSLAY=-lwslay > Makefile.local

Building on OSX

With thanks to a contributor from Prague. First make sure you've installed brew, which you can get here. Then do:

brew install protobuf lzlib zstd h2o eigen

And then:

git clone --recursive
cd galmon

Running in Docker

We publish official Docker images for galmon on docker hub for multiple architectures.

To run a container with a shell in there (this will also expose a port so you can view the UI too and assumes a ublox GPS device too - you may need to tweak as necessary):

docker run -it --rm --device=/dev/ttyACM0 -p 10000:10000 berthubert/galmon

Running a daemonized docker container reporting data to a remote server might look like:

docker run -d --restart=always --device=/dev/ttyACM0 --name=galmon berthubert/galmon ubxtool --wait --port /dev/ttyACM0 --gps --galileo --glonass --destination [server] --station [station-id] --owner [owner]

To make your docker container update automatically you could use a tool such as watchtower.


On u-blox: Once compiled, run for example ./ubxtool --wait --port /dev/ttyACM0 --station 1 --stdout --galileo | ./navparse --bind [::1]:10000

For Septentrio, try: nc 29000 | ./septool --station x --stdout | ./navparse --bind [::1]:10000, assuming your Septentrio can be reached on and you have defined an SBF stream on port 29000. For more details, please see below.

Next up, browse to http://[::1]:10000 (or try http://localhost:10000/ and you should be in business. ubxtool changes (non-permanently) the configuration of your u-blox receiver so it emits the required frames for GPS and Galileo. If you have a u-blox timing receiver it will also enable the doppler frames.

By default the ublox receiver module will be configured to use the USB port, if you want to use a different interface port on the ublox module then add the --ubxport <id> option using one of the following numeric IDs:

0 : DDC (aka. I2C)
1 : UART[1]
2 : UART2
3 : USB (default)
4 : SPI

To see what is going on, try:

./ubxtool --wait --port /dev/ttyACM0 --station 1 --stdout --galileo | ./navdump

To distribute data to a remote navrecv, use:

./ubxtool --wait --port /dev/ttyACM0 --galileo --station 255 --destination

This will send protobuf to You can add as many destinations as you want, they will buffer and automatically reconnect. To also send data to stdout, add --stdout.


  • ubxtool: can configure a u-blox 8 chipset, parses its output & will convert it into a protbuf stream of GNSS NAV frames + metadata Adds 64-bit timestamps plus origin information to each message
  • septool: ingests the Septentrio binary format (SBF) and converts it to our protobuf format. Supports same protocol as ubxtool.
  • rtcmtool: ingest ntripclient output, decodes RTCM messages and converts them to our protobuf format
  • xtool: if you have another chipset, build something that extracts NAV frames & metadata. Not done yet.
  • navrecv: receives GNSS NAV frames and stores them on disk, split out per sender.
  • navnexus: tails the files stored by navrecv, makes them available over TCP
  • navparse: consumes these ordered nav updates for a nice website and puts "ready to graph" data in influxdb - this is the first step that breaks "store everything in native format". Also does computations on ephemerides.
  • grafana dashboard: makes pretty graphs

Linux Systemd

First make sure 'ubxtool' has been compiled (run: make ubxtool). Then, as root:

mkdir /usr/local/ubxtool
cp ubxtool /usr/local/ubxtool/
cp ubxtool.service /etc/systemd/system/

Then please reach out as indicated in to obtain your station ID and the receiver hostname and run:

echo RECEIVER-NAME > /usr/local/ubxtool/destination
echo STATION-NUMBER > /usr/local/ubxtool/station

Then start up the service (as root):

systemctl enable ubxtool
systemctl start ubxtool

To check if it is all working, do 'service ubxtool status'.

NOTE! If you don't use one of the AliExpress or Navilock devices, it may be that your U-blox is not connected to the USB-port of the U-blox chip but to the UART1 or UART2 port. If so, you'll need to edit the script so it finds your USB-to-serial adapter. At the very least you'll have to update the DEVICE line. You'll likely also have to add --ubxport 1 at the end, and likely also the baudrate (-b) and/or --rtscts=0.

To change the default constellations, create a file called /usr/local/ubxtool/constellations and set your favorites. To set all four constellations (which only F9-receivers support), do as root:

echo --gps --glonass --beidou --galileo > /usr/local/ubxtool/constellations

And then 'service ubxtool restart'.

Distributed setup

Run navrecv -b :: --storage ./storage to receive frames on port 29603 of ::, aka all your IPv6 addresses (and IPv4 too on Linux). This allows anyone to send you frames, so be aware.

Next up, run navnexus --storage ./storage -b ::, which will serve your recorded data from port 29601. It will merge messages coming in from all sources and serve them in time order.

Finally, you can do nc 29601 | ./navdump, which will give you all messages over the past 24 hours, and stream you more. This also works for navparse for the pretty website and influx storage, nc 29601 | ./navparse --influxdb=galileo, if you have an influxdb running on localhost with a galileo database in there. The default URL is

Septentrio specifics

Unlike ubxtool, our septool does not (re)configure your Septentrio device. Instead, the tool expects Septentrio Binary Format (SBF) on input, and that this stream includes at least the following messages:

  • MeasEpoch
  • PVTCartesian

We currently parse and understand:


Support will be added soon for:

  • GPSRawCA
  • GPSRawL2C
  • GPSRawL5
  • GLORawCA
  • BDSRaw
  • BDSRawB1C
  • BDSRawB2a

A typical invocation of septool looks like this:

nc 29000 | ./septool --station x --destination

Or to test, try:

nc 29000 | ./septool --station x --stdout | ./navdump

This is assuming that you can reach your Septentrio on and that you have defined a TCP server stream on port 29000.

Septool will also accept input from a serial port or basically anything that can provide SBF. Please let us know if our tooling can make your life easier.


The transport format consists of repeats of:

  1. Four byte magic value
  2. Two-byte frame length
  3. A protobuf frame

The magic value is there to help us resync from partially written data.

The whole goal is that we can continue to rebuild the database by rerunning 'navstore' and 'navinflux'.


Data sources

The software can interpret SP3 files, good sources:

  • ESA/ESOC: - pick the relevant GPS week number, and then a series (.sp3 extension):
    • ESU = ultra rapid, 2-8h delay, only GPS and GLONASS
    • ESR = rapid, 2-26h delay, only GPS and GLONASS
    • ESM = finals, 6-13d delay, GPS, GLONASS, Galileo, BeiDou, QZSS
    • File format is esXWWWWD.sp3 - where X is U, R or M, WWWW is the (non-wrapping) GPS week number and D is day of week, Sunday is 0.
    • Further description:
  • GFZ Potsdam:
    • The GBM series covers GPS, GLONASS, Galileo, BeiDou, QZSS and appears to have less of a delay than the ESA ESM series.
    • GBU = ultra rapid, still a few days delay, but much more recent.

To get SP3 GBM from GFZ Potsdam for GPS week number 2111:

lftp -c "mget${WN}/gbm*sp3.Z"
gunzip gbm*sp3.Z

To feed data, use:

./sp3feed --sp3src=gbm --influxdb=galileo gbm*sp3

This will populate the sp3 tables in the database. A subsequent run of reporter, while setting the --sp3src parameter, will provide SP3 deviation statistics, and fill out the sp3delta table in there, which stores deviations from the SP3 provided position, per sp3src.

Further interesting (ephemeris) data is on


RTCM is the Radio Technical Commission for Maritime Services, and confusingly, also the name of a protocol.

This protocol is proprietary, but search for a file called RTCM3.2.pdf or 104-2013-SC104-STD - Vers. 3.2.docx and you might find a copy.

This project can parse RTCM 10403.1 messages, and currently processes State Space Representation (SSR) messages, specifically types 1057/1240 (GPS/Galileo Orbit corrections to broadcast ephemeris) and 1058/1241 (GPS/Galileo Clock corrections to broadcast ephemeris).

RTCM messages need to be converted to protobuf format, and the rtcmtool is provided for this purpose.

RTCM is frequently transmitted over the internet using 'ntrip', a typical commandline to process RTCM in our project is:

$ ntripclient ntrip:CLKA0_DEU1/ | ./rtcmtool --station x --destination y

User and password can be obtained from - the Galileo operating company.

The IGS also offers excellent streams, but without Galileo. Information is here. A typical commandline is:

$ ntripclient ntrip:IGS01/ | ./rtcmtool --station x --destination y

User and password can be requested through

An interesting list is here:

There are many other sources of RTCM but currently not many offer the SSR messages we can use.


  • ubxtool: Configure and use a Ublox chip to gather messages, and send as protobuf to standard output or a remote server (with buffering).
  • navdump: convert protobuf format data into a textual display of messages
  • navparse: consume protobuf and turn into a webserver with data, plus optionally fill an influxdb time-series database for graphing and analysis purposes.
  • navrecv: receive protobuf messages over the network and store them on disk
  • navnexus: serve protobuf messages from disk over the network
  • navcat: serve protobuf messages from disk directly to stdout
  • reporter: make "the weekly galileo report"
  • rinreport: rinex analysis tooling (not generically useful yet)
  • galmonmon: monitor a navparse instance for changes, tweet them out
  • navdisplay: some eye-candy that converts protobuf into a live display (not very good)
  • rtcmtool: accepts RTCM messages on standard input (for example coming from ntripclient) and transmits them as protobuf messages, either to stdout or to a navrecv server. This is the equivalent of 'ubxtool' except for submitting RTCM messages.

Sample command lines

Look at old data:

$ ./navcat storage "2020-01-01 00:00" "2020-01-02 00:00" | ./navdump  

Global coverage (via volunteers)

In alphabetical order:

  • Austria (Vienna area)
  • Brazil
  • Holland (Nootdorp, Hilversum, etc)
  • India (New Delhi area)
  • Israel (Jerusalem)
  • Italy (Rome)
  • New Zealand (Auckland area)
  • Rusia (Moscow area)
  • Singapore
  • South Africa (Cape Town area)
  • Spain
  • Tonga
  • USA
    • Alaska (Anchorage)
    • California (Santa Cruz, Los Angeles area, etc)
    • Massachusetts (Boston area)
  • Uruguay

Additional sites are welcome (and encouraged) as the more data receiving sites that exist, then more accurate data and absolute coverage of each constellation can be had.

The galmon project is very grateful to all its volunteering receiving stations.


  • Will also spool raw serial data to disk (in a filename that includes the start date)
  • Can also read from disk
  • Careful to add the right timestamps