This package is a set of tools and libraries for decoding and encoding the GDL 90 protocol used for ADS-B in transmissions. The focus of this package is on a client application within an aircraft that is receiving a data stream from an ADS-B hardware device. Any sending tools are meant to simulate the hardware device for a listening client application.
Unless otherwise stated in the included files, the files within this package are subject to the following copyright and license.
Copyright (c) 2016-2024 Eric Dey
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
The package requires a minimum of Python 3.8, has been tested with Python 3.13, and makes use of the Python Standard Library for all functions except where noted. The primary tool components are:
gdl90_receiver.py-- receives a live or recorded data stream from ADS-B hardwaregld90_recorder.py-- records the raw data stream from ADS-B hardware to filegld90_sender.py-- sends a previously recorded data stream to network
The gdl90 subdirectory contains the libraries for decoding and encoding the
GDL 90 and UAT messages.
The Python unittest framework is used for automated tests. All of
the unit tests can be executed with the run_tests.sh shell script
on Linux or MacOS, or with the run_tests.ps1 PowerShell script on
Windows.
This is a description of the utilities that accompany and use the GDL 90 library. These utilities make use of external Python packages, so pay attention to the environment setup.
See the requirements.txt file a list of required external packages. The setup step are:
- (Optional) Python virtual environment setup
- Install venv:
pip3 install venv - Setup within source tree:
python3 -m venv .venv
- Install venv:
- (Optional) Activate the venv:
source .venv/bin/activate - Install dependencies:
pip3 install -r requirements.txt - (Optional) Install code coverage package:
pip3 install coverage
If you install the dependencies within a Python virtual environment, you will need to activate it each time that you will use one of the utilities that depend upon them. Once you are finished with the virtual environment, you can terminiate it with the deactivate command.
If you are completely finished with the virtual environment, make sure it is deactivated and then you can simply remove the .venv directory tree.
The receiver can be used decode a live data stream or process a recorded GLD 90 file. The output is a line-by-line decoding of the individual message types, including the optional UAT messages, or a compact text record format that allows for automated processing.
$ ./gdl90_receiver.py --help
Usage: gdl90_receiver.py {requiredOptions} [otherOptions]
GDL-90 Receiver is a data receiver and decoder.
Options:
--version show program's version number and exit
-h, --help show this help message and exit
-v, --verbose Verbose reporting on STDERR
Optional:
-p NUM, --port=NUM receive port (default=43211)
-s BYTES, --maxsize=BYTES
maximum packet size (default=9000)
-r PACKETS, --reportcount=PACKETS
report after receiving this many packets (default=100)
-i FILE, --inputfile=FILE
read from input file instead of network
--date=YYYY-MM-DD UTC starting date for data (default=now)
--plotflight output plotflight format
--uat output UAT messages
Example usage:
$ ./gdl90_receiver.py -i skyradar.20121028.001 --plotflight > ../KML/PlotFlight/skyradar.track.20121028.001.txt
The decoding library makes use of a non-standard MSG101 from the SkyRadar hardware for time-of-day (hh:mm) since the MSG00 timestamp is not usable as defined in the GDL 90 protocol. Since seconds information is not available when using the SkyRadar hardware, the decoding library self-corrects its internal estimation of the number of seconds past the minute as messages are received.
The recorder captures the raw data stream from an ADS-B device and saves it to
a file. It is designed to be run within a device like the RaspberryPi attached
to a wifi network within an aircraft. The raw files are later downloaded and
processed by the gdl90_receiver.py program.
$ ./gdl90_recorder.py --help
Usage: gdl90_recorder.py {requiredOptions} [otherOptions]
GDL-90 Recorder is a data receiver.
Options:
--version show program's version number and exit
-h, --help show this help message and exit
-v, --verbose Verbose reporting on STDERR
--slowexit Delay error exit for 15 seconds
Optional:
--interface=name receive interface name (default=)
-p NUM, --port=NUM receive port (default=43211)
-s BYTES, --maxsize=BYTES
maximum packet size (default=1500)
--dataflush=SECS seconds between data file flush (default=10)
--logprefix=PATH path prefix for log file names
(default=/root/skyradar)
--rebroadcast=name rebroadcast interface (default=off)
When running the recorder in a head-less device like the RPi, this should be run as root with the ability to automatically start and restart.
This is the most commonly used startup system on Linux distributions since about 2015. For automatic startup at boot, do the following as root:
- Edit the configuration items in the
gdl90_service_wrapperfile. - Copy service unit file:
cp gdl90.service /etc/systemd/system/. - Reload systemd configuration:
systemctl daemon-reload - Start the GDL 90 service:
systemctl start gdl90 - Confirm operation:
systemctl status gdl90
The service wrapper is used by the gdl90.service unit and systemd for start/stop/restart operations. You should edit the following items based on your system's network and install path:
NETWORK_DEV=wlan0
LISTEN_PORT=4000
ADSB_DIRECTORY=/root/adsb
This is less common on newer Linux systems. For automatic startup at boot, you will add an
/etc/inittab entry such as this:
#Run GDL90 recorder
fdr1:23:respawn:/usr/bin/python3 /root/gdl90_recorder.py --slowexit
The --slowexit option should be used when running from inittab in order to
prevent init from disabling respawns at boot time when the wifi network is
still initializing. Until a valid network interface exists, the recorder will
exit and needs to be restarted.
The sender is useful for replaying a previously recorded data stream from an ADS-B hardware device. This can be used for testing an application or the decoder library.
$ ./gdl90_sender.py --help
Usage: gdl90_sender.py {requiredOptions} [otherOptions]
GDL-90 Sender transmits data to the network.
Options:
--version show program's version number and exit
-h, --help show this help message and exit
-v, --verbose Verbose reporting on STDERR
-f FILE, --file=FILE input file (default=STDIN)
Optional:
-d IP, --dest=IP destination IP (default=255.255.255.255)
-p NUM, --port=NUM destination port (default=43211)
-s BYTES, --size=BYTES
packet size (default=50)
--delay=MSEC time between packets (default=10)