ais_to_gdl90

A small script to receive AIS data (via a UDP port from rtl-ais or aisdeco2 and an SDR receiver or via serial port NMEA data), translate it to GDL90 data, and transmit the GDL90 data out on a UDP port.

Allows vessel locations reported via AIS to be shown as "traffic" on EFB applications such as ForeFlight, etc.

Setup

A source of VHF AIS data is required. As-is, this script is set up to receive AIS data provided from an RTL SDR dongle by rtl-ais or aisdeco2 via a UDP port or from NMEA serial data from a receiver such as the dAISy HAT.

By default, the script will attempt to auto-detect a USB dAISy NMEA serial port AIS receiver on startup. If it cannot find one, it will open up a UDP port and wait for AIS data from rtl-ais, aiseco2, or any other source. A serial port can also be manually specified using command line arguments (use this when using a non-USB dAISy hat, for example). If you'd like to see auto-detect support for a USB serial port AIS receiver other than the dAISy please let me know.

rtl-ais and this script can be installed on a Stratux or a standalone Raspberry Pi used only for VHF AIS reception. If installed on a Stratux, an additional SDR dongle used to receive the VHF AIS data is required. If installed on another Pi, that second Pi should be connected to the Stratux WiFi network.

Dependencies

To install rtl-ais, follow the instructions at: https://github.com/dgiardini/rtl-ais

AIS sentence decoding in Python: https://github.com/M0r13n/pyais

install pip3 (not installed by default on a Stratux):

sudo apt-get install python3-pip

install pyais:

pip3 install pyais

PySerial is needed to get AIS data from a serial port source such as a dAISy receiver (instead of rtl-ais)

pip3 install pyserial

A partial fork of the gdl90 library is used to encode the gdl90 data. This partial fork is included in this repository, so installing it separately is not required. Modifications were made to adapt it for compatibility with Python 3 since the pyais library requires Python 3.

Running

Once installed, rtl-ais can be run (if using an SDR as the AIS receiver) as follows (example: use rtl-sdr device index 2, receive AIS traffic, send UDP NMEA sentences to 127.0.0.1 port 10110 and log the sentences to console):

./rtl_ais -n -d 2  

Once rtl-ais is running (or if a dAISy is connected), this script can be run with:

python3 ais_to_gdl90.py

Or to manually specify the serial port to use with an external AIS receiver:

python3 ais_to_gdl90.py --SerialPortName /dev/serial0 --SerialPortBaud 38400

Limitations

• The GDL90 data format only allocates 8 ASCII characters for the "callsign" field so vessel names received via AIS will be truncated to 8 characters when sent via GDL90
• AIS data does not included altitude. GDL90 data is currently populated with an altitude of 0 ft MSL.
• While AIS position reports are sent every 2 to 10 seconds while underway, static reports that contain the vessel name are only sent every 6 minutes. If a position report is received before a static report is received, the first 8 characters of the MMSI are used to populate the GDL90 "callsign" field. Once the vessel name has been recieved via a static report, the "callsign" field will change to the first 8 characters of the vessel name. MMSI to vessel name mapping is stored in a JSON file for later use after restarts.