Console

AIS-catcher -o mode

The output of NMEA messages to screen can be regulated with the -o switch. To suppress any messages to screen use -o 0 or -q. This can be useful if you run AIS-catcher as a background process. To show only simple and pure NMEA lines, use the switch -o 1 or -n. Example output:

!AIVDM,1,1,,B,33L=LN051HQj3HhRJd7q1W=`0000,0*03

By default, and using the command -o 2, AIS-catcher displays NMEA messages with some additional information:

!AIVDM,1,1,,B,33L=LN051HQj3HhRJd7q1W=`0000,0*03 ( MSG: 3, REPEAT: 0, MMSI: 230907000, signalpower: -44.0, ppm: 0, timestamp: 20220729191340)

This same information but wrapped in JSON to facilitate further processing downstream is generated with the switch -o 3 :

{"class":"AIS","device":"AIS-catcher","channel":"B","rxtime":"20220729191502","signalpower":-44.0,"ppm":0,"mmsi":230907000,"type":3,"nmea":["!AIVDM,1,1,,B,33L=LN051HQj3HhRJd7q1W=`0000,0*03"]}

And finally, full decoding of the AIS message is activated via -o 5:

{"class":"AIS","device":"AIS-catcher","rxtime":"20220729191610","scaled":true,"channel":"B","nmea":["!AIVDM,1,1,,B,33L=LN051HQj3HhRJd7q1W=`0000,0*03"],"signalpower":-44.0,"ppm":0.000000,"type":3,"repeat":0,"mmsi":230907000,"status":0,"status_text":"Under way using engine","turn":18,"speed":8.800000,"accuracy":true,"lon":24.915239,"lat":60.148106,"course":231.000000,"heading":230,"second":52,"maneuver":0,"raim":false,"radio":0}

Meta data is not calculated by default to keep the program as light as possible when running as a server on low spec devices but can be activated with the -M switch. The calculation of signal power (in dB) and applied frequency correction (in ppm) are activated with -M D. NMEA messages are timestamped with -M T and additional country information from the station derived from the MMSI is included in JSON output with -M M.

There are many libraries for decoding AIS messages in NMEA format to JSON format. I encourage you to use your favorite library. Some excellent choices include libais, gpsdecode and pyais.