Conversion from AIS to NMEA Radar $RATTM

Past couple of weeks I’ve been working hard on a very interesting project commissioned by SeaBird Exploration. They provide seismic services for the international gas and oil industry and run a fleet of 8 vessels equipped with highly sophisticated equipment.
SeaBird asked Sailsoft to develop software for dynamically converting AIS messages of type 1 to NMEA RADAR $RATTM sentences in order to feed the survey software aboard Hugin Explorer. The vessel is currently in operation in the Mediterranian.

This assignment was a real challenge because a number of parameters in the TTM sentence have no direct counterpart in the AIS message type 1 and have either to be calculated or defaulted, including the calculation of CPA (Closest Point of Approach) in time and distance units. The Target Name parameter in the TTM sentence is filled with the MMSI number from the AIS message 1, since we decided not to interpret message type 5. The program keeps a table for maximum 99 targets, because this is the maximum the NMEA $RATTM sentence can bear.

Different threads are maintained for incoming and outgoing messages. Message handling is complicated by the fact that we have to deal with different speeds for incoming and outgoing messages, 38400 and 4800 bps respectively.

The application is currently in operation aboard the Hugin Explorer, and as it looks so far without problems. Although a very interesting project for me it has delayed the release of NemaStudio for a couple of weeks unfortunately. I hope my beta testers will forgive me.