GH AIS Message Format
NMEA Message Formats
The NMEA message formats are specified in /IEC 61162-1/ these are encoded/decoded using the AIS codec.
NMEA messages originate from transponders (information from ships) or from users (sending AtoN e.g.).
Internal Message Formats
Internal message formats are modelled after the NMEA message formats (see /IEC 61162-1/). Internal messages originate from within the AIS system, basically all other messages than those received by ships or users are encapsulated in the internal message formats.
Two different internal formats are specified in the following, as well as the date format used for the internal messages.
Date format
The date format will be in UTC time and are specified as follows:
Date format=<year>,<month>,<day>,<hour>,<minut>,<second>,<millisecond>
Example=2004,12,31,23,59,59,999
GH Internal Message Type 1
Note: This information has not been confirmed, but is believed to be correct
GH internal message type 1 are used for “encapsulating” NMEA messages. The “encapsulation” basically takes places by sending a GH specific message before sending the NMEA message. This has the advantage that GIS systems still should be able to handle the message stream since the unknown GH message would be ignored and the NMEA message interpreted is usual.
The internal message type 1 are specified as follows:
$PGHP,<msgtype>,<date format>,<country>,<region>,<pss>,<online data>,<cc>*hh<CR><LF>
<NMEA message>
- <msgtype> is 1 for this message type (Gatehouse internal message type 1)
- <date format> as specified above
- <country> is the MMSI country code where the message originates from.
- <region> the MMSI number of the region
- <pss> the MMSI number of the site transponder
- <online data> buffered data from a BSC will be designated with 0. Online data with 1.
- <cc> the checksum value of the following NMEA sentence
- <*hh> checksum as described in /IEC 61162-1/
- <NMEA message> is the NMEA message that follows immediately after the $PGHP sentence
Example:
$PGHP,1,2008,5,9,0,0,0,10,338,2,,1,09*17
!AIVDM,1,1,,B,15NBj>PP1gG>1PVKTDTUJOv00<0M,0*09