Calculating and validating nmea checksums
It provides exchange of AIS data in raw NMEA format; all AISHub members share their own received AIS data and receive the merged feed from all other participating parties.It is open-source friendly, offering a Linux port in source of its software for collecting and forwarding AIS data.He also communicated some critical information from [IEC-PAS], and supplied information about new messages and fields in ITU-1371-3.Descriptions of messages 25 and 26 are based on AIS transceiver vendor documentation was originally forwarded to me by a source wishing to remain anonymous; I later checked them against ITU1371-4.Sat View is a real-time interactive data logging and display application for use with Sea-Bird radiometers.
ITU-R M.1371 revision 4 became available for free download, apparently at some point in early 2011, well after most of this document was assembled.
ITU Recommendation M.1371, "Technical Characteristics for a Universal Shipborne Automatic Identification System Using Time Division Multiple Access" [ITU1371], issued in 2001, first described the bit-level format of AIS radio messages.
This standard was proprietary and expensive when issued.
Kurt Schwehr is a research scientist at the Center for Coastal and Ocean Mapping at the University of New Hampshire. His work blog at [Schwehr] contains sample messages and descriptions of AIS operation in the wild that shed light on various obscure corners of the specification.
He has explained the otherwise undocumented Repeat Indicator field and USCG extended AIVDM to me by email.