Specification Format for AIS Binary Messages for Providing Hydrographic-related Information


UNH is working with the USCG and NOAA to use XML (Extensible Markup Language) to define binary messages for maritime-based AIS (Automatic Identification System). The draft specification format will enable hydrographic and maritime safety agencies to define message contents by providing a bit level description in XML (informally the "AIS Binary Message Decoder Ring"). This format improves the clarity of message specifications aiding both people defining the messages and software engineers implementing maritime systems. The XML file specifies of the order, length, and type of fields following a subset of that used by the ITU-R.M.1371-1. To reduce issues with accidents and errors caused by miscommunication (e.g., the Mars Climate Orbiter loss in 1999), units are declared for the numerical values, along with the standard descriptions and notes. The specification is independent of programming language (e.g., can be implemented in C, C++, C sharp, Java, Python, etc.) to allow vendors to integrate the system into their individual design requirements. Along with the XML specification, the draft specification contains a reference implementation of an AIS XML to Python compiler written in Python that has been released as open source under the GNU General Public License (GPL) version 2. A XML schema and an additional program will provide validation of the XML message definitions. A XSLT style sheet produces reference documentation in 'html' format. Although the XML message definition file specifies the order, size, and type of the bit stream, it does not specify semantics or how binary messages should be presented on an ECDIS or other display device. A demonstration of this specification for sending tide/water level messages will be part of the Elizabeth River Demonstration Project at the US HYDRO 2007.


Center for Coastal and Ocean Mapping

Publication Date


Journal or Conference Title

U.S. Hydrographic Conference

Conference Date

May 14 - May 18, 2007

Publisher Place

Norfolk, VA, USA


Hydrographic Society of America

Document Type

Conference Proceeding

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