NMEA Data Explained

By Spirent On April 1, 2010
NMEA data

The navigation industry often refers to NMEA data. But what is it? And why is it so important for the GNSS receiver industry?

The NMEA is the US National Marine Electronics Association, which acts, among other things, as a standards body for the industry. And one of its most important standards is NMEA 0183, which defines electrical and data specifications for serial communications between all manner of marine electronic devices. These include everything from echo sounders, sonars and anemometers to gyrocompasses, autopilots and (importantly) GNSS receivers.

NMEA data comes in the form of “sentences” that are unique to each piece of equipment, but which can be read by all other equipment adhering to the standard. Each sentence begins with a dollar sign and ends with a carriage return, and can comprise no more than 80 characters of ASCII text. A number of standard sentences are defined, each identified by a prefix such as the “GP” used for GNSS (GPS) receivers.

The standard also allows hardware manufacturers to define their own proprietary sentences. All proprietary sentences begin with the letter P and are followed by three letters that identify the manufacturer controlling that sentence. For example a proprietary Garmin sentence would start with “PGRM”.

While these NMEA sentences are designed to be used for communication between navigational devices, they can also be used in the test laboratory. For example, the output recorded from a GNSS receiver in the field can be used to program motion profiles into a GNSS simulator to test other units.

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