Short answer
A serial-line ASCII protocol for marine and consumer GNSS receivers. Sentences like $GPGGA (fix), $GPRMC (recommended minimum), $GPGSV (satellites in view) are broadcast at ~1 Hz. The dominant output format for low-cost receivers; survey receivers also use binary formats like RTCM and proprietary streams.
Detailed explanation
NMEA 0183 is a 4800-baud (default) or 38400-baud serial protocol where the receiver continuously broadcasts ASCII sentences each starting with $ and ending with a CR+LF and a *XX checksum. Each sentence is a comma-separated field list — easy to parse, easy to debug with a serial monitor.
Common GNSS sentences: $GPGGA (Global Positioning System Fix Data — the primary fix sentence), $GPRMC (Recommended Minimum Specific GPS data — timestamp + position + speed + heading), $GPGSV (Satellites in View — one per satellite), $GPGSA (DOP and active satellites). A modern multi-constellation receiver replaces the GP prefix with GN (combined) or GL (GLONASS only), GA (Galileo), GB (BeiDou), etc.
NMEA 2000 is a more modern CAN-bus-based extension used in marine networks — incompatible with 0183 but conceptually similar. Most consumer GPS still uses 0183.
NMEA is fine for low-precision applications (position output to laptops, mobile robots, marine plotters) but lacks the raw measurement detail needed for survey-grade post-processing. For RTK / PPP / CORS you'll use RINEX or proprietary binary formats; for typical receiver integration you'll use NMEA.
Related terms
RINEX
The standard text-based file format for storing raw GNSS observations (.YYo files), navigation messages (.YYn), and meteorological data (.YYm). All survey-grade receivers can write RINEX, and all post-processing software can read it. Versions 2.11 and 3.05 are the most common.
TTFF
The elapsed time from receiver power-on (or warm/cold start) to the first valid position fix. Cold start (no almanac, no recent position, no time) is typically 30–60 seconds; warm start (with valid almanac and approximate position) is 5–15 seconds; hot start (with current ephemeris) is <1 second.
DOP
A geometric quality metric expressing how the spatial distribution of visible satellites amplifies ranging errors into position errors. Lower is better: PDOP < 4 is good, < 2 is excellent. PDOP depends only on satellite geometry, not signal quality.