NMEA Sentences

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NMEA Sentences
for GPS Receivers

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

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Introduction

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Who?
- The National Marine Electronics Association (NMEA)
What?
- A standard (NMEA-0183) for the formatting of Global Positioning System (GPS) information.
Why?
- Boats/ships were some of the first users of GPS

Some Sentences for Marine Navigation

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AAM - Waypoint arrival alarm
BOD - Bearing, origin to destination
BWC - Bearing and distance to waypoint, great circle
BWR - Bearing and distance to waypoint, rhumb line (overridden by BWC if available)
DPT - Depth of water
HDM - Heading, magnetic north
HDT - Heading, true north
MTW - Mean water temperature
WCV - Waypoint closure velocity
WPL - Waypoint location

Some General Sentences

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GGA - Global Positioning System Fix Data
GLL - Geographic position, latitude and longitude (and time)
GSA - GPS DOP and active satellites
GSV - Satellites in view

The GGA Sentence

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Example:
- $GPGGA,210230,3855.4487,N,09446.0071,W,1,07,1.1,370.5,M,-29.5,M,,*7A
Fields:
- The sentence type
- Current time (if available; UTC; may include a decimal point)
- Latitude (in DDMM.MMM format)
- Latitude compass direction
- Longitude (in DDDMM.MMM format)
- Longitude compass direction
- Fix type (0 for no fix, 1 for GPS, 2 for DGPS)
- Number of satellites used for fix
- Horizontal dilution of precision
- Altitude above mean sea level
- Altitude units (M for meters)
- Height of mean sea level above WGS-84 earth ellipsoid
- Units of the above geoid seperation (M for meters)
- Time since last differential correction (ignored if inactive)
- Differential station ID (ignored if inactive)
- The checksum validation value (in hexadecimal)

The GSV Sentence

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Example:
- $GPGSV,2,1,08,02,74,042,45,04,18,190,36,07,67,279,42,12,29,323,36*77
- $GPGSV,2,2,08,15,30,050,47,19,09,158,,26,12,281,40,27,38,173,41*7B
Fields:
- The sentence type
- The number of sentences in the sequence
- The number of this sentence
- The number of satellites
- The satellite number, elevation, azimuth, and signal to noise ratio for each satellite
- The checksum validation value (in hexadecimal)

There's Always More to Learn

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