NMEA Protocol

NMEA 0183 (or NMEA for short) is a combined electrical and data specification for communication between marine electronics and also, more generally, GPS receivers.

The NMEA 0183 protocol is a means by which marine instruments and also most GPS receivers can communicate with each other. It has been defined by, and is controlled by, the US based National Marine Electronics Association.

The 0183 standard, uses a simple serial protocol transmitting a “sentence” from one “talker” to one or more “listeners”.

See Wikipedia: NMEA

  • $GPAAM - Waypoint Arrival Alarm
  • $GPALM - GPS Almanac Data
  • $GPAPA - Autopilot format “A”
  • $GPAPB - Autopilot format “B”
  • $GPASD - Autopilot System Data
  • $GPBEC - Bearing & Distance to Waypoint, Dead Reckoning
  • $GPBOD - Bearing, Origin to Destination
  • $GPBWC - Bearing & Distance to Waypoint, Great Circle
  • $GPBWR - Bearing & Distance to Waypoint, Rhumb Line
  • $GPBWW - Bearing, Waypoint to Waypoint
  • $GPDBT - Depth Below Transducer
  • $GPDCN - Decca Position
  • $GPDPT - Depth
  • $GPFSI - Frequency Set Information
  • $GPGGA - Global Positioning System Fix Data
  • $GPGLC - Geographic Position, Loran-C
  • $GPGLL - Geographic Position, Latitude/Longitude
  • $GPGRS - GPS Range Residuals
  • $GPGSA - GPS DOP and Active Satellites
  • $GPGST - GPS Pseudorange Noise Statistics
  • $GPGSV - GPS Satellites in View
  • $GPGXA - TRANSIT Position
  • $GPHDG - Heading, Deviation & Variation
  • $GPHDT - Heading, True
  • $GPHSC - Heading Steering Command
  • $GPLCD - Loran-C Signal Data
  • $GPMSK - Control for a Beacon Receiver
  • $GPMSS - Beacon Receiver Status
  • $GPMTA - Air Temperature (to be phased out)
  • $GPMTW - Water Temperature
  • $GPMWD - Wind Direction
  • $GPMWV - Wind Speed and Angle
  • $GPOLN - Omega Lane Numbers
  • $GPOSD - Own Ship Data
  • $GPR00 - Waypoint active route (not standard)
  • $GPRMA - Recommended Minimum Specific Loran-C Data
  • $GPRMB - Recommended Minimum Navigation Information
  • $GPRMC - Recommended Minimum Specific GPS/TRANSIT Data
  • $GPROT - Rate of Turn
  • $GPRPM - Revolutions
  • $GPRSA - Rudder Sensor Angle
  • $GPRSD - RADAR System Data
  • $GPRTE - Routes
  • $GPSFI - Scanning Frequency Information
  • $GPSTN - Multiple Data ID
  • $GPTRF - Transit Fix Data
  • $GPTTM - Tracked Target Message
  • $GPVBW - Dual Ground/Water Speed
  • $GPVDR - Set and Drift
  • $GPVHW - Water Speed and Heading
  • $GPVLW - Distance Traveled through the Water
  • $GPVPW - Speed, Measured Parallel to Wind
  • $GPVTG - Track Made Good and Ground Speed
  • $GPWCV - Waypoint Closure Velocity
  • $GPWNC - Distance, Waypoint to Waypoint
  • $GPWPL - Waypoint Location
  • $GPXDR - Transducer Measurements
  • $GPXTE - Cross-Track Error, Measured
  • $GPXTR - Cross-Track Error, Dead Reckoning
  • $GPZDA - UTC Date / Time and Local Time Zone Offset
  • $GPZFO - UTC & Time from Origin Waypoint
  • $GPZTG - UTC & Time to Destination Waypoint


Waypoint Arrival Alarm

This sentence is generated by some units to indicate the Status of arrival (entering the arrival circle, or passing the perpendicular of the course line) at the destination waypoint.


    AAM    Arrival Alarm
    A      Arrival circle entered
    A      Perpendicular passed
    0.10   Circle radius
    N      Nautical miles
    WPTNME Waypoint name
    *43    Checksum data


GPS Almanac Data

A set of sentences transmitted by some Garmin units in response to a received $PGRMO,GPALM,1 sentence. It can also be received by some GPS units (eg. Garmin GPS 16 and GPS 17) to initialize the stored almanac information in the unit.

Example 1: $GPALM,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,*CC

1 = Total number of sentences in set
2 = Sentence sequence number in set
3 = Satellite number
4 = GPS week number
5 = Bits 17 to 24 of almanac page indicating SV health
6 = Eccentricity
7 = Reference time of almanac
8 = Inclination angle
9 = Right ascension rate
10 = Semi major axis route
11 = Argument of perigee (omega)
12 = Ascension node longitude
13 = Mean anomaly
14 = af0 clock parameter
15 = af1 clock parameter

Example 2: $GPALM,1,1,15,1159,00,441d,4e,16be,fd5e,a10c9f,4a2da4,686e81,58cbe1,0a4,001*5B

Field Example Comments
Sentence ID $GPALM
Number of messages 1 Total number of messages in sequence
Sequence number 1 This is first message in sequence
Satellite PRN 15 Unique ID (PRN) of satellite message relates to
GPS week number 1159
SV health 00 Bits 17-24 of almanac page
Eccentricity 441d
Reference time 4e Almanac reference time
Inclination angle 16be
Rate of right ascension fd5e
Roor of semi-major axis a10c9f
Argument of perigee 4a2da4
Longitude of ascension node 686e81
Mean anomoly 58cbe1
F0 clock parameter 0a4
F1 clock parameter 001
Checksum *5B


Autopilot format “B”

This sentence is sent by some GPS receivers to allow them to be used to control an autopilot unit. This sentence is commonly used by autopilots and contains navigation receiver warning flag status, cross-track-error, waypoint arrival status, initial bearing from origin waypoint to the destination, continuous bearing from present position to destination and recommended heading-to-steer to destination waypoint for the active navigation leg of the journey.

Note: Some autopilots, Robertson in particular, misinterpret “bearing from origin to destination” as “bearing from present position to destination”. This is likely due to the difference between the APB sentence and the APA sentence. for the APA sentence this would be the correct thing to do for the data in the same field. APA only differs from APB in this one field and APA leaves off the last two fields where this distinction is clearly spelled out. This will result in poor performance if the boat is sufficiently off-course that the two bearings are different.


    APB     Autopilot format B
    A       Loran-C blink/SNR warning, general warning
    A       Loran-C cycle warning
    0.10    cross-track error distance
    R       steer Right to correct (or L for Left)
    N       cross-track error units - nautical miles (K for kilometers)
    V       arrival alarm - circle
    V       arrival alarm - perpendicular
    011,M   magnetic bearing, origin to destination
    DEST    destination waypoint ID
    011,M   magnetic bearing, present position to destination
    011,M   magnetic heading to steer (bearings could True as 033,T)


Bearing Origin to Destination

eg.  BOD,045.,T,023.,M,DEST,START
           045.,T       bearing 045 degrees True from "START" to "DEST"
           023.,M       breaing 023 degrees Magnetic from "START" to "DEST"
           DEST         destination waypoint ID
           START        origin waypoint ID

Example 1: $GPBOD,099.3,T,105.6,M,POINTB,*01
Waypoint ID: “POINTB” Bearing 99.3 True, 105.6 Magnetic
This sentence is transmitted in the GOTO mode, without an active route on your GPS. WARNING: this is the bearing from the moment you press enter in the GOTO page to the destination waypoint and is NOT updated dynamically! To update the information, (current bearing to waypoint), you will have to press enter in the GOTO page again.

Example 2: $GPBOD,097.0,T,103.2,M,POINTB,POINTA*52
This sentence is transmitted when a route is active. It contains the active leg information: origin waypoint “POINTA” and destination waypoint “POINTB”, bearing between the two points 97.0 True, 103.2 Magnetic. It does NOT display the bearing from current location to destination waypoint! WARNING Again this information does not change until you are on the next leg of the route. (The bearing from POINTA to POINTB does not change during the time you are on this leg.)


Bearing and distance to waypoint, great circle

eg1. $GPBWC,081837,,,,,,T,,M,,N,*13

           225444       UTC time of fix 22:54:44
           4917.24,N    Latitude of waypoint
           12309.57,W   Longitude of waypoint
           051.9,T      Bearing to waypoint, degrees true
           031.6,M      Bearing to waypoint, degrees magnetic
           001.3,N      Distance to waypoint, Nautical miles
           004          Waypoint ID

eg2. $GPBWC,220516,5130.02,N,00046.34,W,213.8,T,218.0,M,0004.6,N,EGLM*11
               1      2    3     4    5    6  7   8   9    10  11 12 13

      1    220516    timestamp
      2    5130.02   Latitude of next waypoint
      3    N         North/South
      4    00046.34  Longitude of next waypoint
      5    W         East/West
      6    213.0     True track to waypoint
      7    T         True Track
      8    218.0     Magnetic track to waypoint
      9    M         Magnetic
      10   0004.6    range to waypoint
      11   N         unit of range to waypoint, N = Nautical miles
      12   EGLM      Waypoint name
      13   *11       checksum


Global Positioning System Fix Data

eg1. $GPGGA,170834,4124.8963,N,08151.6838,W,1,05,1.5,280.2,M,-34.0,M,,,*75

Name Example Data Description
Sentence Identifier $GPGGA Global Positioning System Fix Data
Time 170834 17:08:34 UTC
Latitude 4124.8963, N 41d 24.8963' N or 41d 24' 54“ N
Longitude 08151.6838, W 81d 51.6838' W or 81d 51' 41” W
Fix Quality:
* 0 = Invalid
* 1 = GPS fix
* 2 = DGPS fix
1 Data is from a GPS fix
Number of Satellites 05 5 Satellites are in view
Horizontal Dilution of Precision (HDOP) 1.5 Relative accuracy of horizontal position
Altitude 280.2, M 280.2 meters above mean sea level
Height of geoid above WGS84 ellipsoid -34.0, M -34.0 meters
Time since last DGPS update blank No last update
DGPS reference station id blank No station id
Checksum *75 Used by program to check for transmission errors

Global Positioning System Fix Data.
Time, position and fix related data for a GPS receiver.

eg2. $GPGGA,hhmmss.ss,ddmm.mmm,a,dddmm.mmm,b,q,xx,p.p,a.b,M,c.d,M,x.x,nnnn

hhmmss.ss = UTC of position
ddmm.mmm = latitude of position
a = N or S, latitutde hemisphere
dddmm.mmm = longitude of position
b = E or W, longitude hemisphere
q = GPS Quality indicator (0=No fix, 1=Non-differential GPS fix, 2=Differential GPS fix, 6=Estimated fix)
xx = number of satellites in use
p.p = horizontal dilution of precision
a.b = Antenna altitude above mean-sea-level

M = units of antenna altitude, meters
c.d = Geoidal height
M = units of geoidal height, meters
x.x = Age of Differential GPS data (seconds since last valid RTCM transmission)
nnnn = Differential reference station ID, 0000 to 1023


Geographic Position, Latitude / Longitude and time.

eg1. $GPGLL,3751.65,S,14507.36,E*77
eg2. $GPGLL,4916.45,N,12311.12,W,225444,A

           4916.46,N    Latitude 49 deg. 16.45 min. North
           12311.12,W   Longitude 123 deg. 11.12 min. West
           225444       Fix taken at 22:54:44 UTC
           A            Data valid

eg3. $GPGLL,5133.81,N,00042.25,W*75
               1    2     3    4 5

      1    5133.81   Current latitude
      2    N         North/South
      3    00042.25  Current longitude
      4    W         East/West
      5    *75       checksum

$–GLL,lll.ll,a,yyyyy.yy,a,hhmmss.ss,A llll.ll = Latitude of position

a = N or S
yyyyy.yy = Longitude of position
a = E or W
hhmmss.ss = UTC of position
A = status: A = valid data


GPS Range Residuals

Example: $GPGRS,024603.00,1,-1.8,-2.7,0.3,,,,,,,,,*6C

Field Example Comments
Sentence ID $GPGRS
UTC Time 024603.00 UTC time of associated GGA fix
Mode 1 0 = Residuals used in GGA, 1 = residuals calculated after GGA
Sat 1 residual -1.8 Residual (meters) of satellite 1 in solution
Sat 2 residual -2.7 The order matches the PRN numbers in the GSA sentence
Sat 3 residual 0.3
Sat 4 residual Unused entries are blank
Sat 5 residual
Sat 6 residual
Sat 7 residual
Sat 8 residual
Sat 9 residual
Sat 10 residual
Sat 11 residual
Sat 12 residual
Checksum *6C


GPS DOP and active satellites

eg1. $GPGSA,A,3,,,,,,16,18,,22,24,,,3.6,2.1,2.2*3C
eg2. $GPGSA,A,3,19,28,14,18,27,22,31,39,,,,,1.7,1.0,1.3*34

1    = Mode:
       M=Manual, forced to operate in 2D or 3D
       A=Automatic, 3D/2D
2    = Mode:
       1=Fix not available
3-14 = PRN's of Satellite Vechicles (SV's) used in position fix (null for unused fields)
15   = Position Dilution of Precision (PDOP)
16   = Horizontal Dilution of Precision (HDOP)
17   = Vertical Dilution of Precision (VDOP)


GPS Pseudorange Noise Statistics

Example: $GPGST,024603.00,3.2,6.6,4.7,47.3,5.8,5.6,22.0*58

Field Example Comments
Sentence ID $GPGST
UTC Time 024603.00 UTC time of associated GGA fix
RMS deviation 3.2 Total RMS standard deviation of ranges inputs to the navigation solution
Semi-major deviation 6.6 Standard deviation (meters) of semi-major axis of error ellipse
Semi-minor deviation 4.7 Standard deviation (meters) of semi-minor axis of error ellipse
Semi-major orientation 47.3 Orientation of semi-major axis of error ellipse (true north degrees)
Latitude error deviation 5.8 Standard deviation (meters) of latitude error
Longitude error deviation 5.6 Standard deviation (meters) of longitude error
Altitude error deviation 22.0 Standard deviation (meters) of latitude error
Checksum *58


GPS Satellites in view

eg. $GPGSV,3,1,11,03,03,111,00,04,15,270,00,06,01,010,00,13,06,292,00*74


1    = Total number of messages of this type in this cycle
2    = Message number
3    = Total number of SVs in view
4    = SV PRN number
5    = Elevation in degrees, 90 maximum
6    = Azimuth, degrees from true north, 000 to 359
7    = SNR, 00-99 dB (null when not tracking)
8-11 = Information about second SV, same as field 4-7
12-15= Information about third SV, same as field 4-7
16-19= Information about fourth SV, same as field 4-7


Heading, True.

Actual vessel heading in degrees Ture produced by any device or system producing true heading.

x.x = Heading, degrees True


Control for a Beacon Receiver


       318.0      Frequency to use
       A          Frequency mode, A=auto, M=manual
       100        Beacon bit rate
       M          Bitrate, A=auto, M=manual
       2          frequency for MSS message status (null for no status)
       *45        checksum


Beacon Receiver Status

Example 1: $GPMSS,55,27,318.0,100,*66

       55         signal strength in dB
       27         signal to noise ratio in dB
       318.0      Beacon Frequency in KHz
       100        Beacon bitrate in bps
       *66        checksum

Example 2: $GPMSS,0.0,0.0,0.0,25,2*6D

Field Example Comments
Sentence ID $GPMSS
Signal strength 0.0 Signal strength (dB 1uV)
SNR 0.0 Signal to noise ratio (dB)
Frequency 0.0 Beacon frequency (kHz)
Data rate 25 Beacon data rate (BPS)
Unknown field 2 Unknown field sent by GPS receiver used for test
Checksum *6D


List of waypoint IDs in currently active route

eg2. $GPR00,MINST,CHATN,CHAT1,CHATW,CHATM,CHATE,003,004,005,006,007,,,*05

List of waypoints. This alternates with $GPWPL cycle
which itself cycles waypoints.


Recommended minimum specific Loran-C data

eg. $GPRMA,A,lll,N,lll,W,x,y,ss.s,ccc,vv.v,W*hh
A    = Data status
lll  = Latitude
N    = N/S
lll  = longitude
S    = W/E
x    = not used
y    = not used
ss.s = Speed over ground in knots
ccc  = Course over ground
vv.v = Variation
W    = Direction of variation E/W
hh   = Checksum


Recommended minimum navigation information (sent by nav. receiver when a destination waypoint is active)

eg1. $GPRMB,A,0.66,L,003,004,4917.24,N,12309.57,W,001.3,052.5,000.5,V*0B

           A            Data status A = OK, V = warning
           0.66,L       Cross-track error (nautical miles, 9.9 max.),
                                steer Left to correct (or R = right)
           003          Origin waypoint ID
           004          Destination waypoint ID
           4917.24,N    Destination waypoint latitude 49 deg. 17.24 min. N
           12309.57,W   Destination waypoint longitude 123 deg. 09.57 min. W
           001.3        Range to destination, nautical miles
           052.5        True bearing to destination
           000.5        Velocity towards destination, knots
           V            Arrival alarm  A = arrived, V = not arrived
           *0B          mandatory checksum

eg2. $GPRMB,A,4.08,L,EGLL,EGLM,5130.02,N,00046.34,W,004.6,213.9,122.9,A*3D
            1   2  3   4    5    6     7   8      9   10    11    12   13

      1    A         validity
      2    4.08      off track
      3    L         Steer Left (L/R)
      4    EGLL      last waypoint
      5    EGLM      next waypoint
      6    5130.02   Latitude of Next waypoint
      7    N         North/South
      8    00046.34  Longitude of next waypoint
      9    W         East/West
      10   004.6     Range
      11   213.9     bearing to waypt.
      12   122.9     closing velocity
      13   A         validity
      14   *3D       checksum

eg3. $GPRMB,A,x.x,a,c--c,d--d,llll.ll,e,yyyyy.yy,f,g.g,h.h,i.i,j*kk
1    = Data Status (V=navigation receiver warning)
2    = Crosstrack error in nautical miles
3    = Direction to steer (L or R) to correct error
4    = Origin waypoint ID#
5    = Destination waypoint ID#
6    = Destination waypoint latitude
7    = N or S
8    = Destination waypoint longitude
9    = E or W
10   = Range to destination in nautical miles
11   = Bearing to destination, degrees True
12   = Destination closing velocity in knots
13   = Arrival status; (A=entered or perpendicular passed)
14   = Checksum


Recommended minimum specific GPS/Transit data

eg1. $GPRMC,081836,A,3751.65,S,14507.36,E,000.0,360.0,130998,011.3,E*62
eg2. $GPRMC,225446,A,4916.45,N,12311.12,W,000.5,054.7,191194,020.3,E*68

           225446       Time of fix 22:54:46 UTC
           A            Navigation receiver warning A = Valid position, V = Warning
           4916.45,N    Latitude 49 deg. 16.45 min. North
           12311.12,W   Longitude 123 deg. 11.12 min. West
           000.5        Speed over ground, Knots
           054.7        Course Made Good, degrees true
           191194       UTC Date of fix, 19 November 1994
           020.3,E      Magnetic variation, 20.3 deg. East
           *68          mandatory checksum

eg3. $GPRMC,220516,A,5133.82,N,00042.24,W,173.8,231.8,130694,004.2,W*70
              1    2    3    4    5     6    7    8      9     10  11 12

      1   220516     Time Stamp
      2   A          validity - A-ok, V-invalid
      3   5133.82    current Latitude
      4   N          North/South
      5   00042.24   current Longitude
      6   W          East/West
      7   173.8      Speed in knots
      8   231.8      True course
      9   130694     Date Stamp
      10  004.2      Variation
      11  W          East/West
      12  *70        checksum

eg4. for NMEA 0183 version 3.00 active the Mode indicator field is added
Field #
1    = UTC time of fix
2    = Data status (A=Valid position, V=navigation receiver warning)
3    = Latitude of fix
4    = N or S of longitude
5    = Longitude of fix
6    = E or W of longitude
7    = Speed over ground in knots
8    = Track made good in degrees True
9    = UTC date of fix
10   = Magnetic variation degrees (Easterly var. subtracts from true course)
11   = E or W of magnetic variation
12   = Mode indicator, (A=Autonomous, D=Differential, E=Estimated, N=Data not valid)
13   = Checksum



           1 2 3 4 5 ..
  • Number of sentences in sequence
  • Sentence number
  • 'c' = Current active route, 'w' = waypoint list starts with destination waypoint
  • Name or number of the active route
  • onwards, Names of waypoints in Route


Transit Fix Data

Time, date, position, and information related to a TRANSIT Fix.

hhmmss.ss = UTC of position fix

xxxxxx = Date: dd/mm/yy
llll.ll,a = Latitude of position fix, N/S
yyyyy.yy,a = Longitude of position fix, E/W
x.x = Elevation angle
x.x = Number of iterations
x.x = Number of Doppler intervals
x.x = Update distance, nautical miles
x.x = Satellite ID


Multiple Data ID.

This sentence is transmitted before each individual sentence where there is a need for the Listener to determine the exact source of data in the system. Examples might include dual-frequency depthsounding equipment or equipment that integrates data from a number of sources and produces a single output.

xx = Talker ID number, 00 to 99


Dual Ground / Water Speed

Water referenced and ground referenced speed data.

x.x = Longitudinal water speed, knots
x.x = Transverse water speed, knots
A = Status: Water speed, A = Data valid

x.x = Longitudinal ground speed, knots
x.x = Transverse ground speed, knots
A = Status: Ground speed, A = Data valid


Track Made Good and Ground Speed.

eg1. $GPVTG,360.0,T,348.7,M,000.0,N,000.0,K*43
eg2. $GPVTG,054.7,T,034.4,M,005.5,N,010.2,K*41

           054.7,T      True course made good over ground, degrees
           034.4,M      Magnetic course made good over ground, degrees
           005.5,N      Ground speed, N=Knots
           010.2,K      Ground speed, K=Kilometers per hour

eg3. for NMEA 0183 version 3.00 active the Mode indicator field
     is added at the end
           A            Mode indicator (A=Autonomous, D=Differential,
                        E=Estimated, N=Data not valid)


Waypoint location

eg1. $GPWPL,4917.16,N,12310.64,W,003*65

           4917.16,N    Latitude of waypoint
           12310.64,W   Longitude of waypoint
           003          Waypoint ID

             When a route is active, this sentence is sent once for each
             waypoint in the route, in sequence. When all waypoints have
             been reported, GPR00 is sent in the next data set. In any
             group of sentences, only one WPL sentence, or an R00
             sentence, will be sent.

eg2.  $GPWPL,5128.62,N,00027.58,W,EGLL*59
         1     2     3    4  5   6

      1    5128.62   Latitude of nth waypoint on list
      2    N         North/South
      3    00027.58  Longitude of nth waypoint
      4    W         East/West
      5    EGLL      Ident of nth waypoint
      6    *59       checksum


Cross Track Error, Measured

eg1. $GPXTE,A,A,0.67,L,N

           A            General warning flag V = warning
                                (Loran-C Blink or SNR warning)
           A            Not used for GPS (Loran-C cycle lock flag)
           0.67         cross track error distance
           L            Steer left to correct error (or R for right)
           N            Distance units - Nautical miles

eg2. $GPXTE,A,A,4.07,L,N*6D
            1 2  3   4 5 6

      1    A         validity
      2    A         cycle lock
      3    4.07      distance off track
      4    L         steer left (L/R)
      5    N         distance units
      6    *6D       checksum


UTC Date / Time and Local Time Zone Offset

Example 1: $GPZDA,hhmmss.ss,xx,xx,xxxx,xx,xx

hhmmss.ss = UTC
xx = Day, 01 to 31
xx = Month, 01 to 12
xxxx = Year
xx = Local zone description, 00 to +/- 13 hours
xx = Local zone minutes description (same sign as hours)

Example 2: $GPZDA,024611.08,25,03,2002,00,00*6A

Field Example Comments
Sentence ID $GPZDA
UTC Time 024611.08 UTC time
UTC Day 25 UTC day (01 to 31)
UTC Month 03 UTC month (01 to 12)
UTC Year 2002 UTC year (4 digit format)
Local zone hours 00 Offset to local time zone in hours (+/- 00 to +/- 59)
Local zone minutes 00 Offset to local time zone in minutes (00 to 59)
Checksum *6A