Glenn Baddeley - GPS - NMEA sentence information


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All $GPxxx sentence codes and short descriptions


26 interpreted sentences transmitted by GPS unit

   $GPAAM - Waypoint Arrival Alarm
   $GPALM - GPS Almanac Data (Can also be received by GPS unit)
   $GPAPB - Autopilot format "B"
   $GPBOD - Bearing, origin to destination
   $GPBWC - Bearing and distance to waypoint, great circle
   $GPGGA - Global Positioning System Fix Data
   $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
   $GPHDT - Heading, True
   $GPMSK - Control for a Beacon Receiver
   $GPMSS - Beacon Receiver Status
   $GPR00 - List of waypoints in currently active route
   $GPRMA - Recommended minimum specific Loran-C data
   $GPRMB - Recommended minimum navigation info
   $GPRMC - Recommended minimum specific GPS/TRANSIT data
   $GPRTE - Routes
   $GPTRF - TRANSIT Fix Data
   $GPSTN - Multiple Data ID
   $GPVBW - Dual Ground / Water Speed
   $GPVTG - Track made good and ground speed
   $GPWPL - Waypoint location
   $GPXTE - Cross-track error, Measured
   $GPZDA - UTC Date / Time and Local Time Zone Offset

There is a full list of $GPxxx sentence codes available, without links to format details.



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*77

Sentence ID$GPALM 
Number of messages1Total number of messages in sequence
Sequence number1This is first message in sequence
Satellite PRN15Unique ID (PRN) of satellite message relates to
GPS week number1159 
SV health00Bits 17-24 of almanac page
Reference time4eAlmanac reference time
Inclination angle16be 
Rate of right ascensionfd5e 
Roor of semi-major axisa10c9f 
Argument of perigee4a2da4 
Longitude of ascension node686e81 
Mean anomoly58cbe1 
F0 clock parameter0a4 
F1 clock parameter001 



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,*48
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*4A
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*21 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,,,*59

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

Courtesy of Brian McClure, N8PQI.

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

eg2. $GPGGA,,ddmm.mmm,a,dddmm.mmm,b,q,xx,p.p,a.b,M,c.d,M,x.x,nnnn = 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*31

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,,A llll.ll = Latitude of position

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


GPS Range Residuals

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

Sentence ID$GPGRS 
UTC Time024603.00UTC time of associated GGA fix
Mode10 = Residuals used in GGA, 1 = residuals calculated after GGA
Sat 1 residual-1.8Residual (meters) of satellite 1 in solution
Sat 2 residual-2.7The order matches the PRN numbers in the GSA sentence
Sat 3 residual0.3 
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  



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 2=2D 3=3D 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

Sentence ID$GPGST 
UTC Time024603.00UTC time of associated GGA fix
RMS deviation3.2Total RMS standard deviation of ranges inputs to the navigation solution
Semi-major deviation6.6Standard deviation (meters) of semi-major axis of error ellipse
Semi-minor deviation4.7Standard deviation (meters) of semi-minor axis of error ellipse
Semi-major orientation47.3Orientation of semi-major axis of error ellipse (true north degrees)
Latitude error deviation5.8Standard deviation (meters) of latitude error
Longitude error deviation5.6Standard deviation (meters) of longitude error
Altitude error deviation22.0Standard deviation (meters) of latitude error



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

Sentence ID$GPMSS 
Signal strength0.0Signal strength (dB 1uV)
SNR0.0Signal to noise ratio (dB)
Frequency0.0Beacon frequency (kHz)
Data rate25Beacon data rate (BPS)
Unknown field2Unknown field sent by GPS receiver used for test



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*20

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 $GPRMC,,A,llll.ll,a,yyyyy.yy,a,x.x,x.x,ddmmyy,x.x,a,m*hh 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 ..
  1. Number of sentences in sequence
  2. Sentence number
  3. 'c' = Current active route, 'w' = waypoint list starts with destination waypoint
  4. Name or number of the active route
  5. onwards, Names of waypoints in Route



Time, date, position, and information related to a TRANSIT Fix. The $GPTRF and $GPGXA sentences became obsolete when the TRANSIT satellite navigation system was replaced with GPS in 1996, refer to Wikipedia for further details.

$--TRF,,xxxxxx,llll.ll,a,yyyyy.yy,a,x.x,x.x,x.x,x.x,xxx = 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*34
eg2. $GPVTG,054.7,T,034.4,M,005.5,N,010.2,K*48

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 $GPVTG,054.7,T,034.4,M,005.5,N,010.2,K,A*25 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*6F

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,,xx,xx,xxxx,xx,xx = 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

Sentence ID$GPZDA 
UTC Time024611.08UTC time
UTC Day25UTC day (01 to 31)
UTC Month03UTC month (01 to 12)
UTC Year2002UTC year (4 digit format)
Local zone hours00Offset to local time zone in hours (+/- 00 to +/- 59)
Local zone minutes00Offset to local time zone in minutes (00 to 59)

[ Top ]

12 interpreted Garmin proprietary sentences transmitted by GPS unit

   $HCHDG  - Compass Heading
   $PGRMB  - DGPS Beacon Information
   $PGRMC  - Sensor Configuration Information
   $PGRMC1 - Additional Sensor Configuration Information
   $PGRME  - Estimated Position Error
   $PGRMF  - GPS Position Fix Data
   $PGRMI  - Sensor Initialization Information
   $PGRMM  - Map Datum
   $PGRMT  - Sensor Status Information
   $PGRMV  - 3D Velocity Information
   $PGRMZ  - Altitude Information
   $PSLIB  - Tune DPGS Beacon Receiver



Compass Heading

This sentence is used on Garmin eTrex summit, Vista and GPS76S receivers to output the value of the internal flux-gate compass. Only the magnetic heading and magnetic variation is shown in the message.


     HCHDG    Magnetic heading, deviation, variation
     101.1    heading
     ,,       deviation (no data)
     7.1,W    variation


DGPS Beacon Information

1 = Tune frequency, Kilohertz (283.5 - 325.0 in 0.5 steps)
2 = Bit rate, Bits / second (0, 25, 50, 100, 200)
3 = SNR (Signal to Noise Ratio), 0 - 31
4 = Data Quality, 0 - 100
5 = Distance to beacon reference station
6 = Distance unit (K=Kilometres)
7 = Receiver communication status (0=Check wiring, 1=No signal, 2=Tuning, 3=Receiving, 4=Scanning)
8 = Fix source (R=RTCM, W=WAAS, N=Non-DPGS fix)
9 = DGPS Mode (A=Automatic, W=WAAS only, R=RTCM Only, N=None; DGPS disabled)
HH = Checksum


Estimated Position Error

eg. $PGRME,15.0,M,45.0,M,25.0,M*1C

15.0,M Estimated horizontal position error (HPE), M=metres 45.0,M Estimated vertical position error (VPE), M=metres 25.0,M Overall spherical equivalent position error, M=metres


GPS Position Fix Data

1 = GPS week number
2 = GPS seconds in current week
3 = UTC date, ddmmyy format
4 = UTC time, hhmmss format
5 = GPS leap second count
6 = Latitude, dddmm.mmmm format
7 = Latitude hemisphere, N or S
8 = Longitude, dddmm.mmmm format
9 = Longitude hemisphere, E or W
10 = Mode (M=Manual, A=Automatic)
11 = Fix type (0=No fix, 1=2D fix, 2=3D fix)
12 = Speed over ground, kilometres / hour
13 = Course over ground, degrees true
14 = PDOP (Position dilution of precision), rounded to nearest integer
15 = TDOP (Time dilution of precision), rounded to nearest integer
HH = Checksum


Map datum

Example 1: $PGRMM,Astrln Geod '66*51

'Astrln Geod 66' = Name of currently active datum

Example 2: $PGRMM,NAD27 Canada*2F

'NAD27 Canada' = Name of currently active datum


Sensor Status Information

1 = Garmin product model and software version (eg. GPS 16 VER 2.10)
2 = ROM checksum test (P=Pass, F=Fail)
3 = Receiver failure discrete (P=Pass, F=Fail)
4 = Stored data lost (R=Retained, L=Lost)
5 = Real time clock lost (R=Retained, L=Lost)
6 = Oscillator drift discrete (P=Pass, F=Excessive drift detected)
7 = Data collection discrtete (C=Collecting, Null=Not Collecting)
8 = GPS sensor temperature (Degrees C)
9 = GPS sensor configuration data (R=Retained, L=Lost)
HH = Checksum


3D Velocity Information

1 = True east velocity, metres / sec
2 = True north velocity, metres / sec
3 = Upward velocity, metres / sec
HH = Checksum


Altitude Information

eg1. $PGRMZ,246,f,3*1B
eg2. $PGRMZ,93,f,3*21

93,f Altitude in feet 3 Position fix dimensions 2 = user altitude 3 = GPS altitude This sentence shows in feet, regardless of units shown on the display.
eg3. $PGRMZ,201,f,3*18 1 2 3
1 201 Altitude 2 F Units - f-Feet 3 checksum


Tune DPGS Beacon Receiver

Proprietary Differential Control sentences to control a Starlink differential beacon receiver, assuming Garmin's DBR is made by Starlink.

eg1.    $PSLIB,290.5,100,J*33
eg2.    $PSLIB,300.0,200,K*3C

These two sentences are normally sent together in each group of sentences from the GPS.

The three fields are: Frequency, bit Rate, Request Type. The value in the third field may be: J = status request, K = configuration request, blank = tuning message.

When the GPS receiver is set to change the DBR frequency or baud rate, the "J" sentence is replaced (just once) by (for example): $PSLIB,320.0,200*59 to set the DBR to 320 KHz, 200 baud.

To tune a Garmin GBR 21, GBR 23 or equivalent beacon receiver.

1 = Beacon tune frequency, Kilohertz (283.5 - 325.0 in 0.5 steps)
2 = Beacon bit rate, Bits / second (0, 25, 50, 100, 200
HH = Checksum

[ Top ]

8 interpreted Garmin proprietary sentences received by GPS unit

   $PGRMC   - Sensor Configuration Information
   $PGRMCE  - Sensor Configuration Information Enquiry
   $PGRMC1  - Additional Sensor Configuration Information
   $PGRMC1E - Additional Sensor Configuration Information Enquiry
   $PGRMI   - Sensor Initialization Information
   $PGRMIE  - Sensor Initialization Information Enquiry
   $PGRMO   - Output Sentence Enable / Disable
   $PSLIB   - Tune DPGS Beacon Receiver

A few Garmin GPS receiver units are known to receive these sentences, including the GPS 16 and GPS 17 modules.



Sensor Configuration Information

Used to configure the GPS sensor's operation. The GPS will also transmit this sentence upon receiving this same sentence or the $PGRMCE sentence.

1 = Fix mode (A=Automatic, 2=2D exclusively; host system must supply altitude, 3=3D exclusively)
2 = Altitude above/below mean sea level, metres
3 = Earth datum index. If the user datum index is specified (96), fields 4 to 8 must contain valid values, otherwise they must be blank.
4 = Semi-major axis, metres, 0.001 metre resolution
5 = Inverse flattening factor, 285 to 310, 10e-9 resolution
6 = Delta X earth centred coordinate, metres, -5000 to 5000, 1 metre resolution
7 = Delta Y earth centred coordinate, metres, -5000 to 5000, 1 metre resolution
8 = Delta Z earth centred coordinate, metres, -5000 to 5000, 1 metre resolution
9 = Differential mode (A=Automatic; output DGPS fixes when available otherwise non-DGPS, D=Only output differential fixes)
10 = NMEA 0183 baud rate (1=1200, 2=2400, 3=4800, 4=9600, 5=19200, 6=300, 7=600)
11 = Velocity filter (0=None, 1=Automatic, 2-255=Filter time constant; seconds)
12 = PPS mode (1=None, 2=1 Hertz)
13 = PPS pulse length, N = 0 to 48. Length (milliseconds) = (N+1)*20
14 = Dead reckoning valid time, 1 to 30, seconds
HH = Checksum


Sensor Configuration Information Enquiry

The unit will respond by transmitting a $PGRMC sentence containing the current default values.

HH = Checksum


Additional Sensor Configuration Information

Used to configure additional aspects of the GPS sensor's operation. The GPS will also transmit this sentence upon receiving this same sentence or the $PGRMC1E sentence.

1 = NMEA 0183 output time, 1-900, seconds (Not applicable to GPS16A)
2 = Binary phase output data (1=Off, 2=On)
3 = Position pinning (1=Off, 2=On)
4 = DGPS beacon frequency, Kilohertz, 283.5 to 325.0 in 0.5 steps
5 = DGPS beacon bit rate (0, 25, 50, 100, 200)
6 = DGPS beacon scanning (1=Off, 2=On)
7 = NMEA 0183 version 3.00 mode indicator (1=Off, 2=On)
8 = DGPS mode (A=Automatic, W=WAAS only, R=RTCM only, N=None; DGPS disabled)
9 = Power save mode (P=Activated, N=Normal)
HH = Checksum


Additional Sensor Configuration Information Enquiry

The unit will respond by transmitting a $PGRMC1 sentence containing the current default values.

HH = Checksum


Sensor Initialization Information

Used to set the GPS sensor's set time and position and then commences satellite acquisition. The GPS will also transmit this sentence upon receiving this same sentence or the $PGRMIE sentence.

1 = Latitude, dddmm.mmm format
2 = Latitude hemisphere, N or S
3 = Longitude, dddmm.mmm format
4 = Longitude hemisphere, N or S
5 = Current UTC date, ddmmyy format
6 = Current UTC time, hhmmss format
7 = Receiver command (A=Auto locate, R=Unit reset)
HH = Checksum


Sensor Initialization Information Enquiry

The unit will respond by transmitting a $PGRMI sentence containing the current default values.

HH = Checksum


Output Sentence Enable / Disable

xxxxx = Target sentence name (eg. GPGGA, GPGSA)
n = Target mode (0=Disable specified sentence, 1=Enable specified sentence, 2=Disable all output sentences except PSLIB, 3=Enable all output sentences except GPALM, 4=Restore factory defaults)
HH = Checksum

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Format of latitudes and longitudes

Where a numeric latitude or longitude is given, the two digits immediately to the left of the decimal point are whole minutes, to the right are decimals of minutes, and the remaining digits to the left of the whole minutes are whole degrees.

eg. 4533.35 is 45 degrees and 33.35 minutes. ".35" of a minute is exactly 21 seconds.

eg. 16708.033 is 167 degrees and 8.033 minutes. ".033" of a minute is about 2 seconds.

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This information on NMEA sentences has been sourced from all over the 'net and I make no apologies for any inaccuracies or errors. Still, it's useful stuff. I wish to thank all the sources, which are listed on my GPS Links page. Please contact me if you know of freely available interpretations of sentences which are not on this page.


Copyright © Glenn Baddeley 2002, 2011 was last updated 24th May 2011.
Report problems and send comments to Glenn Baddeley.