Understanding GPS NMEA Sentences: GPGGA, GPGLL, GPVTG, and GPRMC

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This page describes GPS Sentences or NMEA Sentences with example patterns. These GPS Sentences (i.e. NMEA Sentences) covers GPGGA, GPGLL, GPVTG, GPRMC etc.

Introduction

  • A GPS receiver module requires only DC power supply for its operation. It will start outputting data as soon as it has identified GPS satellites within its range.
  • GPS module uses plain ASCII protocol known as NMEA developed by National Marine Electronics Association. Hence they are also known as NMEA sentences.
  • Each block of data is referred to as a “sentence”. Each of these sentences are parsed independently.
  • The default transmission rate of these gps sentences is 4800 bps. Certain GPS modules use a serial rate of 9600 bps also. It uses 8 bits for ASCII character, no parity and 1 stop bit.
  • Sentence begins with two letters to represent GPS device. For example, “GP” represents a GPS device and so on.
  • The remainder of the sentence consists of letters/numerals in plain ASCII. A sentence cannot have more than 80 characters.
  • A sentence carries latitude, longitude, altitude and time of readings obtained from satellites.
  • Some sentence data structures are proprietary, developed by device manufacturers, and begin with the letter “P”.

Following is the generic table which mentions functional description of NMEA output messages.

GPS Sentences or NMEA Sentences

NMEA SentenceMeaning
GPGGAGlobal positioning system fix data (time, position, fix type data)
GPGLLGeographic position, latitude, longitude
GPVTGCourse and speed information relative to the ground
GPRMCTime, date, position, course and speed data
GPGSAGPS receiver operating mode, satellites used in the position solution, and DOP values.
GPGSVThe number of GPS satellites in view satellite ID numbers, elevation, azimuth and SNR values.
GPMSSSignal to noise ratio, signal strength, frequency, and bit rate from a radio beacon receiver.
GPTRFTransit fix data
GPSTNMultiple data ID
GPXTEcross track error, measured
GPZDADate and time (PPS timing message, synchronized to PPS). 150 OK to send message.

GPS sentence | GPGGA

Following table mentions GPGGA sentence description with example.

Example of GPGGA GPS sentence: $GPGGA, 161229.487, 3723.2475, N, 12158.3416, W, 1, 07, 1.0, 9.0, M, , , , 0000*18

Name or FieldExampleDescription
Message ID$GPGGAGGA protocol header
UTC time161229.487hhmmss.sss
Latitude3723.2475(37 degrees, 23.2475 minutes) ddmm.mmmm
N/S IndicatorNN = North, S = South
Longitude12158.3416(121 degrees, 58.3416 minutes) dddmm.mmmm
E/W indicatorWE = East or W = West
Position Fix Indicator1GPS Sentences Position Fix Indicator
Satellites used07Range is 0 to 12
HDOP1.0Horizontal Dilution of Precision
MSL Altitude9.0Meters
UnitsMMeters
Geoid SeparationMeters
UnitsMMeters
Age of diff. corr.Second
Diff. ref. station ID0000
Checksum*18
<CR><LF>End of message termination

GPS sentence | GPGLL

Following table mentions GPGLL sentence description with example.

Example of GPGLL GPS sentence: $GPGLL, 3723.2475, N, 12158.3416, W, 161229.487, A, A*41

Name or FieldExampleDescription
Message ID$GPGLLGLL protocol header
Latitude3723.2475ddmm.mmmm
N/S indicatorNN =North or S = south
Longitude12158.3416dddmm.mmmm
E/W indicatorWE =East or W = West
UTC time161229.487hhmmss.sss
StatusAA = data valid or V = data not valid
ModeAA =Autonomous , D =DGPS, E =DR (This field is only present in NMEA version 3.0)
Checksum*41
<CR><LF>End of message termination

GPS sentence | GPVTG

Following table mentions GPVTG sentence description with example.

Example of GPVTG GPS sentence: $GPVTG, 309.62, T, ,M, 0.13, N, 0.2, K, A*23

Name or FieldExampleDescription
Message ID$GPVTGVTG protocol header
Course309.62degrees
ReferenceTTrue Course
DegreesReference M Magnetic
Speed0.13Knots, measured horizontal speed
UnitsNKnots
Speed0.2Km/Hr, Measured horizontal speed
UnitsKKilometers per hour
ModeAA = Autonomous, D = DGPS, E = DR
Checksum*23
<CR><LF>End of message termination

GPS sentence | GPRMC

Following table mentions GPRMC sentence description with example.

Example of GPRMC GPS sentence: $GPRMC, 161229.487, A, 3723.2475, N, 12158.3416, W, 0.13, 309.62, 120598, , *10

Name or FieldExampleDescription
Message ID$GPRMCRMC Protocol Header
UTC time161229.487hhmmss.sss
StatusAA = data valid or V = data not valid
Latitude3723.2475ddmm.mmmm
N/S indicatorNN = North or S = South
Longitude12158.3416dddmm.mmmm
E/W indicatorWE = East or W = West
Speed over ground0.13knots
Course over ground309.62degrees
Date120598ddmmyy
Magnetic VariationDegrees (E= East or W = West)
ModeAA = Autonomous, D = DGPS, E =DR
Checksum*10
<CR><LF>End of message termination

Conclusion

NMEA sentences play a crucial role in GPS communication by providing structured data formats for location, speed, time, and other navigation parameters. These sentences, such as GGA (Global Positioning Fix Data), RMC (Recommended Minimum Specific GNSS Data), GSV (Satellites in View), and GSA (GNSS DOP and Active Satellites), enable GPS receivers to interpret and share positioning information accurately. Each sentence follows a standardized format, ensuring compatibility across different GPS devices and applications. Understanding NMEA sentences is essential for developers, engineers, and GPS enthusiasts looking to analyze or integrate GPS data into various tracking, mapping, and navigation systems.

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