Tech Chat | Common NMEA Messages Used in RTK Devices
In our previous blogs, we introduced NMEA-0183 and the key message $GPGGA. For RTK devices, providing Positioning, Navigation and Timing (PNT) data to different software and platforms often involves the use of standard NMEA messages. In this blog, we will introduce the most common NMEA messages used in RTK devices, in addition to $GPGGA.
Read previous blog: Tech Chat – What is NMEA-0183 & GPGGA?
Overview of Common NMEA-0183 Messages:
- $GPGLL: Provides information about time, latitude, longitude, and more.
- $GPZDA: Offers UTC time and date information.
- $GPGSV: Includes PRN numbers, elevation, azimuth, and SNR values of satellites in view.
- $GPRMC: Contains data on time, date, speed, and true heading.
Tip: In the output messages of RTK devices, the first two characters of the message header may vary depending on the satellite system. For example:
- "GP" for GPS satellites
- "GL" for GLONASS satellites
- "GA" for Galileo satellites
- "GB/BD" for BDS (BeiDou) satellites
- "GN" for satellites from multiple systems
Here's a more detailed look at the common NMEA messages:
$GPGLL - Geographic Position Log
The $GPGLL log provides information such as time, latitude, and longitude. It is essential for determining the geographic position.
Standard Format:
$GPGLL,<1>,<2>,<3>,<4>,<5>,<6>*<7>
Example:
$GNGLL,3109.99185951,N,12117.39226328,E,081135.00,A,D*77
- field1: Latitude (ddmm.mmmm)
- field2: Latitude direction (N=North, S=South)
- field3: Longitude (dddmm.mmmm)
- field4: Longitude direction (E=East, W=West)
- field5: UTC (hhmmss.sss)
- field6: Data status (A=Data valid, V=Data invalid)
- field7: Checksum
$GPZDA - UTC Time and Date Log
The $GPZDA log provides UTC time and date information, which is crucial for timing applications.
Standard Format:
$GPZDA,<1>,<2>,<3>,<4>,<5>,<6>*<7>
Example:
$GNZDA,024231.00,29,08,2023,,*7E
- field1: UTC time
- field2: Day (01 to 31)
- field3: Month (01 to 12)
- field4: Year
- field5: Local zone description (not available)
- field6: Local zone minutes description (not available)
- field7: Checksum
$GPGSV - Satellite Information Log
The $GPGSV log provides detailed information about satellites in view, including PRN numbers, elevation, azimuth, and SNR values.
Standard Format:
$GPGSV,<1>,<2>,<3>,<4>,<5>,<6>,<7>,…,<4>,<5>,<6>,<7>*<8>
Example:
$GPGSV,2,1,07,05,35,095,45,13,32,042,43,15,60,014,47,18,57,295,46,1*6F
- field1: Total number of messages (1-9)
- field2: Message number (1-9)
- field3: Total number of satellites in view (00-12)
- field4: Satellite PRN number (GPS=1 to 32, SBAS=120 to 138, GLO=1 to 36, BD2=141 to 177)
- field5: Elevation (degrees, maximum 90)
- field6: Azimuth (degrees True, 000 to 359)
- field7: SNR (Signal-to-Noise Ratio, 00-99 dB, null when not tracking)
- field8: Checksum
$GPRMC - GNSS Heading Data
The $GPRMC log includes essential data such as time, date, speed over ground, and true heading. It is a fundamental NMEA message for navigation.
Standard Format:
$GPRMC,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>*<13>
Example:
$GNRMC,024230.00,A,3109.99208720,N,12117.39264295,E,0.002,314.1,290823,6.3,W,R,V*51
- field1: UTC (hhmmss.sss)
- field2: Position status (A=data valid, V=data invalid)
- field3: Latitude (ddmm.mmmm)
- field4: Latitude direction (N=North, S=South)
- field5: Longitude (dddmm.mmmm)
- field6: Longitude direction (E=East, W=West)
- field7: Speed over ground (knots)
- field8: Track made good (degrees True)
- field9: Date (dd/mm/yy)
- field10: Magnetic variation (degrees)
- field11: Magnetic variation direction (E/W)
- field12: Positioning system mode indicator
- field13: Checksum
These common NMEA messages are indispensable for RTK devices to provide accurate PNT data. Each message serves a specific purpose, and understanding them is vital for accurate and reliable navigation and timing applications.
Learn more about SingularXYZ RTK receivers and systems:
https://www.singularxyz.com/X1.html
https://www.singularxyz.com/SV100.html
https://www.singularxyz.com/Sfaira_One.html
