Knowledgebase
Supported NMEA Strings
Posted by - NA - on 17 October 2018 10:28 AM

This document outlines the various NMEA String messages that FieldGenius or Evidence Recorder can use for communicating with a GPS receiver: 

$GPGGA, $GPGSA, $GPGSV, $GPVTG, $GPZDA, $GPGST

Further detail can be found at this website.

Supported NMEA Strings


If your GPS receiver uses NMEA strings for communication with FieldGenius, you may be able to
turn on or off many different NMEA message types in the receiver. With a high enough baud
rate, it is typically safe to just have them all enabled, and FieldGenius will simply ignore the
messages it does not need. However, turning off unnecessary messages can help prevent
bottlenecking, especially at low baud rates, as less information is constantly being sent from the
receiver to FieldGenius. Below are the NMEA strings that FieldGenius can use.

$GPGGA (Required)
The GPGGA message contains detailed GPS position information data. This is the only message
that is absolutely required for FieldGenius to operate.  Below is an explanation of each attribute:

$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47

Where:
     GGA          Global Positioning System Fix Data
     123519       Fix taken at 12:35:19 UTC
     4807.038,N   Latitude 48 deg 07.038' N
     01131.000,E  Longitude 11 deg 31.000' E
     1 Fix quality:       0 = invalid
                               1 = GPS fix (SPS)
                               2 = DGPS fix
                               3 = PPS fix
			       4 = Real Time Kinematic
			       5 = Float RTK
                               6 = estimated (dead reckoning) (2.3 feature)
			       7 = Manual input mode
			       8 = Simulation mode
     08           Number of satellites being tracked
     0.9          Horizontal dilution of position
     545.4,M      Altitude, Meters, above mean sea level
     46.9,M       Height of geoid (mean sea level) above WGS84 ellipsoid
     (empty field) time in seconds since last DGPS update
     (empty field) DGPS station ID number
     *47          the checksum data, always begins with *

 

 

$GPGSA
The GPGSA message contains the number of active satellites, and the DOP information of
satellites that were used in the position computation. This message is not required, but will
provide additional information that FieldGenius can use.  Below is an explanation of each attribute:

$GPGSA,A,3,04,05,,09,12,,,24,,,,,2.5,1.3,2.1*39

Where:
     GSA      Satellite status
     A        Auto selection of 2D or 3D fix (M = manual) 
     3        3D fix - values include: 1 = no fix
                                                 2 = 2D fix
                                                 3 = 3D fix
     04,05... PRNs of satellites used for fix (space for 12) 
     2.5      PDOP (dilution of precision) 
     1.3      Horizontal dilution of precision (HDOP) 
     2.1      Vertical dilution of precision (VDOP)
     *39      the checksum data, always begins with *

 

$GPGSV
The GPGSV message contains satellite information, including the number of satellites in view,
and the ID number, position, and signal-to-noise ratio of each satellite. This message is not
required, but will provide additional information that FieldGenius can use.  Below is an explanation of each attribute:

$GPGSV,2,1,08,01,40,083,46,02,17,308,41,12,07,344,39,14,22,228,45*75

Where:
      GSV        Satellites in view
      2             Number of sentences for full data
      1             sentence 1 of 2
      08           Number of satellites in view
      01           Satellite PRN number
      40           Elevation, degrees
      083         Azimuth, degrees
      46           SNR - higher is better for up to 4 satellites per sentence
      *75         the checksum data, always begins with *

$GPVTG
The GPVTG message contains ground course and ground velocity information. This message is
not required, but will provide additional information that FieldGenius can use.

$GPVTG,054.7,T,034.4,M,005.5,N,010.2,K*48

where:
        VTG            Track made good and ground speed
        054.7,T       True track made good (degrees)
        034.4,M      Magnetic track made good
        005.5,N      Ground speed, knots
        010.2,K      Ground speed, Kilometers per hour
        *48            Checksum

$GPZDA
The GPZDA message contains UTC time and date information. This message is not required,
but will provide additional information that FieldGenius can use.

  $GPZDA,hhmmss.ss,dd,mm,yyyy,xx,yy*CC
  $GPZDA,201530.00,04,07,2002,00,00*60

where:
	hhmmss             HrMinSec(UTC)
        dd,mm,yyy         Day,Month,Year
        xx                      local zone hours -13..13
        yy                      local zone minutes 0..59
        *CC                   checksum

 



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