NMEA-0183 message: VTG

Track made good and speed over ground

The heading computation in this message is derived from consecutive positions. For heading using a moving baseline system, see NMEA-0183 message: PTNL,AVR.

An example of the VTG message string is:

$GPVTG,140.88,T,,M,8.04,N,14.89,K,D*05

VTG message fields

Field

Meaning

0

Message ID $GPVTG

1

Track made good (degrees true)

2

T: track made good is relative to true north

3

Track made good (degrees magnetic)

4

M: track made good is relative to magnetic north

5

Speed, in knots

6

N: speed is measured in knots

7

Speed over ground in kilometers/hour (kph)

8

K: speed over ground is measured in kph

9

Mode indicator:

A: Autonomous mode
D: Differential mode
E: Estimated (dead reckoning) mode
M: Manual Input mode
S: Simulator mode
N: Data not valid

10

The checksum data, always begins with *

From firmware 5.15 onward, when the Receiver Motion (Dynamic model) field in the Receiver Configuration - Position screen (see Position) is set to Marine, the following threshold behavior occurs in the NMEA VTG message:

  • When the antenna Speed over Ground (SOG) is less that 0.1 knot (0.05 m/s) then SOG and Course over ground (COG) will be output as 0.0°.

  • When the receiver is in RTK or RTX positioning modes, the velocity is based on the more precise Doppler-based method.