VTG - Velocity made good.

VTG - Velocity made good. The gps receiver may use the LC prefix instead of GP if it is emulating Loran output.

$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

Note that, as of the 2.3 release of NMEA, there is a new field in the VTG sentence at the end just prior to the checksum. For more information on this field see here.