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Old 01-22-2013
kellysails
Puget Sound Pounder

Join Date: Nov 2008
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Re: Calculating true wind

Hmmm, so wouldn't the NMEA (\$GPVTG - Track made good and ground speed) serve as the current heading? It seems as though the GPS is reporting TMG via Magnetic heading. Jeeze I could be all wet here. But I remember even my ancient old GPS's would provide the current Magnetic heading.

\$GPVTG

Track Made Good and Ground Speed.

eg1. \$GPVTG,360.0,T,348.7,M,000.0,N,000.0,K*43
eg2. \$GPVTG,054.7,T,034.4,M,005.5,N,010.2,K

005.5,N Ground speed, knots
010.2,K Ground speed, Kilometers per hour

eg3. \$GPVTG,t,T,,,s.ss,N,s.ss,K*hh
2 = Fixed text 'T' indicates that track made good is relative to true north
3 = not used
4 = not used
5 = Speed over ground in knots
6 = Fixed text 'N' indicates that speed over ground in in knots
7 = Speed over ground in kilometers/hour
8 = Fixed text 'K' indicates that speed over ground is in kilometers/hour
9 = Checksum

The actual track made good and speed relative to the ground.

\$--VTG,x.x,T,x.x,M,x.x,N,x.x,K
x.x,T = Track, degrees True
x.x,M = Track, degrees Magnetic
x.x,N = Speed, knots
x.x,K = Speed, Km/hr
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