Help calculating $GPRMB value ("true bearing to destination")

Hi everyone,

In the $GPRMB data string, the 11th byte gives the "true bearing to
destination". I need to verify this parameter and was wondering how to
calculate it based on the LAT and LONG data. I have come across a
variey of formulas on the web:

TB1 =
acos((sin(LAT_DEST)-sin(LAT_START)*cos(D))/(sin(D)*cos(LAT_START)))
TB2 = 360 -
acos((sin(LAT_DEST)-sin(LAT_START)*cos(D))/(sin(D)*cos(LAT_START)))
TB3 = atan2((LAT_DEST - LAT_START),(LONG_DEST - LONG_START))

I think TB2 (law of cosines) is probably the most accurate and
efficient way to calculate this value, right?

Thanks in advance,
weg

weg22@drexel.edu writes

From

http://williams.best.vwh.net/avform.htm#GCF

Initial great circle heading from point 1 to 2

tc1=mod(atan2(sin(lon1-lon2)*cos(lat2),
cos(lat1)*sin(lat2)-sin(lat1)*cos(lat2)*cos(lon1-lon2)),
2*pi)

That page has lots of other god stuff too.

Hop it helps.

--

Dominic Sexton