help calculating "true bearing to destination" from $GPRMB string

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 think the following
formula is probably the most accurate and efficient way of doing this,
right?

TB2 = acos([sin(LAT_START)*sin(LAT_DEST) +
cos(D/60)]/[sin(D/60)*cos(LAT_START)]

where D = 60*acos[sin(LAT_START)*sin(LAT_DEST) +
cos(LAT_START)*cos(LAT_DEST)*cos(LONG_START-LONG_DEST)]

and LAT_DEST and LONG_DEST are the lattitude and longtitude coordinates
to the destination.


Thanks in advance,
weg

The earth is not a perfect sphere. See
http://www.ngs.noaa.gov/PC_PROD/Inv_Fwd/
for .exe and FORTRAN source.