help calculating "true bearing to destination" value in $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

You may want to adjust if the azimuth is NW or SW of TB2..
(if east of start TB2 the same, if west TB2 = 360 - TB2)

TB2 =ARCCOS [(SIN(Lat_Dest) - SIN(Lat_Start) * COS(D/60))/(SIN(D/60) *
COS(Lat_Dest))]

But why are you calculating bearing from the start point/ In navigation
wouldn't you want to calculate from the CURRENT position? That's just the
pilot in me talking.

Raoul Watson wrote:


Some GPS displays will show a route starting point to destination line
while you are following a route.

I don't use it but if you were on a one leg route it would give you a
visual representation of the cross track error. Not sure what other
purposes it would have.

Jack


--
Jack Erbes in Ellsworth, Maine, USA - jackerbes at adelphia dot net
(also receiving email at jacker at midmaine.com)