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Cellular forums Home > Archive > Garmin GPS > April 2006 > help calculating "true bearing to destination" value in $GPRMB string
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help calculating "true bearing to destination" value in $GPRMB string
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| weg22@drexel.edu 2006-04-10, 11:48 pm |
| 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(& #91;sin(LAT_START)*s
in(LAT_DEST) +
cos(D/60)]/[sin(D/60)*cos(LAT_START)]
where D = 60*acos& #91;sin(LAT_START)*s
in(LAT_DEST) +
cos(LAT_START)*cos(L
AT_DEST)*cos(LONG_ST
ART-LONG_DEST)]
and LAT_DEST and LONG_DEST are the lattitude and longtitude coordinates
to the destination.
Thanks in advance,
weg
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| Raoul Watson 2006-04-19, 11:48 pm |
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<weg22@drexel.edu> wrote in message
news:1144706198.954245.231590@v46g2000cwv.googlegroups.com...
> 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(& #91;sin(LAT_START)*s
in(LAT_DEST) +
> cos(D/60)]/[sin(D/60)*cos(LAT_START)]
>
> where D = 60*acos& #91;sin(LAT_START)*s
in(LAT_DEST) +
> cos(LAT_START)*cos(L
AT_DEST)*cos(LONG_ST
ART-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.
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