Calculate a bearing

[scruffyduck]

Hi all

I am writing a program which uses FSCUIPC to control different things like weather etc depending on location. I have an algorithm to calculated distance between two points but wondered if anyone could point me at where to find one to determine the bearing of one location (position of the aircraft) to another (waypoint).

thanks in advance

[Pete Dowson]

... wondered if anyone could point me at where to find one to determine the bearing of one location (position of the aircraft) to another (waypoint).

The formula I use in TrafficLook is very approximate, being normal plane trigonometry. That'd be reasonably close for near waypoints, but progressively worse as distance increases due to the curvature of the Earth. Also, I think my formula would be pretty bad anywhere near the poles (> 60 degrees N or S).

// Everything in double floats, angles in degrees, result is True not Mag

double Wrk = cos(PI * (fabs(MyLat+WayLat))/360.0)*(WayLon-MyLon);

double Bearing = (MyLat == WayLat) ? 90.0 : (180.0 * atan(fabs(Wrk/(WayLat-MyLat))) / PI);

if (MyLat >= WayLat)
{	if (MyLon >= WayLon) Bearing = 180.0 + Bearing;
	else Bearing = 180.0 - Bearing;
}
else if (MyLon > WayLon) Bearing = 360.0 - Bearing;

If you want accurate bearings for longer distances or for anywhere in the world, you need spherical trig. Then I'm rather lost. You can find formulae on the 'net but you need to search.

Regards,

Pete

[scruffyduck]

Hi Pete

Many thanks for that - at the moment I think I only need to be accurate to within +/- 10deg over relatively short distances so that should work fine