iPhone Compass GPS Direction

Question

I\'m trying to develop an application that use the GPS and Compass of the iPhone in order to point some sort of pointer to a specific location (like the compass always point

Answer 1

Use this. You will have to subtract out your actual compass heading from the result of getHeadingForDirection to determine the proper relative heading. Return value is heading in radians.

-(float) angleToRadians:(float) a {
    return ((a/180)*M_PI);
}


- (float) getHeadingForDirectionFromCoordinate:(CLLocationCoordinate2D)fromLoc toCoordinate:(CLLocationCoordinate2D)toLoc
{

    float fLat = [self angleToRadians:fromLoc.latitude];
    float fLng = [self angleToRadians:fromLoc.longitude];
    float tLat = [self angleToRadians:toLoc.latitude];
    float tLng = [self angleToRadians:toLoc.longitude];

    return atan2(sin(tLng-fLng)*cos(tLat), cos(fLat)*sin(tLat)-sin(fLat)*cos(tLat)*cos(tLng-fLng));         
}