Question

I have a method that that is suppose to calculate the bearing between two geographic coordinates (in 40.7486, -73.9864 example format).

I am however, having an issue where the heading that it calculates is different from the heading I calculate using a tried and tested application.

For example, the initial bearing between of the following points is 074 degrees, however my method returns 047.

40.7486, -73.9864

40.9486, -72.9866

Here is the relevant snippit of code.

        /// <summary>
    /// Calculate the inital bearing between two Locations
    /// </summary>
    /// <param name="pointA"></param>
    /// <param name="pointB"></param>
    /// <param name="headingType"></param>
    /// <returns></returns>
    public static double BearingToLocation(Location pointA, Location pointB)
    {
        // Convert both locations from degrees to radians
        pointA = LocationToRad(pointA);
        pointB = LocationToRad(pointB);

        double partOne = exMath.Sin(pointB.Longitude - pointA.Longitude) * exMath.Cos(pointB.Latitude);
        double partTwo = exMath.Cos(pointA.Latitude) * exMath.Sin(pointB.Latitude) - exMath.Sin(pointA.Latitude) * exMath.Cos(pointB.Latitude) * exMath.Cos(pointB.Longitude - pointA.Longitude);
        double heading = AdditionalMath.ToDeg(exMath.Atan2(partOne, partTwo) % 2 * exMath.PI);

        // Solve for compass wrap around
        if (heading < 0)
            heading += 360;

        return heading;
    }

    /// <summary>
    /// Return a new location in radians
    /// </summary>
    /// <param name="pointA"></param>
    /// <returns></returns>
    public static Location LocationToRad(Location pointA)
    {
        return new Location(AdditionalMath.ToRad(pointA.Latitude), AdditionalMath.ToRad(pointA.Longitude), pointA.Altitude);
    }

}

/// <summary>
/// Misc. math functions not available in Elze Kool's lib
/// </summary>
public static class AdditionalMath
{
    /// <summary>
    /// Degrees to radians
    /// </summary>
    /// <param name="x"></param>
    /// <returns></returns>
    public static double ToRad(double x)
    {
        return exMath.PI * x / 180.00F;
    }

    /// <summary>
    /// Radians to degrees
    /// </summary>
    /// <param name="x"></param>
    /// <returns></returns>
    public static double ToDeg(double x)
    {
        return x * 180.00F / exMath.PI;
    }
}

Can anyone see the issue? I looked it over and could not find the issue.

Answer 1

The % looks fishy in this line:

    double heading = AdditionalMath.ToDeg(exMath.Atan2(partOne, partTwo) % 2 * exMath.PI);