/// <summary>
/// Compute the compass direction between two points using the starting bearing as the direction
/// </summary>
/// <param name="fromX">source X ordinate</param>
/// <param name="fromY">source Y ordinate</param>
/// <param name="toX">destination X ordinate</param>
/// <param name="toY">destination Y ordinate</param>
/// <returns>The compass direction from a to b</returns>
public double DirectionStartBearing(double fromX, double fromY, double toX, double toY)
{
fromX = AngleUtils.ToRadians(fromX);
fromY = AngleUtils.ToRadians(fromY);
toX = AngleUtils.ToRadians(toX);
toY = AngleUtils.ToRadians(toY);
double dLon = toX - fromX;
double y = Math.Sin(dLon) * Math.Cos(toY);
double x = Math.Cos(fromY) * Math.Sin(toY) - Math.Sin(fromY) * Math.Cos(toY) * Math.Cos(dLon);
return(AngleUtils.ToDegrees(Math.Atan2(y, x)));
}
/// <summary>
/// Compute the compass direction between two points using the Mid-point of the path as the direction
/// </summary>
/// <param name="fromX">source X ordinate</param>
/// <param name="fromY">source Y ordinate</param>
/// <param name="toX">destination X ordinate</param>
/// <param name="toY">destination Y ordinate</param>
/// <returns>The compass direction from a to b</returns>
public double DirectionMidBearing(double fromX, double fromY, double toX, double toY)
{
fromX = AngleUtils.ToRadians(fromX);
fromY = AngleUtils.ToRadians(fromY);
toX = AngleUtils.ToRadians(toX);
toY = AngleUtils.ToRadians(toY);
double dLon = toX - fromX;
var Bx = Math.Cos(toY) * Math.Cos(dLon);
var By = Math.Cos(toY) * Math.Sin(dLon);
var lat3 = AngleUtils.ToDegrees(Math.Atan2(Math.Sin(fromY) + Math.Sin(toY), Math.Sqrt((Math.Cos(fromY) + Bx) * (Math.Cos(fromY) + Bx) + By * By)));
var lon3 = AngleUtils.ToDegrees(fromX + Math.Atan2(By, Math.Cos(fromY) + Bx));
return(DirectionStartBearing(lon3, lat3, toX, toY));
}