/// <summary>
///計算兩點GPS坐標的距離
/// </summary>
/// <param name="n1">第一點的緯度坐標</param>
/// <param name="e1">第一點的經度坐標</param>
/// <param name="n2">第二點的緯度坐標</param>
/// <param name="e2">第二點的經度坐標</param>
/// <returns></returns>
public static double Distance(double n1, double e1, double n2, double e2)
{
  double jl_jd = 102834.74258026089786013677476285;
  double jl_wd = 111712.69150641055729984301412873;
  double b = Math.Abs((e1 - e2) * jl_jd);
  double a = Math.Abs((n1 - n2) * jl_wd);
  return Math.Sqrt((a * a + b * b));
}
/// <summary>
/// 已知汽車行駛的兩個GPS點，求汽車行駛的方向
/// </summary>
/// <param name="n1">第一個GPS點緯度</param>
/// <param name="e1">第一個GPS點經度</param>
/// <param name="n2">第二個GPS點緯度</param>
/// <param name="e2">第二個GPS點經度</param>
/// <returns></returns>
public static double GetBusDirection( double n1,double e1, double n2, double e2)
{
  double e3 = 0;
  double n3 = 0;
  e3 = e1 + 0.005;
  n3 = n1;
  double a = 0;
  double b = 0;
  double c = 0;
  a = Distance(e1, n1, e3, n3);
  b = Distance(e3, n3, e2, n2);
  c = Distance(e1, n1, e2, n2);
  double cosB = 0;
  if ((a * c) != 0)
  {
 cosB = (a * a + c * c - b * b) / (2 * a * c);
  }
  double B = Math.Acos(cosB) * 180 / Math.PI;
  if(n2<n1)
  {
 B=180+(180-B);
  }
  return B;
}