ASP.NET VB 經緯度距離換算

''' <summary>

''' 換算兩個經緯度的距離(公里)

''' </summary>

''' <param name="lat_a">緯度1</param>

''' <param name="lng_a">經度1</param>

''' <param name="lat_b">緯度2</param>

''' <param name="lng_b">經度2</param>

''' <returns></returns>

''' <remarks></remarks>

Private Function gps2km(ByVal lat_a As Double, ByVal lng_a As Double, ByVal lat_b As Double, ByVal lng_b As Double) As Double

 Dim EARTH_RADIUS As Double = 6378.137

 Dim radLat1 As Double = (lat_a * Math.PI / 180.0)

 Dim radLat2 As Double = (lat_b * Math.PI / 180.0)

 Dim a As Double = radLat1 - radLat2

 Dim b As Double = (lng_a - lng_b) * Math.PI / 180.0

 Dim s As Double = 2 * Math.Asin(Math.Sqrt(Math.Pow(Math.Sin(a / 2), 2) + Math.Cos(radLat1) * Math.Cos(radLat2) * Math.Pow(Math.Sin(b / 2), 2)))

 s = s * EARTH_RADIUS

 s = Math.Round(s * 10000) / 10000

 Return s


End Function