Finding the Midpoint Between Two GPS Coordinates
Previously I showed how to find the distance between coordinates and the bearing, but what if you want to find the midpoint of two coordinates.
The code in C# is rather straightforward – that is, if you know a little bit of trigonometry.
namespace Geodesy
{
public class Geodesy
{
public static double RadToDeg(double radians)
{
return radians * (180 / Math.PI);
}
public static double DegToRad(double degrees)
{
return degrees * (Math.PI / 180);
}
public static void MidpointCoords(double lat1, double long1, double lat2, double long2, ref double midpointLat, ref double midpointLong)
{
//Convert input values to radians
lat1 = Geodesy.DegToRad(lat1);
long1 = Geodesy.DegToRad(long1);
lat2 = Geodesy.DegToRad(lat2);
long2 = Geodesy.DegToRad(long2);
double deltaLat = lat2 - lat1;
double deltaLong = long2 - long1;
double Bx = Math.Cos(lat2) * Math.Cos(deltaLong);
double By = Math.Cos(lat2) * Math.Sin(deltaLong);
midpointLat = Geodesy.RadToDeg(Math.Atan2(Math.Sin(lat1) + Math.Sin(lat2),
Math.Sqrt((Math.Cos(lat1) + Bx) * (Math.Cos(lat1) + Bx) + By * By)));
midpointLong = Geodesy.RadToDeg(long1 + Math.Atan2(By, Math.Cos(lat1) + Bx));
}
}
}Originally posted on my old blog, Smoky Cogs, on 8 Oct 2009