C＃查找两个纬度/经度的中点

Question

I need to find the midpoint between two Latitude/Longitude points.

I am trying to center a map between two locations I have plotted and need to find that point.

I have written this function from other examples I have found and it doesn't seem to work.

    public static void midPoint(double lat1, double lon1, double lat2, double lon2, out double lat3_OUT, out double lon3_OUT)
    {
        //http:// stackoverflow.com/questions/4656802/midpoint-between-two-latitude-and-longitude
        double dLon = DistanceAlgorithm.Radians(lon2 - lon1);

        //convert to radians
        lat1 = DistanceAlgorithm.Radians(lat1);
        lat2 = DistanceAlgorithm.Radians(lat2);
        lon1 = DistanceAlgorithm.Radians(lon1);

        double Bx = Math.Cos(lat2) * Math.Cos(dLon);
        double By = Math.Cos(lat2) * Math.Sin(dLon);
        double lat3 = Math.Atan2(Math.Sin(lat1) + Math.Sin(lat2), Math.Sqrt((Math.Cos(lat1) + Bx) * (Math.Cos(lat1) + Bx) + By * By));
        double lon3 = lon1 + Math.Atan2(By, Math.Cos(lat1) + Bx);

        lat3_OUT = lat3;
        lon3_OUT = lon3;
    }

Here is an example output.

lat1  37.7977008
lat2  37.798392     
lon1  -122.1637914      
lon2  -122.161464       
lat3  0.65970036060147585   
lon3  -2.1321400763480485   

See Lat3 and Lon3.

Thanks!

Answer 1

It appears that your output is correct , except that it is in radians and you are expecting degrees ? you may need to convert from radian to degrees to meet the expected output.

-(2.1321400763480485 radians) = -122.162628 degrees
0.65970036060147585 radians = 37.7980464 degrees

It looks like you are already using the great-circle algorithm that Jon Martin and IanDotKelly mentioned.

Answer 2

I presume you mean great-circle distances.

If so, this question here has been asked before, although if you didn't know the term great-circle it might be hard to find.