c# 4.0 - Calculate distance of two geo points in km c#

Question

I`d like calculate the distance of two geo points. the points are given in longitude and latitude.

the coordinates are:

point 1: 36.578581, -118.291994

point 2: 36.23998, -116.83171

here a website to compare the results:

http://www.movable-type.co.uk/scripts/latlong.html

here the code I used from this link: Calculate distance between two points in google maps V3

    const double PIx = Math.PI;
    const double RADIO = 6378.16;

    /// <summary>
    /// Convert degrees to Radians
    /// </summary>
    /// <param name="x">Degrees</param>
    /// <returns>The equivalent in radians</returns>
    public static double Radians(double x)
    {
        return x * PIx / 180;
    }

    /// <summary>
    /// Calculate the distance between two places.
    /// </summary>
    /// <param name="lon1"></param>
    /// <param name="lat1"></param>
    /// <param name="lon2"></param>
    /// <param name="lat2"></param>
    /// <returns></returns>
    public static double DistanceBetweenPlaces(double lon1, double lat1, double lon2, double lat2)
    {
        double R = 6371; // km
        double dLat = Radians(lat2 - lat1);
        double dLon = Radians(lon2 - lon1);
        lat1 = Radians(lat1);
        lat2 = Radians(lat2);

        double a = Math.Sin(dLat / 2) * Math.Sin(dLat / 2) + Math.Sin(dLon / 2) * Math.Sin(dLon / 2) * Math.Cos(lat1) * Math.Cos(lat2);
        double c = 2 * Math.Atan2(Math.Sqrt(a), Math.Sqrt(1 - a));
        double d = R * c;

        return d;
    }


Console.WriteLine(DistanceAlgorithm.DistanceBetweenPlaces(36.578581, -118.291994, 36.23998, -116.83171));

the issue is that I get two different results.

my result: 163,307 km

result of the website: 136 km

any suggestions???

torti

Answer 1

Your formula is almost correct, but you have to swap parameters for longitude an latitude

Console.WriteLine(DistanceAlgorithm.DistanceBetweenPlaces(-118.291994, 36.578581, -116.83171, 36.23998)); // = 136 km

I'm using simplified formula:

// cos(d) = sin(φА)·sin(φB) + cos(φА)·cos(φB)·cos(λА ? λB),
//  where φА, φB are latitudes and λА, λB are longitudes
// Distance = d * R
public static double DistanceBetweenPlaces(double lon1, double lat1, double lon2, double lat2)
{
    double R = 6371; // km

    double sLat1 = Math.Sin(Radians(lat1));
    double sLat2 = Math.Sin(Radians(lat2));
    double cLat1 = Math.Cos(Radians(lat1));
    double cLat2 = Math.Cos(Radians(lat2));
    double cLon = Math.Cos(Radians(lon1) - Radians(lon2));

    double cosD = sLat1*sLat2 + cLat1*cLat2*cLon;

    double d = Math.Acos(cosD);

    double dist = R * d;

    return dist;
}

Testing:

(Distance at Equator): Longitudes 0, 100; Latitudes = 0,0; DistanceBetweenPlaces(0, 0, 100, 0) = 11119.5 km

(Distance at North Pole): Longitudes 0, 100; Latitudes = 90,90; DistanceBetweenPlaces(0, 90, 100, 90) = 0 km

Longitudes: -118.291994, -116.83171; Latitudes: 36.578581, 36.23998 = 135.6 km

Longitudes: 36.578581, 36.23998; Latitudes: -118.291994, -116.83171 = 163.2 km

Best regards

P.S. At web site you use for result comparison, for every point first text box is latitude, second - longitude