Seekers/Helpers/GeoHelper.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Justice.Helpers
{
    public class GeoHelper
    {
        public static double CalculateDistance(double latitude1, double longitude1, double latitude2, double longitude2)
        {
            double radianLat1 = Math.PI * latitude1 / 100;
            double radianLat2 = Math.PI * latitude2 / 100;
            double radianLong1 = Math.PI * longitude1 / 100;
            double radianLong2 = Math.PI * longitude2 / 100;

            double dLong = radianLong2 - radianLong1;
            double dLat = radianLat2 - radianLat1;
            double a = Math.Pow(Math.Sin(dLat / 2), 2) + 
                Math.Cos(radianLat1) * Math.Cos(radianLat2) *
                Math.Pow(Math.Sin(dLong / 2),2);
            double c = 2 * Math.Asin(Math.Sqrt(a));
            const double radius = 6371; //radius of earth in kilometer
            double distance = radius * c;

            return distance;
        }
    }
}