get the distance between two places using bing maps

private double CalculateDistance(double prevLat, double prevLong, double currLat, double currLong)
       {
           const double degreesToRadians = (Math.PI / 180.0);
           const double earthRadius = 6371; // kilometers

           // convert latitude and longitude values to radians
           var prevRadLat = prevLat * degreesToRadians;
           var prevRadLong = prevLong * degreesToRadians;
           var currRadLat = currLat * degreesToRadians;
           var currRadLong = currLong * degreesToRadians;

           // calculate radian delta between each position.
           var radDeltaLat = currRadLat - prevRadLat;
           var radDeltaLong = currRadLong - prevRadLong;

           // calculate distance
           var expr1 = (Math.Sin(radDeltaLat / 2.0) *
                        Math.Sin(radDeltaLat / 2.0)) +

                       (Math.Cos(prevRadLat) *
                        Math.Cos(currRadLat) *
                        Math.Sin(radDeltaLong / 2.0) *
                        Math.Sin(radDeltaLong / 2.0));

           var expr2 = 2.0 * Math.Atan2(Math.Sqrt(expr1),
                                        Math.Sqrt(1 - expr1));

           var distance = (earthRadius * expr2);
           return distance * 1000;  // return results as meters
       }