根據經緯度和半徑計算經緯度范圍

    public class LatLonUtil
    {
        private static double PI = 3.14159265;
        private static double EARTH_RADIUS = 6378137;
        private static double RAD = Math.PI / 180.0;

        /// <summary>
        /// 根據提供的經度和緯度、以及半徑，取得此半徑內的最大最小經緯度
        /// </summary>
        /// <param name="lat">緯度</param>
        /// <param name="lon">經度</param>
        /// <param name="raidus">半徑(米)</param>
        /// <returns></returns>
        public static double[] GetAround(double lat, double lon, int raidus)
        {

            Double latitude = lat;
            Double longitude = lon;

            Double degree = (24901 * 1609) / 360.0;
            double raidusMile = raidus;

            Double dpmLat = 1 / degree;
            Double radiusLat = dpmLat * raidusMile;
            Double minLat = latitude - radiusLat;
            Double maxLat = latitude + radiusLat;

            Double mpdLng = degree * Math.Cos(latitude * (PI / 180));
            Double dpmLng = 1 / mpdLng;
            Double radiusLng = dpmLng * raidusMile;
            Double minLng = longitude - radiusLng;
            Double maxLng = longitude + radiusLng;
            return new double[] { minLat, minLng, maxLat, maxLng };
        }

        /// <summary>
        /// 根據提供的兩個經緯度計算距離(米)
        /// </summary>
        /// <param name="lng1">經度1</param>
        /// <param name="lat1">緯度1</param>
        /// <param name="lng2">經度2</param>
        /// <param name="lat2">緯度2</param>
        /// <returns></returns>
        public static double GetDistance(double lng1, double lat1, double lng2, double lat2)
        {
            double radLat1 = lat1 * RAD;
            double radLat2 = lat2 * RAD;
            double a = radLat1 - radLat2;
            double b = (lng1 - lng2) * RAD;
            double s = 2 * Math.Asin(Math.Sqrt(Math.Pow(Math.Sin(a / 2), 2) +
             Math.Cos(radLat1) * Math.Cos(radLat2) * Math.Pow(Math.Sin(b / 2), 2)));
            s = s * EARTH_RADIUS;
            s = Math.Round(s * 10000) / 10000;
            return s;
        }
    }