求出在某个经纬度方圆多少公里返回的最大最小经纬度

java代码，计算在地图上某个点，以这个点为中心，覆盖若干公里范围的最大和最小经纬度

package test;

public class MainClass {

    public final static class GpsUtil {
        double pi;
        double distance;

        //地球平均半径6371km
        public static final double EARTH_RADIUS = 6371000;

        public GpsUtil() {
            this.pi = Math.PI;//3.141592654;
            //测试好久，发现3535出来的是附近五公里- -!
            distance = 3535;
        }

        /**
         * 
         * @param lat 维度
         * @param lon 经度
         * @param distance 多少米范围
         * @return
         */
        public double[] compute(double lat, double lon, double distance) {
            
            lat = lat * pi / 180;
            lon = lon * pi / 180;  //先换算成弧度
            double rad_dist = distance / EARTH_RADIUS;  //计算X公里在地球圆周上的弧度
            double lat_min = lat - rad_dist;
            double lat_max = lat + rad_dist;   //计算纬度范围
            double lon_min;
            double lon_max;
            //因为纬度在-90度到90度之间，如果超过这个范围，按情况进行赋值
            if (lat_min > -pi / 2 && lat_max < pi / 2) {
                //开始计算经度范围
                double lon_t = Math.asin(Math.sin(rad_dist) / Math.cos(lat));
                lon_min = lon - lon_t;
                //同理，经度的范围在-180度到180度之间
                if (lon_min < -pi)
                    lon_min += 2 * pi;
                lon_max = lon + lon_t;
                if (lon_max > pi)
                    lon_max -= 2 * pi;
            } else {
                lat_min = Math.max(lat_min, -pi / 2);
                lat_max = Math.min(lat_max, pi / 2);
                lon_min = -pi;
                lon_max = pi;
            }
            //最后置换成角度进行输出
            lat_min = lat_min * 180 / pi;
            lat_max = lat_max * 180 / pi;
            lon_min = lon_min * 180 / pi;
            lon_max = lon_max * 180 / pi;
            double result[] = { lat_min, lat_max, lon_min, lon_max };
            return result;
        }

        /**
         * 转化为弧度(rad)
         */
        private double rad(double d) {
            return d * Math.PI / 180.0;
//            return d;
        }

        /**
         * 基于余弦定理求两经纬度距离
         * 
         * @param lon1
         *            第一点的精度
         * @param lat1
         *            第一点的纬度
         * @param lon2
         *            第二点的精度
         * @param lat2
         *            第二点的纬度
         * @return 返回的距离，单位m
         */

        public double LantitudeLongitudeDist(double lat1, double lat2, double lon1, double lon2) {
            double radLat1 = rad(lat1);
            double radLat2 = rad(lat2);

            double radLon1 = rad(lon1);
            double radLon2 = rad(lon2);

            if (radLat1 < 0)
                radLat1 = Math.PI / 2 + Math.abs(radLat1);// south  
            if (radLat1 > 0)
                radLat1 = Math.PI / 2 - Math.abs(radLat1);// north  
            if (radLon1 < 0)
                radLon1 = Math.PI * 2 - Math.abs(radLon1);// west  
            if (radLat2 < 0)
                radLat2 = Math.PI / 2 + Math.abs(radLat2);// south  
            if (radLat2 > 0)
                radLat2 = Math.PI / 2 - Math.abs(radLat2);// north  
            if (radLon2 < 0)
                radLon2 = Math.PI * 2 - Math.abs(radLon2);// west  
            double x1 = EARTH_RADIUS * Math.cos(radLon1) * Math.sin(radLat1);
            double y1 = EARTH_RADIUS * Math.sin(radLon1) * Math.sin(radLat1);
            double z1 = EARTH_RADIUS * Math.cos(radLat1);

            double x2 = EARTH_RADIUS * Math.cos(radLon2) * Math.sin(radLat2);
            double y2 = EARTH_RADIUS * Math.sin(radLon2) * Math.sin(radLat2);
            double z2 = EARTH_RADIUS * Math.cos(radLat2);

            double d = Math.sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2) + (z1 - z2) * (z1 - z2));
            //余弦定理求夹角  
            double theta = Math.acos((EARTH_RADIUS * EARTH_RADIUS + EARTH_RADIUS * EARTH_RADIUS - d * d)
                    / (2 * EARTH_RADIUS * EARTH_RADIUS));
            double dist = theta * EARTH_RADIUS;
            return dist;
        }

    }

    public static void main(String[] args) {
        GpsUtil gps = new GpsUtil();
        double[] a = gps.compute(30.01254012452224, 121.01244544525456456478797, 3535);
        for (double d : a) {
            System.out.println(d);
        }

        double dis = gps.LantitudeLongitudeDist(a[0], a[1], a[2], a[3]);
        System.out.println("两点之间距离：" + dis + "米");

    }

}