android计算地图上两点距离的算法
接口：

    package com.computedistance;  
    public interface DistanceComputeInterface {  
      
        double getDistance(double lat1, double lng1, double lat2, double lng2);  
      
        double getShortDistance(double lat1, double lon1, double lat2, double lon2);  
      
        double getLongDistance(double lat1, double lon1, double lat2, double lon2);  
      
        double getDistanceBySpeed(double speed, double timeSpace);  
      
        double getAccurancyDistance(double lat_a, double lng_a, double lat_b, double lng_b);  
      
    }  

实现类：

    package com.computedistance.impl;  
    import java.security.InvalidParameterException;  
    import com.baidu.mapapi.utils.DistanceUtil;  
    import com.baidu.platform.comapi.basestruct.GeoPoint;  
    import com.computedistance.DistanceComputeInterface;  
    public class DistanceComputeImpl implements DistanceComputeInterface{  
      
        private final static double DEF_PI = 3.14159265359; // PI  
        private final static double DEF_2PI= 6.28318530712; // 2*PI  
        private final static double DEF_PI180= 0.01745329252; // PI/180.0  
        private final static double DEF_R =6370693.5; // radius of earth  
        private static DistanceComputeImpl instance = null;  
      
        public synchronized static DistanceComputeImpl getInstance(){  
            if (instance == null) {  
                instance = new DistanceComputeImpl();  
            }  
            return instance;  
        }  
      
        private DistanceComputeImpl(){}  
      
        @Override  
        public double getDistance(double lat1, double lng1, double lat2, double lng2) {  
            GeoPoint p1LL = new GeoPoint((int) (lat1*1e6), (int) (lng1*1e6));  
            GeoPoint p2LL = new GeoPoint((int) (lat2*1e6), (int) (lng2*1e6));  
            double distance = DistanceUtil.getDistance(p1LL, p2LL);  
            return distance/1000;  
        }  
      
        @Override  
        public double getShortDistance(double lat1, double lon1, double lat2,double lon2) {  
            double ew1, ns1, ew2, ns2;  
            double dx, dy, dew;  
            double distance;  
            // 角度转换为弧度  
            ew1 = lon1 * DEF_PI180;  
            ns1 = lat1 * DEF_PI180;  
            ew2 = lon2 * DEF_PI180;  
            ns2 = lat2 * DEF_PI180;  
            // 经度差  
            dew = ew1 - ew2;  
            // 若跨东经和西经180 度，进行调整  
            if (dew > DEF_PI)  
                dew = DEF_2PI - dew;  
            else if (dew < -DEF_PI)  
                dew = DEF_2PI + dew;  
            dx = DEF_R * Math.cos(ns1) * dew; // 东西方向长度(在纬度圈上的投影长度)  
            dy = DEF_R * (ns1 - ns2); // 南北方向长度(在经度圈上的投影长度)  
            // 勾股定理求斜边长  
            distance = Math.sqrt(dx * dx + dy * dy);  
            return distance/1000;  
        }  
      
        @Override  
        public double getLongDistance(double lat1, double lon1, double lat2,double lon2) {  
            double ew1, ns1, ew2, ns2;  
            double distance;  
            // 角度转换为弧度  
            ew1 = lon1 * DEF_PI180;  
            ns1 = lat1 * DEF_PI180;  
            ew2 = lon2 * DEF_PI180;  
            ns2 = lat2 * DEF_PI180;  
            // 求大圆劣弧与球心所夹的角(弧度)  
            distance = Math.sin(ns1) * Math.sin(ns2) + Math.cos(ns1) * Math.cos(ns2) * Math.cos(ew1 - ew2);  
            // 调整到[-1..1]范围内，避免溢出  
            if (distance > 1.0){  
                distance = 1.0;  
            } else if (distance < -1.0){  
                distance = -1.0;  
            }  
            // 求大圆劣弧长度  
            distance = DEF_R * Math.acos(distance);  
            return distance/1000;  
        }  
      
        @Override  
        public double getDistanceBySpeed(double speed, double timeSpace) {  
            if (speed  < 0 || timeSpace <= 0) {  
                throw new InvalidParameterException();  
            }  
            return speed * timeSpace;  
        }  
      
        @Override  
        public double getAccurancyDistance(double lat_a, double lng_a,double lat_b, double lng_b) {  
            double pk = (double) (180 / 3.14169);  
            double a1 = lat_a / pk;  
            double a2 = lng_a / pk;  
            double b1 = lat_b / pk;  
            double b2 = lng_b / pk;  
      
            double t1 = Math.cos(a1) * Math.cos(a2) * Math.cos(b1) * Math.cos(b2);  
            double t2 = Math.cos(a1) * Math.sin(a2) * Math.cos(b1) * Math.sin(b2);  
            double t3 = Math.sin(a1) * Math.sin(b1);  
            double tt = Math.acos(t1 + t2 + t3);  
            return 6366000 * tt / 1000;  
        }  
    }