本文思路与代码实现完全参考了这篇文章: gps纠偏数据库及gps纠偏算法PHP
感谢文章作者yanue的无私分享与帮助.
以下代码中所使用到的数据库文件offset.dat请到yanue的网站进行下载.
正文代码如下:
package test.offset;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.URL;
import java.net.URLConnection;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import org.springframework.util.Assert;
import sun.misc.BASE64Decoder;
/**
* @author 200cc
*
*/
public class OffsetReader {
static final double M_PI = 3.14159265358979323846264338327950288;
static final double M_E = 2.71828182845904523536028747135266250;
static final String DIR = "d:\\download\\offset.dat";
/**
* 读取数据库offset.dat文件
* @param count 读取数据计数
* @return
* @throws Exception
*/
public static OffsetData[] readOffset(int count) throws Exception{
/*
* dat文件结构:该文件为0.01精度校正数据,并以lng和lat递增形式组合.
* 其中以8个字节为一组:
* lng : 2字节经度,如12151表示121.51
* lat : 2字节纬度,如3130表示31.30
* x_off : 2字节地图x轴偏移像素值
* y_off : 2字节地图y轴偏移像素值
*
*/
OffsetData[] datas = new OffsetData[count];
File f = new File(DIR);
Assert.isTrue(f.exists() && f.isFile());
FileInputStream fis = new FileInputStream(f);
byte[] buf = new byte[8];
@SuppressWarnings("unused")
int len = 0;
int cnt = 0;
while(-1 != (len = fis.read(buf, 0, buf.length))){
if (cnt >= count) break;
int lngS = byte2short(buf, 0) ; // byte[] to short
int latS = byte2short(buf, 2) ; // byte[] to short
int x = byte2short(buf, 4) ; // byte[] to short
int y = byte2short(buf, 6) ; // byte[] to short
datas[cnt] = new OffsetData(lngS, latS, x, y);
cnt++;
}
return datas;
}
public static void main(String[] args) throws Exception {
OffsetData[] datas = readOffset(10);
for (OffsetData data : datas){
System.out.println(data);
geoLatLng(data);
getBaiduGeo(data.getLat() * 1.0 / 100, data.getLng() * 1.0 / 100);
System.out.println("----------------------");
}
}
/**
* 获取baidu api计算的经纬
* @param lat 纬度
* @param lng 经度
* @throws Exception
*/
public static void getBaiduGeo(double lat, double lng) throws Exception{
//baidu API
String urlAddr = "http://api.map.baidu.com/ag/coord/convert?x=" + lng
+ "&y=" + lat + "&from=0&to=2&mode=1";
System.out.println("request: " + urlAddr);
URL url = new URL(urlAddr);
URLConnection connection = url.openConnection();
connection.setDoOutput(true); //将连接设置为输出模式.即发起一个http请求
//URLConnection通常作为输入来使用,如下载一个web页面.
//但同时也能进行输出,将数据向web页面传送.
OutputStreamWriter out = new OutputStreamWriter(connection.getOutputStream(), "utf-8");
out.flush();
out.close();
//发送成功后,获取得到服务器的响应
InputStream is = connection.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(is));
String line = "";
StringBuilder sb = new StringBuilder();
while(null != (line = br.readLine())){
sb.append(line);
}
System.out.println("response: " + sb.toString());
//[{"error":0,"x":"NzMuNTAzMzU1MDM0NzIy","y":"MzkuMzAwMTQxODcyODM="}]
Pattern p = Pattern.compile("\"x\":\"(.+)\",\"y\":\"(.+)\""); //正则
Matcher m = p.matcher(sb.toString());
String strLng = "", strLat = "";
if(m.find()){
BASE64Decoder decoder = new BASE64Decoder();
strLng = new String(decoder.decodeBuffer(m.group(1)));
strLat = new String(decoder.decodeBuffer(m.group(2)));
}else{
throw new RuntimeException("");
}
System.out.println("baidu Geo: " + strLat + ", " + strLng);
Thread.sleep(1000); //暂停一会. baidu Api有发起次数限制.
}
/**
* byte[] 转 short
* @param b
* @param index
* @return
*/
public static short byte2short(byte[] b, int index){
return (short) (((b[index + 1] << 8) | b[index + 0] & 0xff));
}
/**
* byte[] 转 float
* @param b
* @param index
* @return
*/
public static float getFloat(byte[] b, int index) {
int l;
l = b[index + 0];
l &= 0xff;
l |= ((long) b[index + 1] << 8);
l &= 0xffff;
l |= ((long) b[index + 2] << 16);
l &= 0xffffff;
l |= ((long) b[index + 3] << 24);
return Float.intBitsToFloat(l);
}
public static void geoLatLng(OffsetData data){
geoLatLng(data.getLng() * 1.0 / 100, data.getLat() * 1.0 / 100, data.getOffsetPixelX(), data.getOffsetPixelY());
}
/**
* 使用数据库计算经纬度坐标
* @param lng 实际(gps)经度
* @param lat 实际(gps)纬度
* @param offsetX 地图x轴偏移像素值
* @param offsetY 地图y轴偏移像素值
*/
public static void geoLatLng(double lng, double lat, int offsetX, int offsetY){
double lngPixel = lngToPixel(lng, 18) + offsetX;
double latPixel = latToPixel(lat, 18) + offsetY;
double mixLat = pixelToLat(latPixel, 18);
double mixLng = pixelToLng(lngPixel, 18);
System.out.println("calculate geo: " + mixLat + ", " + mixLng);
}
public static double lngToPixel(double lng, int zoom){
double res = (lng + 180) * (256 << zoom) / 360;
//System.out.println("lngToPixel: lng=" + lng + " --> res=" + res );
return res;
}
public static double latToPixel(double lat , int zoom){
double siny = Math.sin(lat * M_PI / 180);
double y = Math.log((1 + siny) / (1 - siny));
double res = (128 << zoom) * (1 - y / (2 * M_PI));
//System.out.println("latToPixel: lat=" + lat + " --> res=" + res );
return res;
}
public static double pixelToLng(double pixelX, int zoom){
double res = pixelX * 360 / (256 << zoom) - 180;
//System.out.println("pixelToLng: pixelX=" + pixelX + " --> res=" + res );
return res;
}
public static double pixelToLat(double pixelY, int zoom){
double y = 2 * M_PI * (1 - pixelY /(128 << zoom));
double z = Math.pow(M_E , y);
double siny = (z - 1) / (z + 1);
double res = Math.asin(siny) * 180 / M_PI;
//System.out.println("pixelToLat: pixelY=" + pixelY + " --> res=" + res );
return res;
}
public static class OffsetData{
int lng;
int lat;
int offsetPixelX;
int offsetPixelY;
public OffsetData(int lng, int lat, int x, int y){
this.lng = lng;
this.lat = lat;
this.offsetPixelX = x;
this.offsetPixelY = y;
}
public String toString(){
return this.lng + ", " + this.lat + ", " + this.offsetPixelX + ", " + this.offsetPixelY;
}
public int getLng() {
return lng;
}
public void setLng(int lng) {
this.lng = lng;
}
public int getLat() {
return lat;
}
public void setLat(int lat) {
this.lat = lat;
}
public int getOffsetPixelX() {
return offsetPixelX;
}
public void setOffsetPixelX(int offsetPixelX) {
this.offsetPixelX = offsetPixelX;
}
public int getOffsetPixelY() {
return offsetPixelY;
}
public void setOffsetPixelY(int offsetPixelY) {
this.offsetPixelY = offsetPixelY;
}
}
}
运行后结果:
7350, 3930, 624, -35
calculate geo: 39.30014529193229, 73.50334739685061
request: http://api.map.baidu.com/ag/coord/convert?x=73.5&y=39.3&from=0&to=2&mode=1
response: [{"error":0,"x":"NzMuNTAzMzU1MDM0NzIy","y":"MzkuMzAwMTQxODcyODM="}]
baidu Geo: 39.30014187283, 73.503355034722
----------------------
7350, 3931, 624, -36
calculate geo: 39.31014942177512, 73.50334739685061
request: http://api.map.baidu.com/ag/coord/convert?x=73.5&y=39.31&from=0&to=2&mode=1
response: [{"error":0,"x":"NzMuNTAzMzU1MzA1OTk=","y":"MzkuMzEwMTQ2NzU1NjQy"}]
baidu Geo: 39.310146755642, 73.50335530599
----------------------
7350, 3932, 624, -37
calculate geo: 39.32015355042689, 73.50334739685061
request: http://api.map.baidu.com/ag/coord/convert?x=73.5&y=39.32&from=0&to=2&mode=1
response: [{"error":0,"x":"NzMuNTAzMzU1NTc3MjU3","y":"MzkuMzIwMTUxMzY3MTg3"}]
baidu Geo: 39.320151367187, 73.503355577257
----------------------
7350, 3933, 625, -38
calculate geo: 39.33015767788718, 73.50335276126864
request: http://api.map.baidu.com/ag/coord/convert?x=73.5&y=39.33&from=0&to=2&mode=1
response: [{"error":0,"x":"NzMuNTAzMzU2MTE5Nzky","y":"MzkuMzMwMTU1NzA3NDY1"}]
baidu Geo: 39.330155707465, 73.503356119792
----------------------
7350, 3934, 625, -39
calculate geo: 39.34016180415566, 73.50335276126864
request: http://api.map.baidu.com/ag/coord/convert?x=73.5&y=39.34&from=0&to=2&mode=1
response: [{"error":0,"x":"NzMuNTAzMzU2MzkxMDU5","y":"MzkuMzQwMTYwMzE5MDE="}]
baidu Geo: 39.34016031901, 73.503356391059
----------------------
7350, 3935, 625, -40
calculate geo: 39.350165929231935, 73.50335276126864
request: http://api.map.baidu.com/ag/coord/convert?x=73.5&y=39.35&from=0&to=2&mode=1
response: [{"error":0,"x":"NzMuNTAzMzU2NjYyMzI2","y":"MzkuMzUwMTY0NjU5Mjg4"}]
baidu Geo: 39.350164659288, 73.503356662326
----------------------
7350, 3936, 625, -41
calculate geo: 39.36017005311557, 73.50335276126864
request: http://api.map.baidu.com/ag/coord/convert?x=73.5&y=39.36&from=0&to=2&mode=1
response: [{"error":0,"x":"NzMuNTAzMzU2OTMzNTk0","y":"MzkuMzYwMTY4OTk5NTY2"}]
baidu Geo: 39.360168999566, 73.503356933594
----------------------
7350, 3937, 625, -42
calculate geo: 39.37017417580627, 73.50335276126864
request: http://api.map.baidu.com/ag/coord/convert?x=73.5&y=39.37&from=0&to=2&mode=1
response: [{"error":0,"x":"NzMuNTAzMzU3NDc2MTI4","y":"MzkuMzcwMTczMDY4NTc2"}]
baidu Geo: 39.370173068576, 73.503357476128
----------------------
7350, 3938, 625, -43
calculate geo: 39.380178297303594, 73.50335276126864
request: http://api.map.baidu.com/ag/coord/convert?x=73.5&y=39.38&from=0&to=2&mode=1
response: [{"error":0,"x":"NzMuNTAzMzU3NzQ3Mzk2","y":"MzkuMzgwMTc3MTM3NTg3"}]
baidu Geo: 39.380177137587, 73.503357747396
----------------------
7351, 3930, 616, -28
calculate geo: 39.30011623356995, 73.51330448150634
request: http://api.map.baidu.com/ag/coord/convert?x=73.51&y=39.3&from=0&to=2&mode=1
response: [{"error":0,"x":"NzMuNTEzMzEyMTc0NDc5","y":"MzkuMzAwMTEyMDMzNDI="}]
baidu Geo: 39.30011203342, 73.513312174479
----------------------
总结:
从运行结果可以看到,使用数据库计算后的结果,与baidu返回的数据间的差值大约在0.0001左右.误差值还是挺大的.- -b.
本人能力有限,代码中肯定还存在错误,恳请诸位指正.
此外还衍生出一个问题: 我在网上查到
Q：百度坐标为何有偏移？
A：国际经纬度坐标标准为WGS-84,国内必须至少使用国测局制定的GCJ-02,对地理位置进行首次加密。百度坐标在此基础上，进行了BD-09二次加密措施,更加保护了个人隐私。...
使用这个offset.dat数据文件,计算得到的值居然能粗略拟合百度的二次火星坐标,我自己都觉得这是不是有些不可思议了?