Research and arrangement of electronic map coordinate system

「 Blog move 」 New address : Simple books

This article is organized by the reference links at the end of the article 、 Integrate 、 Modified to

---

1. Brief introduction of electronic map coordinate system

• WGS-84 Coordinate system ： The earth coordinate system , International longitude and latitude coordinate standard
• GCJ-02 Coordinate system ： The Mars coordinate system ,WGS84 The encrypted coordinate system , Prepared by China Survey Bureau .
• BD-09 Coordinate system ： Baidu coordinate system ,GCJ02 The encrypted coordinate system .

GCJ-02 Coordinate system , It's in the standard WGS-84 The coordinate system is artificially offset , such as Google Map 、 tencent SOSO Maps and so on use the country directly GCJ-02 Coordinate system , We have an unwritten saying , The former is called earth coordinates , The latter is called Mars coordinates , also , Mars coordinates cannot be converted into earth coordinates 「 Although there are certain methods on the Internet , But they are basically based on the offset database , High precision databases need to be purchased , Of course, this is a means of cracking 」.

All the electronic maps 、 Navigation equipment , All need to add national security plug-ins .

• First step , Mapping company mapping , After surveying and Mapping , To the State Bureau of Surveying and mapping , An electronic map of real coordinates , Encrypted into “ Mars coordinates ”, Such a map can be published and published , Then you can let GPS The company deals with .

• The second step , be-all GPS company , As long as you need car navigation , Need to use navigation electronic map , It is necessary to add the national security algorithm to the software , take COM The real coordinate signal read out by mouth , The encryption is converted into confidential coordinates required by the state . such ,GPS The navigator and the navigation electronic map can be completely matched ,GPS It can work normally .

API	Coordinate system
Baidu Maps API	Baidu coordinates
Tencent search map API	Mars coordinates
Sohu Sogou map API	Sogou coordinates
Alibaba cloud map API	Mars coordinates
Picture bar MapBar Map API	Picture bar coordinates
Gao de MapABC Map API	Mars coordinates
Psychic chart 51ditu Map API	Mars coordinates

• notes 1： Baidu map uses Baidu coordinates , It supports importing earth coordinates and Mars coordinates into Baidu coordinates , But cannot export . And batch coordinate conversion can only be converted at one time 20 individual ( To be verified ).
• notes 2： Sogou map supports direct display of earth coordinates , Support earth coordinates 、 Mars coordinates 、 Baidu coordinates are imported into Sogou coordinates , Again , Sogou coordinates cannot be exported .

Finish the coordinate system , We can naturally know the problem here , Pass the following questions , Let's say my research on this .

---

2、 Mutual transformation of various coordinate systems

---

2.1 Mars coordinate system 「GCJ-02」 And Baidu coordinate system 「BD-09」 The transformation algorithm of

among bd_encrypt take GCJ-02 The coordinates are converted to BD-09 coordinate , bd_decrypt conversely .

void bd_encrypt(double gg_lat, double gg_lon, double &bd_lat, double &bd_lon)  
{  
    double x = gg_lon, y = gg_lat;  
    double z = sqrt(x * x + y * y) + 0.00002 * sin(y * x_pi);  
    double theta = atan2(y, x) + 0.000003 * cos(x * x_pi);  
    bd_lon = z * cos(theta) + 0.0065;  
    bd_lat = z * sin(theta) + 0.006;  
}  
void bd_decrypt(double bd_lat, double bd_lon, double &gg_lat, double &gg_lon)  
{  
    double x = bd_lon - 0.0065, y = bd_lat - 0.006;  
    double z = sqrt(x * x + y * y) - 0.00002 * sin(y * x_pi);  
    double theta = atan2(y, x) - 0.000003 * cos(x * x_pi);  
    gg_lon = z * cos(theta);  
    gg_lat = z * sin(theta);  
}  

---

2.2 The earth coordinate system 「WGS-84」 To the Martian coordinate system 「GCJ-02」 The transformation algorithm of

WGS-84 To GCJ-02 Transformation 「 namely GPS Bias 」 Algorithm

using System;   
namespace Navi  
{  
    class EvilTransform  
    {  
        const double pi = 3.14159265358979324;  
        // 
        // Krasovsky 1940 
        // 
        // a = 6378245.0, 1/f = 298.3 
        // b = a * (1 - f) 
        // ee = (a^2 - b^2) / a^2; 
        const double a = 6378245.0;  
        const double ee = 0.00669342162296594323;  
        // 
        // World Geodetic System ==> Mars Geodetic System 
        public static void transform(double wgLat, double wgLon, out double mgLat, out double mgLon)  
        {  
            if (outOfChina(wgLat, wgLon))  
            {  
                mgLat = wgLat;  
                mgLon = wgLon;  
                return;  
            }  
            double dLat = transformLat(wgLon - 105.0, wgLat - 35.0);  
            double dLon = transformLon(wgLon - 105.0, wgLat - 35.0);  
            double radLat = wgLat / 180.0 * pi;  
            double magic = Math.Sin(radLat);  
            magic = 1 - ee * magic * magic;  
            double sqrtMagic = Math.Sqrt(magic);  
            dLat = (dLat * 180.0) / ((a * (1 - ee)) / (magic * sqrtMagic) * pi);  
            dLon = (dLon * 180.0) / (a / sqrtMagic * Math.Cos(radLat) * pi);  
            mgLat = wgLat + dLat;  
            mgLon = wgLon + dLon;  
        }  
        static bool outOfChina(double lat, double lon)  
        {  
            if (lon < 72.004 || lon > 137.8347)  
                return true;  
            if (lat < 0.8293 || lat > 55.8271)  
                return true;  
            return false;  
        }  
        static double transformLat(double x, double y)  
        {  
            double ret = -100.0 + 2.0 * x + 3.0 * y + 0.2 * y * y + 0.1 * x * y + 0.2 * Math.Sqrt(Math.Abs(x));  
            ret += (20.0 * Math.Sin(6.0 * x * pi) + 20.0 * Math.Sin(2.0 * x * pi)) * 2.0 / 3.0;  
            ret += (20.0 * Math.Sin(y * pi) + 40.0 * Math.Sin(y / 3.0 * pi)) * 2.0 / 3.0;  
            ret += (160.0 * Math.Sin(y / 12.0 * pi) + 320 * Math.Sin(y * pi / 30.0)) * 2.0 / 3.0;  
            return ret;  
        }  
        static double transformLon(double x, double y)  
        {  
            double ret = 300.0 + x + 2.0 * y + 0.1 * x * x + 0.1 * x * y + 0.1 * Math.Sqrt(Math.Abs(x));  
            ret += (20.0 * Math.Sin(6.0 * x * pi) + 20.0 * Math.Sin(2.0 * x * pi)) * 2.0 / 3.0;  
            ret += (20.0 * Math.Sin(x * pi) + 40.0 * Math.Sin(x / 3.0 * pi)) * 2.0 / 3.0;  
            ret += (150.0 * Math.Sin(x / 12.0 * pi) + 300.0 * Math.Sin(x / 30.0 * pi)) * 2.0 / 3.0;  
            return ret;  
        }  
    }  
}  

The above reference is from ：http://www.xue5.com/Mobile/iOS/679842.html

---

2.3 Baidu online conversion API

http://api.map.baidu.com/ag/coord/convert?from=0&to=4&x=longitude&y=latitude
from: Source coordinate system 「0 Express WGS-84 coordinate ;2 Express GCJ-02 coordinate 」
to: Converted coordinates 「4 Express BD-09 coordinate , That is, the line used by Baidu map 」
x: longitude
y: latitude

After the request, a string of Json

{  
    "error":0,  
    "x":"MTIxLjUwMDIyODIxNDk2",  
    "y":"MzEuMjM1ODUwMjYwMTE3"  
}  
error： Is the result error flag bit ,0  It means success 
x:  Coordinate system  2  Hour is longitude ,4  Time is latitude (Base64 code )
y:  Coordinate system  4  Hour is longitude ,2  Time is latitude (Base64 code )

What circumstance , Longitude and latitude are encrypted ？ Then I'll have to see what I can do next

import java.io.BufferedReader;  
import java.io.IOException;  
import java.io.InputStream;  
import java.io.InputStreamReader;  
import java.io.OutputStreamWriter;  
import java.net.URL;  
import java.net.URLConnection;  
import com.sun.org.apache.xerces.internal.impl.dv.util.Base64;  
public class BaiduAPIConverter extends Thread {
      
  public static void testPost(String x, String y) throws IOException {  
    try {  
      URL url = new URL("http://api.map.baidu.com/ag/coord/convert?from=2&to=4&x="+ x + "&y=" + y);  
      URLConnection connection = url.openConnection();  
      connection.setDoOutput(true);  
      OutputStreamWriter out = new OutputStreamWriter(connection.getOutputStream(), "utf-8");  
      // remember to clean up 
      out.flush();  
      out.close();  
      //  Once the transmission is successful , You can get the response from the server by using the following methods ： 
      String sCurrentLine, sTotalString;  
      sCurrentLine = sTotalString = "";  
      InputStream l_urlStream;  
      l_urlStream = connection.getInputStream();  
      BufferedReader l_reader = new BufferedReader(new InputStreamReader(l_urlStream));  
      while ((sCurrentLine = l_reader.readLine()) != null) {  
        if (!sCurrentLine.equals(""))  
          sTotalString += sCurrentLine;  
      }  
      sTotalString = sTotalString.substring(1, sTotalString.length() - 1);  
      String[] results = sTotalString.split("\\,");  
      if (results.length == 3) {  
        if (results[0].split("\\:")[1].equals("0")) {  
          String mapX = results[1].split("\\:")[1];  
          String mapY = results[2].split("\\:")[1];  
          mapX = mapX.substring(1, mapX.length() - 1);  
          mapY = mapY.substring(1, mapY.length() - 1);  
          mapX = new String(Base64.decode(mapX));  
          mapY = new String(Base64.decode(mapY));  
          System.out.println("\t" + mapX + "\t" + mapY);  
        }  
      }  
     sleep(10000);  
    } catch (InterruptedException e) {  
      // TODO Auto-generated catch block 
      e.printStackTrace();  
    }  
  }  
  /** * @param args * @throws IOException */  
  public static void main(String[] args) throws IOException {  
    testPost("120.151379", "30.184678");  
    System.out.println("ok");  
  }  
}  

It's almost good to be here , The main code has been written , Write the rest by yourself .
The above reference is from ：http://scalpel.me/archives/136

---

2.4 Baidu built-in conversion method , Can not be limited to Baidu positioning SDK

Get... In Baidu map WGS-84 coordinate , Call the following methods ：

BMapManager.getLocationManager().setLocationCoordinateType(MKLocationManager.MK_COORDINATE_WGS84);

So from Baidu API The coordinates obtained in are WGS-84 了 , However, if this coordinate is displayed on Baidu map, it will be offset , That is to say, take out a coordinate , The original display is offset , Therefore, in order to display it normally, it is necessary to convert it into... Before drawing it on Baidu map BD-09 .
convert to BD-09, Calling method ：

GeoPoint wgs84;
GeoPoint bd09= CoordinateConvert.bundleDecode(CoordinateConvert.fromWgs84ToBaidu(wgs84));

I really don't understand why it should be designed as CoordinateConvert.fromWgs84ToBaidu(wgs84) Returned a Bundle, So we need to CoordinateConvert.bundleDecode() Again into GeoPoint .

---

3. Reference article

1. Domestic maps API Coordinate system comparison and transformation
2. Research on Baidu map coordinate conversion interface
3. Build your own Baidu map coordinate correction database
4. GPS Rectification algorithm , Apply to google, The map of the Gaud system