Method of converting GPS coordinates to Baidu map coordinates

from ：GPS The method of converting coordinates to Baidu map coordinates - Programmer base

First of all, I need to know GPS The coordinate system of .GPS Coordinate system follows WGS-84 standard , By this standard ,GPS The chip can send different packet formats . According to the difference of its data frame header ,GPS The data can be classified as GPGGA、GPGSA、GPGSV、GPRMC etc. . These frame headers identify the composition of subsequent intra frame data . Usually , The positioning data we are concerned about, such as longitude and latitude 、 Speed 、 Time, etc. can be from GPRMC Get in the frame .

I won't explain the format of specific frames this time , You can easily find it on the Internet , The format of data frame can also be found in the interface document of the general chip . By reading GPRMC package , We can get something similar to “3040.8639,N,10405.7573,E” The location data of , Its field meaning can be found in the document . The result of my analysis here is ： North latitude 30°40.8639', East longitude 104°5.7573'.

After getting these two data , We can try to locate it on the map , We found that most map locations use decimal coordinates . Here we need to talk about how to put a GPS Raw data , Data converted to decimal form .

give an example ：106°14'15" Transformation
Because degrees, minutes and seconds are in hexadecimal
So it can be converted in this way ：
15/60=0.25 branch
(14+0.25)/60=0.2375 degree
106+0.2375=106.2375 degree

So the end result is 106.2375°

After this conversion , My position coordinates 【 North latitude 30°40.8639', East longitude 104°5.7573'】 It can become 【30.681065N,104.095955E】（ This is WGS-84 Coordinates of ） This look . This coordinate is GPS Physical positioning of , According to international standards , This coordinate needs to be GCJ-02 Offset conversion , The converted coordinates can be in google Map 、 Gould map 、 And positioning on Tencent map （ The above three companies follow GCJ-02 encryption ）. As for why this should be done , It's because the coordinates are encrypted . because GCJ-02 It is an irreversible transformation .

You zhuxun is posted here WGS-84 The standard is converted to GCJ-02 Of C++ Source code ：

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;  
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 * sqrt(abs(x));  
ret += (20.0 * sin(6.0 * x * pi) + 20.0 * sin(2.0 * x * pi)) * 2.0 / 3.0;   
ret += (20.0 * sin(y * pi) + 40.0 * sin(y / 3.0 * pi)) * 2.0 / 3.0;   
ret += (160.0 * sin(y / 12.0 * pi) + 320 * 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 * sqrt(abs(x));   
ret += (20.0 * sin(6.0 * x * pi) + 20.0 * sin(2.0 * x * pi)) * 2.0 / 3.0;   
ret += (20.0 * sin(x * pi) + 40.0 * sin(x / 3.0 * pi)) * 2.0 / 3.0;  
ret += (150.0 * sin(x / 12.0 * pi) + 300.0 * sin(x / 30.0 * pi)) * 2.0 / 3.0;   
return ret;  
}   
/* 
 Parameters  
wgLat:WGS-84 latitude wgLon:WGS-84 longitude  
 Return value ： 
mgLat：GCJ-02 latitude mgLon：GCJ-02 longitude  
*/  
void gps_transform( double wgLat, double wgLon, double& mgLat, 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 = sin(radLat);  
magic = 1 - ee * magic * magic; double sqrtMagic = sqrt(magic);  
dLat = (dLat * 180.0) / ((a * (1 - ee)) / (magic * sqrtMagic) * pi);  
dLon = (dLon * 180.0) / (a / sqrtMagic * cos(radLat) * pi);  
mgLat = wgLat + dLat; mgLon = wgLon + dLon;  
}  

After the above conversion , Our coordinates can be followed GCJ-02 The standard map has been deleted , Here is a more useful test Location URL ：http://www.gpsspg.com/maps.htm

Baidu map is a little special , It's in GCJ-02 On this basis, another encryption is carried out , Baidu calls this encryption standard BD-09, But this encryption is not publicly available . But the omnipotent network and omnipotent netizens will always have a way to solve this kind of problem . Here I will post a feasible conversion method , After testing , The positioning is very accurate .

#include <math.h>      
const double x_pi = 3.14159265358979324 * 3000.0 / 180.0;    
// take  GCJ-02  The coordinates are converted to  BD-09  coordinate   
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);    
}   

such , Our coordinates can also be accurately located on Baidu map , They were filled with joy ~~
  In addition, a legend that can easily explain why coordinates need to be converted is pasted , So that we can understand ：
    International conversion practice ：

    Baidu's approach ：

    It also explains , Why? GPS The reason why coordinates need to be converted . Thanks to the people who contributed these materials to the Internet ！
Reference resources ：
http://m.blog.csdn.net/blog/wildboy2001/39497681
http://www.haodaima.net/art/2441684
http://www.gpsspg.com/maps.htm
http://wenda.haosou.com/q/1365472754066079
http://www.geekcome.com/content-10-1464-1.html