struct GeoPoint
{
    double lon;
    double lat;
};

double m_R;

//計算海圖的基準維度，一般取30°

void getR(double lat)
{

 lat = lat*PI / 180;

 double N = 6378137 / sqrt(1 - 0.08189*0.08189*sin(lat)*sin(lat));
 m_R = N*cos(lat);

}

//將墨卡託海圖經緯度座標轉換為平面座標，單位 ：米

void  getMokato(GeoPoint *point)
{

 point->lon = point->lon / m_icoord*PI / 180
 
;
 point->lat = point->lat / m_icoord*PI / 180;
 double Q = log(tan(0.785398163375 + point->lat / 2)) - 0.040945*log((1 + 0.08189*sin(point->lat)) / (1 - 0.08189*sin(point->lat)));
 point->lon = point->lon*m_R ;
 point->lat = m_R*Q ;

}

 

double getLat(double pointx, double x)
{

 double
 
 d_e = 0.08189;
 double G = d_e / 2 * log((1 + d_e *sin(x)) / (1 - d_e * sin(x))) + pointx / m_R;
 return  2 * atan(exp(G)) - PI / 2;
}

 

//將螢幕座標轉換為墨卡託海圖座標，進行多次迭代計算，

void  getLatlon(GeoPoint *point)
{
 point->lat = point->lat;
 double d_x = 0.0;
 d_x = getLat(point->lat, d_x);
 d_x = getLat(point->lat, d_x);
 d_x 
 
= getLat(point->lat, d_x);
 d_x = getLat(point->lat, d_x);
 point->lat= d_x * 180 / PI;
  point->lon = point->lon / m_R * 180 / PI;   
}

參考文章：電子海圖開發，web電子海圖開發，電子海圖二次開發