提要

我们知道GPS坐标是由经度，纬度，海拔组成，精度和纬度都是角度，海报是高度。

在进行基于地理的搜索的时候，常用到KDTree，在构建在KDTree的时候，不能直接用GPS的坐标，要将GPS坐标转换成笛卡尔坐标才能用于构建KDTree。下面就是相关的转换算法。

注：GPS信息由几种标准，这里的采用的是google map的经纬度信息。

js实现

geodecy.js

/*             geodesy routines in JavaScript
                 James R. Clynch NPS / 2003
               
          Done for support of web education pages


          == must convert inputs to numbers for safety ==
          == if string comes in - sometimes works, sometimes not !==
*/

C++实现

就是根据将JS代码转成C艹.

GPS 转笛卡尔

void GPSTransform::gpsPoint2DescartesPoint(const double latitude, const double longitude, const double altitude, double &x;, double &y;, double &z;)
{
	//wgs84 WGS84 Earth Constants
	double wgs84a = 6378.137;
	double wgs84f = 1.0 / 298.257223563;
	double wgs84b = wgs84a * (1.0 - wgs84f);

	//earthcon
	double f = 1 - wgs84b / wgs84a;
	double eccsq = 1 - (wgs84b* wgs84b) / (wgs84a * wgs84a);
	double ecc = sqrt(eccsq);
	double esq = ecc * ecc;

	//llhxyz
	double dtr = M_PI / 180.0;
	//qDebug() << dtr << gpsPoint.latitude << endl;
	double clat = cos(dtr * latitude);
	double slat = sin(dtr * latitude);
	double clon = cos(dtr * longitude);
	double slon = sin(dtr * longitude);
	//qDebug() << clat << slon << endl;

	//radcur compute the radii at the geodetic latitude lat (in degrees)
	double dsq = 1.0 - eccsq * slat *slat;
	double d = sqrt(dsq);
	//qDebug() << d;
	double rn = wgs84a / d;
	double rm = rn * (1.0 - eccsq) / dsq;

	double rho = rn * clat;
	double zz = (1.0 - eccsq) * rn *slat;
	double rsq = rho * rho + zz*zz;
	double r = sqrt(rsq);

	x = (rn + altitude) * clat * clon;
	y = (rn + altitude) * clat * slon;
	z = ((1 - esq)*rn + altitude) * slat;
}

运行结果

验证网站

Geodetic to Cartesian Converter - http://www.apsalin.com/convert-geodetic-to-cartesian.aspx

atitude,Longitude,Height to/from ECEF (X,Y,Z) - http://www.oc.nps.edu/oc2902w/coord/llhxyz.htm