GDAL进行坐标转换的前提是GDAL在编译的时候引入了PROJ库，GDAL的坐标转换功能是基于PROJ库实现的
参考代码

#include <gdal_priv.h>
#include <iostream>
using namespace std;

int main()
{
	OGRSpatialReference ssr;
	ssr.SetWellKnownGeogCS("WGS84");
	OGRSpatialReference dsr;
	dsr.importFromEPSG(3857);
	OGRCoordinateTransformation * OGRCT = OGRCreateCoordinateTransformation(&ssr, &dsr);
	if (OGRCT == NULL)
	{
		cout << "Fail to create OGRCoordinateTransformation!" << endl;
		return 0;
	}
	double y[] = { 121};
	double x[] = { 31 };
	OGRCT->Transform(1, x, y, NULL);
	cout << "转换后点的坐标为：" << endl;
	cout << x[i] << " " << y[i] << endl;
	system("pause");
	return 0;
}