sphmerc.cpp

#include <ogr_srs_api.h>

#include <iostream>
#include <iomanip>


int main(int argc, char *argv[])
{
    const char * proj4_str = "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +towgs84=0,0,0,0,0,0,0 +wktext +no_defs";

    int error = 0;
    void* _handle;
    _handle = OSRNewSpatialReference(nullptr);
    error = OSRImportFromProj4(_handle, proj4_str);

    int err;
    double semi_major_axis = OSRGetSemiMajor( _handle, &err );
    double semi_minor_axis = OSRGetSemiMinor( _handle, &err );

    std::cout << "semi_major_axis=" << std::setprecision(10) << semi_major_axis << std::endl;
    std::cout << "semi_minor_axis=" << std::setprecision(10) << semi_minor_axis << std::endl;


    OSRDestroySpatialReference(_handle);

    return 0;
}