This sample demonstrates that by usage of concepts, external geometries can be handled by GGL, just calling by a one-line registration macro. In this case for the Qt Widget Library.
The example, code shown below, results in this window-output: 
#include <sstream>
#include <QtGui>
#include <boost/geometry/geometry.hpp>
int main(int argc, char *argv[])
{
    
    
    QApplication app(argc, argv);
    
    
    QPolygonF polygon;
    
    polygon
        << QPointF(10, 20) << QPointF(20, 30)
        << QPointF(30, 20) << QPointF(20, 10)
        << QPointF(10, 20);
    
    std::ostringstream out;
    
    QPointF p(20,20);
    out << "Qt contains: "
        << (polygon.containsPoint(p, Qt::WindingFill) ? "yes" : "no")
        << std::endl
        << "Boost.Geometry within: "
        << std::endl;
    
    
    
    
    QPolygonF::const_iterator it;
    for (it = polygon.begin(); it != polygon.end(); ++it)
    {
        
        out << boost::geometry::dsv(*it) << std::endl;
    }
    
    out << boost::geometry::dsv(polygon) << std::endl;
    
    QLabel label(out.str().c_str());
    label.show();
    return app.exec();
}