#include <iostream>

#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/geometries/geometries.hpp>
#include <boost/geometry/multi/geometries/multi_geometries.hpp>
#include <boost/geometry/io/wkt/wkt.hpp>


template <typename T>
inline T round(T const& value, T const& factor)
{
    return floor(0.5 + (value / factor)) * factor;
}

int main()
{
    typedef boost::geometry::model::d2::point_xy<double> point;
    typedef boost::geometry::model::polygon<point> polygon;
    typedef boost::geometry::model::multi_polygon<polygon> multi_polygon;

    multi_polygon mp;
    boost::geometry::read_wkt("MULTIPOLYGON(((0 0,1.123 9.987,8.876 2.234,0 0),(3.345 4.456,7.654 8.765,9.123 5.432,3.345 4.456)))", mp);

    const double factor = 0.1;

    std::vector<point> points;

	boost::geometry::for_each_point
        (
            mp, 
            [&](point& p) 
                { 
                    boost::geometry::set<0>(p, round(boost::geometry::get<0>(p), factor));  
                    boost::geometry::set<1>(p, round(boost::geometry::get<1>(p), factor));  
                    points.push_back(p);
                }
                    
        );
    std::cout << "Rounded: " << boost::geometry::wkt(mp) << std::endl;

    std::for_each(points.begin(), points.end(),
            [](point const& p) 
                { 
                    std::cout << boost::geometry::wkt(p) << std::endl;
                }
        );

    return 0;
}