packing algorithm in rtree in boost

Question

Hi all I understand that if rtree is created with range values in boost it would use packing algorithm. I need an example of rtree using packing algorithm. Here is my code that uses quadratic algorithm

    using  point = bg::model::point < int, 2, bg::cs::cartesian >;
    using  pointI = std::pair<point, std::size_t>;
 vector<point> contourCenters // has some value
bgi::rtree< pointI, bgi::quadratic<16> > rtree;
vector< pointI > cloud;

for (size_t i = 0; i < contourCenters.size(); ++i)
{
    int x = contourCenters[i].get < 0 >();
    int y = contourCenters[i].get < 1 >();

    cout << "Contour Centers: (" << x << "," << y << ")";
    cloud.push_back(mp(x, y, i));
    rtree.insert(make_pair(contourCenters[i], i));
}

I would like to create rtree with packing algorithm as it seems to be the fastest one in boost. Kindly guide me how to create a rtree with packing algorithm in boost.

Answer 1

You'd just need to use the range constructor.

For that to work, the range must have been created before constructing the rtree. The simplest way to achieve that in your example would be to build your cloud vector first, and then construct the index from it:

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#include <boost/geometry/index/rtree.hpp>
#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point.hpp>
#include <boost/geometry/geometries/box.hpp>
#include <vector>
#include <iostream>

namespace bg = boost::geometry;
namespace bgi = bg::index;
using  point  = bg::model::point <int, 2, bg::cs::cartesian>;
using  pointI = std::pair<point, std::size_t>;

pointI mp(int x, int y, size_t v) {
    return std::make_pair(point(x,y), v);
}

int main()
{
    std::vector<point> contourCenters; // has some value
    std::vector<pointI> cloud;

    size_t id_gen = 0;
    std::transform(
            contourCenters.begin(), contourCenters.end(),
            back_inserter(cloud), 
            [&](point const& p) { return std::make_pair(p, id_gen++); }
        );

    for(pointI& pi : cloud)
        std::cout << "Contour Centers: (" << bg::get<0>(pi.first) << "," << bg::get<1>(pi.first) << ")";

    bgi::rtree<pointI, bgi::quadratic<16> > rtree(cloud);
}

I replaced the loop with std::transform for good style, but you could keep the loop as you had it.