Find Boost rtree elements inside a polygon

Question

I would like to find all the elements indexed in a rtree that intersects with the exterior ring of a polygon with holes but that are not completely inside any of the holes using Boost C++ libraries.

I know how to get the element intersecting the exterior ring with:

// Constructing the exterior ring polygon
Boost2dRing p;
for (int i = 0; i < numPunts; i++)
{
    x = Punts.at(i).x;
    y = Punts.at(i).y;
    p.push_back(Boost2dPoint(x, y));
}

// Getting the intersecting elements with that polygon
m_RTree.query(bgi::intersects(p), std::back_inserter(res));
...
// Constructing the polygon for the inner ring (hole)
Boost2dRing p;
for (int i = 0; i < numPuntsHole; i++)
{
    x = PuntsHole.at(i).x;
    y = PuntsHole.at(i).y;
    pHole.push_back(Boost2dPoint(x, y));
}

// Now I try to get the elements inside completely this polygon but I get a compilation error
m_RTree.query(bgi::within(pHole), std::back_inserter(res));

Error message:

error C2664: 'int boost::mpl::assertion_failed(boost::mpl::assert::type)': cannot convert argument 1 from 'boost::mpl::failed ************(__cdecl boost::geometry::strategy::within::services::default_strategy::NOT_IMPLEMENTED_FOR_THESE_TYPES::* ***********)(boost::mpl::assert_::types)' to 'boost::mpl::assert::type' 1> with 1> [ 1> Geometry1=Boost2dBox, 1> Geometry2=Boost2dRing, 1>
GeometryContained=Boost2dBox, 1>
GeometryContaining=Boost2dRing 1> ] note: No constructor could take the source type, or constructor overload resolution was ambiguous

Any hint to achieve this goal?

Answer 1

The within predicate isn't implemented for your choice of geometry operands.

However, you can do what you want with much less work. Let's say you have your rings, for example:

Boost2dRing exterior, interior;
bg::read_wkt("POLYGON((0.1 0.1,0.1 0.5,0.5 0.5,0.5 0.1,0.1 0.1))", exterior);
bg::read_wkt("POLYGON((0.2 0.2,0.2 0.4,0.4 0.4,0.4 0.2,0.2 0.2))", interior);

Now, Boost Geometry has the concept of a Polygon which is an outer ring and (multiple) inner rings:

A polygon is A polygon is a planar surface defined by one exterior boundary and zero or more interior boundaries (OGC Simple Feature Specification)

So, let's use that instead:

bg::reverse(interior);
Boost2dPolygon polygon;
polygon.outer() = exterior;
polygon.inners().push_back(interior);

Note that the orientation of the inner ring is inverted.

Or, indeed, directly using the constructor:

Boost2dPolygon polygon({exterior, interior});

Or, even reading it from WKT at once:

bg::read_wkt("POLYGON((0.1 0.1,0.1 0.5,0.5 0.5,0.5 0.1,0.1 0.1) (0.2 0.2,0.4 0.2,0.4 0.4,0.2 0.4,0.2 0.2))", polygon);

Now you can just query in one pass:

std::vector<RTree::value_type> res;
m_RTree.query(bgi::intersects(polygon), std::back_inserter(res));

Full Demo!

Given the following sample() tree contents:

using RTree = bgi::rtree<std::pair<Boost2dBox, std::string>, bgi::rstar<16> >;
RTree sample() {
    RTree tree;

    std::pair<std::string, std::string> items[] = {
        { "BOX(0.2 0.2,0.2 0.4,0.4 0.4,0.4 0.2,0.2 0.2)",           "ok" },
        { "BOX(0.28 0.28,0.28 0.32,0.32 0.32,0.32 0.28,0.28 0.28)", "within gap" },
        { "BOX(0.28 0.28,0.28 0.32,0.36 0.32,0.36 0.28,0.28 0.28)", "small overlap" },
        { "BOX(2 2,2 4,4 4,4 2,2 2)",                               "outside exterior" },
    };
    for (auto& item : items) {
        Boost2dBox box;
        bg::read_wkt(item.first, box);
        checks("box", box);
        tree.insert({box, item.second});
    }

    return tree;
}

We can test things manually:

RTree const m_RTree = sample();

std::cout << "Sample tree:\n";
for (auto& value : m_RTree) {
    std::cout << " - " << std::quoted(value.second) << ": " << bg::wkt(value.first) << "\n";

    Boost2dMultiPolygon mp;
    if (bg::intersection(polygon, value.first, mp))
        std::cout << "      (intersection is " << bg::wkt(mp) << ")\n";
}

Which prints

Sample tree:
 - "ok": POLYGON((0.2 0.2,0.2 0.4,0.4 0.4,0.4 0.2,0.2 0.2))
      (intersection is MULTIPOLYGON(((0.2 0.2,0.2 0.4,0.4 0.4,0.4 0.2,0.2 0.2),(0.25 0.25,0.35 0.25,0.35 0.35,0.25 0.35,0.25 0.25))))
 - "within gap": POLYGON((0.28 0.28,0.28 0.32,0.32 0.32,0.32 0.28,0.28 0.28))
      (intersection is MULTIPOLYGON())
 - "small overlap": POLYGON((0.28 0.28,0.28 0.32,0.36 0.32,0.36 0.28,0.28 0.28))
      (intersection is MULTIPOLYGON(((0.35 0.32,0.36 0.32,0.36 0.28,0.35 0.28,0.35 0.32))))
 - "outside exterior": POLYGON((2 2,2 4,4 4,4 2,2 2))
      (intersection is MULTIPOLYGON())

And verify the results comparing to the tree query:

m_RTree.query(bgi::intersects(polygon), std::back_inserter(matches));

std::cout << "Intersecting with: ";
for (auto& match : matches) std::cout << " " << std::quoted(match.second) << " ";

Which prints:

Intersecting with:  "ok"  "small overlap" 

See it all Live On Coliru

#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/geometries/multi_polygon.hpp>
#include <boost/geometry/geometries/linestring.hpp>
#include <boost/geometry/geometries/multi_polygon.hpp>
#include <boost/geometry/core/cs.hpp>
#include <boost/geometry/arithmetic/arithmetic.hpp>
#include <boost/geometry/algorithms/within.hpp>
#include <boost/geometry/algorithms/intersects.hpp>
#include <boost/geometry/algorithms/envelope.hpp>
#include <boost/geometry/algorithms/intersection.hpp>
#include <boost/geometry/index/rtree.hpp>
#include <boost/geometry/index/predicates.hpp>
#include <boost/geometry/index/adaptors/query.hpp>
#include <boost/geometry/io/io.hpp>
#include <iostream>
#include <fstream>

namespace bg = boost::geometry;
namespace bgi = boost::geometry::index;

using Boost2dPoint        = bg::model::d2::point_xy<double>;
using Boost2dRing         = bg::model::ring<Boost2dPoint>;
using Boost2dPolygon      = bg::model::polygon<Boost2dPoint>;
using Boost2dMultiPolygon = bg::model::multi_polygon<Boost2dPolygon>;
using Boost2dBox          = bg::model::box<Boost2dPoint>;

template <typename G> void checks(std::string name, G& geom) {
    std::cout << name << ": " << bg::wkt(geom) << "\n";

    std::string reason;
    if (!bg::is_valid(geom, reason)) {
        std::cout << name << ": " << reason << "\n";

        bg::correct(geom);

        std::cout << bg::wkt(geom) << "\n";
        if (!bg::is_valid(geom, reason)) {
            std::cout << name << " corrected: " << reason << "\n";
        }
    }
}

using RTree = bgi::rtree<std::pair<Boost2dBox, std::string>, bgi::rstar<16> >;
RTree sample() {
    RTree tree;

    std::pair<std::string, std::string> items[] = {
        { "BOX(0.2 0.2,0.2 0.4,0.4 0.4,0.4 0.2,0.2 0.2)",           "ok" },
        { "BOX(0.28 0.28,0.28 0.32,0.32 0.32,0.32 0.28,0.28 0.28)", "within gap" },
        { "BOX(0.28 0.28,0.28 0.32,0.36 0.32,0.36 0.28,0.28 0.28)", "small overlap" },
        { "BOX(2 2,2 4,4 4,4 2,2 2)",                               "outside exterior" },
    };
    for (auto& item : items) {
        Boost2dBox box;
        bg::read_wkt(item.first, box);
        checks("box", box);
        tree.insert({box, item.second});
    }

    return tree;
}

int main() {
    Boost2dPolygon polygon;
    bg::read_wkt("POLYGON((0.1 0.1,0.1 0.5,0.5 0.5,0.5 0.1,0.1 0.1) (0.25 0.25,0.35 0.25,0.35 0.35,0.25 0.35,0.25 0.25))", polygon);
    checks("polygon", polygon);

    RTree const m_RTree = sample();

    std::cout << "Sample tree:\n";
    for (auto& value : m_RTree) {
        std::cout << " - " << std::quoted(value.second) << ": " << bg::wkt(value.first) << "\n";

        Boost2dMultiPolygon mp;
        if (bg::intersection(polygon, value.first, mp))
            std::cout << "      (intersection is " << bg::wkt(mp) << ")\n";
    }
    std::cout << "\n";

    std::vector<RTree::value_type> matches;
    m_RTree.query(bgi::intersects(polygon), std::back_inserter(matches));

    std::cout << "Intersecting with: ";
    for (auto& match : matches) std::cout << " " << std::quoted(match.second) << " ";
    std::cout << "\n";
}