c++ - 使用 boost 将几何体切割成碎片

Question

boost::geometry 中是否有任何内置工具可以像下图那样切割几何体？我的想法是找到一个交叉点几何图形，并从两个来源中减去它们。但感觉这不是最佳解决方案，因为有超过 2 个相交的矩形共享相同的区域。

因此，将输入数据转换为代码中的同构测试用例:

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#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/io/io.hpp>
#include <iostream>
#include <fstream>

namespace bg  = boost::geometry;
namespace bgm = bg::model;

using point = bgm::d2::point_xy<int>;
using poly  = bgm::polygon<point>;
using mpoly = bgm::multi_polygon<poly>;

int main()
{
    poly a, b, c;
    bg::read_wkt("POLYGON((0 0 0 6 6 6 6 0 0 0))", a);
    bg::read_wkt("POLYGON((4 -1 4 4 5 4 5 -1 4 -1))", b);
    bg::read_wkt("POLYGON((3 -3 3 3 9 3 9 -3 3 -3))", c);

    std::cout << bg::wkt(a) << "\n";
    std::cout << bg::wkt(b) << "\n";
    std::cout << bg::wkt(c) << "\n";

    {
        std::ofstream svg("output.svg");
        boost::geometry::svg_mapper<point> mapper(svg, 400, 400);
        mapper.add(a);
        mapper.add(b);
        mapper.add(c);

        mapper.map(a, "fill-opacity:0.2;fill:rgb(0,0,153);stroke:rgb(0,0,200);stroke-width:2");
        mapper.map(b, "fill-opacity:0.2;fill:rgb(153,0,0);stroke:rgb(200,0,0);stroke-width:2");
        mapper.map(c, "fill-opacity:0.2;fill:rgb(0,153,0);stroke:rgb(0,200,0);stroke-width:2");
    }
}

它反射(reflect)了以下 SVG:

Answer 1

考虑以下代码:

#include <boost/geometry.hpp>
#include <boost/geometry/geometries/polygon.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/geometries/multi_polygon.hpp>
#include <boost/geometry.hpp>

#include <boost/foreach.hpp>
#include <boost/foreach.hpp>


namespace bg  = boost::geometry;
namespace bgm = bg::model;

typedef  bgm::d2::point_xy<int> point;
typedef  bgm::polygon<point> poly;
typedef  bgm::multi_polygon<poly> mpoly;

int main()
{
    poly a, b, c;
    bg::read_wkt("POLYGON((0 0 0 6 6 6 6 0 0 0))", a);
    bg::read_wkt("POLYGON((4 -1 4 4 5 4 5 -1 4 -1))", b);
    bg::read_wkt("POLYGON((3 -3 3 3 9 3 9 -3 3 -3))", c);

    std::vector<poly> polies;
    polies.push_back(a);
    polies.push_back(b);
    polies.push_back(c);

        std::vector<poly> res;
        for (size_t i = 0; i < polies.size(); ++i)
        {
            for (size_t j = i; j < polies.size(); ++j)
            {
                boost::geometry::model::multi_polygon<poly> output;
                boost::geometry::union_(polies[i], polies[j], output);

                for (auto it = output.begin(); it != output.end(); ++it)
                {
                    res.push_back(*it);
                }    
            }
        }

        for (size_t i = 0; i < polies.size(); ++i)
        {
            for (size_t j = i; j < polies.size(); ++j)
            {
                boost::geometry::model::multi_polygon<poly> multi;
                boost::geometry::sym_difference(polies[i], polies[j], multi);

                for (auto it = multi.begin(); it != multi.end(); ++it)
                {
                    res.push_back(*it);
                }
            }
        }


    {
        std::ofstream svg("output2.svg");
        boost::geometry::svg_mapper<point> mapper(svg, 400, 400);
        size_t i = 0;
        BOOST_FOREACH(poly& p, res)
        {
            std::stringstream ss;
            ss << ++i * 10;
            std::stringstream ss2;
            ss2 << 255 - i * 10;
            mapper.add(p);
            mapper.map(p, "fill-opacity:0.2;fill:rgb("+ ss.str() + "," + ss2.str() +",153);stroke:rgb(0,0,200);stroke-width:2");
        }
    }

    return 0;
}

产生以下输出: 为此，您必须遍历所有组合并计算初始多边形的并集和 sym_differences。

抱歉，颜色没有你的好看。

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