C++ 上不正确的工作 boost::geometry::union_

Posted 2023-02-21

【中文标题】C++ 上不正确的工作 boost::geometry::union_

【英文标题】：Incorrect work boost::geometry::union_ on C++

【发布时间】：2021-04-24 07:10:17

【问题描述】：

我想在图片上使用带有多边形的 boost::geometry::union_，但它看不到点 E（例如，多边形 ABCDE 的面积为 ABCD）。我该如何解决？

【问题讨论】：

您需要显示代码。图片不反映您如何表示多边形。

【参考方案1】：

我会这样写你的练习。我设计了一个类似的场景（这些点的名称可能不同，但这不是 [原文如此] 点）：

注意：我已经将坐标四舍五入到最接近的整数（然后缩放 x10）

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

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

using Point   = bgm::d2::point_xy<int>;
using Polygon = bgm::polygon<Point>;
using Multi   = bgm::multi_polygon<Polygon>;

int main() 
    auto prepare = [](auto name, auto& geo) 
        std::string r;
        if (!bg::is_valid(geo, r)) 
            std::cout << "Correcting " << name << ": " << bg::wkt(geo) << " (" << r << ")\n";
            bg::correct(geo);
        
        std::cout << name << ": " << bg::wkt(geo) << "\n";
    ;

    Point A-120, 50, B-60, 70, C-70, 50, D-40, 00, E-130, 10;
    Point F-20, -20, G40, -10, H80, 60, I50, 80, J-20, 50, K30, 30;

    Polygon ABCDE(A, B, C, D, E, A);
    Polygon DFGHIJK(D, F, G, H, I, J, K, D);

    prepare("ABCDE", ABCDE);
    prepare("DFGHIJK", DFGHIJK);

    Multi out;
    bg::union_(ABCDE, DFGHIJK, out);
    prepare("union", out);

    
        namespace bs = bg::strategy::buffer;
        const double buffer_distance   = 3;

        bs::distance_symmetric<double> distance(buffer_distance);
        bs::join_miter    join;
        bs::end_flat      end;
        bs::point_circle  circle(6);
        bs::side_straight side;

        Multi outline;
        bg::buffer(out, outline, distance, side, join, end, circle);

        std::ofstream svg("output.svg");
        boost::geometry::svg_mapper<Point> mapper(svg, 400, 400);
        mapper.add(ABCDE);
        mapper.add(DFGHIJK);
        mapper.add(outline);

        mapper.map(ABCDE,
                   "fill-opacity:0.3;fill:rgb(153,0,0);stroke:rgb(153,0,0);"
                   "stroke-width:1;stroke-dasharray:1 2");
        mapper.map(DFGHIJK,
                   "fill-opacity:0.3;fill:rgb(0,0,153);stroke:rgb(0,0,153);"
                   "stroke-width:1;stroke-dasharray:1 2 2 1");
        mapper.map(outline,
                   "fill-opacity:0.1;fill:rgb(153,204,0);stroke:rgb(153,204,0);"
                   "stroke-width:1");
    

    std::cout << "Areas: " << bg::area(ABCDE) << " + " << bg::area(DFGHIJK)
              << " = " << bg::area(out) << "\n";

打印预期的：

ABCDE: POLYGON((-120 50,-60 70,-70 50,-40 0,-130 10,-120 50))
Correcting DFGHIJK: POLYGON((-40 0,-20 -20,40 -10,80 60,50 80,-20 50,30 30,-40 0)) (Geometry has wrong orie
ntation)
DFGHIJK: POLYGON((-40 0,30 30,-20 50,50 80,80 60,40 -10,-20 -20,-40 0))
union: MULTIPOLYGON(((-40 0,-130 10,-120 50,-60 70,-70 50,-40 0)),((-40 0,30 30,-20 50,50 80,80 60,40 -10,-
20 -20,-40 0)))
Areas: 3600 + 5800 = 9400

它还会生成以下 SVG：

我希望我处理它的方式，特别是诊断代码对您有所帮助。