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Question

創建boost.geometry.model.polygon假設我有以下數據集

double * data = (double *) malloc(sizeof(double) * 100 * 2); 
for (ii = 0; ii < 100; ii++) { 
    data[2*ii] = ii; 
    data[2*ii + 1] = ii; 
} 

我怎麼可以創建從該數據提振多邊形？

感謝

Answer 1

一個完整的例子

#include <iostream> 
#include <boost/polygon/polygon.hpp> 
#include <vector> 

// Some typedefs 
namespace bpl = boost::polygon; 
typedef bpl::polygon_data<double> Polygon; 
typedef bpl::polygon_traits<Polygon>::point_type Point; 

int main() { 

    // Your C-style data (assumed (x,y) pairs) 
    double * data = (double *) malloc(sizeof(double) * 100 * 2); 
    for (int ii = 0; ii < 100; ii++) { 
    data[2*ii] = ii; 
    data[2*ii + 1] = ii; 
    } 

    // Convert to points 
    std::vector<Point> points; 
    for (int i=0;i<100;++i) 
    points.push_back(Point(data[2*i],data[2*i+1])); 

    // Create a polygon 
    Polygon polygon; 
    polygon.set(points.begin(),points.end()); 

    // Do something with the polygon 
    std::cout << "Perimeter : " << bpl::perimeter(polygon) << std::endl; 
    std::cout << "Area  : " << bpl::area(polygon) << std::endl; 

    return 0; 
} 

只是爲了說明你確實有彈性：有一點額外的typedef工作，它可以定義你自己的一雙兩雙的點型，其可以使用別名到您的數據，避免了中間副本...

#include <iostream> 
#include <boost/polygon/polygon.hpp> 
#include <vector> 

// Define a point type which can be aliased to your 'C' points 
struct Pt { 
    double x; 
    double y; 
}; 

// Some typedefs 
namespace bpl = boost::polygon; 
typedef bpl::polygon_data<double> Polygon; 

// Add the necessary to use Pt 
namespace boost { 
    namespace polygon { 

    template <> struct geometry_concept<Pt> {typedef point_concept type;}; 

    template <> struct point_traits<Pt> { 
     typedef double coordinate_type; 

     static inline coordinate_type get(const Pt& pt,orientation_2d orient) { 
    return (orient == HORIZONTAL ? pt.x : pt.y); 
     } 
    }; 

    template <> struct point_mutable_traits<Pt> { 
     static inline void set(Pt& pt, orientation_2d orient, int value) { 
    if(orient == HORIZONTAL) 
     pt.x = value; 
    else 
     pt.y = value; 
     } 
     static inline Pt construct(double x,double y) { 
    Pt r; 
    r.x=x; 
    r.y=y; 
    return r; 
     } 
    }; 
    } 
} 

int main() { 

    // Your C-style data (assumed (x,y) pairs) 
    double * data = (double *) malloc(sizeof(double) * 100 * 2); 
    for (int ii = 0; ii < 100; ii++) { 
    data[2*ii] = ii; 
    data[2*ii + 1] = ii; 
    } 

    // Reinterpret your data as an array of Pt 
    const Pt*const pts=reinterpret_cast<const Pt*>(data); 

    // Create a polygon 
    Polygon polygon; 
    polygon.set(pts,pts+100); 

    // Do something with the polygon 
    std::cout << "Perimeter : " << bpl::perimeter(polygon) << std::endl; 
    std::cout << "Area  : " << bpl::area(polygon) << std::endl; 

    return 0; 
} 

而且這種趨勢可能會持續到custom polygon class。