c – 从2D C列表创建boost.geometry.model.polygon

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

```#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;
}```

```#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;
}```