假设我有以下数据集
double * data = (double *) malloc(sizeof(double) * 100 * 2);
for (ii = 0; ii < 100; ii++) {
data[2*ii] = ii;
data[2*ii + 1] = ii;
}
如何从这些数据创建一个提升多边形？
谢谢
解决方法
一个完整的例子
#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;
}
只是为了说明你实际拥有的灵活性：通过一些额外的typedef工作,可以定义你自己的双精度点类型,它可以别名到你的数据,这避免了中间副本……
#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;
}
这种趋势可能持续到custom polygon class.
