mirror of https://github.com/CGAL/cgal
70 lines
2.0 KiB
C++
70 lines
2.0 KiB
C++
#include <CGAL/Cartesian.h>
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#include <CGAL/Min_ellipse_2.h>
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#include <CGAL/Min_ellipse_2_traits_2.h>
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#include <CGAL/Exact_rational.h>
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#include <cassert>
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#include <array>
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typedef CGAL::Exact_rational NT;
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typedef CGAL::Cartesian<NT> K;
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typedef CGAL::Point_2<K> Point;
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typedef CGAL::Min_ellipse_2_traits_2<K> Traits;
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typedef CGAL::Min_ellipse_2<Traits> Min_ellipse;
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int
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main( int, char**)
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{
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const int n = 200;
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std::array<Point, n> P;
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for ( int i = 0; i < n; ++i)
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P.at(i) = Point( i % 2 ? i : -i , 0);
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// (0,0), (-1,0), (2,0), (-3,0)
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std::cout << "Computing ellipse (without randomization)...";
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std::cout.flush();
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Min_ellipse me1( P.begin(), P.end(), false); // very slow
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std::cout << "done." << std::endl;
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std::cout << "Computing ellipse (with randomization)...";
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std::cout.flush();
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Min_ellipse me2( P.begin(), P.end(), true); // fast
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std::cout << "done." << std::endl;
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// because all input points are collinear, the ellipse is
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// degenerate and equals a line segment; the ellipse has
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// two support points
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assert(me2.is_degenerate());
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assert(me2.number_of_support_points()==2);
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// prettyprinting
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CGAL::IO::set_pretty_mode( std::cout);
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std::cout << me2;
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// in general, the ellipse is not explicitly representable
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// over the input number type NT; when you use the default
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// traits class CGAL::Min_ellipse_2_traits_2<K>, you can
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// get double approximations for the coefficients of the
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// underlying conic curve. NOTE: this curve only exists
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// in the nondegenerate case!
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me2.insert(Point(0,1)); // resolves the degeneracy
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assert(!me2.is_degenerate());
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// get the coefficients
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double r,s,t,u,v,w;
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me2.ellipse().double_coefficients( r, s, t, u, v, w);
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std::cout << "ellipse has the equation " <<
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r << " x^2 + " <<
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s << " y^2 + " <<
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t << " xy + " <<
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u << " x + " <<
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v << " y + " <<
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w << " = 0." << std::endl;
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return 0;
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}
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