84 lines
2.2 KiB
C++
84 lines
2.2 KiB
C++
// Boost.Geometry (aka GGL, Generic Geometry Library)
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// Copyright (c) 2007-2012 Barend Gehrels, Amsterdam, the Netherlands.
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// Copyright (c) 2008-2012 Bruno Lalande, Paris, France.
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// Copyright (c) 2009-2012 Mateusz Loskot, London, UK.
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// Use, modification and distribution is subject to the Boost Software License,
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// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//
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// Custom Triangle Example
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#include <iostream>
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#include <boost/array.hpp>
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#include <boost/geometry/algorithms/area.hpp>
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#include <boost/geometry/algorithms/centroid.hpp>
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#include <boost/geometry/geometries/point_xy.hpp>
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#include <boost/geometry/geometries/register/ring.hpp>
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#include <boost/geometry/strategies/strategies.hpp>
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#include <boost/geometry/io/dsv/write.hpp>
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struct triangle : public boost::array<boost::geometry::model::d2::point_xy<double>, 4>
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{
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inline void close()
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{
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(*this)[3] = (*this)[0];
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}
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};
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// Register triangle as a ring
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BOOST_GEOMETRY_REGISTER_RING(triangle)
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// Specializations of algorithms, where useful. If not specialized the default ones
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// (for linear rings) will be used for triangle. Which is OK as long as the triangle
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// is closed, that means, has 4 points (the last one being the first).
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namespace boost { namespace geometry {
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template<>
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inline double area<triangle>(const triangle& t)
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{
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/* C
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/ \
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/ \
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A-----B
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((Bx - Ax) * (Cy - Ay)) - ((Cx - Ax) * (By - Ay))
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-------------------------------------------------
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2
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*/
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return 0.5 * ((t[1].x() - t[0].x()) * (t[2].y() - t[0].y())
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- (t[2].x() - t[0].x()) * (t[1].y() - t[0].y()));
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}
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}} // namespace boost::geometry
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int main()
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{
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triangle t;
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t[0].x(0);
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t[0].y(0);
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t[1].x(5);
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t[1].y(0);
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t[2].x(2.5);
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t[2].y(2.5);
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t.close();
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std::cout << "Triangle: " << boost::geometry::dsv(t) << std::endl;
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std::cout << "Area: " << boost::geometry::area(t) << std::endl;
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boost::geometry::model::d2::point_xy<double> c;
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boost::geometry::centroid(t, c);
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std::cout << "Centroid: " << boost::geometry::dsv(c) << std::endl;
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return 0;
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}
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