c04_b_custom_triangle_example.cpp

This second custom triangle example shows an alternative implementation for a custom shape, showing a partial specialization for the area calculation.

    // Boost.Geometry (aka GGL, Generic Geometry Library)

    // Copyright (c) 2007-2012 Barend Gehrels, Amsterdam, the Netherlands.
    // Copyright (c) 2008-2012 Bruno Lalande, Paris, France.
    // Copyright (c) 2009-2012 Mateusz Loskot, London, UK.

    // Use, modification and distribution is subject to the Boost Software License,
    // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
    // http://www.boost.org/LICENSE_1_0.txt)
    //
    // Custom triangle template Example

    #include <iostream>

    #include <boost/array.hpp>
    #include <boost/tuple/tuple.hpp>

    #include <boost/geometry/algorithms/area.hpp>
    #include <boost/geometry/algorithms/centroid.hpp>
    #include <boost/geometry/geometries/adapted/boost_tuple.hpp>
    #include <boost/geometry/geometries/register/ring.hpp>
    #include <boost/geometry/strategies/strategies.hpp>
    #include <boost/geometry/io/dsv/write.hpp>

    BOOST_GEOMETRY_REGISTER_BOOST_TUPLE_CS(cs::cartesian)

    template <typename P>
    struct triangle : public boost::array<P, 3>
    {
    };

    // Register triangle<P> as a ring
    BOOST_GEOMETRY_REGISTER_RING_TEMPLATED(triangle)

    namespace boost { namespace geometry { namespace dispatch {

    // Specializations of area dispatch structure, implement algorithm
    template<typename Point>
    struct area<triangle<Point>, ring_tag>
    {
        template <typename Strategy>
        static inline double apply(triangle<Point> const& t, Strategy const&)
        {
            return 0.5  * ((get<0>(t[1]) - get<0>(t[0])) * (get<1>(t[2]) - get<1>(t[0]))
                         - (get<0>(t[2]) - get<0>(t[0])) * (get<1>(t[1]) - get<1>(t[0])));
        }
    };

    }}} // namespace boost::geometry::dispatch

    int main()
    {
        //triangle<boost::geometry::point_xy<double> > t;
        triangle<boost::tuple<double, double> > t;
        t[0] = boost::make_tuple(0, 0);
        t[1] = boost::make_tuple(5, 0);
        t[2] = boost::make_tuple(2.5, 2.5);

        std::cout << "Triangle: " << boost::geometry::dsv(t) << std::endl;
        std::cout << "Area: " << boost::geometry::area(t) << std::endl;

        //boost::geometry::point_xy<double> c;
        boost::tuple<double, double> c;
        boost::geometry::centroid(t, c);
        std::cout << "Centroid: " << boost::geometry::dsv(c) << std::endl;

        return 0;
    }

April 2, 2011 | Copyright © 2007-2011 Barend Gehrels, Amsterdam, the Netherlands Copyright © 2008-2011 Bruno Lalande, Paris, France Copyright © 2009-2010 Mateusz Loskot, London, UK