geometry/example/c11_custom_cs_transform_example.cpp at develop · boostorg/geometry · GitHub

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

// 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)

// Example: Custom coordinate system example, using transform

#include <iostream>

#include <boost/geometry/geometry.hpp>

// See also c10_custom_cs_example

// 1: declare, for example two cartesian coordinate systems

struct cart {};

struct cart_shifted5 {};

// 2: register to which coordinate system family they belong

namespace boost { namespace geometry { namespace traits

{

template<> struct cs_tag<cart> { typedef cartesian_tag type; };

template<> struct cs_tag<cart_shifted5> { typedef cartesian_tag type; };

}}} // namespaces

// 3: sample implementation of a shift

// to convert coordinate system "cart" to "cart_shirted5"

struct shift

{

template <typename P1, typename P2>

inline bool apply(P1 const& p1, P2& p2) const

{

namespace bg = boost::geometry;

bg::set<0>(p2, bg::get<0>(p1) + 5);

bg::set<1>(p2, bg::get<1>(p1));

return true;

}

};

// 4: register the default strategy to transform any cart point to any cart_shifted5 point

namespace boost { namespace geometry { namespace strategy { namespace transform { namespace services

{

template <typename P1, typename P2>

struct default_strategy<cartesian_tag, cartesian_tag, cart, cart_shifted5, 2, 2, P1, P2>

{

typedef shift type;

};

}}}}} // namespaces

// 5: implement a distance strategy between the two different ones

struct shift_and_calc_distance

{

template <typename P1, typename P2>

inline double apply(P1 const& p1, P2 const& p2) const

{

P2 p1_shifted;

boost::geometry::transform(p1, p1_shifted);

return boost::geometry::distance(p1_shifted, p2);

}

};

// 6: Define point types using this explicitly

typedef boost::geometry::model::point<double, 2, cart> point1;

typedef boost::geometry::model::point<double, 2, cart_shifted5> point2;

// 7: register the distance strategy

namespace boost { namespace geometry { namespace strategy { namespace distance { namespace services

{

template <>

struct tag<shift_and_calc_distance>

{

typedef strategy_tag_distance_point_point type;

};

template <typename P1, typename P2>

struct return_type<shift_and_calc_distance, P1, P2>

{

typedef double type;

};

template <>

struct default_strategy<point_tag, point_tag, point1, point2, cartesian_tag, cartesian_tag>

{

typedef shift_and_calc_distance type;

};

}}}}}

int main()

{

point1 p1_a(0, 0), p1_b(5, 5);

point2 p2_a(2, 2), p2_b(6, 6);

// Distances run for points on the same coordinate system.

// This is possible by default because they are cartesian coordinate systems.

double d1 = boost::geometry::distance(p1_a, p1_b);

double d2 = boost::geometry::distance(p2_a, p2_b);

std::cout << d1 << " " << d2 << std::endl;

// Transform from a to b:

boost::geometry::model::point<double, 2, cart_shifted5> p1_shifted;

boost::geometry::transform(p1_a, p1_shifted);

// Of course this can be calculated now, same CS

double d3 = boost::geometry::distance(p1_shifted, p2_a);

// Calculate distance between them. Note that inside distance the

// transformation is called.

double d4 = boost::geometry::distance(p1_a, p2_a);

// The result should be the same.

std::cout << d3 << " " << d4 << std::endl;

return 0;

}

geometry/example/c11_custom_cs_transform_example.cpp at develop · boostorg/geometry · GitHub

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