76 lines
3.6 KiB
Plaintext
76 lines
3.6 KiB
Plaintext
[/============================================================================
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Boost.Geometry (aka GGL, Generic Geometry Library)
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Copyright (c) 2009-2012 Mateusz Loskot, London, UK.
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Copyright (c) 2009-2012 Barend Gehrels, Amsterdam, the Netherlands.
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Copyright (c) 2009-2012 Bruno Lalande, Paris, France.
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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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[section:concept_point Point Concept]
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[heading Description]
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[concept Point..point]
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A point is ['an entity that has a location in space or on a plane, but has no extent] ([@http://en.wikipedia.org/wiki/Point_(geometry) wiki]).
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The point is the most basic geometry of Boost.Geometry, most other geometries consist of points.
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['(Exceptions are box and segment, which might consist of two points but that is not necessarily the case.)]
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[heading Concept Definition]
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The Point Concept is defined as following:
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* there must be a specialization of `traits::tag`, defining `point_tag` as type
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* there must be a specialization of `traits::coordinate_type`, defining the type of its coordinates
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* there must be a specialization of `traits::coordinate_system`, defining its coordinate system
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(cartesian, spherical, etc)
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* there must be a specialization of `traits::dimension`, defining its number of dimensions (2, 3, ...)
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(hint: derive it conveniently from `boost::mpl::int_<X>` for X Dimensional)
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* there must be a specialization of `traits::access`, per dimension, with two functions:
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* `get` to get a coordinate value
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* `set` to set a coordinate value (this one is not checked for ConstPoint)
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[heading Example]
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While you can `#include boost/geometry/geometries/adapted/std_array.hpp` to use `std::array<T, D>` to model the Point concept,
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the following code spells it out in detail, as you might use for your own point types:
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```
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namespace boost { namespace geometry { namespace traits
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{
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template <typename T, std::size_t D> struct tag<std::array<T, D>> { using type = point_tag; };
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template <typename T, std::size_t D> struct dimension<std::array<T, D>> : boost::mpl::int_<D> {};
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template <typename T, std::size_t D> struct coordinate_type<std::array<T, D>> { using type = T; };
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template <typename T, std::size_t D> struct coordinate_system<std::array<T, D>> { using type = boost::geometry::cs::cartesian; };
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template <typename T, std::size_t D, std::size_t Index>
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struct access<std::array<T, D>, Index> {
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static_assert(Index < D, "Out of range");
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using Point = std::array<T, D>;
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using CoordinateType = typename coordinate_type<Point>::type;
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static inline CoordinateType get(Point const& p) { return p[Index]; }
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static inline void set(Point& p, CoordinateType const& value) { p[Index] = value; }
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};
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}}} // namespace boost::geometry::traits
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```
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[heading Available Models]
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* [link geometry.reference.models.model_point model::point]
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* [link geometry.reference.models.model_d2_point_xy model::d2::point_xy]
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* a lat long point (currently in an extension)
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* [link geometry.reference.adapted.c_array C array]
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* [link geometry.reference.adapted.std_array C++ array container]
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* [link geometry.reference.adapted.boost_array Boost.Array]
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* [link geometry.reference.adapted.boost_fusion Boost.Fusion]
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* [link geometry.reference.adapted.boost_polygon Boost.Polygon]
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* [link geometry.reference.adapted.boost_tuple Boost.Tuple]
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* other point types, adapted e.g. using one of the [link geometry.reference.adapted registration macro's]
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[endsect]
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