103 lines
3.5 KiB
C++
103 lines
3.5 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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// Example: Custom coordinate system example
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#include <iostream>
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#include <boost/geometry/geometry.hpp>
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// 1: declare a coordinate system. For example for Mars
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// Like for the Earth, we let the use choose between degrees or radians
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// (Unfortunately, in real life Mars has two coordinate systems:
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// http://planetarynames.wr.usgs.gov/Page/MARS/system)
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template<typename DegreeOrRadian>
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struct martian
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{
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typedef DegreeOrRadian units;
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};
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// 2: give it also a family
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struct martian_tag;
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// 3: register to which coordinate system family it belongs to
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// this must be done in namespace boost::geometry::traits
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namespace boost { namespace geometry { namespace traits
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{
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template <typename DegreeOrRadian>
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struct cs_tag<martian<DegreeOrRadian> >
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{
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typedef martian_tag type;
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};
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}}} // namespaces
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// NOTE: if the next steps would not be here,
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// compiling a distance function call with martian coordinates
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// would result in a MPL assertion
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// 4: so register a distance strategy as its default strategy
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namespace boost { namespace geometry { namespace strategy { namespace distance { namespace services
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{
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template <typename Point1, typename Point2>
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struct default_strategy<point_tag, point_tag, Point1, Point2, martian_tag, martian_tag>
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{
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typedef haversine<double> type;
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};
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}}}}} // namespaces
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// 5: not worked out. To implement a specific distance strategy for Mars,
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// e.g. with the Mars radius given by default,
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// you will have to implement (/register) several other metafunctions:
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// tag, return_type, similar_type, comparable_type,
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// and structs:
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// get_similar, get_comparable, result_from_distance
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// See e.g. .../boost/geometry/extensions/gis/geographic/strategies/andoyer.hpp
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int main()
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{
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typedef boost::geometry::model::point
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<
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double, 2, martian<boost::geometry::degree>
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> mars_point;
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// Declare two points
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// (Source: http://nssdc.gsfc.nasa.gov/planetary/mars_mileage_guide.html)
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// (Other sources: Wiki and Google give slightly different coordinates, resulting
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// in other distance, 20 km off)
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mars_point viking1(-48.23, 22.54); // Viking 1 landing site in Chryse Planitia
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mars_point pathfinder(-33.55, 19.33); // Pathfinder landing site in Ares Vallis
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double d = boost::geometry::distance(viking1, pathfinder); // Distance in radians on unit-sphere
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// Using the Mars mean radius
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// (Source: http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html)
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std::cout << "Distance between Viking1 and Pathfinder landing sites: "
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<< d * 3389.5 << " km" << std::endl;
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// We would get 832.616 here, same order as the 835 (rounded on 5 km) listed
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// on the mentioned site
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#ifdef OPTIONALLY_ELLIPSOIDAL
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// Optionally the distance can be calculated more accurate by an Ellipsoidal approach,
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// giving 834.444 km
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d = boost::geometry::distance(viking1, pathfinder,
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boost::geometry::strategy::distance::andoyer<mars_point>
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(boost::geometry::srs::spheroid<double>(3396.2, 3376.2)));
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std::cout << "Ellipsoidal distance: " << d << " km" << std::endl;
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#endif
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return 0;
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}
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