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