geometry/example/c10_custom_cs_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

#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

{

using units = DegreeOrRadian;

};

// 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> >

{

using type = martian_tag;

};

}}} // 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()

{

using mars_point = boost::geometry::model::point

double, 2, martian<boost::geometry::degree>

// 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 const viking1(-48.23, 22.54); // Viking 1 landing site in Chryse Planitia

mars_point const pathfinder(-33.55, 19.33); // Pathfinder landing site in Ares Vallis

// To calculate distance, declare and construct a strategy with Mars mean radius, in KM

// (Source: http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html)

boost::geometry::strategies::distance::spherical<> const spherical(3389.5);

double d = boost::geometry::distance(viking1, pathfinder, spherical);

std::cout << "Distance between Viking1 and Pathfinder landing sites: "

<< d << " km" << std::endl;

// We would get 832.616 here, same order as the 835 (rounded on 5 km) listed

// on the mentioned site

// The distance can be calculated more accurately by an Ellipsoidal approach,

// giving 834.444 km

boost::geometry::srs::spheroid<double> spheroid(3396.2, 3376.2);

boost::geometry::strategy::distance::geographic<> const ellipsoidal(spheroid);

d = boost::geometry::distance(viking1, pathfinder, ellipsoidal);

std::cout << "Ellipsoidal distance: " << d << " km" << std::endl;

return 0;

}

geometry/example/c10_custom_cs_example.cpp at develop · boostorg/geometry · GitHub

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